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Food quality, food preservation, and food safety are the most significant concerns in the food industry currently.1 Moreover, consumers demand for minimally processed foods and ready-to-eat fruits and vegetables because of its convenience since they do not need to process the product later.
Keywords: Nanoemulsions; Properties; Enzymes; Microscopy
Mini Review Essential Oil Nanoemulsions and Food * *Corresponding author Applications Kanika Bhargava, MS, PhD Department of Human Environmental Sciences * Daniel Mathias Fuzette Amaral and Kanika Bhargava University of Central Oklahoma 100 N University Dr Edmond, OK 73034, USA Department of Human Environmental Sciences, University of Central Oklahoma, 100 N Tel. 405-974-5556 University Dr, Edmond, OK 73034, USA E-mail: kbhargava@uco.edu Volume 1 : Issue 4 KEYWORDS: Nanoemulsions; Properties; Enzymes; Microscopy. Article Ref. #: 1000AFTNSOJ1115 ABBREVIATIONS: EIP: Emulsion Inversion Point; PIC: Phase Inversion Composition; PIT: Phase Inversion Temperature; EOs: Essential Oils; SE: Spontaneous Emulsification. Article History th Received: July 20th, 2015 rd INTRODUCTION Accepted: August 3 , 2015 th Published: August 4th, 2015 Citation and ready-to-eat fruits and vegetables because of its convenience since they do not need to Amaral DMF, Bhargava K. Essen- 2 tial oil nanoemulsions and food applications. Adv Food Technol Nutr Sci Open J. 2015; 1(4): 84-87. 3 doi: 10.17140/AFTNSOJ-1-115 decrease of the shelf life. Therefore, microbial and enzymatic activity is a leading concern in Copyright carvacrol and cinnamaldehyde in kiwifruit and melon by dipping the food products in solution. ©2015 Bhargava K. This is an The study showed that the natural flora of the product was reduced significantly after the EOs open access article distributed un- 3 der the Creative Commons Attribu- tion 4.0 International License (CC BY 4.0), which permits unrestricted Although essential oils have been shown to be promising alternative to chemical pre- use, distribution, and reproduction servatives against foodborne in any medium, provided the origi- in food products. Low water nal work is properly cited.
Food quality, food preservation, and food safety are the most significant concerns in the food industry currently.1 Moreover, consumers demand for minimally processed foods process the product later. However, minimally processed foods are known for high chances of microbial contamination and high enzymatic activity. When the product is cut, the nutrients inside the fruits and vegetables are exposed to enzymes and microorganisms that will provide the food industry in regards to proving food safety and convenience for the consumers. Due to this challenge, food industries have been using chemical substances to inactivate some of the enzymes, and specially, to reduce the microbial population. Nevertheless, these kinds of chemi- cals are most of the time corrosive, ineffective in the presence of high organic loads, may form 3-5 organochlorides and may have long-term toxicological implications.3-5 Because of this issue, new technologies are being developed in order to find out new alternatives for replacement of chemical treatments.6 Currently, there is a growing interest in the utilization of new preservative methods that are from natural origin. Essential Oils (EOs) are natural compounds that have been shown promising treatment for food application because of its strong antifungal, antiviral, and anti- 7-9 bacterial activities.7-9 EOs present photo-chemicals, such as 1,8-cineole, carvacrol, eugenol, cinnamaldehyde, carvone, citral, estragole, geraniol, perillaldehyde, terpineol, thymol, and vanillin which are able to extend shelf life of processed food products by preventing lipid oxi- 7,10,11 dation and antimicrobial properties. Moreover, EOs also have been proved to have other 12,13 14 diverse beneficial functions, such as antidiabetic, antiradical, and antioxidant effects. The antimicrobial properties of EOs is associated with the dissolving of the cytoplasmic membrane of bacterial cells in the hydrophobic domain.15 Previous studies have shown that EOs were able 15 16 to inhibit Bacillus cereus,15 Zygosaccharomycesbailli,16 Listeria monocytogenes, and Staphy- lococcus aureus.17 Pandit and Shelef have applied rosemary oil in pork liver sausage and veri- fied that it was effective against Listeria monocytogenes.18 Another study evaluated the use of application.
pathogens, they present special limitations that preclude its use solubility, high volatility, and strong odor of EOs are the main properties that make it difficult for food application. It is also a big challenge to incorporate oil-based compounds in aqueous food products because it shows physical and chemical instability when it is applied in food sys- tems.19 However, several studies have shown that the use of na- noemulsions can be a great choice for application of EOs in food matrix.20 NANOEMULSIONS AS ANTIMICROBIAL DELIVERY SYSTEM Nanoemulsion presents differences in their physi- cal properties and structures. They are stable colloidal systems within nanometric size (≤100 nm) that usually consist of oil, sur- factant and water, presenting as transparent or slightly turbid.21 Nanoemulsions differ appreciably from conventional emulsions in their functional activity due to the decreased size.19 For ex- ample, these emulsions may not scatter light strongly in the visible region and can thus be transparent. Nanoemulsion has the advantages of high surface area and kinetic stability against coalescence or creaming. As a result, nanoemulsions are impor- tant vehicles for hydrophobic bioactive substances through the formation of nano-dispersions. Hence, these systems permit the application of essential oils in food since they present solubiliza- tion in the water phase through molecular dispersion.20 Nanoemulsions can be formulated using low-energy methods or high-energy emulsification methods. High-energy methods include high-pressure homogenization, microfluidiza- tion and sonication. In this case, energy is necessary to provide intense disruptive forces and minimized droplet size. Low-ener- gy methods include Spontaneous Emulsification (SE) method, Emulsion Inversion Point (EIP) method, Phase Inversion Com- position (PIC) method and Phase Inversion Temperature (PIT) method. In these methods, emulsion is formed spontaneously by mixing the ingredients together. The droplet size can be reduced by varying the composition and altering the environmental fac- tors.15 Ultrasonic emulsification is one of the methods, which has been showing promising properties for application of EOs in foods. It is a high-energy method of formulation nanoemulsions that is able to decrease the size of droplets in the emulsion, which Antimicrobial Target Microorganism Oregano oil Salmonella Typhimurium, Carvacrol Carvacrol Mandarin oil Listeria innocua Mandarin oil Listeria innocua Lemongrass oil Salmonella Typhimurium E. coli Plums Cinnamaldehyde Saccharomyces cerevisiae Eugenol can promote very small droplet diameter, high physical stability, 22,23 high bioavailability, and optical transparency. Because of the small size of the droplets, gravitational separation, flocculation, and coalescence often occur at a reduced rate in nanoemulsions.
Nanoemulsion presents a very interesting application in certain food and beverage since the small droplet size promotes trans- parency or only slightly turbid in the food product.24 In nanoemulsions, the choice of surfactants is very crit- ical since emulsifiers have to rapidly cover the many new sur- faces that are formed. Generally, in food emulsions two classes of surface-active species are used: (1) small-molecule surfac- tants such as monoglycerides, sucrose esters, and others and (2) macro-molecular emulsifiers such as protein or modifiedstarch- es.25 EOs have to be associated or combined with surfactants in order to enhance the antimicrobial activities by increasing the solubility of EOs in the aqueous phase. Tween 80 has a high hy- drophilic and lipophilic balance. Tween 80 is non-ionic in nature and stabilizes emulsion droplets by stearic stabilization. More- over, being a low molecular weight surfactant, it is efficient in minimizing droplet size better than polymeric surfactants.26 Nanoemulsion based delivery system could be char- acterized by dynamic light scattering, zeta potential, thermody- namic stability studies, pH, refractive index and viscosity. Dy- namic light scattering is used to determine the size distribution profile of particles in nanoemulsions and zeta potential indicate stability of emulsions. Imaging techniques such as transmission electron microscopy, scanning electron microscopy and atomic force microscopy is used to confirm diameter of particles and understand distribution of nanoparticles.27 APPLICATIONS IN FOOD MODELS Recently, few studies have applied EOs in food sys- tems, which makes these studies even more exciting and needed.
Table 1 summarizes the most recent studies that apply EOs and nanoemulsions in food systems.
Food System Reference Listeria monocytogenes, Lettuce E.coli O157:H7 Salmonella enteric Enteritidis 29 Broccoli and Radish seed E. coli Salmonella enteric Enteritidis 30 Mung bean and Alfalfa seeds E. coli Green beans Green beans Lactobacillus delbrueckii Apple and Pear Juice Escherichia coli Escherichia coli O157:H7 Fruit Juice 15 Listeria monocytogenes Bhargava, et al. applied oregano oil nanoemulsion to control the foodborne on fresh lettuce.28 The food product was evaluated against Listeria monocytogenes, Salmonella Ty- phimurium and Escherichia coli O157:H7. The data suggested that applying oregano oil nanoemulsion to fresh produce may be an effective antimicrobial control strategy. Another similar study evaluated the effectiveness of carvacrol nanoemulsion against Salmonella enterica Enteritidis and E. coli on broccoli, radish 29 29 seed,29 mung bean, and alfalfa seeds.29 The experiments have shown that the nanoemulsion is effective on radish seed, mung beans, and alfalfa seed but not affective on broccoli seeds. The antibacterial and physical effects of modified chitosan based- coating containing nanoemulsion of mandarin essential oil on green beans is recently being analyzed. The experiments were associated with different non-thermal treatments against Listeria innocua and the results have shown promising applica- tion of this type of nano-emulsion in food products.
A very interesting food application of EOs nanoemul- sion has been observed in plums. Recently, lemongrass oil nano- emulsionwas used to evaluate antimicrobial properties, physical, and chemical changes in plums.33 The nanoemulsion was able to inhibit Salmonella and E. coli population without changing fla- vor, fracturability, and glossiness of the product. It was also able to reduce the ethylene production and retard changes in lightness and concentration of phenolic compounds.
Essential oil emulsion based delivery system is emerg- ing as viable solution to control growth of food borne pathogens on food. However, limited studies are performed on food model and there exist several challenges in application of this system in complex food matrices such as meat and meat products. Ap- plication of nanoemulsions in food models will also offer chal- lenges to government and industry.35 Food industry has to build consumer confidence on acceptance on nano food ingredients such as antimicrobial essential oil nanoemulsions. On the other side, regulatory agencies such as FDA should ensure safety of these antimicrobial delivery systems.
CONFLICTS OF INTEREST The authors declare that they have no conflicts of interest.