Design of biosystems to provide healthy and safe food. Part A: effect of emulsifier and preparation technique on physicochemical, antioxidant and antimicrobial properties

In this study, the effect of emulsifier and preparation technique on physicochemical properties and antioxidant/antimicrobial activity of plant oil (lemongrass and oregano, 1:1)/citrus extracts incorporated in oil-in-water (O/W) microemulsion in comparison to coarse emulsion, was investigated. The optimization of O/W microemulsion was performed by two surfactants with different hydrophilic-lipophilic balance values and two techniques of preparation such as sonication and microfluidization. The stability of microemulsions during storage time regarding to the droplet size, zeta-potential, viscosity, total polyphenolics content, total flavonoids content, antioxidant, antiradical and antimicrobial activity were assessed. Micro-emulsification increased the bioactivity of plant oil/citrus extracts by increasing the surface area of droplets induced by size decrement. Microfluidized and sonicated emulsions showed the same relatively stable profile during storage time. Micro-emulsification improves the functionality of plant oil/citrus extracts, such as antioxidant and antiradical activity. An increment about 16-32 times in antimicrobial activity of plant oil/citrus extracts was also attained. Furthermore, the morphology of microemulsions observed by transmission electron microscopy, confirmed a mono-dispersed nano-sized emulsion.