Fabrication and characterization of novel biodegradable active films based on Eremurus luteus root gum incorporated with nanoemulsions of rosemary essential oil

In this paper, the rosemary essential oil (REO) nanoemulsions with various droplet sizes were obtained by sonication treatment. The influence of incorporation of REO nanoemulsions with the smallest and largest droplets' size at different concentrations (0.5, 1, 2, and 4 % v/v) in Eremurus luteus root gum (ELRG) film on its physicochemical, barrier, mechanical, structure, antioxidant and antimicrobial characteristics were investigated. Also, the effect of particle size and concentration of nanoemulsions on their retention in the film structure during storage at 25 degrees C were evaluated. The results indicated that the increase in the concentration of REO nano -emulsions decreased their moisture content, solubility, tensile strength, and elastic modulus while increased the contact angle, water vapor permeability (WVP), and elongation at break. The analysis of color attributes of films revealed more opacity, yellowness, and Delta E values of the active films in comparison to the control film. The FTIR spectrums demonstrated the hydrogen bonding interactions of film components at the molecular level. The SEM images showed non-uniform and spongy structures in dried active films after the incorporation of REO nano -emulsions. The loss of REO was raised in dried films by increasing the concentration and diameter of droplets of REO nanoemulsions. The highest bacterial growth inhibition was obtained in the presence of films containing 4 % REO nanoemulsion. The antioxidant activity of ELRG film after the addition of REO improved from 16.45 to 47.78 %. Generally, some of the properties of the active ELRG films were more affected by the concentration of REO emulsions than their droplet size. According to the results, these biodegradable ELRG active films can be considered in the future as edible packaging for improving food shelf-life.