Application of chitosan films in the quality control of fresh shredded vegetables

The objective of this study was to investigate the antimicrobial effects of chitosan gelatin films with or without added essential oils against Listeria monocytogenes on fresh shredded cabbage, carrot and black radish. Samples of fresh shredded vegetables were inoculated with L. monocytogenes and then stored between two layers of edible chitosan films at various concentrations, with or without added essential oils. The inoculated, film treated samples were stored at 4 °C. Samples were taken every day,during six days, for enumeration of surviving L. monocytogenes by plating on appropriate media. Compared to control,1% chitosan film and 0.5% filminduced to 4.7 and 2.9 log CFU/g reductions on shredded cabbage 3rd day respectively. After3 days, films with 1% chitosan reduced L. monocytogenes population by 3 log CFU/g on carrots. Antimicrobial activity of chitosan film increases with increasing concentrations of applied chitosan, where 1% chitosan film has the highest antimicrobial activity compared to 0.5% chitosan film. Nevertheless, chitosan films were more effective on black radish than on cabbage and carrot. Addition of thyme essential oils, significantly improves the activity of the antimicrobial film and reduce the time required for the inhibition of bacteria in vegetables. Also, changes of color, taste, aroma and chemical composition of non-treated and treated samples were determined. The application of chitosan films exerts a significant influence on the pH changes and content of soluble solids of stored vegetables. Chitosan films improved sample appearance, since they diminished the occurrence of the color changes during storage. The results of this experiment showed that the use of chitosan films is a viable alternative in controlling the microorganisms present in minimally processed vegetables, improving its sensory quality. The advantages of edible films were the simple manufacturing process, biodegradability and usage of natural and safe compounds.