Physical, mechanical, and antimicrobial properties of chitosan films with microemulsions of cinnamon bark oil and soybean oil

Antimicrobial films prepared with essential oil emulsions often have a high degree of opacity. This may be prevented using transparent microemulsions. The objective of this study was to characterize physical, mechanical, and antimicrobial properties of films prepared from mixtures with 1% w/w chitosan solution and microemulsions containing 1:0, 2:1, and 4:1 mass ratios of cinnamon bark oil (CBO) (1, 2 and 3% w/w) and soybean oil. Changes in solvent polarity after mixing chitosan solution and microemulsions increased droplet dimension from 88 nm of the film–forming mixtures and induced different extents of coalescence after film formation. Despite these physical changes, films prepared from microemulsions were transparent and had low opacity. The incorporation of microemulsions increased the thickness and water vapor permeability of films and significantly reduced the moisture content and swelling ratio. The retention of CBO was improved for films prepared from microemulsions with 2 and 3% CBO immediately following film formation and after ambient storage, when compared to control films prepared with emulsions with less Tween 80. Large zones of inhibition against foodborne pathogens were observed for film discs prepared with 2 and 3% CBO. These characteristics show the potential of using microemulsions as an easy approach to incorporate EOs in biopolymer antimicrobial films to improve microbiological safety and film transparency.