**2.** *Salmonella*

*Salmonella* is a gram negative, non-spore forming bacilli belonging to the family Enterobacteriaceae and is one of the most prominent food pathogenic bacteria. This pathogen has the ability to grow at a wide range of temperatures (8-45 °C), pH (4 to 9) and foods with high moisture content (thus high water activity). Since the organism is heat sensitive, it is more prevalent in raw and under-cooked foods. In general, consumption of

Recent Advances in the Application

Irradiation

UV radiation

HPP

HPCD

PEF

Natural antimicrobials

**3. Thermal processing** 

attention (table 2).

of Non Thermal Methods for the Prevention of *Salmonella* in Foods 289

Effective for several foods Many different sources available (Gamma rays, electron beam)

No chemicals are used Non-heat related method

of food

liquid samples.

non-toxic

Can be used in a batch or continuous process

no generation of heat Less usage of energy

Have "GRAS" status

Lesser changes in quality attributes

Independent of the shape of food Can be used for both solid and

CO2 is GRAS, nonflammable and

Pulse applied for a short period so

Natural "green" preservatives

Table 1. Limitations and advantages of non thermal processing techniques

Heating of food is the most common and effective method for eliminating pathogens. Thermal pasteurization, involving the reduction or inactivation of micro-organisms, was traditionally the most common method for the production of microbiologically safe food products. The method involves generation of heat outside the food which gets transferred into the food through conduction or convection. Although the method is inexpensive, preservative free and environmental friendly, it does result in undesirable changes related to the nutritional and organoleptical properties of foods. At the same time, the content or bioavailability of some bioactive compounds such as ascorbic acid, phenolic compounds or carotenoids may be severely diminished. The case becomes even worse if the food product is heat sensitive. Nonetheless the extent of destruction depends on the temperature used for processing in addition to the time for which it is applied. In order to circumvent the shortcomings of thermal processing, several non-thermal methods such as the use of radiation, high pressure processing and natural antimicrobials are receiving considerable

**Advantages Limitations** 

Limited public acceptance Lipid oxidation of meat products

Long term exposure can be harmful to the industry workers

Changes in quality of food has

Not very successful for solid

Commercial application is still

Cannot be applied to foods that

Can have a negative effect on the sensory properties of foods

Cannot be applied to foods which cannot withstand high

been observed

not a success

form bubbles

foods

fields

contaminated foods such as raw or under-cooked eggs, meat, poultry or even dairy products can act as vehicles for salmonellosis in humans. Because of the ability of *Salmonella* cells to exist under dormant conditions and regain active growth phase when favourable conditions return, it also has the ability to survive in dry products. As fresh cut fruits lack any skin barrier they are also likely to be contaminated by *Salmonella*. Storage of raw or pasteurized foods under refrigerated conditions or with treatments that reduce pH can help to increase the shelf life by retarding or avoiding the growth but certain strains of *Salmonella* have been reported to survive even under chilling conditions. It is now evident that these conditions cannot stop the chromosomal replication and are only bacteriostatic in nature (Tahergorabi et al., 2011). Risco (2009) reported survival of *Salmonella* inoculated into chicken nuggets during 16 weeks at -20ºC. This further adds to the problems that can arise by the consumption of ready to eat frozen products that are just pre-warmed in a microwave prior to consumption.

Although any person can contract food poisoning due to *Salmonella*, the disease can be more serious in infants, elderly and people with weak immune system. Treatment with antibiotics becomes essential for the eradication of this bacterial species. However, excessive use of antibiotics has made several strains to develop resistance against such drugs resulting in increased prevalence of these resistant strains in humans and animals. In order to minimize its presence in foods, synthetic antimicrobial agents such as sodium benzoate and sodium nitrite were used. However, these are also losing popularity due to consumer demand for food products with natural preservatives. Thermal processing is the most efficient way for eliminating *Salmonella* from foods. However, consumer's demand for minimally processed foods in addition to the negative effect of heat on nutritional properties of foods is making this technology less popular in the food industry. Novel remedies for safe and efficient removal of this bacterium from foods are becoming vital. Nowadays, non thermal techniques such as the addition of naturally occurring compounds having antibacterial activity, the use of high pressure carbon dioxide (HPCD), use of electrolysed water, high intensity pulsed electric field (PEF) or irraditation are increasingly gaining attention as a means of food preservation. In addition, it is imperative for the non thermal applications to have similar or higher inactivation as compared to the traditional heat treatments. According to US-FDA guidelines, the main requirement is to reduce the pathogen load by 5 logs (FDA, 2001). The major advantage of these non-thermal technologies (table 1) is that they are environmentally friendly and act at ambient or sub-lethal temperatures resulting in minimal impact on color, flavor and nutritional quality of foods. These techniques help in retaining the "fresh-like" characteristics of food and may also help to preserve functionalities.

However, the use of essential oils and other plant extracts is often limited by organoleptical criteria. Moreover, high pressures can cause cell wall breakdown and result in loss of cell turgidity. Thus, under these conditions, it might be necessary to combine two or more technologies in order to achieve the desired preservative effect. The technique of combination or "hurdle technology" is slowly becoming eminent. Thus, the use of natural antimicrobials along with pulsed electric field, ozone or super critical carbon dioxide can be used to curtail the growth of *Salmonella* with a minimal effect on the sensory characteristics such as flavor.

contaminated foods such as raw or under-cooked eggs, meat, poultry or even dairy products can act as vehicles for salmonellosis in humans. Because of the ability of *Salmonella* cells to exist under dormant conditions and regain active growth phase when favourable conditions return, it also has the ability to survive in dry products. As fresh cut fruits lack any skin barrier they are also likely to be contaminated by *Salmonella*. Storage of raw or pasteurized foods under refrigerated conditions or with treatments that reduce pH can help to increase the shelf life by retarding or avoiding the growth but certain strains of *Salmonella* have been reported to survive even under chilling conditions. It is now evident that these conditions cannot stop the chromosomal replication and are only bacteriostatic in nature (Tahergorabi et al., 2011). Risco (2009) reported survival of *Salmonella* inoculated into chicken nuggets during 16 weeks at -20ºC. This further adds to the problems that can arise by the consumption of ready to eat frozen products that are just pre-warmed in a

Although any person can contract food poisoning due to *Salmonella*, the disease can be more serious in infants, elderly and people with weak immune system. Treatment with antibiotics becomes essential for the eradication of this bacterial species. However, excessive use of antibiotics has made several strains to develop resistance against such drugs resulting in increased prevalence of these resistant strains in humans and animals. In order to minimize its presence in foods, synthetic antimicrobial agents such as sodium benzoate and sodium nitrite were used. However, these are also losing popularity due to consumer demand for food products with natural preservatives. Thermal processing is the most efficient way for eliminating *Salmonella* from foods. However, consumer's demand for minimally processed foods in addition to the negative effect of heat on nutritional properties of foods is making this technology less popular in the food industry. Novel remedies for safe and efficient removal of this bacterium from foods are becoming vital. Nowadays, non thermal techniques such as the addition of naturally occurring compounds having antibacterial activity, the use of high pressure carbon dioxide (HPCD), use of electrolysed water, high intensity pulsed electric field (PEF) or irraditation are increasingly gaining attention as a means of food preservation. In addition, it is imperative for the non thermal applications to have similar or higher inactivation as compared to the traditional heat treatments. According to US-FDA guidelines, the main requirement is to reduce the pathogen load by 5 logs (FDA, 2001). The major advantage of these non-thermal technologies (table 1) is that they are environmentally friendly and act at ambient or sub-lethal temperatures resulting in minimal impact on color, flavor and nutritional quality of foods. These techniques help in retaining the "fresh-like" characteristics of food and may also help to preserve

However, the use of essential oils and other plant extracts is often limited by organoleptical criteria. Moreover, high pressures can cause cell wall breakdown and result in loss of cell turgidity. Thus, under these conditions, it might be necessary to combine two or more technologies in order to achieve the desired preservative effect. The technique of combination or "hurdle technology" is slowly becoming eminent. Thus, the use of natural antimicrobials along with pulsed electric field, ozone or super critical carbon dioxide can be used to curtail the growth of *Salmonella* with a minimal effect on the

microwave prior to consumption.

functionalities.

sensory characteristics such as flavor.


Table 1. Limitations and advantages of non thermal processing techniques
