Evaluation of antioxidant, antibacterial and physicochemical properties of whey protein-based edible films incorporated with different soy sauces

Soy sauce is a traditional seasoning for foods available at the global market that is consumed all over the world. This sauce has a unique flavor and also antimicrobial and antioxidant properties. There is a wide range of soy sauces and their differences are mainly based on the manufacturing methods. Variation in chemical composition is mainly due to differences in fermentation process and the addition of supplementary ingredients like flavor enhancers, among others. The present work, firstly evaluated several physico-chemical parameters of five commercial soy sauces (pH, titratable acidity, acetic acid and potassium sorbate, total solids, total phenol and total carbonyl derivatives). In addition, antimicrobial activity of soy sauces in liquid medium was analyzed against three food-borne bacterial pathogens, namely Escherichia coli, Listeria monocytogenes and Salmonella Typhimurium. Subsequently, whey protein concentrate (WPC)-based edible films were prepared with the addition of soy sauces (5% v/v). Next the films were characterized according to physicochemical properties (thickness, moisture content, solubility in water), optical parameters (transparency, color, Fourier transform infrared spectrum), tensile properties and antioxidant and antimicrobial activities. Our results confirmed that addition of soy sauces not only improved films organoleptic properties but also conferred antioxidant activity and antimicrobial activity on film surface.