*2.1.1 Application of essential oils in direct contact and their effect on sensory attributes*

The application of EOs by direct contact has been tested on different foods such as meat products (meat burgers, ground meat, sausages, and fish, among others) and fruits (pineapple, mango, guava, and apple). Cinnamon (*Cinnamomum verum*), mint (*Mentha spicata*), lemon balm *(Melissa officinalis*), savory (*Satureja montana*), and juniper (*Juniperus communis*) EOs have exhibited good results against pathogenic bacteria such as *Pseudomonas aeruginosa*, *Salmonella typhimurium*, and *Escherichia coli* [10–14]. Rosemary (*Salvia rosmarinus*) and cinnamon EOs reduced and prevented the growth of Gram-positive bacteria such as *Staphylococcus aureus* and *Listeria monocytogenes* [11, 13] that are generally more sensitive to the presence of EOs [15].

The effect on the sensory attributes of EOs applied by direct contact in food systems is displayed in **Table 1**; some authors report their application for fish preservation [13]. [13] added 4 types of EOs: fennel (*Foeniculum vulgare*), cardamom (*Elettaria cardamomum*), cinnamon, or rosemary to fish fingers and ten untrained judges evaluated their acceptability (appearance, aroma, and texture) during storage at 4°C; the authors report that in addition to extending the shelf life (to 12 d while in the control without EOs it was 4 d) of the product during storage, they also improved their sensory characteristics. Rosemary EO had the best results since it was greatly accepted in the three studied attributes, and it can be use as antimicrobial.

**EO Concentration Food Sensory attribute Results Reference** Sage (*Sage officinalis*), rosemary (*Salvia rosmarinus),* thyme (*Thymus vulgaris*), and clove (*Syzygium aromaticum*) 600 ppm Smoked rainbow trout Appearance, taste, and aroma Clove EO best accepted in all attributes [16] Hisopo (*Hyssopus officinalis*) and coriander (*Coriandrum sativum*) 0.02% Ground beef Aroma and taste Coriander EO best accepted in both attributes evaluated [17] Mint (*Mentha spicata*) and toronjil (*Melissa officinalis*) 0.625 and 1.25 μL/mL, respectively Pineapple, mango, guava and apple cashew juices Appearance, aroma, viscosity, taste, aftertaste, and general acceptability Both EOs had negative effects on taste, aftertaste, and overall acceptability; however, mint EO was more accepted in other studied attributes [10] Combination of Chinese cinnamon (*Cinnamomun cassia*) and cinnamon bark (*Cinnamomum verum*) 0.05% Ready-to-eat meat and lean ground meat Taste and aroma in both types of meat The EO showed better acceptability in both meats in the two evaluated attributes [11] Fennel (*Foeniculum vulgare),* cardamom (*Elettaria cardamomum),* cinnamon, and rosemary 10 mL/kg Fish fingers Appearance, aroma, and texture Rosemary EO best accepted in all attributes until the 12th day of storage [13] Clove, basil (*Ocimum basilicum),* thyme, and Chinese cinnamon 0.25, 0.125, 0.25, and 0.125% Chicken sausages Appearance, taste, juiciness, texture, and overall acceptability 0.25% Chinese cinnamon EO was best accepted in all attributes [12] Clove and Curry (*Murraya koenigii*) 0.05, 0.15, and 0.25% Burfi Taste, texture, color, appearance and overall acceptability Overall taste and acceptability were affected as the concentration of EO increased. Being clove EO at 0.15% the best accepted. [18]

## *Methods of Application of Essential Oils in Foods and Their Effects on Sensory Attributes DOI: http://dx.doi.org/10.5772/intechopen.105162*


#### **Table 1.**

*Effect of selected essential oils applied by direct contact on the sensory attributes of various foods.*

One of the most common uses of EOs by direct contact is in meat products as antimicrobials. It has been reported that the combination of Chinese cinnamon (*Cinnamomum cassia*) at a concentration of 0.25 and 0.05% cinnamon bark generate good sensory acceptability. Generate good sensory acceptability in ready-to-eat meat and chicken sausages, respectively [11, 12]. Also, Chinese pepper EO in sashimi, where the studied sensory attributes were acceptable [21].

In adittion, EOs of rosemary, thyme (*Thymus vulgaris*), sage (*Salvia officinalis*), and clove (*Syzygium aromaticum*) were evaluated in smoked trout fillets stored at 4°C [16]. Fish fillets with rosemary EO had lower sensory acceptability compared to other studied EOs (thyme, sage, and clove), which could be because these trout fillets were evaluated smoked and not raw like fish fingers [13], affecting the EOs' sensory affinity with the food product.

It has been reported [4] that the negative sensory effect can be minimized by properly selecting the EO according to the type of food; for example, cinnamon has better affinity with various fruits and their products [22, 23]. However, it was observed in burfi (an Indian dessert) added with clove and curry (*Murraya koenigii*) EOs [18] as well as in guava, pineapple, mango, and cashew apple juices with mint and lemon balm EOs [10]. In both studies, inhibition of microorganisms was achieved; but sensory properties were negatively affected, as the taste of the EO decreased sensory acceptability (taste, aroma, residue, and overall acceptability).

*Methods of Application of Essential Oils in Foods and Their Effects on Sensory Attributes DOI: http://dx.doi.org/10.5772/intechopen.105162*

When savory EO was applied to pork sausage [19] and beef marinated with wine [20]. In both cases, the taste of the EO negatively affected sensory attributes (aroma and taste). the sensory attributes aroma and taste were negatively affected by the presence of the EO. It is known that the composition of the EO can be different depending on several factors, including the extraction method. [19] were able to improve the sensory acceptability of savory EO by changing the extraction method from hydro-distillation to supercritical fluid extraction. This technology decreased the number of volatile compounds (terpenes) and improved sensory acceptability.

#### **2.2 Vapor phase**

The vapor phase consists of evaluating the vapor generated by the EOs on different food systems. This method has been reported to have a greater antimicrobial effect compared to EOs in liquid form applied by direct contact, because more volume of liquid EOs is needed to achieve the same biological effect as in gaseous form [24].

The volatility of EOs depends on factors such as the molecular weight of their components; since the smaller the molecule, the diffusivity is higher [25]. Similarly, increasing the temperature of the environment encourages migration of volatile compounds [8]. It is difficult to compare vapor phase antimicrobial activity results because there is no standard method and there is variation in the composition of EOs. However, one of the most promising methods for this purpose seems to be the disk volatilization test [26], which can be modified for food preservation by generating "active packages", which allow volatilization and migration of the active components from the "disc in the package" into the food [8].

### *2.2.1 Application of essential oils in vapor phase and their effect on sensory attributes*

The effect on different sensory attributes of a selection of EOs applied in vapor phase to different food systems is shown in **Table 2**. EOs have been used in fruits such as apples and grapes to prevent/reduce the growth of pathogenic molds such as *Aspergillus*, *Alternaria*, *Penicillium*, and *Botrytis*. In the case of grapes, a sensory analysis was performed through a triangular test to evaluate if the exposure time of the EOs affected sensory attributes; results indicated that lavender (*Lavandula*), rosemary (*Salvia rosmarinus*), and mint (*Mentha piperita*) EOs could be perceived even 24 h after treatment, due to the large number of aromatic compounds that they contain [29].

Apples treated with oregano (*Origanum vulgare*), cinnamon (*C. verum*), and clove (*S. aromaticum*) EOs [28] in vapor phase were evaluated for sensory acceptability using an unstructured scale. When the concentration of oregano and cinnamon EOs increased, they passed on different aromas to the apples. Although oregano EO showed better antifungal activity (MIC: 2 μL of EO/Lair), it negatively affected sensory attributes when utilized at this concentration. This may be because oregano EO has been reported to provide an herbaceous flavor unlike to the sweet flavor imparted by cinnamon EO [22, 23]. This effect has also been reported in vegetables such as mushrooms [27]. [29] have proposed that reducing the time of exposure to EO vapors or extending the time between treatment and consumption could be strategies to minimize the sensory changes in the product.

Similarly, other authors [31, 32] evaluated the exposure of different EOs to bread for the inhibition of *Penicillium* (lemongrass -*Cymbopogon citratus-* EO) and *Aspergillus* [Thyme -*T. vulgaris*-, clove, cumin -*Cuminum cyminum*- and oregano EOs],


#### **Table 2.**

*Effect of selected essential oils applied by vapor phase on the sensory attributes of various foods.*

respectively. In both papers they reported that sensory attributes of aroma, taste, and general acceptability were acceptable even after 21 d of storage with lemongrass EO and 14 d with thyme and cumin EOs.

The antimicrobial activity in vapor phase of allspice (*Pimenta dioica*), thyme and rosemary EOs against *L***.** *monocytogenes* and *S. typhimurium* in alfalfa seeds was evaluated [30]. In addition, a sensory analysis was made using a triangular test. The

## *Methods of Application of Essential Oils in Foods and Their Effects on Sensory Attributes DOI: http://dx.doi.org/10.5772/intechopen.105162*

results showed that the difference among samples was moderate between allspice and thyme EOs, and slightly for germinated seeds treated with rosemary EO. The authors emphasize that most panelists preferred the sprouts from seeds treated with allspice and rosemary EOs to the control samples that did not contain EOs. This proves that some EOs in vapor phase at an adequate concentration can have a positive impact on the sensory attributes of different food products.

## **2.3 Nanoemulsions**

Another alternative for EO application is encapsulation; it is defined as a technology that allows trapping sensitive components in a homogeneous or heterogeneous matrix, which provides protection, and increases its stability to adverse conditions; in addition, it helps to control its release [33]. There are different encapsulation methods, including simple or complex coacervation, spray drying, fluidized bed coating, or emulsions/nanoemulsions [34].

Emulsions have proven to be good carriers for the delivery of lipid substances such as EOs. Emulsions are composed of two phases, the oily (O) and the aqueous (W). The oil-in-water (O/W) emulsion consists of small drops of oil as a dispersed phase contained in water as a continuous phase while in the water-in-oil (W/O) emulsion the drops of the dispersed phase are water, and the continuous phase is oil. In the food industry, the most common emulsions are O/W.

Emulsions can also be classified into micro- or nano-emulsions dependinf of the size of the droplets. The droplet size of nanoemulsion ranges between 20 and 1000 nm; it can be prepared using different methods, such as high-pressure homogenization, microfluidization, high-speed mechanical homogenization, ultrasound, spontaneous emulsion, and phase inversion, among others [35, 36]. Its importance is that the nanometric particle size allows increasing bioavailability, bio-efficiency and stability [37].
