Optimized antimicrobial edible whey protein films against spoilage and pathogenic bacteria
E. T. RODRIGUES, J. H. Han, and R. A. Holley. Department of Food Science, The University of Manitoba, 250 Ellis Building, Winnipeg, MB R3T 2N2, Canada
Consumers demand packaging systems that not only, protect the food commodity, but are environmentally friendly and extend shelf life. A previous study determined the minimum inhibitory concentrations (MICs) for several antimicrobials that can be included in packaging films. Recently, we optimized whey protein isolate (WPI) films to incorporate a mixture of antimicrobials (nisin, lysozyme, EDTA and propyl paraben) at various concentrations (50% MIC, MIC and 150% MIC). These biodegradable films may replace conventional plastic packaging and improve food quality. Our objectives were to: (1) test the effectiveness of the mixed antimicrobial films against certain spoilage and pathogenic microorganisms, (2) identify significant variables and (3) optimize the films' composition for maximum antimicrobial activity. The films were produced by mixing heat-denatured solutions of WPI and glycerin with combinations of antimicrobials, then drying the solutions on casting dishes. We determined each film's antimicrobial activity by the zone of inhibition it produced on agar plates; which were inoculated with Brochothrix thermosphacta, Listeria monocytogenes, Salmonella typhimurium and Staphylococcus aureus. Regression analysis was performed to determine significant factors. Our results showed that an increase in nisin concentration increased film antimicrobial activity against all four microorganisms. The most effective antimicrobials were: nisin for B. thermosphacta, nisin-lysozyme for S. typhimurium, nisin and nisin-EDTA for S. aureus and, propyl paraben, nisin and lysozyme-propyl paraben for L. monocytogenes. In some combinations, it was more effective to use 50% MIC than 150% MIC of an individual antimicrobial when other agents were kept at constant concentrations. Such that, with EDTA-nisin combinations, a higher EDTA concentration reduced nisinís inhibitory effects against S. typhimurium and S. aureus. The most effective films were composed of nisin at its highest concentration with the MIC or sub-MIC levels of the other antimicrobials. These resulting edible films may extend product shelf life and reduce plastic packaging waste.
Session 100B, Food Packaging