*2.3.1 Application of essential oils by nanoemulsions in foods and their effect on sensory attributes*

The use and incorporation of EOs' nanoemulsions in foods is a technique that has become relevant, because increase of the contact surface improves antimicrobial activity since active components are more available [38]. Although nanoemulsions have had more application in foods than other methods, sensory studies are still scarce, only a few reports have studied the effect of nanoemulsions on the sensory properties of foods.

The application of nanoemulsions in foods has been tested mainly for fish conservation (**Table 3**). The antimicrobial effect of nanoemulsions of rosemary (*Salvia rosmarinus*), laurel (*Laurus nobilis*), thyme (*T. vulgaris),* and *aloe vera* EOs at 4% on the quality of rainbow trout were evaluated [40]. The results of the microbiological analysis indicated that EOs reduced the count of mesophilic anaerobic bacteria, psychotrophic bacteria (main microorganisms responsible for fresh fish deterioration) and enterobacteria by 3 Log CFU/g. The EOs also increased the shelf life by 3 d more (17 d in total while the control without EOs was 14 d) of the fish treated with the EOs. Similarly, [39] evaluated the antimicrobial effect of lemon EO (Citrus × lemon) at 0.3% against the same bacteria, resulting in the reduction of only 2 Log CFU/g. For sensory evaluation, both studies used a hedonic scale of 9 and 10 points respectively, for the evaluation of taste, aroma, and texture in fish. The EOs tested on both of the


#### **Table 3.**

*Effect of selected essential oils applied by means of nanoemulsions on the sensory attributes of various foods.*

studied fish had good acceptability for all attributes, except for the rosemary EO, which obtained the lowest rating, since it gave a bitter taste to the trout.

Oregano (*O. vulgare*), thyme, and star anise (*Illicium verum*) nanoemulsions have been evaluated EOs Chinese carp [41] and, oregano, thyme, and garlic in salmon and cod [44]. In these studies, oregano EO was found to have the best antimicrobial activity against *Pseudomonas* (reduction of 1 Log CFU/g) and *Listeria* (CMI 0.02%) while also displaying the best sensory acceptability in terms of aroma, color, and texture and extending the shelf life of Chinese carp by 2 d (4 d in total, the shelf life if the control sample without EOs was 2 d). However, the EOs did not have a positive effect on the sensory properties of all the fish. Fot the cod, the EOs tested masked the characteristic taste of the fish.

Dávila-Rodríguez et al. [42] evaluated the antimicrobial activity of cinnamon (*C. verum*), rosemary, and oregano EOs encapsulated by (O/W) nanoemulsions against *E. coli* and *L***.** *monocytogenes* and compared them to that of the non- encapsulated EOs.

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

The latter were less effective than the nanoemulsions at inhibiting the same microbial load (5 Log CFU/g); 50% less EO was required when applied as a nanoemulsion. At the same time, the authors performed sensory analysis using a 9-point hedonic scale to evaluate the attributes of aroma, color, texture, appearance, taste, and overall acceptability by applying the EOs nanoemulsions to fresh celery. As a result, they found that celery with cinnamon EO nanoemulsions was the best accepted, as it masked the typical flavor of celery, which is not usually accepted by some consumers. Similarly, [40] found that rosemary EO was the least accepted, due to the herbaceous aroma and bitter taste that this EO imparts, it was not accepted in various types of foods.

## **2.4 Edible films**

The use of biodegradable materials can be an important means for incorporation of EOs. To reduce the consumption of plastic packaging, biodegradable packaging, edible films and coatings have been developed for the storage of fresh or processed foods.

An edible film (EF) is a preformed layer made from edible materials that can be applied to foods to extend their shelf life. They are elaborated from biopolymers such as carbohydrates, proteins, and lipids [45]. Previous studies have shown that films made from carbohydrates are widely utilized because they have good mechanical properties and act as a barrier against low polarity compounds; however, they can present high permeability against moisture [46]. On the other hand, edible films made from proteins, such as gelatin, are excellent barriers to oxygen, carbon dioxide, and some aromatic compounds; but their mechanical properties are not as efficient [47].

In addition to the main polymer matrix, it is necessary to incorporate some additives as plasticizing agents. These are non-volatile substances of low molecular weight that when added to a polymeric material modify its physical and mechanical properties; for example, its flexibility, manageability, and extension ability [48].
