Microwave Heating for Food Preservation

*Jean-Claude Laguerre and Mohamad Mazen Hamoud-Agha*

#### **Abstract**

Since food is generally of low thermal conductivity, heating by conventional methods remains relatively slow. Thanks to its volumetric and rapid heating, microwave (MW) technology is successfully used in many applications of food processing. In this chapter, fundamental principles of MW heating are briefly presented. MW drying and MW microbial decontamination are extensively reviewed as innovative methods for food preservation. However, the complex interactions between microwaves and materials to be heated are not yet sufficiently controlled. Moreover, MW heating heterogeneity and thermal runaway are the main drawbacks of this technology. Several methods have been proposed and investigated in the literature to overcome these problems in order to assure the microbiological safety and quality of food products.

**Keywords:** microwave heating, microwave modeling, drying, pasteurization, sterilization, microbial decontamination, food safety, food quality

#### **1. An overview of microwave heating**

Microwaves (MWs) are electromagnetic (EM) waves, which are synchronized perpendicularly oscillations of electric and magnetic fields that propagate at the speed of light in a free space. MWs are characterized by the frequency (between 300 MHz and 300 GHz) and the wavelength (ranging from 1 m to 1 mm). According to the countries and regions, five frequencies (433, 896, 915, 2375, and 2450 MHz) are authorized for MW heating operations. The 2450 MHZ is the exclusive frequency for home appliances.

#### **1.1 Mechanisms of microwave heating**

The interaction of a wave with the material depends on its own characteristics (frequencies, wavelength) and the nature of the material, particularly its absolute permittivity ε\*, a complex number that determines how the material stores the electrical energy of the EF and its dissipation into heat. The readers can consult more specialized references for detailed information [1]. We can define rapidly here the real permittivity, or dielectric constant, of a material which denotes the capacity of the material to store electrical energy and the effective loss factor which expresses the ability of the material to absorb energy of the wave and dissipate it into the heat by dielectric relaxation and ionic conduction. If a material contains free charges (ions) and polar molecules (e.g., water molecule) when this material is subjected to an EF, the ions will move at an accelerated rate according to their charge, which will cause collisions between them and, by the result, a conversion of the kinetic energy into heat (ohmic heating). In the same way, the polar molecules of this material, which was initially randomly oriented, will be oriented according to the polarity of the field. If the EF is an alternative, these molecules will rotate to remain aligned on it. This dipolar rotation will generate frictions between the molecules which will lead to an internal generation of heat (dielectric heating).

#### **1.2 Penetration and absorption of a wave in a material**

When an EM wave is directed toward a material, a part of the wave is reflected on the surface, while the other part penetrates it to be absorbed. The absorption of the wave during its crossing results in a decrease of the amplitude of the internal EF and so of its power. For small or thin materials, the accurate calculation of the internal electric field is recommended by using the Maxwell equations. Lambert's law (exponential EF decayed) may be used for larger objects.

The penetration depth is defined as the penetration distance in the material for which the 63% of incident power of the incident wave has been absorbed. This depth depends on the dielectric properties of the material as well as the wavelength. The penetration depth at 915 MHz is larger than the penetration depth at 2450 MHz at the same conditions. More power will be absorbed when the loss factor is high [1].

#### **1.3 About the heterogeneity of microwave heating**

MW heating is inherently heterogeneous for several reasons:


**37**

drying were resumed in the literature [6].

**2.2 Microwave drying versus hot air drying**

During MW drying of strong moisture content product, EM energy is supplied directly to the volume of the product, which causes a rapid increase of the product temperature and an instantaneous vaporization of water inside the product [7]. This phenomenon causes an increase in the internal pressure and drives the water to liquid state toward the product surface [8]. This forced outflow of water increases the drying rate and so reduces the operation time (up to five times less than HA air drying for many products). Likewise, the increase in internal pressure prevents

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

Drying is one of the most used methods for preserving food and preventing microbiological degradation. Food drying is also used for economic interests by lightening the product to minimize the transport costs (e.g., milk powder) or even for consumption aspects by creating new textures and/or products (e.g., prunes). This process aims to reduce the water activity (Aw) of the food product by removing some of its water. The amount of water to be removed to achieve the microbiological stability can be determined thanks to the sorption isotherm curve which shows the relationship between the water content and the water activity of a product. Generally, the water activity threshold from which there is no further development of pathogenic bacteria is 0.85–0.86 and 0.7 and 0.6 for yeasts and molds, respectively. It is interesting to note that Aw does not only control the development of microorganisms, it also influences the rate of the chemical and biochemical reactions that take place within the food. The nonenzymatic browning (Maillard reaction) has a maximal activity for an Aw of 0.6–0.7, while the oxidation of lipids develops rather at very low and very high values of Aw. Thus, it is proper to adjust the final moisture of the product according to these considerations. The area generally targeted for good stability of the dried product is the range of Aw between 0.3 and 0.4. An important aspect must be emphasized here, namely, that drying has almost no lethal effect on the microorganisms present on the product due to insufficient product temperatures reached during drying. Proper packaging is therefore essential to avoid moisture recovery and keep the quality of the dehydrated product. Industrial drying techniques are very varied depending on the nature of the product to dry (liquid, pasty, solid, or particulate) and of the desired final qualities. Most often, hot air (HA) convective drying is the main dehydration technique used in food industries. However, this method undergoes several problems such as poor end-product quality and low operation performance. Generally, in conventional drying method, two steps take place: a heat transfer from hot and dry surrounding medium to the product and then a mass (water and/or volatile compounds) transfer from the product to the surrounding atmosphere. In general, external heat and mass transfer can be easily controlled by a good monitoring of the drying air characteristics (velocity, temperature, relative humidity); thus, the internal transfer is the limiting step and the effective driving force for the drying operation. The drying rate decreases with time, and the removal of water becomes difficult. Therefore, conventional HA drying requires the application of severe conditions, particularly at the end of operation, which result in overheating and overdrying of the product surface. These reasons have greatly encouraged engineers to develop and propose new drying techniques such as MW drying. For example, MW drying was successfully applied to dry potatoes chips, pasta, and snacks [5]. Several studies of MW

**2. Microwave drying**

**2.1 Introduction**

#### **2. Microwave drying**

#### **2.1 Introduction**

*Food Preservation and Waste Exploitation*

lead to an internal generation of heat (dielectric heating).

**1.2 Penetration and absorption of a wave in a material**

law (exponential EF decayed) may be used for larger objects.

MW heating is inherently heterogeneous for several reasons:

exist in the oven, particularly in a multimode cavity.

overheating (thermal runaway).

and/or hot spots (transmitted and reflected waves add up).

**1.3 About the heterogeneity of microwave heating**

cause collisions between them and, by the result, a conversion of the kinetic energy into heat (ohmic heating). In the same way, the polar molecules of this material, which was initially randomly oriented, will be oriented according to the polarity of the field. If the EF is an alternative, these molecules will rotate to remain aligned on it. This dipolar rotation will generate frictions between the molecules which will

When an EM wave is directed toward a material, a part of the wave is reflected on the surface, while the other part penetrates it to be absorbed. The absorption of the wave during its crossing results in a decrease of the amplitude of the internal EF and so of its power. For small or thin materials, the accurate calculation of the internal electric field is recommended by using the Maxwell equations. Lambert's

The penetration depth is defined as the penetration distance in the material for which the 63% of incident power of the incident wave has been absorbed. This depth depends on the dielectric properties of the material as well as the wavelength. The penetration depth at 915 MHz is larger than the penetration depth at 2450 MHz at the same conditions. More power will be absorbed when the loss factor is high [1].

• For most cases, product size is very large compared to the penetration depth; thus, the energy of the EM wave will be completely absorbed before being able to reach the core or the bottom of the product. All the parts of the product not crossed by the EM wave will not undergo heating. Smaller products will heat faster than large ones, because MWs are able to penetrate the entire product. However, small products are also more sensitive to variations in EM fields that

• Dimensional resonance phenomena: sometimes, the wave is reflected against the lower edge of the product leading to interference phenomena. This results in producing cold spots (transmitted and reflected waves cancel each other)

• If the product is made of several components, the component with the highest dielectric constant tends to concentrate the energy, and its temperature will increase strongly compared to the other components which leads to selective overheating. The dependence of dielectric properties with the temperature often leads to increase the local temperature of the already hot points. As foods are generally low thermal conductivities, this phenomenon leads to local

• The shape of the product plays a major role in the heterogeneity of MW heating. The shape of the sample influences the penetration depth of the MWs and the location of the hot spots. In general, the presence of sharp edges and right angles

[2, 3] found that the power density at the edge decreased with the increase of the opening angle; thus, oval or circular forms may in some cases reduce this problem. However, in these forms the MW power is concentrated in the center [4].

leads to significant local overheating at these locations. Sundberg et al.

**36**

Drying is one of the most used methods for preserving food and preventing microbiological degradation. Food drying is also used for economic interests by lightening the product to minimize the transport costs (e.g., milk powder) or even for consumption aspects by creating new textures and/or products (e.g., prunes). This process aims to reduce the water activity (Aw) of the food product by removing some of its water. The amount of water to be removed to achieve the microbiological stability can be determined thanks to the sorption isotherm curve which shows the relationship between the water content and the water activity of a product. Generally, the water activity threshold from which there is no further development of pathogenic bacteria is 0.85–0.86 and 0.7 and 0.6 for yeasts and molds, respectively.

It is interesting to note that Aw does not only control the development of microorganisms, it also influences the rate of the chemical and biochemical reactions that take place within the food. The nonenzymatic browning (Maillard reaction) has a maximal activity for an Aw of 0.6–0.7, while the oxidation of lipids develops rather at very low and very high values of Aw. Thus, it is proper to adjust the final moisture of the product according to these considerations. The area generally targeted for good stability of the dried product is the range of Aw between 0.3 and 0.4. An important aspect must be emphasized here, namely, that drying has almost no lethal effect on the microorganisms present on the product due to insufficient product temperatures reached during drying. Proper packaging is therefore essential to avoid moisture recovery and keep the quality of the dehydrated product.

Industrial drying techniques are very varied depending on the nature of the product to dry (liquid, pasty, solid, or particulate) and of the desired final qualities. Most often, hot air (HA) convective drying is the main dehydration technique used in food industries. However, this method undergoes several problems such as poor end-product quality and low operation performance. Generally, in conventional drying method, two steps take place: a heat transfer from hot and dry surrounding medium to the product and then a mass (water and/or volatile compounds) transfer from the product to the surrounding atmosphere. In general, external heat and mass transfer can be easily controlled by a good monitoring of the drying air characteristics (velocity, temperature, relative humidity); thus, the internal transfer is the limiting step and the effective driving force for the drying operation. The drying rate decreases with time, and the removal of water becomes difficult. Therefore, conventional HA drying requires the application of severe conditions, particularly at the end of operation, which result in overheating and overdrying of the product surface. These reasons have greatly encouraged engineers to develop and propose new drying techniques such as MW drying. For example, MW drying was successfully applied to dry potatoes chips, pasta, and snacks [5]. Several studies of MW drying were resumed in the literature [6].

#### **2.2 Microwave drying versus hot air drying**

During MW drying of strong moisture content product, EM energy is supplied directly to the volume of the product, which causes a rapid increase of the product temperature and an instantaneous vaporization of water inside the product [7]. This phenomenon causes an increase in the internal pressure and drives the water to liquid state toward the product surface [8]. This forced outflow of water increases the drying rate and so reduces the operation time (up to five times less than HA air drying for many products). Likewise, the increase in internal pressure prevents

food shrinkage and case hardening during drying, which have a positive impact on the texture of the MW dried product. Indeed, it promotes a greater porosity and increases the rehydration ability [9].

The action of conservation provided by the drying to foodstuffs is mainly due to the decrease of Aw which thus makes it possible to limit the development of microorganisms. However, an additional action is observed in the case of MW drying. In fact, the rapid rise in temperature for water-rich products seems to produce a thermal shock effect on thermosensitive microorganisms. Laguerre et al. [10] have shown, in a comparative study of drying of onions either by HA or by MWs, a reduction of the total microbial count ten times greater for MW drying (about one to two log reductions). This is a significant advantage of MW drying compared to hot air drying.

Although the selectivity of EF may cause heating heterogeneity, this selectivity is rather an advantage in the case of MW drying. The level of energy absorption is controlled by the wet parts, resulting in positive selective heating of the inner layers of the product still having a relatively high moisture content without affecting the relatively dry outer layers, thereby facilitating the outflow of water to the surface.

However, even if the MW drying is faster than that of HA method, the MW drying efficiency is limited because of the rapid saturation of the surrounded air due to its low temperature. For this reason, MWs are usually associated with HA flow to improve water transfer at the surface of the product. Another difference between MW and HA drying is the surface temperature. During HA drying, the surface temperature does not exceed the controlled surrounding air temperature, which may be low (30–40°C) during thermosensitive product drying (e.g., aromatic plants), whereas excessive surface temperature may occur during MW drying, especially along the corner or edges, resulting in product carbonization and production of off-flavors especially during the final stages of operation [6].

#### **2.3 Controlled power microwave drying: innovative method to prevent runaway heating**

In many works, a constant MW applied power is usually used throughout the drying period. This practice promotes the phenomena of thermal runaway (local overheating) at the end of drying. During MW drying performed at constant power, the applied specific power (power/product mass) increases exponentially as can be seen in **Figure 1** for the drying of tomato as an example [11]. Thus, the product receives more and more energy over time while it needs less and less. Moreover, the thermal properties of the product (specific heat and thermal diffusivity) decrease at the same time as the moisture of the product; therefore, it becomes easier to heat the product while the heat accumulated in a zone can less easily diffuse to the whole product. All this, combined with the phenomenon of dimensional resonance, can lead to thermal runaway. This phenomenon can be observed in the case of drying onions [10, 12]. **Figure 2** shows the evolution of hot spots up to charring on onion slices during MW drying. The fact that the black spots are very localized initially confirms the presence of dimensional resonance phenomena in this case.

To improve the quality of MW dried foods, the control of the applied power throughout the drying was studied in the literature. Li et al. [13] proposed the control of applied power according to the set product temperature, whereas Soysal et al. [14] adapted the applied power as a function of processing time. A very good quality product was obtained by Laguerre et al. [10, 15]. The authors controlled the power as a function of the product mass. This method was successfully tested for drying onions and tomatoes as presented in **Table 1**. A final product of fresh-like color, without any black spots, was obtained.

**39**

**Figure 2.**

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

**2.4 Combined microwave drying technologies**

drying, and MW freeze drying.

**Figure 1.**

*during drying of tomatoes [11].*

*2.4.1 MW-assisted hot air drying*

Despite its several advantages over the conventional methods, MW drying has some crucial problems as explained above. However, MW drying combined with other conventional heating methods enhances the drying efficiency as well as the dried product quality compared to MW drying alone. Applications of combined MW drying, principally, include MW-assisted hot air (HA) drying, MW vacuum

*Evolution of the specific power (W/g) as a function of time (min) for different initial specific power values* 

The application of MW energy (internal heating) associated with hot air flow (superficial heating) is a good method to overcome certain problems related to the use of these two methods separately. MW heating may be applied at the beginning of the drying process to heat the internal layers of the product rapidly. MW heating can be also applied at the second step of drying process, when the temperature profile is established, to force vapor out of the product which leads to create a porous structure. MW heating can also be applied at the end of drying process, where the mass transfer is reduced to improve the drying rate by removing the bound water [9]. For example, MW drying combined with HA drying at the last stage reduced the drying time by 64% as compared to convective air drying [16]. Saving drying time and improved quality were also reported, using this method, for other fruits

such as blueberries [17], macadamia nuts [18], and green peas [19].

*Evolution of hot spot during MW drying of onion slices [10].*

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

#### **Figure 1.**

*Food Preservation and Waste Exploitation*

increases the rehydration ability [9].

hot air drying.

**heating**

food shrinkage and case hardening during drying, which have a positive impact on the texture of the MW dried product. Indeed, it promotes a greater porosity and

The action of conservation provided by the drying to foodstuffs is mainly due to the decrease of Aw which thus makes it possible to limit the development of microorganisms. However, an additional action is observed in the case of MW drying. In fact, the rapid rise in temperature for water-rich products seems to produce a thermal shock effect on thermosensitive microorganisms. Laguerre et al. [10] have shown, in a comparative study of drying of onions either by HA or by MWs, a reduction of the total microbial count ten times greater for MW drying (about one to two log reductions). This is a significant advantage of MW drying compared to

Although the selectivity of EF may cause heating heterogeneity, this selectivity is rather an advantage in the case of MW drying. The level of energy absorption is controlled by the wet parts, resulting in positive selective heating of the inner layers of the product still having a relatively high moisture content without affecting the relatively dry outer layers, thereby facilitating the outflow of water to the surface. However, even if the MW drying is faster than that of HA method, the MW drying efficiency is limited because of the rapid saturation of the surrounded air due to its low temperature. For this reason, MWs are usually associated with HA flow to improve water transfer at the surface of the product. Another difference between MW and HA drying is the surface temperature. During HA drying, the surface temperature does not exceed the controlled surrounding air temperature, which may be low (30–40°C) during thermosensitive product drying (e.g., aromatic plants), whereas excessive surface temperature may occur during MW drying, especially along the corner or edges, resulting in product carbonization and produc-

tion of off-flavors especially during the final stages of operation [6].

confirms the presence of dimensional resonance phenomena in this case.

color, without any black spots, was obtained.

To improve the quality of MW dried foods, the control of the applied power throughout the drying was studied in the literature. Li et al. [13] proposed the control of applied power according to the set product temperature, whereas Soysal et al. [14] adapted the applied power as a function of processing time. A very good quality product was obtained by Laguerre et al. [10, 15]. The authors controlled the power as a function of the product mass. This method was successfully tested for drying onions and tomatoes as presented in **Table 1**. A final product of fresh-like

**2.3 Controlled power microwave drying: innovative method to prevent runaway** 

In many works, a constant MW applied power is usually used throughout the drying period. This practice promotes the phenomena of thermal runaway (local overheating) at the end of drying. During MW drying performed at constant power, the applied specific power (power/product mass) increases exponentially as can be seen in **Figure 1** for the drying of tomato as an example [11]. Thus, the product receives more and more energy over time while it needs less and less. Moreover, the thermal properties of the product (specific heat and thermal diffusivity) decrease at the same time as the moisture of the product; therefore, it becomes easier to heat the product while the heat accumulated in a zone can less easily diffuse to the whole product. All this, combined with the phenomenon of dimensional resonance, can lead to thermal runaway. This phenomenon can be observed in the case of drying onions [10, 12]. **Figure 2** shows the evolution of hot spots up to charring on onion slices during MW drying. The fact that the black spots are very localized initially

**38**

*Evolution of the specific power (W/g) as a function of time (min) for different initial specific power values during drying of tomatoes [11].*

#### **2.4 Combined microwave drying technologies**

Despite its several advantages over the conventional methods, MW drying has some crucial problems as explained above. However, MW drying combined with other conventional heating methods enhances the drying efficiency as well as the dried product quality compared to MW drying alone. Applications of combined MW drying, principally, include MW-assisted hot air (HA) drying, MW vacuum drying, and MW freeze drying.

#### *2.4.1 MW-assisted hot air drying*

The application of MW energy (internal heating) associated with hot air flow (superficial heating) is a good method to overcome certain problems related to the use of these two methods separately. MW heating may be applied at the beginning of the drying process to heat the internal layers of the product rapidly. MW heating can be also applied at the second step of drying process, when the temperature profile is established, to force vapor out of the product which leads to create a porous structure. MW heating can also be applied at the end of drying process, where the mass transfer is reduced to improve the drying rate by removing the bound water [9]. For example, MW drying combined with HA drying at the last stage reduced the drying time by 64% as compared to convective air drying [16]. Saving drying time and improved quality were also reported, using this method, for other fruits such as blueberries [17], macadamia nuts [18], and green peas [19].

**Figure 2.** *Evolution of hot spot during MW drying of onion slices [10].*

#### **Table 1.**

*Effect of the adaptation of the power applied on the color of the dried product.*

#### *2.4.2 MW vacuum drying*

In order to reduce the boiling point of water and to prevent the oxidation reactions, MW heating can be associated with a vacuum to maintain the quality (color and flavor) of the dried products. This method was successfully used to dry apple slices [20], pumpkin [21], and cranberries [22]. This method is better than MW air drying in terms of energy consumption, drying time, and quality of the dried products [6].

#### *2.4.3 MW freeze drying*

Lyophilization, also known as freeze drying, is a low-temperature dehydration process, which involves freezing the product at the first step and then removing the ice by sublimation under low-pressure conditions. It is used for dehydration of very heat-sensitive materials particularly in food and pharmaceutical industries. This method preserves the structure and minimizes the loss of valuable compounds. However, this technology is limited by its high cost. In MW freeze drying, MW heating can be applied concurrently during the sublimation to supply the heat under vacuum conditions. MW heating can also be applied separately after a traditional lyophilization step. MW freeze drying offers many advantages due to its low processing temperature and lack of oxygen in the processing environment [23, 24]. However, as the MW energy does not interact with frozen water, thermal runaway might take place which may result in poor product quality [6].

#### **3. Microwave pasteurization and sterilization of foods**

Pasteurization and sterilization are widely used to extend the shelf life of most foods. The main goals of pasteurization are to destroy vegetative pathogenic microorganisms and to deactivate some enzymes in foods. Pasteurization temperatures and treatment time vary, primarily, depending on the nature, the pH of the product,

**41**

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

conventional heating.

**3.1 Microbial decontamination by microwave heating**

and the target microorganism. In most pasteurization processes, the food is heated up to 60–85°C for a time varying from a few seconds to an hour. Pasteurization requires refrigerated storage conditions (3–4°C) for a storage life of 2–6 weeks. Sterilization, which can be seen as further pasteurization, destroys bacterial spores [25]. In solid or semisolid products, the heat transfer takes place mainly by conduction from the surface to the center often considered as the "cold" point. This leads to apply more severe conditions to reach the target temperature at the cold point, which results in an overcooking of the surface and a degradation of the quality of products. Optimizing thermal treatments (i.e., maximizing inactivation of bacteria while minimizing nutrient degradation) is therefore an important issue. However, this is not an easy task and it is always a technical and scientific challenge. Thanks to the direct and volumetric interaction between MWs and food, MW heating has the advantage of overcoming the limitation imposed by slow thermal diffusion of

Many studies demonstrated the effectiveness of using MW heating for pasteurization and sterilization of food [26–28]. Furthermore, different strains of microorganisms have been inactivated by MW heating, for example, *Bacillus cereus*, *Campylobacter jejuni*, *Clostridium perfringens*, *Escherichia coli*, *Enterococcus faecalis*,

**3.2 Thermal and athermal effects of microwave heating on microorganisms**

The study of microbial destruction mechanisms during an MW heating has attracted a lot of interest [31, 32]. In particular, the possible existence of nonthermal (athermal) effects of microwaves is a subject of debate. Several theories have been proposed to explain how electromagnetic fields can inactivate microorganisms at sublethal temperature conditions. This effect would be due to the interaction between microwaves and certain cellular constituents. In contrast, many studies have refuted the lethal nonthermal effect of MWs. To distinguish between thermal and nonthermal effects, most studies are based on the experimental evaluation of

Fujikawa et al. [33] showed no difference between inactivation treatments for *E. coli* (suspended in PB phosphate buffer) in a conventional water bath and in a MW oven. Welt et al. [34] have developed a device to evaluate the possible nonthermal effects of microwaves. They compared the inactivation of *Clostridium sporogenes* spores in a model medium (a phosphate buffer) under a same time-temperature condition for conventional and MW treatment. The results demonstrate

On the other hand, several studies demonstrated that the microwaves have a more important bactericidal effect [35, 36]. Sato et al. [37] found that the inactivation of *E. coli* K12 exposed to MW radiation was higher than that obtained in a

Some authors support the thesis of improved bactericidal effect of microwaves. Kozempel et al. [38] developed an experimental device for detecting a possible nonthermal effect of microwaves on microorganisms at low temperature. The process combines instantaneous energy input to the food system by microwaves with rapid removal of thermal energy. The system used is a double-tube heat exchanger installed inside a continuous MW tunnel. The outer tube is microwaveable, while the inner tube is stainless steel and was used to cool the system instantly to keep the temperature at 45°C. The nonthermal effect of MW radiation has not been

*Listeria monocytogenes*, *Staphylococcus aureus*, and *Salmonella* [29, 30].

conventional and MW inactivation under identical heating conditions.

the absence of a nonthermal effect.

water bath at the same temperature (45, 47, and 50°C).

#### *Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

*Food Preservation and Waste Exploitation*

**Product MW/hot air drying**

Onion [10]

Tomato [11]

**Table 1.**

*2.4.2 MW vacuum drying*

*2.4.3 MW freeze drying*

In order to reduce the boiling point of water and to prevent the oxidation reactions, MW heating can be associated with a vacuum to maintain the quality (color and flavor) of the dried products. This method was successfully used to dry apple slices [20], pumpkin [21], and cranberries [22]. This method is better than MW air drying in terms

**Without MW power adaptation With MW power adaptation**

Lyophilization, also known as freeze drying, is a low-temperature dehydration process, which involves freezing the product at the first step and then removing the ice by sublimation under low-pressure conditions. It is used for dehydration of very heat-sensitive materials particularly in food and pharmaceutical industries. This method preserves the structure and minimizes the loss of valuable compounds. However, this technology is limited by its high cost. In MW freeze drying, MW heating can be applied concurrently during the sublimation to supply the heat under vacuum conditions. MW heating can also be applied separately after a traditional lyophilization step. MW freeze drying offers many advantages due to its low processing temperature and lack of oxygen in the processing environment [23, 24]. However, as the MW energy does not interact with frozen water, thermal runaway

Pasteurization and sterilization are widely used to extend the shelf life of most foods. The main goals of pasteurization are to destroy vegetative pathogenic microorganisms and to deactivate some enzymes in foods. Pasteurization temperatures and treatment time vary, primarily, depending on the nature, the pH of the product,

of energy consumption, drying time, and quality of the dried products [6].

*Effect of the adaptation of the power applied on the color of the dried product.*

might take place which may result in poor product quality [6].

**3. Microwave pasteurization and sterilization of foods**

**40**

and the target microorganism. In most pasteurization processes, the food is heated up to 60–85°C for a time varying from a few seconds to an hour. Pasteurization requires refrigerated storage conditions (3–4°C) for a storage life of 2–6 weeks. Sterilization, which can be seen as further pasteurization, destroys bacterial spores [25]. In solid or semisolid products, the heat transfer takes place mainly by conduction from the surface to the center often considered as the "cold" point. This leads to apply more severe conditions to reach the target temperature at the cold point, which results in an overcooking of the surface and a degradation of the quality of products. Optimizing thermal treatments (i.e., maximizing inactivation of bacteria while minimizing nutrient degradation) is therefore an important issue. However, this is not an easy task and it is always a technical and scientific challenge. Thanks to the direct and volumetric interaction between MWs and food, MW heating has the advantage of overcoming the limitation imposed by slow thermal diffusion of conventional heating.

#### **3.1 Microbial decontamination by microwave heating**

Many studies demonstrated the effectiveness of using MW heating for pasteurization and sterilization of food [26–28]. Furthermore, different strains of microorganisms have been inactivated by MW heating, for example, *Bacillus cereus*, *Campylobacter jejuni*, *Clostridium perfringens*, *Escherichia coli*, *Enterococcus faecalis*, *Listeria monocytogenes*, *Staphylococcus aureus*, and *Salmonella* [29, 30].

#### **3.2 Thermal and athermal effects of microwave heating on microorganisms**

The study of microbial destruction mechanisms during an MW heating has attracted a lot of interest [31, 32]. In particular, the possible existence of nonthermal (athermal) effects of microwaves is a subject of debate. Several theories have been proposed to explain how electromagnetic fields can inactivate microorganisms at sublethal temperature conditions. This effect would be due to the interaction between microwaves and certain cellular constituents. In contrast, many studies have refuted the lethal nonthermal effect of MWs. To distinguish between thermal and nonthermal effects, most studies are based on the experimental evaluation of conventional and MW inactivation under identical heating conditions.

Fujikawa et al. [33] showed no difference between inactivation treatments for *E. coli* (suspended in PB phosphate buffer) in a conventional water bath and in a MW oven. Welt et al. [34] have developed a device to evaluate the possible nonthermal effects of microwaves. They compared the inactivation of *Clostridium sporogenes* spores in a model medium (a phosphate buffer) under a same time-temperature condition for conventional and MW treatment. The results demonstrate the absence of a nonthermal effect.

On the other hand, several studies demonstrated that the microwaves have a more important bactericidal effect [35, 36]. Sato et al. [37] found that the inactivation of *E. coli* K12 exposed to MW radiation was higher than that obtained in a water bath at the same temperature (45, 47, and 50°C).

Some authors support the thesis of improved bactericidal effect of microwaves. Kozempel et al. [38] developed an experimental device for detecting a possible nonthermal effect of microwaves on microorganisms at low temperature. The process combines instantaneous energy input to the food system by microwaves with rapid removal of thermal energy. The system used is a double-tube heat exchanger installed inside a continuous MW tunnel. The outer tube is microwaveable, while the inner tube is stainless steel and was used to cool the system instantly to keep the temperature at 45°C. The nonthermal effect of MW radiation has not been

observed for yeast, *Pediococcus* sp., *Escherichia coli*, *Listeria innocua*, or *Enterobacter aerogenes*, in various liquids. However, the author has reported that MWs can improve or amplify the thermal effect in lethal conditions [38]. In the same context, Ramaswamy et al. [39] found that the inactivation of *S. cerevisiae* inoculated in apple juice treated with steam, hot water, or MW was not significantly different at sublethal temperature (<40°C). However, they found that MW radiations enhanced inactivation for same lethal temperature conditions (55–65°C).

Numerous studies on the interactions between MWs and certain cellular constituents, such as DNA, the cell membrane, enzymes, and proteins, have been carried out. Kakita et al. [40] studied the survival of bacteriophage PL-1, which is specific for *Lactobacillus casei*, under MW irradiation. More viral DNA fragmentation was found for MW heating over conventional heating. Shamis et al. [41] studied the effects of MW radiation on the membrane of the *E. coli* cell under sublethal temperature conditions (<40°C). Compared to conventional treatment, a different cellular morphology was observed (the cells are contracted and dehydrated). Nevertheless, this effect seems to be temporary; 10 min after the end of the exposure, the morphology of the cell seemed to return to the initial state of untreated controls. In this experiment, cell viability test revealed that the MW treatment was not bactericidal, since 88% of the cells were recovered. Similarly, Woo et al. [42] reported that MW radiation of *Escherichia coli* and *Bacillus subtilis* resulted in an increase in the amounts of nucleotides and protein released from cells. This leak was strongly correlated to MW power. The authors observed, by scanning electron microscopy, a significant damage on the surface of MW-treated *E. coli* cells; however, there was no significant change observed for *B. subtilis* cells. Likewise, Shin and Pyun [43] showed that MW treatment (at 50°C) causes irreversible damage to the membrane of *Lactobacillus plantarum*, associated with increase of the permeability. Also, observations by electron microscopy showed a change in cellular morphology on *Candida albicans* treated with MW [44].

To prove the existence of nonthermal effect of microwaves on microorganisms, exactly the same thermal history must be reproduced for MW and conventional treatments. Most of studies previously cited applied temperature measurement techniques inappropriate to MW heating, where the temperature was monitored at a single point of the sample. In addition, it is also important to eliminate the heating heterogeneity inherent in MW processing. Consequently, microorganisms are subjected to uneven heating as a result of the presence of cold and hot spots within the same sample. In summary, so far, the existence of nonthermal effect of MWs on microorganisms has not been proven; even if this effect exists, it has no significant consequence on the MW heating of foods.

#### **3.3 Advantages and limitations of microwave microbial decontamination**

In fact, it is difficult to compare the efficiency of MW over conventional heating process because of the inherent differences of heating principle between the two technologies [45].

In the case of conventional heating, a slow heat exchange occurs between the heating medium and the product. The heat diffusion inside the product depends on its physical properties (specific heat, thermal conductivity, porosity, etc.). However, it is well known that foods are bad thermal conductors, heat diffusion toward the cold spot is usually slow, and MW heating is generally faster than conventional heating. The heat is generated directly within the food. This direct volumetric heating significantly reduces the processing time resulting in greater retention of nutrients, sensitive vitamins, and aromatic constituents. Microwave-processed foods may also have better texture, taste, and appearance than products processed by conventional methods. For example, a two times faster MW pasteurization treatment of pickled

**43**

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

surface cooking, for example [50].

asparagus at 915 MHz was published [46]. This advantage reduced significantly the thermal degradation of asparagus compared to a conventional treatment in a water bath. Similarly, an acceptable MW pasteurization of foie gras was reported with a time saving of 50% and better organoleptic qualities compared to a traditional method [47]. Moreover, MW pasteurization of packaged products is possible for different packaging materials (plastic, paper, and glass) [48, 49]. Furthermore, this technology can be combined with other technologies such as infrared heating for

Despite the numerous advantages of MW decontamination technology, heating heterogeneity is a serious problem that leads to incomplete inactivation of microorganisms. Several studies have reported the survival of pathogens such as *Salmonella*

Goksoy et al. [53, 54] studied the effect of short-time MW exposures on *Escherichia coli* K12 and *Campylobacter jejuni* inoculated on chicken meat. A temperature variation of 20°C was measured between different parts of the sample. The auteurs reported that the samples subjected to MWs showed signs of partial cooking areas. There was no evidence that short-time exposure (up to 30 s) to MWs had any bactericidal effect on microorganisms. Apostolou et al. [55] confirmed these results. MW heating of chicken portions did not eliminate *E. coli O157: H7*. A significant

On the other hand, the heterogeneous heating causes a severe deterioration of food quality. Local overheating often results in irremediable changes of color where the temperature is highest [56]. These phenomena are mainly observed at the

Another difficulty concerning MW decontamination is the problem of cold spot localization. During a typical thermal process, the cold point is well defined and located often at the center of the product. During MW pasteurization, one point temperature monitoring within the product is not sufficient to ensure food safety [57]. For example, Schnepf and Barbeau [58] studied the inactivation of inoculated *Salmonella* in poultry. Their results showed that measuring the internal temperature during MW treatment does not reflect the surface inactivation, where the temperature was lower. To locate the cold spot, the chemical marker method developed by Kim and Taub [59] was successfully used [60–62]. Combined with experimental investigations, numerical simulations are highly recommended to find the cold spot and to achieve an

accurate study to develop a reliable MW decontamination process [57, 63, 64].

Before accepting MW technology as a reliable method for pasteurization and/ or sterilization of food, it is important to ensure uniform heating during treatment. Several studies have been conducted to improve the quality and safety of

Fung and Cunningham [65] reported that MW heating in combination with conventional heating results in more uniform heating of food and better inactivation of bacteria. Datta et al. [66] found that MW heating in combination with infrared heating or air jets decreases the nonuniformity of temperature distribution. In the same field, Maktabi et al. [67] investigated the synergistic killing effect of laser, MW, and UV radiation on *E. coli* and on some other spoilage and pathogenic bacteria. It was found that the overall reduction in viable counts was significantly higher than the sum of the reduction values for the individual treatments. The order of the treatment processes had also a significant influence on microbial destruction. A successive process by laser, MW, and then UV was the most effective. Similarly, Lau and Tang [46] studied the heating uniformity and textural quality of pickled

spp. [51] and *L. monocytogenes* [52], in foods heated in MW ovens.

variation of temperature (from 66.7 to 92°C) was also observed.

corners and the edges of the product due to wave reflection.

**3.4 Minimizing the heterogeneity of microwave heating**

MW-treated products, and various solutions have been proposed.

#### *Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

*Food Preservation and Waste Exploitation*

consequence on the MW heating of foods.

**3.3 Advantages and limitations of microwave microbial decontamination**

In fact, it is difficult to compare the efficiency of MW over conventional heating process because of the inherent differences of heating principle between the two

In the case of conventional heating, a slow heat exchange occurs between the heating medium and the product. The heat diffusion inside the product depends on its physical properties (specific heat, thermal conductivity, porosity, etc.). However, it is well known that foods are bad thermal conductors, heat diffusion toward the cold spot is usually slow, and MW heating is generally faster than conventional heating. The heat is generated directly within the food. This direct volumetric heating significantly reduces the processing time resulting in greater retention of nutrients, sensitive vitamins, and aromatic constituents. Microwave-processed foods may also have better texture, taste, and appearance than products processed by conventional methods. For example, a two times faster MW pasteurization treatment of pickled

observed for yeast, *Pediococcus* sp., *Escherichia coli*, *Listeria innocua*, or *Enterobacter aerogenes*, in various liquids. However, the author has reported that MWs can improve or amplify the thermal effect in lethal conditions [38]. In the same context, Ramaswamy et al. [39] found that the inactivation of *S. cerevisiae* inoculated in apple juice treated with steam, hot water, or MW was not significantly different at sublethal temperature (<40°C). However, they found that MW radiations enhanced

Numerous studies on the interactions between MWs and certain cellular constituents, such as DNA, the cell membrane, enzymes, and proteins, have been carried out. Kakita et al. [40] studied the survival of bacteriophage PL-1, which is specific for *Lactobacillus casei*, under MW irradiation. More viral DNA fragmentation was found for MW heating over conventional heating. Shamis et al. [41] studied the effects of MW radiation on the membrane of the *E. coli* cell under sublethal temperature conditions (<40°C). Compared to conventional treatment, a different cellular morphology was observed (the cells are contracted and dehydrated). Nevertheless, this effect seems to be temporary; 10 min after the end of the exposure, the morphology of the cell seemed to return to the initial state of untreated controls. In this experiment, cell viability test revealed that the MW treatment was not bactericidal, since 88% of the cells were recovered. Similarly, Woo et al. [42] reported that MW radiation of *Escherichia coli* and *Bacillus subtilis* resulted in an increase in the amounts of nucleotides and protein released from cells. This leak was strongly correlated to MW power. The authors observed, by scanning electron microscopy, a significant damage on the surface of MW-treated *E. coli* cells; however, there was no significant change observed for *B. subtilis* cells. Likewise, Shin and Pyun [43] showed that MW treatment (at 50°C) causes irreversible damage to the membrane of *Lactobacillus plantarum*, associated with increase of the permeability. Also, observations by electron microscopy showed a change in cellular morphology on *Candida albicans* treated with MW [44]. To prove the existence of nonthermal effect of microwaves on microorganisms, exactly the same thermal history must be reproduced for MW and conventional treatments. Most of studies previously cited applied temperature measurement techniques inappropriate to MW heating, where the temperature was monitored at a single point of the sample. In addition, it is also important to eliminate the heating heterogeneity inherent in MW processing. Consequently, microorganisms are subjected to uneven heating as a result of the presence of cold and hot spots within the same sample. In summary, so far, the existence of nonthermal effect of MWs on microorganisms has not been proven; even if this effect exists, it has no significant

inactivation for same lethal temperature conditions (55–65°C).

**42**

technologies [45].

asparagus at 915 MHz was published [46]. This advantage reduced significantly the thermal degradation of asparagus compared to a conventional treatment in a water bath. Similarly, an acceptable MW pasteurization of foie gras was reported with a time saving of 50% and better organoleptic qualities compared to a traditional method [47]. Moreover, MW pasteurization of packaged products is possible for different packaging materials (plastic, paper, and glass) [48, 49]. Furthermore, this technology can be combined with other technologies such as infrared heating for surface cooking, for example [50].

Despite the numerous advantages of MW decontamination technology, heating heterogeneity is a serious problem that leads to incomplete inactivation of microorganisms. Several studies have reported the survival of pathogens such as *Salmonella* spp. [51] and *L. monocytogenes* [52], in foods heated in MW ovens.

Goksoy et al. [53, 54] studied the effect of short-time MW exposures on *Escherichia coli* K12 and *Campylobacter jejuni* inoculated on chicken meat. A temperature variation of 20°C was measured between different parts of the sample. The auteurs reported that the samples subjected to MWs showed signs of partial cooking areas. There was no evidence that short-time exposure (up to 30 s) to MWs had any bactericidal effect on microorganisms. Apostolou et al. [55] confirmed these results. MW heating of chicken portions did not eliminate *E. coli O157: H7*. A significant variation of temperature (from 66.7 to 92°C) was also observed.

On the other hand, the heterogeneous heating causes a severe deterioration of food quality. Local overheating often results in irremediable changes of color where the temperature is highest [56]. These phenomena are mainly observed at the corners and the edges of the product due to wave reflection.

Another difficulty concerning MW decontamination is the problem of cold spot localization. During a typical thermal process, the cold point is well defined and located often at the center of the product. During MW pasteurization, one point temperature monitoring within the product is not sufficient to ensure food safety [57]. For example, Schnepf and Barbeau [58] studied the inactivation of inoculated *Salmonella* in poultry. Their results showed that measuring the internal temperature during MW treatment does not reflect the surface inactivation, where the temperature was lower. To locate the cold spot, the chemical marker method developed by Kim and Taub [59] was successfully used [60–62]. Combined with experimental investigations, numerical simulations are highly recommended to find the cold spot and to achieve an accurate study to develop a reliable MW decontamination process [57, 63, 64].

#### **3.4 Minimizing the heterogeneity of microwave heating**

Before accepting MW technology as a reliable method for pasteurization and/ or sterilization of food, it is important to ensure uniform heating during treatment. Several studies have been conducted to improve the quality and safety of MW-treated products, and various solutions have been proposed.

Fung and Cunningham [65] reported that MW heating in combination with conventional heating results in more uniform heating of food and better inactivation of bacteria. Datta et al. [66] found that MW heating in combination with infrared heating or air jets decreases the nonuniformity of temperature distribution. In the same field, Maktabi et al. [67] investigated the synergistic killing effect of laser, MW, and UV radiation on *E. coli* and on some other spoilage and pathogenic bacteria. It was found that the overall reduction in viable counts was significantly higher than the sum of the reduction values for the individual treatments. The order of the treatment processes had also a significant influence on microbial destruction. A successive process by laser, MW, and then UV was the most effective. Similarly, Lau and Tang [46] studied the heating uniformity and textural quality of pickled

asparagus pasteurized by MW in comparison with the conventional hot-water pasteurization method. Two successive heating steps, first in water bath and then in 915 MHz MW oven, were successfully applied. Moreover, covering the top onethird of the product glass bottle with aluminum foil eliminated the overheating at the edges. MW pasteurization also reduced the cook value for pickled asparagus and reduced textural degradation.

On the other hand, the presence of an absorbent medium around the product can reduce the overheating of edges and corners. For example, some authors reported that immersion of the sample in hot water [48] or the use of a steam flow into the oven cavity [68] may be used to ensure a safer and better quality end product. Microwave-circulated water combination (MCWC) heating system demonstrated a relatively uniform heat distribution within packaged food products. Guan et al. [48] reported that microbial destruction by a pilot-scale MCWC heating system matched with designed degrees of sterilization (F0 value) for a conventional treatment.

Koskiniemi et al. [69] improved the heating uniformity of packaged acidified vegetables using a continuous 915 MHz MW system with a two-stage rotation device to rotate the products 180° during treatment. This method increased also the average temperature at the cold point to meet the industrial standard for in-pack pasteurization of acidified vegetables.

Pulsed MW heating technique was also successfully tested. In this method, pulsed application of energy—i.e., turning the magnetron power "on" and "off" intermittently—leads to thermal energy equalization via conduction from hot to cold region during the power-off periods. This results in more uniform temperature distribution within the sample than during continuous application of energy [70, 71]. Sato et al. [37] reported also an enhanced killing rate of *Escherichia coli* K12 by using pulsed waves compared to continuous treatment.

#### **3.5 Modeling and optimization of microwave heating**

Computational fluid dynamics (CFD) is widely used as an established approach for understanding and then optimizing food processing based on the solution to partial differential equations of mass, momentum, and energy transport. MW heating is a multiphysics phenomenon that requires electromagnetic propagation equations (i.e., Maxwell's equation) to be combined simultaneously with the heat transfer equation to predict the MW power absorption as well as the temperature distribution inside the product [72]. Modeling of MW heating is widely studied in the literature. Interested readers can consult specialized references for more details [73].

In order to design and optimize a reliable MW pasteurization and/or sterilization process, heating model needs to be coupled with kinetic models correlating microbial decontamination. The resulting global model has to mimic the spatial temperature distribution as well as the microbial inactivation at every point within the sample. Few coupled numerical studies of bacterial inactivation by MW heating are reported in the literature. Recently, Masood et al. [64] published an excellent review about emerging technologies modeling to ensure microbial safety of foods.

The classical concept of decimal reduction time and thermal resistance constant (D and z values) was also used to characterize the microbial inactivation by MW heating. Cañumir et al. [74] determined D-values at constant power levels and proposed a z-value in watt to represent the resistance of a target germ during MW heating. Laguerre et al. [75] proposed new specific power destruction parameters, Dp- and zp-values, to qualify MW heating. The decimal reduction time (Dp value) is the treatment time required to reduce microbial population by 90% at a constant applied specific power expressed in W/mL or in W/g. The zp value is the change of specific power necessary to cause a tenfold change in the Dp values

**45**

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

for MW sterilization of infant food was also determined.

temperature distribution within the sample [57, 63].

and (4) uncontrolled factors cannot be taken into account.

processes (beef burgundy, fish) [82, 83].

**4. Conclusions**

of microorganism under specified conditions. This concept has been successfully tested for sterilization of infant food in a lab-scale MW pilot. The optimal condition

Because of the heterogeneity of MW heating, microbial inactivation kinetics need to be coupled with nonlinear heat transfer model to calculate the temporospatial survival of bacteria [63]. Mallikarjunan et al. [76] developed a mathematical model that includes mass heat transfer to microbial inactivation kinetics. The variation of the dielectric properties with respect to the temperature is taken into account in the simulation process. A good agreement with experimental data was obtained. Hamoud-Agha et al. [57, 63] used COMSOL Multiphysics to investigate the inactivation of *E. coli* K12 suspended in a gel medium, comparing MW processing with conventional thermal treatment in a water bath. The authors coupled the thermal nonlinear microbiological inactivation model of Geeraerd et al. [77] with heat transfer and Maxwell's equations integrated into a finite element model under dynamic heating conditions. The results revealed uneven temperature distribution during MW heating which led to a lower inactivation efficiency than water bath treatment. Simulation results were in good agreement with experimental data. The modeling approach to estimate efficiency of microbial inactivation was reliable despite the thermal heterogeneity inherent in the MW treatment. Application of holding time at lethal temperatures (55 and 57°C) did not help to homogenize the

However, because of digital resources required and time consumption, the use of physical models as presented before could be delicate for real industrial applications in the food industry. On the other hand, another approach based on experimental designs (EDs) and response surface methodology (RSM) can be relatively easy, fast to implement, and quite useful [78]. Nevertheless, RSM has some limitations [8]: (1) it uses a priori models (quadratic model whatever the studied response); (2) the number of tests to be reset can increase very quickly with the number of factors in the plan; (3) the factors must be completely independent;

Another method proposed by Lesty et al. [79], based on iconographic correlations (CORICO), makes it possible to circumvent these difficulties [8]. After analysis of the experimental plan data, CORICO proposes regression models whose regressors are logical interactions (AND, Exclusive OR, IF, etc.) between factors. In addition, CORICO tolerates linked factors and allows the consideration of uncontrolled factors. Furthermore, it needs few numbers of essays comparatively to classical EDs, (17 essays for a 9-factor CORICO designs against 533 for a 9-factor Doehlert design), which allows to minimize costs. This method has recently been used in the agri-food sector for the optimization of the drying process of different food products (tomato, microalgae, apple) [11, 80, 81] as well as for MW cooking

Conventional heat treatments for food preservation are generally characterized by poor end-product quality. Furthermore, these methods are not optimized for solid foods because of slow heat transfer from the surface to the cold point, often at the center of the product. Enhanced organoleptic and nutritional food properties combined with food safety is the aim of modern food processing technologies. Microwave (MW) heating has the advantages to overcome the limitation of slow thermal diffusion imposed by conventional heating. This technology knows a growing industrial demand thanks to its flexible and rapid heating performance. MW

#### *Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

*Food Preservation and Waste Exploitation*

and reduced textural degradation.

pasteurization of acidified vegetables.

asparagus pasteurized by MW in comparison with the conventional hot-water pasteurization method. Two successive heating steps, first in water bath and then in 915 MHz MW oven, were successfully applied. Moreover, covering the top onethird of the product glass bottle with aluminum foil eliminated the overheating at the edges. MW pasteurization also reduced the cook value for pickled asparagus

On the other hand, the presence of an absorbent medium around the product can reduce the overheating of edges and corners. For example, some authors reported that immersion of the sample in hot water [48] or the use of a steam flow into the oven cavity [68] may be used to ensure a safer and better quality end product. Microwave-circulated water combination (MCWC) heating system demonstrated a relatively uniform heat distribution within packaged food products. Guan et al. [48] reported that microbial destruction by a pilot-scale MCWC heating system matched with designed degrees of sterilization (F0 value) for a conventional treatment. Koskiniemi et al. [69] improved the heating uniformity of packaged acidified vegetables using a continuous 915 MHz MW system with a two-stage rotation device to rotate the products 180° during treatment. This method increased also the average temperature at the cold point to meet the industrial standard for in-pack

Pulsed MW heating technique was also successfully tested. In this method, pulsed application of energy—i.e., turning the magnetron power "on" and "off" intermittently—leads to thermal energy equalization via conduction from hot to cold region during the power-off periods. This results in more uniform temperature distribution within the sample than during continuous application of energy [70, 71]. Sato et al. [37] reported also an enhanced killing rate of *Escherichia coli*

Computational fluid dynamics (CFD) is widely used as an established approach for understanding and then optimizing food processing based on the solution to partial differential equations of mass, momentum, and energy transport. MW heating is a multiphysics phenomenon that requires electromagnetic propagation equations (i.e., Maxwell's equation) to be combined simultaneously with the heat transfer equation to predict the MW power absorption as well as the temperature distribution inside the product [72]. Modeling of MW heating is widely studied in the literature.

In order to design and optimize a reliable MW pasteurization and/or sterilization process, heating model needs to be coupled with kinetic models correlating microbial decontamination. The resulting global model has to mimic the spatial temperature distribution as well as the microbial inactivation at every point within the sample. Few coupled numerical studies of bacterial inactivation by MW heating are reported in the literature. Recently, Masood et al. [64] published an excellent review about emerging technologies modeling to ensure microbial safety of foods. The classical concept of decimal reduction time and thermal resistance constant (D and z values) was also used to characterize the microbial inactivation by MW heating. Cañumir et al. [74] determined D-values at constant power levels and proposed a z-value in watt to represent the resistance of a target germ during MW heating. Laguerre et al. [75] proposed new specific power destruction parameters, Dp- and zp-values, to qualify MW heating. The decimal reduction time (Dp value) is the treatment time required to reduce microbial population by 90% at a constant applied specific power expressed in W/mL or in W/g. The zp value is the change of specific power necessary to cause a tenfold change in the Dp values

Interested readers can consult specialized references for more details [73].

K12 by using pulsed waves compared to continuous treatment.

**3.5 Modeling and optimization of microwave heating**

**44**

of microorganism under specified conditions. This concept has been successfully tested for sterilization of infant food in a lab-scale MW pilot. The optimal condition for MW sterilization of infant food was also determined.

Because of the heterogeneity of MW heating, microbial inactivation kinetics need to be coupled with nonlinear heat transfer model to calculate the temporospatial survival of bacteria [63]. Mallikarjunan et al. [76] developed a mathematical model that includes mass heat transfer to microbial inactivation kinetics. The variation of the dielectric properties with respect to the temperature is taken into account in the simulation process. A good agreement with experimental data was obtained. Hamoud-Agha et al. [57, 63] used COMSOL Multiphysics to investigate the inactivation of *E. coli* K12 suspended in a gel medium, comparing MW processing with conventional thermal treatment in a water bath. The authors coupled the thermal nonlinear microbiological inactivation model of Geeraerd et al. [77] with heat transfer and Maxwell's equations integrated into a finite element model under dynamic heating conditions. The results revealed uneven temperature distribution during MW heating which led to a lower inactivation efficiency than water bath treatment. Simulation results were in good agreement with experimental data. The modeling approach to estimate efficiency of microbial inactivation was reliable despite the thermal heterogeneity inherent in the MW treatment. Application of holding time at lethal temperatures (55 and 57°C) did not help to homogenize the temperature distribution within the sample [57, 63].

However, because of digital resources required and time consumption, the use of physical models as presented before could be delicate for real industrial applications in the food industry. On the other hand, another approach based on experimental designs (EDs) and response surface methodology (RSM) can be relatively easy, fast to implement, and quite useful [78]. Nevertheless, RSM has some limitations [8]: (1) it uses a priori models (quadratic model whatever the studied response); (2) the number of tests to be reset can increase very quickly with the number of factors in the plan; (3) the factors must be completely independent; and (4) uncontrolled factors cannot be taken into account.

Another method proposed by Lesty et al. [79], based on iconographic correlations (CORICO), makes it possible to circumvent these difficulties [8]. After analysis of the experimental plan data, CORICO proposes regression models whose regressors are logical interactions (AND, Exclusive OR, IF, etc.) between factors. In addition, CORICO tolerates linked factors and allows the consideration of uncontrolled factors. Furthermore, it needs few numbers of essays comparatively to classical EDs, (17 essays for a 9-factor CORICO designs against 533 for a 9-factor Doehlert design), which allows to minimize costs. This method has recently been used in the agri-food sector for the optimization of the drying process of different food products (tomato, microalgae, apple) [11, 80, 81] as well as for MW cooking processes (beef burgundy, fish) [82, 83].

#### **4. Conclusions**

Conventional heat treatments for food preservation are generally characterized by poor end-product quality. Furthermore, these methods are not optimized for solid foods because of slow heat transfer from the surface to the cold point, often at the center of the product. Enhanced organoleptic and nutritional food properties combined with food safety is the aim of modern food processing technologies. Microwave (MW) heating has the advantages to overcome the limitation of slow thermal diffusion imposed by conventional heating. This technology knows a growing industrial demand thanks to its flexible and rapid heating performance. MW

heating is successfully used for food drying and decontamination. However, this process is still relatively poorly controlled because of complex interactions between foods and MWs. Furthermore, the heating heterogeneity is the major drawback of this technology. Several methods were, nevertheless, proposed in the literature to improve the heating homogeneity. In general, coupling MW heating with other heating methods largely improved the microbiological safety, the drying efficiency, and the quality of various food products. Physical modeling and simulation are important tools to understand and to optimize MW heating processes. The application of these models is limited in industrial scale; however, experimental designbased approaches could be promising methods. Even so, developing a reliable industrial MW heating process is still a challenge.

#### **Author details**

Jean-Claude Laguerre1 \* and Mohamad Mazen Hamoud-Agha<sup>2</sup>

1 Institut Polytechnique UniLaSalle, Beauvais, France

2 Minoteries Paulic, St-Gerand, France

\*Address all correspondence to: jean-claude.laguerre@unilasalle.fr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**47**

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

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*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

#### **References**

*Food Preservation and Waste Exploitation*

industrial MW heating process is still a challenge.

heating is successfully used for food drying and decontamination. However, this process is still relatively poorly controlled because of complex interactions between foods and MWs. Furthermore, the heating heterogeneity is the major drawback of this technology. Several methods were, nevertheless, proposed in the literature to improve the heating homogeneity. In general, coupling MW heating with other heating methods largely improved the microbiological safety, the drying efficiency, and the quality of various food products. Physical modeling and simulation are important tools to understand and to optimize MW heating processes. The application of these models is limited in industrial scale; however, experimental designbased approaches could be promising methods. Even so, developing a reliable

**46**

**Author details**

Jean-Claude Laguerre1

provided the original work is properly cited.

2 Minoteries Paulic, St-Gerand, France

1 Institut Polytechnique UniLaSalle, Beauvais, France

\*Address all correspondence to: jean-claude.laguerre@unilasalle.fr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\* and Mohamad Mazen Hamoud-Agha<sup>2</sup>

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sporogenes (PA 3679) spores. Applied and Environmental Microbiology.

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1994;**60**:482-488

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

by microwave irradiation. Applied and Environmental Microbiology. 1992;**58**:920-924

*Food Preservation and Waste Exploitation*

blueberry (*Vaccinium corymbosum* L.) fruits: Drying kinetics, polyphenols, anthocyanins, antioxidant capacity, colour and texture. Food Chemistry.

mealworms (*Tenebrio molitor*).

[25] Ahmed J, Ramaswamy HS, Raghavan VGS. Dielectric properties of butter in the MW frequency range as affected by salt and temperature. Journal of Food Engineering.

Technologies. 2018;**50**:20-25

Fluid Foods. 2012. pp. 31-46

[27] Shaheen MS, El-massry KF, El-ghorab AH, et al. Microwave Applications in Thermal Food Processing. 2012. pp. 3-16

[28] Guo Q , Sun D, Cheng J, et al. Microwave processing techniques and their recent applications in the food industry. Trends in Food Science & Technology. 2017;**67**:236-247

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[30] Zhou BW, Shin SG, Hwang KH, et al. Effect of microwave irradiation on cellular disintegration of gram positive and negative cells. Applied Microbiology and Biotechnology.

[31] Heddleson RA, Doores S. Factors affecting microwave heating of foods and microwave induced destruction

[32] Valsechi OAA, Horii J, De Angelis DF, et al. The effect of microwaves on microorganisms. Arquivos do Instituto

[33] Fujikawa H, Ushioda H, Kudo Y. Kinetics of *Escherichia coli* destruction

of foodborne pathogens—A review. Journal of Food Protection.

Biológico. 2004;**71**:399-404

2007;**82**:351-358

2008;**2**:67-71

2010;**87**:765-770

1994;**57**:1025-1037

Innovative Food Science and Emerging

[26] Salazar-gonzález C. Recent Studies Related to Microwave Processing of

[18] Silva FA, Marsaioli A, Maximo GJ, et al. Microwave assisted drying of macadamia nuts. Journal of Food Engineering. 2006;**77**:550-558

[19] Chahbani A, Fakhfakh N, Amine M, et al. Food bioscience microwave drying effects on drying kinetics, bioactive compounds and antioxidant activity of green peas (*Pisum sativum* L.). Food

Bioscience. 2018;**25**:32-38

2014;**57**:426-433

2017;**85**:204-211

[20] Schulze B, Hubbermann EM, Schwarz K. LWT—Food science and technology stability of quercetin derivatives in vacuum impregnated apple slices after drying (microwave vacuum drying , air drying , freeze drying) and storage. LWT— Food Science and Technology.

[21] Lemos R, Varaschim J, Tribuzi G, et al. Effect of multi-flash drying and microwave vacuum drying on the microstructure and texture of pumpkin

slices. LWT—Food Science and Technology. 2018;**96**:612-619

[22] Zielinska M, Ropelewska E, Markowski M. Thermophysical properties of raw, hot-air and microwave-vacuum dried cranberry fruits (*Vaccinium macrocarpon*). LWT—Food Science and Technology.

[23] Li CUI, Li-ying NIU, Da-jing LI, et al. Effects of different drying methods on quality, bacterial viability and storage stability of probiotic enriched apple snacks. Journal of Integrative Agriculture. 2018;**17**:247-255

[24] Kröncke N, Böschen V,

Woyzichovski J, et al. Comparison of suitable drying processes for

2016;**212**:671-680

**48**

[34] Welt BA, Tong CH, Rossen JL, et al. Effect of microwave radiation on inactivation of clostridium sporogenes (PA 3679) spores. Applied and Environmental Microbiology. 1994;**60**:482-488

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[37] Sato S, Shibata C, Yazu M. Nonthermal killing effect of microwave irradiation. Biotechnology Techniques. 1996;**10**:145-150

[38] Kozempel M, Cook RD, Scullen OJ, et al. Nonthermal effects of microwave energy on microorganisms at low temperature. Journal of Food Processing and Preservation. 2000;**24**:287-301

[39] Ramaswamy HS, Koutchma T, Tajchakavit S. Enhanced thermal effects under microwave heating conditions. In: Group CP-T& F, editor. Engineering and Food for the 21st Century. Boca Raton: CRC Press; 2002. pp. 739-761

[40] Kakita Y, Kashige N, Watanabe K, et al. Inactivation of lactobacillus bacteriophage PL-1 by microwave irradiation. Microbiology and Immunology. 1995;**39**:571-576

[41] Shamis Y, Taube A, Mitik-Dineva N, et al. Specific electromagnetic effects of microwave radiation on *Escherichia* 

*coli*. Applied and Environmental Microbiology. 2011;**77**:3017-3022

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[43] Shin JK, Pyun YR. Inactivation of *Lactobacillus plantarum* by pulsedmicrowave irradiation. Journal of Food Science. 1997;**62**:163-166

[44] Rosaspina S, Salvatorelli G, Anzanel D, et al. Effect of microwave radiation on *Candida albicans*. Microbios. 1994;**78**:55-59

[45] Shamis Y, Croft R, Taube A, et al. Review of the specific effects of microwave radiation on bacterial cells. Applied Microbiology and Biotechnology. 2012;**96**:319-325

[46] Lau MH, Tang J. Pasteurization of pickled asparagus using 915 MHz microwaves. Journal of Food Engineering. 2002;**51**:283-290

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[52] Farber JM, D'Aoust JY, Diotte M, et al. Survival of listeria spp. on raw whole chickens cooked in microwave ovens. Journal of Food Protection. 1998;**61**:1465-1469

[53] Goksoy EO, James C, James SJ. Non-uniformity of surface temperatures after microwave heating of poultry meat. Journal of Microwave Power and Electromagnetic Energy. 1999;**34**:149-160

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**51**

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J, et al. Improvement of heating uniformity in packaged acidified vegetables pasteurized with a 915 MHz continuous microwave system. Journal of Food Engineering. 2011;**105**:149-160

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2004;**64**:445-453

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Publisher 2011;27-28

in model food cylinders based on Maxwell's equations and Lambert's law during pulsed microwave

*Microwave Heating for Food Preservation DOI: http://dx.doi.org/10.5772/intechopen.82543*

*Food Preservation and Waste Exploitation*

Anantheswaran RC, et al. Viability loss of salmonella species, *Staphylococcus aureus*, and *Listeria monocytogenes* in complex foods heated by microwave energy. Journal of Food Protection.

convection microwave, and a

Food Safety. 1989;**9**:245-252

assisted thermal sterilization.

1993;**47**:91-97

2018;**96**:551-559

conventional electric oven. Journal of

[59] Kim HJ, Taub IA. Intrinsic chemical markers for aseptic processing of particulate foods. Food Technology.

[60] Auksornsri T, Bornhorst ER, Tang J, et al. Developing model food systems with rice based products for microwave

LWT—Food Science and Technology.

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[63] Hamoud-Agha MM, Curet S, Simonin H, et al. Microwave

inactivation of *Escherichia coli* K12 CIP 54.117 in a gel medium: Experimental and numerical study. Journal of Food Engineering. 2013;**116**:315-323

[64] Masood H, Trujillo FJ, Knoerzer K,

[65] Fung DYC, Cunningham FE. Effect of microwaves on microorganisms in foods. Journal of Food Protection.

[66] Datta AK, Geedipalli SSR, Almeida MF. Microwave combination heating. Food Technology. 2005;**59**:36-40

et al. Designing, Modeling, and Optimizing Processes to Ensure Microbial Safety and Stability Through Emerging Technologies. Elsevier Inc. Epub ahead of print 2018. DOI: 10.1016/

B978-0-12-811031-7.00006-6

1980;**43**:641-650

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[52] Farber JM, D'Aoust JY, Diotte M, et al. Survival of listeria spp. on raw whole chickens cooked in microwave ovens. Journal of Food Protection.

[53] Goksoy EO, James C, James SJ. Non-uniformity of surface temperatures after microwave heating of poultry meat. Journal of Microwave Power and Electromagnetic Energy.

[54] Göksoy EO, James C, Corry JEL. Effect of short-time microwave exposures on inoculated pathogens on chicken and the shelf-life of uninoculated chicken meat. Journal of Food Engineering. 2000;**45**:153-160

[55] Apostolou I, Papadopoulou C, Levidiotou S, et al. The effect of short-time microwave exposures on *Escherichia coli* O157:H7 inoculated onto chicken meat portions and whole chickens. International Journal of Food

Microbiology. 2005;**101**:105-110

10.1111/1750-3841.12959

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[58] Schnepf M, Barbeau WE. Survival of Salmonella Typhimurium in roasting chickens cooked in a microwave,

[56] Tang J. JFS Special Issue: 75 Years of Advancing Food Science, and Preparing for the Next 75 Unlocking Potentials of Microwaves for Food Safety and Quality. 80. Epub ahead of print. 2015. DOI:

[51] Heddleson RA, Doores S,

1996;**59**:813-818

1998;**61**:1465-1469

1999;**34**:149-160

**50**

[67] Maktabi S, Watson I, Parton R. Synergistic effect of UV, laser and microwave radiation or conventional heating on *E. coli* and on some spoilage and pathogenic bacteria. Innovative Food Science and Emerging Technologies. 2011;**12**:129-134

[68] Lacroix K, Orsat V, Nattress DF, et al. Dielectric heating of fresh meat for antimicrobial treatment. In: The 93rd Annual International Meeting of American Society of Agricultural Engineers (ASAE); Milwaukee. 2000

[69] Koskiniemi CB, Den TV, Simunovic J, et al. Improvement of heating uniformity in packaged acidified vegetables pasteurized with a 915 MHz continuous microwave system. Journal of Food Engineering. 2011;**105**:149-160

[70] Yang HW, Gunasekaran S. Comparison of temperature distribution in model food cylinders based on Maxwell's equations and Lambert's law during pulsed microwave heating. Journal of Food Engineering. 2004;**64**:445-453

[71] Gunasekaran S, Yang HW. Effect of experimental parameters on temperature distribution during continuous and pulsed microwave heating. Journal of Food Engineering. 2007;**78**:1452-1456

[72] Curet S, Rouaud O, Boillereaux L. Microwave tempering and heating in a single-mode cavity: Numerical and experimental investigations. Chemical Engineering and Processing: Process Intensification. 2008;**47**:1656-1665

[73] Zhao X, Huang K, Yan L. Review of Numerical Simulation of Microwave Heating Process. Intech Open Access Publisher 2011;27-28

[74] Cañumir JA, Celis JE, de Bruijn J, et al. Pasteurisation of apple juice by using microwaves. LWT—Food Science and Technology. 2002;**35**:389-392

[75] Laguerre JC, Pascale GW, David M, et al. The impact of microwave heating of infant formula model on neo-formed contaminant formation, nutrient degradation and spore destruction. Journal of Food Engineering. 2011;**107**:208-213

[76] Mallikarjunan P, Hung Y-C, Gundavarapu S. Modeling microwave cooking of cocktail shrimp. Journal of Food Process Engineering. 1996;**19**:97-111

[77] Geeraerd AH, Herremans CH, Van Impe JF. Structural model requirements to describe microbial inactivation during a mild heat treatment. International Journal of Food Microbiology. 2000;**59**:185-209

[78] Bas D, Boyacı İH. Modeling and optimization I: Usability of response surface methodology. Journal of Food Engineering. 2007;**78**:836-845

[79] Lesty M. Une nouvelle approche dans le choix des régresseurs de la régression multiple en présence d'interactions et de colinéarités. La Revue Modulad. 1999;**22**: 41-77

[80] Laguerre J-C, Ratoandromalala LP, Humeau A, et al. Iconographic correlation method and Fourier transform infrared spectroscopy (FTIR) for the optimization of a combined microwave hot air drying of the microalgae Isochrysis sp. In: Procedings of the 17th World Congress of Food Science and Technology—IUFOST. Montreal; 2014

[81] Laguerre J-C, Ratovoarisoa LG, Vivant A-C, et al. An iconographic correlation method for optimizing a combined microwave/hot air drying of apple *Malus domestica sp*. Journal of Food Processing & Technology. 2017;**8**:7110

#### *Food Preservation and Waste Exploitation*

[82] Jouquand C, Tessier FJ, Bernard J, et al. Optimization of microwave cooking of beef burgundy in terms of nutritional and organoleptic properties. LWT—Food Science and Technology. 2015;**60**:271-276

[83] Laguerre J-C, Douiri-Bedoui I, Chireux C, et al. The iconographic correlation (CORICO) method, a new approach for the optimization of microwave cooking processes: Application for cooking fish. In: EFFOST Annual Meeting. 2013

**53**

**Chapter 4**

**Abstract**

**1. Introduction**

of microbes in foods [1, 3].

Efficacy of Plant Antimicrobials as

Safe and hygienic food is a requirement for a healthy society. The problem of food-borne outbreaks has built a challenge against the food and health regulatory authorities to control the pathogenic microorganisms. Chemical preservative has created some health problems in foods, so the recent trend is towards the use of natural antimicrobials in foods. Plants are valuable source of bioactive molecules exhibiting antimicrobial activities. The plant antimicrobial compounds have diverse chemical nature such as alkaloids, phenolics, terpenes, terpenoids, flavonoids, essential oil, etc. Many plant antimicrobials possess antimicrobial activity against pathogens and spoilage microorganisms. But variation in effectiveness of these compounds against microorganisms in laboratory system and in real food systems is major determinant in their food use. Several plant extract or purified compounds are part of human diet since thousands of years. Although some plant compounds enjoy the status of generally recognised as safe (GRAS), typical toxicological information of their use in food is not available. So the improvement in cost-effective isolation and toxicological information of these compounds is helpful in their use as biopreservative in foods.

Preservative in Food

*Romika Dhiman and Neeraj Kumar Aggarwal*

**Keywords:** biopreservative, antimicrobial, essential oil, flavonoids

foods. Pressure used in DPCD damages the tissues of the fruits [3–5].

Food preservation is dominant features in all food sectors and mainly comprises curbing the rise of microorganisms that increase the health-related issues in consumers [1]. The food attributes that attract the attention of the consumer are freshness and their naturalness and minimal processing. The perception of naturalness drives the consumer towards the food without chemical preservatives [2]. Modernization coupled with the change in the life style of the consumer shifts them towards the use of ready-to-use food. Thermal processing, drying, freezing, refrigeration, irradiation, modified atmosphere packaging (MAP) and addition of antimicrobial agents or salts are some conventional methods to prevent the growth

Thermal processing is commonly applied in food industry to inactivate the microorganisms and enhance shelf life of food. However, pasteurisation reduces the level of some bioactive compounds such as anthocyanin pigment, carotenoids and vitamin c that has been reported in several fruits. Emerging nonthermal technology like high hydrostatic pressure (HHP), ultraviolet, ozone processing, pulsed electric fields and ultrasound has promising role in maintaining the nutritional and sensory quality of food. Dense phase carbon dioxide (DPCD) technique is generally employed for liquid

#### **Chapter 4**

*Food Preservation and Waste Exploitation*

[82] Jouquand C, Tessier FJ, Bernard J, et al. Optimization of microwave cooking of beef burgundy in terms of nutritional and organoleptic properties. LWT—Food Science and Technology.

[83] Laguerre J-C, Douiri-Bedoui I, Chireux C, et al. The iconographic correlation (CORICO) method, a new approach for the optimization of microwave cooking processes: Application for cooking fish. In: EFFOST Annual Meeting. 2013

2015;**60**:271-276

**52**

## Efficacy of Plant Antimicrobials as Preservative in Food

*Romika Dhiman and Neeraj Kumar Aggarwal*

#### **Abstract**

Safe and hygienic food is a requirement for a healthy society. The problem of food-borne outbreaks has built a challenge against the food and health regulatory authorities to control the pathogenic microorganisms. Chemical preservative has created some health problems in foods, so the recent trend is towards the use of natural antimicrobials in foods. Plants are valuable source of bioactive molecules exhibiting antimicrobial activities. The plant antimicrobial compounds have diverse chemical nature such as alkaloids, phenolics, terpenes, terpenoids, flavonoids, essential oil, etc. Many plant antimicrobials possess antimicrobial activity against pathogens and spoilage microorganisms. But variation in effectiveness of these compounds against microorganisms in laboratory system and in real food systems is major determinant in their food use. Several plant extract or purified compounds are part of human diet since thousands of years. Although some plant compounds enjoy the status of generally recognised as safe (GRAS), typical toxicological information of their use in food is not available. So the improvement in cost-effective isolation and toxicological information of these compounds is helpful in their use as biopreservative in foods.

**Keywords:** biopreservative, antimicrobial, essential oil, flavonoids

#### **1. Introduction**

Food preservation is dominant features in all food sectors and mainly comprises curbing the rise of microorganisms that increase the health-related issues in consumers [1]. The food attributes that attract the attention of the consumer are freshness and their naturalness and minimal processing. The perception of naturalness drives the consumer towards the food without chemical preservatives [2]. Modernization coupled with the change in the life style of the consumer shifts them towards the use of ready-to-use food. Thermal processing, drying, freezing, refrigeration, irradiation, modified atmosphere packaging (MAP) and addition of antimicrobial agents or salts are some conventional methods to prevent the growth of microbes in foods [1, 3].

Thermal processing is commonly applied in food industry to inactivate the microorganisms and enhance shelf life of food. However, pasteurisation reduces the level of some bioactive compounds such as anthocyanin pigment, carotenoids and vitamin c that has been reported in several fruits. Emerging nonthermal technology like high hydrostatic pressure (HHP), ultraviolet, ozone processing, pulsed electric fields and ultrasound has promising role in maintaining the nutritional and sensory quality of food. Dense phase carbon dioxide (DPCD) technique is generally employed for liquid foods. Pressure used in DPCD damages the tissues of the fruits [3–5].

The high intensity and longer duration time used in PEF affect the nutritional quality of foods. [6]. High dosage of ozone processing used for decontaminating food surface alters the sensory quality of the food. Nonetheless, the main limitation of applying UV-C light in food is its penetration, so it is only effective for the surface decontamination of food [7].

Besides, these some chemical preservatives such as sodium benzoate, potassium sorbate and nitrites have been used commercially in fruit juices, dairy products, confectionary, meat and meat products, etc. Nitrites and nitrates are applied in meat industry to inhibit the growth of the microorganisms, retain the red colour of the meat and reduce the oxidation of lipid. However, blue baby syndrome occurs in children owing to the presence of high amount of nitrites in their blood [8]. Some chemical preservatives such as sodium benzoate and potassium sorbate used in fruit juice industry have also constraints like benzoic acid that is converted into benzene in foods, and *S. cerevisiae* and *Pichia anomala* are able to decarboxylate sorbic acid to 1,3 pentadiene which cause kerosene-like off-odour. *Schizosaccharomyces pombe* may produce off-flavours in the presence of sulphite. Due to growing evidences about the harmful effects of chemical preservatives, there is continuous pressure to reduce the amount of added preservative in foods [9–12].

To avoid the health risks associated with the consumption of foods, natural antimicrobial compounds like bacteriocins, chitosan-fermented ingredients and plant antimicrobials provide another alternative for preserving food. Spices and herbs are used in food since the ancient time not for flavouring but also for the preservation. Plant extracts, essential oil and peptides exhibit a broad-spectrum activity. The antimicrobial and antioxidant properties of plants are attributed to secondary metabolites such as phenylpropanoids, terpenes, flavonoids and anthocyanins [3, 11, 13-14]. Several studies have been conducted around the globe to prove the efficacy of plant products, and various compounds isolated from these plants are secondary metabolites which possess antimicrobial and medicinal properties [3, 11, 13, 15, 16]. The main purpose of this review article is to examine application of plant antimicrobials in food and their chemical diversity and limitation.

#### **2. Current scenario of food-borne outbreaks**

Food-borne diseases occur at a fast rate. The key concern of public health authorities are now more concerted on food pathogens and food-borne outbreaks. Due to lack of awareness, a large number of food-borne-associated incidences become unnoticed. Food-borne diseases are only reported when this pathogen cause infection in a large number of people which resulted in an outbreak. Therefore, it is essential to shrink the load of food-borne diseases through vigilant monitoring of the food-borne outbreaks and causal organism [17].

Consumption of raw foods such as fruits, vegetables, fruit juices and raw sprouts is the main cause of food-borne outbreaks. The major food-borne pathogens are *Salmonella enterica*, *E. coli*, *Clostridium perfringens*, *Staphylococcus aureus*, *Shigella* spp., *Campylobacter* spp., *Bacillus cereus*, *Vibrio parahaemolyticus*, *Clostridium botulinum* and *Listeria monocytogenes*. In the USA, norovirus is implicated in a number of food-borne outbreaks associated with consumption of salad, and millions of people are affected [18, 19]. *Salmonella* and *E. coli* are involved in multistate outbreak in the USA. *E. coli* that causes severe haemolytic diarrhoea infected 3000 people in Germany and killed 53 people. Fresh produce and water is the main source of protozoan infection [18]. *Listeria monocytogenes* was implicated in 31 outbreaks in Switzerland during 2013–2014 which is associated with consumption of readyto-eat salad [20]. *L. monocytogenes* has also been observed where frozen corn and

**55**

membrane [15].

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

**3. Antimicrobial from plants**

**3.1 Essential oil**

frozen vegetable mixes including corn, frozen spinach and frozen green bean were consumed in European countries [21]. Consumption of frozen berry was responsible for hepatitis A in Italy. Hepatitis A was found in people who travelled to Italy during 2013–2014 [22]. *Salmonella* and *S. aureus* were involved in a large number of outbreaks associated with consumption of pork or pork products in the USA during 1998–2015 [23]. Hennekinne et al. [24] reviewed the occurrence of *S. aureus* food poisoning worldwide. The major share of food-borne outbreak in Canada is related to nontyphoidal *Salmonella* spp., *Campylobacter* and *Listeria monocytogenes* [25].

To circumvent the losses due to food-borne outbreaks, an effective method of preservation should be adopted in food factories and restaurant for controlling the food-borne outbreaks. Application of antimicrobials in foods retards the growth of spoilage microorganisms and prevents the growth of pathogenic microorganisms. Natural antimicrobial compounds are obtained from plant, animal and microbes. Lactoferrin, lactoperoxidase and lysozyme are naturally occurring antimicrobials in animals. Bacteriocins like nisin and pediocin are biopreservative from microbial origin used commercially in food. Several forms of plant products such as essential oil, plant extract either in pure or crude form and plant antimicrobial peptide have

Essential oils are oily liquids derived from several plant parts (flower, buds, leaves, fruits, twigs, bark, seed, wood and roots) belonging to angiospermic families that can be used by several industries for different purposes [26]. The essential oils are mainly investigated for their pharmacological attributes [27–30]. Food companies utilise essential oil as flavouring agent; however, antimicrobial and antioxidant aspects of essential oil make it the best candidate for food preservation [31]. Methods employed for the extraction of essential oil are steam distillation, hydro distillations, critical carbon dioxide, subcritical water, solvent extraction,

Harvesting time, types of plant, season and methods adopted for the extraction of essential oil influence the chemical diversity of the essential oil. The active groups that leverage the antimicrobial property of essential oil have been categorised into four main groups: terpenes, terpenoids, phenylpropenes, and other chemical groups [33, 34].

The mode of action of essential oil is not clearly defined till date. One particular mechanism does not justify the activity of diverse chemical groups present in the essential oil. Several researchers advocate that essential oil penetrates the bacterial cell membrane due to their lipophilic nature and disrupts the cell functioning [35–37]. Phenolic compounds alter the cell membrane permeability of the bacteria and hinder the generation of ATP and proton-motive force [38]. The hydrophobicity of essential oil displayed more activity against Gram-positive bacteria than Gram-negative bacteria which is attributed to difference in their cell structure [9]. The antimicrobial potential of essential oil is also influenced by concentration. Low concentration inhibits enzymes that are involved in energy production, and high concentration precipitates the protein. Thymol, eugenol and carvacrol inhibit ATPase activity and release of intracellular ATP and other components of cell

Different studies have demonstrated the effectiveness of Eos and their active compounds to control or inhibit the growth of pathogenic and spoilage

also potential to utilise as a biopreservative in food [5, 11].

hydrodiffusion and solvent-free microwave [32].

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

frozen vegetable mixes including corn, frozen spinach and frozen green bean were consumed in European countries [21]. Consumption of frozen berry was responsible for hepatitis A in Italy. Hepatitis A was found in people who travelled to Italy during 2013–2014 [22]. *Salmonella* and *S. aureus* were involved in a large number of outbreaks associated with consumption of pork or pork products in the USA during 1998–2015 [23]. Hennekinne et al. [24] reviewed the occurrence of *S. aureus* food poisoning worldwide. The major share of food-borne outbreak in Canada is related to nontyphoidal *Salmonella* spp., *Campylobacter* and *Listeria monocytogenes* [25].

#### **3. Antimicrobial from plants**

To circumvent the losses due to food-borne outbreaks, an effective method of preservation should be adopted in food factories and restaurant for controlling the food-borne outbreaks. Application of antimicrobials in foods retards the growth of spoilage microorganisms and prevents the growth of pathogenic microorganisms. Natural antimicrobial compounds are obtained from plant, animal and microbes. Lactoferrin, lactoperoxidase and lysozyme are naturally occurring antimicrobials in animals. Bacteriocins like nisin and pediocin are biopreservative from microbial origin used commercially in food. Several forms of plant products such as essential oil, plant extract either in pure or crude form and plant antimicrobial peptide have also potential to utilise as a biopreservative in food [5, 11].

#### **3.1 Essential oil**

*Food Preservation and Waste Exploitation*

surface decontamination of food [7].

reduce the amount of added preservative in foods [9–12].

**2. Current scenario of food-borne outbreaks**

the food-borne outbreaks and causal organism [17].

The high intensity and longer duration time used in PEF affect the nutritional quality of foods. [6]. High dosage of ozone processing used for decontaminating food surface alters the sensory quality of the food. Nonetheless, the main limitation of applying UV-C light in food is its penetration, so it is only effective for the

Besides, these some chemical preservatives such as sodium benzoate, potassium sorbate and nitrites have been used commercially in fruit juices, dairy products, confectionary, meat and meat products, etc. Nitrites and nitrates are applied in meat industry to inhibit the growth of the microorganisms, retain the red colour of the meat and reduce the oxidation of lipid. However, blue baby syndrome occurs in children owing to the presence of high amount of nitrites in their blood [8]. Some chemical preservatives such as sodium benzoate and potassium sorbate used in fruit juice industry have also constraints like benzoic acid that is converted into benzene in foods, and *S. cerevisiae* and *Pichia anomala* are able to decarboxylate sorbic acid to 1,3 pentadiene which cause kerosene-like off-odour. *Schizosaccharomyces pombe* may produce off-flavours in the presence of sulphite. Due to growing evidences about the harmful effects of chemical preservatives, there is continuous pressure to

To avoid the health risks associated with the consumption of foods, natural antimicrobial compounds like bacteriocins, chitosan-fermented ingredients and plant antimicrobials provide another alternative for preserving food. Spices and herbs are used in food since the ancient time not for flavouring but also for the preservation. Plant extracts, essential oil and peptides exhibit a broad-spectrum activity. The antimicrobial and antioxidant properties of plants are attributed to secondary metabolites such as phenylpropanoids, terpenes, flavonoids and anthocyanins [3, 11, 13-14]. Several studies have been conducted around the globe to prove the efficacy of plant products, and various compounds isolated from these plants are secondary metabolites which possess antimicrobial and medicinal properties [3, 11, 13, 15, 16]. The main purpose of this review article is to examine application

of plant antimicrobials in food and their chemical diversity and limitation.

Food-borne diseases occur at a fast rate. The key concern of public health authorities are now more concerted on food pathogens and food-borne outbreaks. Due to lack of awareness, a large number of food-borne-associated incidences become unnoticed. Food-borne diseases are only reported when this pathogen cause infection in a large number of people which resulted in an outbreak. Therefore, it is essential to shrink the load of food-borne diseases through vigilant monitoring of

Consumption of raw foods such as fruits, vegetables, fruit juices and raw sprouts

is the main cause of food-borne outbreaks. The major food-borne pathogens are *Salmonella enterica*, *E. coli*, *Clostridium perfringens*, *Staphylococcus aureus*, *Shigella* spp., *Campylobacter* spp., *Bacillus cereus*, *Vibrio parahaemolyticus*, *Clostridium botulinum* and *Listeria monocytogenes*. In the USA, norovirus is implicated in a number of food-borne outbreaks associated with consumption of salad, and millions of people are affected [18, 19]. *Salmonella* and *E. coli* are involved in multistate outbreak in the USA. *E. coli* that causes severe haemolytic diarrhoea infected 3000 people in Germany and killed 53 people. Fresh produce and water is the main source of protozoan infection [18]. *Listeria monocytogenes* was implicated in 31 outbreaks in Switzerland during 2013–2014 which is associated with consumption of readyto-eat salad [20]. *L. monocytogenes* has also been observed where frozen corn and

**54**

Essential oils are oily liquids derived from several plant parts (flower, buds, leaves, fruits, twigs, bark, seed, wood and roots) belonging to angiospermic families that can be used by several industries for different purposes [26]. The essential oils are mainly investigated for their pharmacological attributes [27–30]. Food companies utilise essential oil as flavouring agent; however, antimicrobial and antioxidant aspects of essential oil make it the best candidate for food preservation [31]. Methods employed for the extraction of essential oil are steam distillation, hydro distillations, critical carbon dioxide, subcritical water, solvent extraction, hydrodiffusion and solvent-free microwave [32].

Harvesting time, types of plant, season and methods adopted for the extraction of essential oil influence the chemical diversity of the essential oil. The active groups that leverage the antimicrobial property of essential oil have been categorised into four main groups: terpenes, terpenoids, phenylpropenes, and other chemical groups [33, 34].

The mode of action of essential oil is not clearly defined till date. One particular mechanism does not justify the activity of diverse chemical groups present in the essential oil. Several researchers advocate that essential oil penetrates the bacterial cell membrane due to their lipophilic nature and disrupts the cell functioning [35–37]. Phenolic compounds alter the cell membrane permeability of the bacteria and hinder the generation of ATP and proton-motive force [38]. The hydrophobicity of essential oil displayed more activity against Gram-positive bacteria than Gram-negative bacteria which is attributed to difference in their cell structure [9]. The antimicrobial potential of essential oil is also influenced by concentration. Low concentration inhibits enzymes that are involved in energy production, and high concentration precipitates the protein. Thymol, eugenol and carvacrol inhibit ATPase activity and release of intracellular ATP and other components of cell membrane [15].

Different studies have demonstrated the effectiveness of Eos and their active compounds to control or inhibit the growth of pathogenic and spoilage microorganisms in both fresh-cut fruit and fruit juices. Literature study reveals the effectiveness of essential oil and their active compounds to retard the growth of microorganisms (**Table 1**).

The pink pepper tree (*Schinus terebinthifolius* Raddi) is a native plant of Brazil, Paraguay and Argentina. Essential oil obtained from pink pepper exhibit antimicrobial and antioxidant activity in cheese. Two percent essential oil concentration was effective in cheese for controlling the growth of microorganisms [1].

Sharafati-Chaleshtori et al. [39] studied the use of basil essential oil in beef burger reduced the growth of *Staphylococcus aureus* PTCC 1189 from 3log cfu/g to 2log cfu/g at 4°C after 24 hours. The clove oil enhanced the shelf life of red meat at 2°C for 15 days and reduced the 3.78 log cycles of bacterial count as comparison to control that contain untreated meat. Similar results were obtained in cumin oil treatment [40].

The combination of thyme EO (at 0.4, 0.8 and 1.2%) and nisin (at 500 or 1000 IU/g) decreases *Listeria monocytogenes* population below the acceptable level (2 log cfu/g) and displayed strong antibacterial activity than the individual usage of EO or nisin in minced fish meat during storage period (4°C for 12 days) [41]. Samy Selim [42] studied the effect of eucalyptus, juniper, mint, rosemary, sage, clove and thyme oils on vancomycin-resistant *Enterococci* (VRE) and *E. coli* O157:H7 in minced beef meat and observed that sage and thyme oil exhibit strong antimicrobial activity against the tested microorganism.

The combination of *Zataria multiflora* Boiss essential oil (ZEO) and grape seed extract (GSE) at a concentration of 0.1% and 0.2%, respectively, was more effective for controlling the growth of the *Listeria monocytogenes* in raw buffalo patty than individual usage of *Zataria multiflora* Boiss essential oil (ZEO) and grape seed extract and showed antioxidant activity and confirmed the synergistic effect against the tested microorganism [43]. In another study the synergistic effect of *Mentha piperita* essential oil and bacteriocin was significant to prevent the growth of microorganisms in minced beef meat as comparison to individual role [44].

#### **3.2 Antimicrobial peptides**

Plants are easily attacked by the insects, fungi and bacteria. To nullify the effect of plant pathogens, plants develop an efficient defence system with the synthesis of secondary metabolite phenols, oxygen-substituted derivatives, terpenoids, quinines, tannins and antimicrobial peptides (AMPs) [45]. AMPs are widely distributed in plants and plant parts [46] and integral part of the immune system, enzymatic network needed during metabolism, as a nutrient and a storage molecule. Antimicrobial peptides are the first line of defence during pathogen encounter with the host [47]. Over the last two decades, about 1500 antimicrobial peptides are identified in various sources such as insects, plants, microorganisms, amphibians and mammals [48]. Antimicrobial peptides are biologically active peptides that exhibit antimicrobial, antioxidant, antithrombotic, antihypertensive and immunomodulatory attributes [49–53].

Antimicrobial peptides are grouped into two types on the basis of their biosynthetic pathway. The first group comprises the peptides that are not ribosomally made (bacitracins and glycopeptides), and the second group comprises the ribosomally synthesised peptides involved in innate defence system of the body of the organisms [54]. To realise the need of the basic information of AMPs, an online antimicrobial peptide database (APD) was framed in 2003. The current version of APD was issued in 2016 comprises more than 2600 peptides from different sources [55].

Amphiphilic nature and presence of positively charged residues in antimicrobial peptide enable them to partition into bacterial membrane and alter the

**57**

**Essential oil** Thyme EO (0.6%)

Oregano essential oil

Thyme or marjoram EOs

Thyme essential oil

Thyme essential oil

Hydroalcoholic extracts *Lithospermum erythrorhizon*

*Cuminum cyminum* (cumin) seed essential oil

Oregano and garlic essential oil

Bay leaf EO *Satureja horvatii* essential oil

Clove oil Cumin oil Thyme EO

*L. monocytogenes*

Native microflora

Native microflora

*Listeria monocytogenes*

Minced fish

4 °C for 12 days

Reduce the populations of

[41]

*L. monocytogenes* below the acceptable

level (2 log cfu/g) after 6 days

Meat

2 °C for 12 days

15 days

Enhanced the shelf life of meat up to

[40]

Pork meat

Meat

4°C, 72 hours 2 °C for 12 days

15 days

Native microflora

Coliforms

Spoilage moulds

Wheat and

Room

temperature

chickpea samples

Chicken breast

Tuscan sausage

7 °C, 14 days

3 log CFU/g reduction in coliform

[107]

population and extend the shelf life of

product for 2 days

Inhibit the growth of *L*. *monocytogenes*

Enhanced the shelf life of meat up to

[108]

[40]

4 °C, 13 days

Enhanced shelf life from 6 days to

[106]

13 days

Vancomycin-resistant Enterococci (VRE) and *E. coli* O157:H7

Vancomycin-resistant Enterococci (VRE) and *E. coli* O157:H7

Mesophilic Aerobic plate counts

Tomato juice

5 °C for 9 days

*E. coli*

Minced pork Feta soft cheese

Minced beef meat

7°C for 14 days

Reduce the bacteria growth as comparison to control

No significant change in microbial population as compared to control

Control the growth of moulds

[105]

[104]

7°C for 14 days

Reduce the bacteria growth as comparison to control

5 °C for 24 h

1 log cfu reduction of *E. coli* population after 24 hours

[103]

**Target microorganism**

*E. coli* O157:H7 *Salmonella* enteritidis

Minced sheep meat

4 °C or 10°C for 12 days

0.9% concentration of essential oil inhibits the growth of *Salmonella*

enteritidis

[102]

**Food** Minced beef

4 °C or 10°C

Inhibitory effect at 10°C not at 4°C against *E. coli* O157:H7

**Process**

**Effect**

**Reference**

[101]

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

> [42]

[42]


#### *Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

*Food Preservation and Waste Exploitation*

microorganisms (**Table 1**).

microorganisms in both fresh-cut fruit and fruit juices. Literature study reveals the effectiveness of essential oil and their active compounds to retard the growth of

untreated meat. Similar results were obtained in cumin oil treatment [40].

bial activity against the tested microorganism.

**3.2 Antimicrobial peptides**

modulatory attributes [49–53].

The combination of thyme EO (at 0.4, 0.8 and 1.2%) and nisin (at 500 or 1000 IU/g) decreases *Listeria monocytogenes* population below the acceptable level (2 log cfu/g) and displayed strong antibacterial activity than the individual usage of EO or nisin in minced fish meat during storage period (4°C for 12 days) [41]. Samy Selim [42] studied the effect of eucalyptus, juniper, mint, rosemary, sage, clove and thyme oils on vancomycin-resistant *Enterococci* (VRE) and *E. coli* O157:H7 in minced beef meat and observed that sage and thyme oil exhibit strong antimicro-

The combination of *Zataria multiflora* Boiss essential oil (ZEO) and grape seed extract (GSE) at a concentration of 0.1% and 0.2%, respectively, was more effective for controlling the growth of the *Listeria monocytogenes* in raw buffalo patty than individual usage of *Zataria multiflora* Boiss essential oil (ZEO) and grape seed extract and showed antioxidant activity and confirmed the synergistic effect against the tested microorganism [43]. In another study the synergistic effect of *Mentha piperita* essential oil and bacteriocin was significant to prevent the growth of microorganisms in minced beef meat as comparison to individual role [44].

Plants are easily attacked by the insects, fungi and bacteria. To nullify the effect of plant pathogens, plants develop an efficient defence system with the synthesis of secondary metabolite phenols, oxygen-substituted derivatives, terpenoids, quinines, tannins and antimicrobial peptides (AMPs) [45]. AMPs are widely distributed in plants and plant parts [46] and integral part of the immune system, enzymatic network needed during metabolism, as a nutrient and a storage molecule. Antimicrobial peptides are the first line of defence during pathogen encounter with the host [47]. Over the last two decades, about 1500 antimicrobial peptides are identified in various sources such as insects, plants, microorganisms, amphibians and mammals [48]. Antimicrobial peptides are biologically active peptides that exhibit antimicrobial, antioxidant, antithrombotic, antihypertensive and immuno-

Antimicrobial peptides are grouped into two types on the basis of their biosynthetic pathway. The first group comprises the peptides that are not ribosomally made (bacitracins and glycopeptides), and the second group comprises the ribosomally synthesised peptides involved in innate defence system of the body of the organisms [54]. To realise the need of the basic information of AMPs, an online antimicrobial peptide database (APD) was framed in 2003. The current version of APD was issued in 2016 comprises more than 2600 peptides from different

Amphiphilic nature and presence of positively charged residues in antimicrobial peptide enable them to partition into bacterial membrane and alter the

The pink pepper tree (*Schinus terebinthifolius* Raddi) is a native plant of Brazil, Paraguay and Argentina. Essential oil obtained from pink pepper exhibit antimicrobial and antioxidant activity in cheese. Two percent essential oil concentration was effective in cheese for controlling the growth of microorganisms [1]. Sharafati-Chaleshtori et al. [39] studied the use of basil essential oil in beef burger reduced the growth of *Staphylococcus aureus* PTCC 1189 from 3log cfu/g to 2log cfu/g at 4°C after 24 hours. The clove oil enhanced the shelf life of red meat at 2°C for 15 days and reduced the 3.78 log cycles of bacterial count as comparison to control that contain

**56**

sources [55].



**59**

*3.2.1 Thionins*

**Figure 1.**

*3.2.2 Defensins*

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

membrane permeability [56]. Antifungal property of AMPs lies in the attack of peptide on chitin, component of fungal cell wall, which hinders its synthesis and changes the membrane permeability (**Figure 1**) [46, 57]. AMPs bind the glycosaminoglycan moiety of cell membrane and prevent the virus-cell interaction as evident by the cationic lactoferrin peptide [58]. Bacterial antimicrobial peptides, such as bacteriocins, have been used in food preservation over many years [59]. The first antimicrobial peptide identified in plant is purothionin, which displays antimicrobial activity against *Pseudomonas solanacearum*, *Xanthomonas phaseoli* and *X. campestris*, *Erwinia amylovora*, *Corynebacterium flaccumfaciens*, *C. michiganense*, *C. poinsettiae*, *C. sepedonicum* and *C. fascians* [58]. The main groups incorporate thionins (types I–V), defensins, cyclotides, 2S albumin-like proteins and lipid transfer proteins [60, 61] along with knottin peptides, impatiens, puroindolines, vicilin like, glycine-rich, shepherins, snakins and heveins [62, 63] based on their sequence similarity, Cys motifs and distinctive disulphide bond patterns which, in

Thionins are cationic peptide comprised of 45–48 amino acids with 3 to 4 disulphide bond. Previously it was considered as toxic compound. Microbial attack on plant elicits the expressions of thionins, which belong to the release of the hormone methyl jasmonate. α-Purothionin was isolated from the endosperm of wheat. Crambin, viscotoxins, apratoxin A, α-/β-purothionins, α-/β-hordothionins, hellethionin-D, *Pyrularia pubera* thionin (Pp-TH) and *Tulipa gesneriana* bulb-purified AMPs (Tu-AMPs) belong to thionins [46]. Thionins from wheat flour showed antibacterial activity against food pathogen *Listeria monocytogenes* and *Listeria ivanovii* in vitro with MIC of 2 μg/mL [64].

Plant defensins are cationic peptides comprising 45–54 amino acids with 4 to 5 disulphide bonds [65]. They exhibit several biological functions such as antifungal, antibacterial, α-amylase and trypsin inhibitory activity [46]. Firstly, they were recognised as γ-thionin from wheat and barley grains. Plant defensins are found

turn, determine their tertiary structure folding [46].

*Mechanism of action of antimicrobial peptide (adapted from [53]).*

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

#### **Figure 1.**

*Food Preservation and Waste Exploitation*

[43]

**58**

**Essential oil** Eucalyptus EO *Ocimum basilicum* L.) Essential oil

0.1% *Zataria multiflora* Boiss essential oil

TMVC

TPVC

*Pseudomonas*

spp.

LAB and yeast populations and

*Listeria monocytogenes*

Aerobic and psychrotrophic count

Minced beef meat

Pomegranate

20°C for 16 days

Essential oil was more effective for

[110]

controlling the growth of yeast and

mould

juice

4 °C for 21 days

to control

Reduce the bacterial count as compared

[44]

Enterobacteriaceae, Pseudomonas

Mentha piperita essential oil

Origanum elongatum essential oil

**Table 1.**

*Application of essential oil as a preservative in food.*

TMVC

(ZEO) and 0.2% grape seed extract (GSE) at a

concentration of 0.1% and 0.2%

*Staphylococcus aureus* PTCC 1189

Beef burger Buffalo patties

8°C for 9 days

4 °C for 12 days

Sensory quality of the product

[39]

acceptable up to 12 days

Decrease the bacterial growth of

microbes

**Target microorganism**

*Saccharomyces cerevisiae*

Apple and orange

Room

Decrease the population of yeast as

compared to control

temperature,

8 days

mixed juice

**Food**

**Process**

**Effect**

**Reference**

[109]

*Mechanism of action of antimicrobial peptide (adapted from [53]).*

membrane permeability [56]. Antifungal property of AMPs lies in the attack of peptide on chitin, component of fungal cell wall, which hinders its synthesis and changes the membrane permeability (**Figure 1**) [46, 57]. AMPs bind the glycosaminoglycan moiety of cell membrane and prevent the virus-cell interaction as evident by the cationic lactoferrin peptide [58]. Bacterial antimicrobial peptides, such as bacteriocins, have been used in food preservation over many years [59].

The first antimicrobial peptide identified in plant is purothionin, which displays antimicrobial activity against *Pseudomonas solanacearum*, *Xanthomonas phaseoli* and *X. campestris*, *Erwinia amylovora*, *Corynebacterium flaccumfaciens*, *C. michiganense*, *C. poinsettiae*, *C. sepedonicum* and *C. fascians* [58]. The main groups incorporate thionins (types I–V), defensins, cyclotides, 2S albumin-like proteins and lipid transfer proteins [60, 61] along with knottin peptides, impatiens, puroindolines, vicilin like, glycine-rich, shepherins, snakins and heveins [62, 63] based on their sequence similarity, Cys motifs and distinctive disulphide bond patterns which, in turn, determine their tertiary structure folding [46].

#### *3.2.1 Thionins*

Thionins are cationic peptide comprised of 45–48 amino acids with 3 to 4 disulphide bond. Previously it was considered as toxic compound. Microbial attack on plant elicits the expressions of thionins, which belong to the release of the hormone methyl jasmonate. α-Purothionin was isolated from the endosperm of wheat. Crambin, viscotoxins, apratoxin A, α-/β-purothionins, α-/β-hordothionins, hellethionin-D, *Pyrularia pubera* thionin (Pp-TH) and *Tulipa gesneriana* bulb-purified AMPs (Tu-AMPs) belong to thionins [46]. Thionins from wheat flour showed antibacterial activity against food pathogen *Listeria monocytogenes* and *Listeria ivanovii* in vitro with MIC of 2 μg/mL [64].

#### *3.2.2 Defensins*

Plant defensins are cationic peptides comprising 45–54 amino acids with 4 to 5 disulphide bonds [65]. They exhibit several biological functions such as antifungal, antibacterial, α-amylase and trypsin inhibitory activity [46]. Firstly, they were recognised as γ-thionin from wheat and barley grains. Plant defensins are found

in wide variety of plants [66, 67]. Defensins attach to glucosylceramides which are present on the fungal cell membrane resulted into the insertion and repulsion between defensins owing to their positive charges which disrupt the cell membrane [68]. γ-Hordothionin, PhD1 from *Petunia hybrida* and defensins 1 and 2 from *Vigna radiata* belong to defensins [69].

Plant defensins exhibit lower antibacterial activity against *Listeria monocytogenes* and *Listeria ivanovii* [64]. Defensin KT43C from cowpea seeds delays the growth of yeast in dough for about 2 days [67].

#### *3.2.3 Hevein-like peptides*

Hevein-like peptides contain 29–45 amino acids with 3 to 5 disulphide bonds rich in Gly. It comprises conserved chitin-binding motif that distinguishes it from other peptides. Hevein was first observed in the latex of the rubber tree *Hevea brasiliensis*, displayed antifungal activity in vitro. IWF4 from *Beta vulgaris*, Ac-AMP1 from *Amaranthus caudatus*, EAFP1 and EAFP2 from the bark of *Eucommia ulmoides*, PMAPI from paper mulberry, WjAMP1 from the leaves of *Wasabia japonica* L and vaccatides vH1 and vH2 from *Vaccaria hispanica* are under hevein-like peptides [61, 70]. Hevein is effective against Gram-positive bacteria and fungi, but it shows some allergic reaction creating a hurdle in the use of it as a biopreservative [71].

#### *3.2.4 Knottin-type peptides*

Plant knottins contain 30 amino acids and comprises inhibitors of α-amylase, trypsin and carboxypeptidase families as well as cyclotides. They perform several functions like enzyme-inhibitory, cytotoxic, antimicrobial, insecticidal and anti-HIV activities [72, 73]. Initially, it was identified as protease inhibitors [74]. Linear knottins are observed in plants as well as in fungi, insects and spiders also. However, cyclotides and their acyclic variants are only found in plants [75]. They exhibit antibacterial as well as antifungal activity [64].

#### *3.2.5 Lipid transfer protein (LTP)*

LTPs consist of 70 and 90 amino acids cationic proteins with 8 Cys residues. They are implicated in lipid transfer activity between the membranes in vitro. Hydrophobic cavity covered by four helices is the common structural feature in all LTPs [76]. They are identified in several plants such radish, barley, maize, Arabidopsis, spinach, grapevine, wheat and onion [61].

#### *3.2.6 Snakin*

Snakin-1 and snakin-2 consist of 63 and 66 amino acid long residues, respectively, which are identified in potato tubers [77]. Snakin showed strong antibacterial activity against *Listeria monocytogenes* and *Listeria ivanovii* [78].

#### **3.3 Plant extracts**

Spices and herb are used as flavouring agents as well as a preservative since the ancient time. Plant parts are used as spice like leaves (mint, rosemary), flower (clove), bulb (garlic, onion) and fruit (cumin, red chilli). They enjoy the status of GRAS [79]. Factors that affect the antimicrobial efficacy of a compound incorporate target microorganism, initial microflora of the food and environmental factors. The chemical nature of the phytochemicals determines its activity against microorganisms. Plant extracts are widely used in the food industry, and

**61**

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

fer from the positive control (0.24% propionate) [88].

synthesis and causes cell death [80].

antimicrobial nature of the plant extract is influenced by its phytochemicals [13, 34, 64]. Phenolics, phenolic acids, quinones, saponins, flavonoids, tannins, coumarins, terpenoids and alkaloids are the major classes of chemical constituents that influence the antimicrobial and antioxidant activity as well as flavours of the plant. The hydroxyl group of the phenolic compounds imparts its antimicrobial activity. OH group interferes with the function of the cell membrane and shifts the electrons that act as proton exchangers, disintegrates proton-motive force, inhibits ATP

Clove exhibits antibacterial activity against *Escherichia coli*, *Listeria monocytogenes*, *Salmonella enterica*, *Campylobacter jejuni* and *Staphylococcus aureus* [81] and antifungal activity against *Candida albicans* and *Trichophyton mentagrophytes* [82]. The antimicrobial activity of the clove is owing to the presence of eugenol [11]. Cinnamaldehyde, cinnamyl alcohol and eugenol confer the antimicrobial activity of cinnamon. Cinnamaldehyde exerts its action on bacteria via inhibiting their cell wall synthesis, impairing cell membrane function and affecting the synthesis of nucleic acids [83]. Phenolic compounds of black pepper damage the bacterial membrane and affect the antimicrobial activity. In addition to antibacterial activity, antifungal activity of black pepper was also observed against the *Fusarium graminearum* and *Penicillium viridicatum* [84]. Carnosic acid and phenolic compounds influence the antimicrobial and antioxidant activity of rosemary plant [85] (Almela et al., 2006). Polyphenolic compounds such as 6-gingerol present in ginger confer the antimicrobial and antioxidant activity of the ginger [86]. Carbazole alkaloids and coumarins influence the antimicrobial activity of curry leaves [87]. Raisin extract in wheat at a concentration of 7.5% is effective for control of spoilage mould and enhances the shelf life of bread; however, this result does not significantly dif-

The plants that possess antioxidant property which belong to Lamiaceae, rosemary, oregano, thyme, sage, marjoram, basil, coriander and pimento are predominant [79]. Lipid peroxidation is the main culprit in the rejection of meat and meat products. Antioxidant compound decreases the lipid peroxidation. Plant extract comprises antioxidant activity attributed to their phenolic component. Selection of solvent is an important tool for the extraction of antioxidant property of the plant. Several studies support the antioxidant activity of plants in meat. The antioxidant activity of grape seed extract in pork patties stored at −18°C for 6 months was higher than that of oregano extract, oleoresin rosemary, butylated hydroxyanisole and butylated hydroxytoluene [89]. Similar results of antioxidant activity of grape seed extract were observed in beef patties, and the freshness and sensory quality of the product were retained for 4 months at −18°C and 6 months at the same temperature [90, 91] and in frankfurters [92], restructured mutton slices at refrigeration temperature [93]. The 0.1% of clove essential oil had higher antioxidant activity in

buffalo patties at 8°C for 9 days in comparison to grape seed extract [94].

Plant antimicrobial compounds have an efficacy as preservative and food ingredients. Before October 1994, food additives from plant sources are used without any regulatory test. Currently the trend has moved towards the rapid expansion of utilisation of plant antimicrobials as additive, ingredient or supplement in several health food products [95]. The US FDA and European commission approved some essential oil as food preservative. The main barrier encountered in the use of essential oil in food is the inability of the reproducibility of their activity. Although they contain diverse nature of the chemical compounds, they have different qualitative

**4. Hurdles in plant antimicrobials as preservative in foods**

#### *Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

*Food Preservation and Waste Exploitation*

*radiata* belong to defensins [69].

*3.2.3 Hevein-like peptides*

*3.2.4 Knottin-type peptides*

yeast in dough for about 2 days [67].

creating a hurdle in the use of it as a biopreservative [71].

antibacterial as well as antifungal activity [64].

Arabidopsis, spinach, grapevine, wheat and onion [61].

*3.2.5 Lipid transfer protein (LTP)*

in wide variety of plants [66, 67]. Defensins attach to glucosylceramides which are present on the fungal cell membrane resulted into the insertion and repulsion between defensins owing to their positive charges which disrupt the cell membrane [68]. γ-Hordothionin, PhD1 from *Petunia hybrida* and defensins 1 and 2 from *Vigna* 

Plant defensins exhibit lower antibacterial activity against *Listeria monocytogenes* and *Listeria ivanovii* [64]. Defensin KT43C from cowpea seeds delays the growth of

Hevein-like peptides contain 29–45 amino acids with 3 to 5 disulphide bonds rich in Gly. It comprises conserved chitin-binding motif that distinguishes it from other peptides. Hevein was first observed in the latex of the rubber tree *Hevea brasiliensis*, displayed antifungal activity in vitro. IWF4 from *Beta vulgaris*, Ac-AMP1 from

*Amaranthus caudatus*, EAFP1 and EAFP2 from the bark of *Eucommia ulmoides*, PMAPI from paper mulberry, WjAMP1 from the leaves of *Wasabia japonica* L and vaccatides vH1 and vH2 from *Vaccaria hispanica* are under hevein-like peptides [61, 70]. Hevein is effective against Gram-positive bacteria and fungi, but it shows some allergic reaction

Plant knottins contain 30 amino acids and comprises inhibitors of α-amylase, trypsin and carboxypeptidase families as well as cyclotides. They perform several functions like enzyme-inhibitory, cytotoxic, antimicrobial, insecticidal and anti-HIV activities [72, 73]. Initially, it was identified as protease inhibitors [74]. Linear knottins are observed in plants as well as in fungi, insects and spiders also. However, cyclotides and their acyclic variants are only found in plants [75]. They exhibit

LTPs consist of 70 and 90 amino acids cationic proteins with 8 Cys residues. They are implicated in lipid transfer activity between the membranes in vitro. Hydrophobic cavity covered by four helices is the common structural feature in all LTPs [76]. They are identified in several plants such radish, barley, maize,

Snakin-1 and snakin-2 consist of 63 and 66 amino acid long residues, respectively, which are identified in potato tubers [77]. Snakin showed strong antibacte-

Spices and herb are used as flavouring agents as well as a preservative since the ancient time. Plant parts are used as spice like leaves (mint, rosemary), flower (clove), bulb (garlic, onion) and fruit (cumin, red chilli). They enjoy the status of GRAS [79]. Factors that affect the antimicrobial efficacy of a compound incorporate target microorganism, initial microflora of the food and environmental factors. The chemical nature of the phytochemicals determines its activity against microorganisms. Plant extracts are widely used in the food industry, and

rial activity against *Listeria monocytogenes* and *Listeria ivanovii* [78].

**60**

*3.2.6 Snakin*

**3.3 Plant extracts**

antimicrobial nature of the plant extract is influenced by its phytochemicals [13, 34, 64]. Phenolics, phenolic acids, quinones, saponins, flavonoids, tannins, coumarins, terpenoids and alkaloids are the major classes of chemical constituents that influence the antimicrobial and antioxidant activity as well as flavours of the plant. The hydroxyl group of the phenolic compounds imparts its antimicrobial activity. OH group interferes with the function of the cell membrane and shifts the electrons that act as proton exchangers, disintegrates proton-motive force, inhibits ATP synthesis and causes cell death [80].

Clove exhibits antibacterial activity against *Escherichia coli*, *Listeria monocytogenes*, *Salmonella enterica*, *Campylobacter jejuni* and *Staphylococcus aureus* [81] and antifungal activity against *Candida albicans* and *Trichophyton mentagrophytes* [82]. The antimicrobial activity of the clove is owing to the presence of eugenol [11]. Cinnamaldehyde, cinnamyl alcohol and eugenol confer the antimicrobial activity of cinnamon. Cinnamaldehyde exerts its action on bacteria via inhibiting their cell wall synthesis, impairing cell membrane function and affecting the synthesis of nucleic acids [83]. Phenolic compounds of black pepper damage the bacterial membrane and affect the antimicrobial activity. In addition to antibacterial activity, antifungal activity of black pepper was also observed against the *Fusarium graminearum* and *Penicillium viridicatum* [84]. Carnosic acid and phenolic compounds influence the antimicrobial and antioxidant activity of rosemary plant [85] (Almela et al., 2006). Polyphenolic compounds such as 6-gingerol present in ginger confer the antimicrobial and antioxidant activity of the ginger [86]. Carbazole alkaloids and coumarins influence the antimicrobial activity of curry leaves [87]. Raisin extract in wheat at a concentration of 7.5% is effective for control of spoilage mould and enhances the shelf life of bread; however, this result does not significantly differ from the positive control (0.24% propionate) [88].

The plants that possess antioxidant property which belong to Lamiaceae, rosemary, oregano, thyme, sage, marjoram, basil, coriander and pimento are predominant [79]. Lipid peroxidation is the main culprit in the rejection of meat and meat products. Antioxidant compound decreases the lipid peroxidation. Plant extract comprises antioxidant activity attributed to their phenolic component. Selection of solvent is an important tool for the extraction of antioxidant property of the plant. Several studies support the antioxidant activity of plants in meat. The antioxidant activity of grape seed extract in pork patties stored at −18°C for 6 months was higher than that of oregano extract, oleoresin rosemary, butylated hydroxyanisole and butylated hydroxytoluene [89]. Similar results of antioxidant activity of grape seed extract were observed in beef patties, and the freshness and sensory quality of the product were retained for 4 months at −18°C and 6 months at the same temperature [90, 91] and in frankfurters [92], restructured mutton slices at refrigeration temperature [93]. The 0.1% of clove essential oil had higher antioxidant activity in buffalo patties at 8°C for 9 days in comparison to grape seed extract [94].

#### **4. Hurdles in plant antimicrobials as preservative in foods**

Plant antimicrobial compounds have an efficacy as preservative and food ingredients. Before October 1994, food additives from plant sources are used without any regulatory test. Currently the trend has moved towards the rapid expansion of utilisation of plant antimicrobials as additive, ingredient or supplement in several health food products [95]. The US FDA and European commission approved some essential oil as food preservative. The main barrier encountered in the use of essential oil in food is the inability of the reproducibility of their activity. Although they contain diverse nature of the chemical compounds, they have different qualitative

and quantitative fluctuations in the content of the compounds which influence their biological effectiveness [96, 97]. The other major obstacle that limits the use of essential oil in food is their strong aroma that alters the organoleptic property of food. Beside that the nature of the food also affects the efficacy of essential oil in food. Food is comprised of different microenvironments; hence, the concentration of essential oil is also increased that leverage the taste of the food resulting in the rejection of food [13, 98]. Strong aroma flavour of essential oil is minimised by meticulously choosing the essential oil according to the type of food. Availability of raw material and risk of the loss of biodiversity also hinder the use of plant essential oil as preservative [95, 99].

The in vitro antimicrobial activity of plants has been demonstrated in several studies. However, hardly an antimicrobial study of plant extract has been available in food. In most of the studies, the results of in vitro antimicrobial activity of plant extract differ from the antimicrobial activity observed in food. The low activity of the plant in food is attributed to involvement of crude extract in most cases, and they possess low activity in contrast to pure compounds. Crude extract which comprises of flavonoids in glycosidic form retards their effectiveness against the microorganisms [13, 100]. The presence of extracting solvent also creates a hurdle for the use of plant extracts in food [11, 13]. The application of antimicrobial peptides derived from plants in food is at its infancy stage. Lots of work have to be done to prove its potential as preservative in food.

#### **5. Conclusion and future remarks**

Plant-derived antimicrobials have promising probability to be used as preservative in food. Literature studies revealed the inefficiency of plant antimicrobial as a preservative in food systems and also have inadequate scientific reports that support their safety in food. Although food authorities around the world have issued guidelines regarding the food additives, there is lacking data related to standardisation of plant extract. There is stringent need for approval of plant antimicrobial as a preservative by the food authorities as its potential as natural preservative is proved. The method of the extraction of plant is also impediment in the passage of preservative action of plant. Development of cost-effective methods for the extraction of plant antimicrobials should be search out, so that there is no loss of original antimicrobial compound, and preservative from plant should be used on large scale. Nanotechnology approach also enhances the potential of plant antimicrobials. Most of the essential oils were incorporated into packaging system where they impart the antimicrobial activity and enhance the shelf life of food. Nanoencapsulation of plant antimicrobial will also helpful for maintaining the bioactivity of plant antimicrobial in food systems.

**63**

**Author details**

Romika Dhiman1

provided the original work is properly cited.

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Department of Microbiology, DAV College for Girls, Yamunangar, Haryana, India

2 Department of Microbiology, Kurukshetra University, Kurukshetra, Haryana, India

\* and Neeraj Kumar Aggarwal<sup>2</sup>

\*Address all correspondence to: romikadhiman@gmail.com

#### **Conflict of interest**

There is no conflict of interest between authors.

*Efficacy of Plant Antimicrobials as Preservative in Food DOI: http://dx.doi.org/10.5772/intechopen.83440*

*Food Preservation and Waste Exploitation*

essential oil as preservative [95, 99].

done to prove its potential as preservative in food.

There is no conflict of interest between authors.

**5. Conclusion and future remarks**

crobial in food systems.

**Conflict of interest**

and quantitative fluctuations in the content of the compounds which influence their biological effectiveness [96, 97]. The other major obstacle that limits the use of essential oil in food is their strong aroma that alters the organoleptic property of food. Beside that the nature of the food also affects the efficacy of essential oil in food. Food is comprised of different microenvironments; hence, the concentration of essential oil is also increased that leverage the taste of the food resulting in the rejection of food [13, 98]. Strong aroma flavour of essential oil is minimised by meticulously choosing the essential oil according to the type of food. Availability of raw material and risk of the loss of biodiversity also hinder the use of plant

The in vitro antimicrobial activity of plants has been demonstrated in several studies. However, hardly an antimicrobial study of plant extract has been available in food. In most of the studies, the results of in vitro antimicrobial activity of plant extract differ from the antimicrobial activity observed in food. The low activity of the plant in food is attributed to involvement of crude extract in most cases, and they possess low activity in contrast to pure compounds. Crude extract which comprises of flavonoids in glycosidic form retards their effectiveness against the microorganisms [13, 100]. The presence of extracting solvent also creates a hurdle for the use of plant extracts in food [11, 13]. The application of antimicrobial peptides derived from plants in food is at its infancy stage. Lots of work have to be

Plant-derived antimicrobials have promising probability to be used as preservative in food. Literature studies revealed the inefficiency of plant antimicrobial as a preservative in food systems and also have inadequate scientific reports that support their safety in food. Although food authorities around the world have issued guidelines regarding the food additives, there is lacking data related to standardisation of plant extract. There is stringent need for approval of plant antimicrobial as a preservative by the food authorities as its potential as natural preservative is proved. The method of the extraction of plant is also impediment in the passage of preservative action of plant. Development of cost-effective methods for the extraction of plant antimicrobials should be search out, so that there is no loss of original antimicrobial compound, and preservative from plant should be used on large scale. Nanotechnology approach also enhances the potential of plant antimicrobials. Most of the essential oils were incorporated into packaging system where they impart the antimicrobial activity and enhance the shelf life of food. Nanoencapsulation of plant antimicrobial will also helpful for maintaining the bioactivity of plant antimi-

**62**

#### **Author details**

Romika Dhiman1 \* and Neeraj Kumar Aggarwal<sup>2</sup>

1 Department of Microbiology, DAV College for Girls, Yamunangar, Haryana, India

2 Department of Microbiology, Kurukshetra University, Kurukshetra, Haryana, India

\*Address all correspondence to: romikadhiman@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[103] Tserennadmid R, Takó M, Galgóczy L, Papp T, Vágvölgyi C, Gerő L, et al. Antibacterial effect of essential oils and interaction with food components. Open Life Sciences. 2010;**5**:641-648. DOI: 10.2478/s11535-010-0058-55):641-8

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[105] Kedia A, Prakash B, Mishra PK, Dubey NK. Antifungal and antiaflatoxigenic properties of *Cuminum cyminum* (L.) seed essential oil and its efficacy as a preservative in stored commodities. International Journal of Food Microbiology. 2014;**168**:1-7. DOI: 10.1016/j.ijfoodmicro.2013.10.008

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Section 3

Exploitation of Food Waste

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Section 3
