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Received Jan 19, 2018; Revised Apr 5, 2018; Accepted Apr 15, 2018
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
Researchers around the world are investigating the use of essential oils to protect food from microbial growth. The antimicrobial activity of essential oils and plant extracts is well known for a long time, and many research results have been published against food-borne pathogens [1] and about their low toxicity to mammals, fewer environmental effects, and low cost, which make them more attractive than synthetic antimicrobials [2]. Based on their traditional use, these extracts obtained from plants are first recommended, due to their broad-spectrum antimicrobial action and low side effects treatments [3]. Essential oils also have the additional effect of maintaining the quality of the food during storage, including sensorial, nutritional, and functional properties [4, 5].
Carvacrol (5-isopropyl-2-methylphenol) and thymol (2-isopropyl-5-methylphenol) are the major components of the essential oils of some species belonging to the Lamiaceae family including oregano, and these are phenolic compounds; isomers of monoterpenes exhibit significant antimicrobial activity in vitro [6, 7]. The WHO recognized thymol and carvacrol as GRAS compounds for consuming as long as they not exceed 50 mg·kg−1 [6].
Natural antimicrobial compounds effectiveness depends on the type, genus, species, and strain of the target microorganism and some food intrinsic and extrinsic factors such as pH, temperature, water content, atmospheric composition, and initial microbial load, with pH being one of the most important factors due to antimicrobial dissociation [3].
Bacterial susceptibility to essential oils increases with a reduction in food pH, since at low pH the hydrophobicity of the oil increases more easily allowing the dissolution of the membrane lipids’ target bacterium [8].
Currently, research has been focused on the use of edible films due to their safety regarding consumption and friendly relation with the environment, and coating materials being used currently include polysaccharides (cellulose derivatives, starch, chitin, and gums), proteins (soy, milk, gelatin, corn zein, and gluten), and lipids (oils, waxes, and resins) [9]. Among them, carboxymethyl cellulose (CMC) and starch (S) are the most widespread and economic biomaterials. In addition, its chemical, physical, and functional...