Phenolic antioxidant mobilization in cranberry pomace by solid-state bioprocessing using food grade fungus Lentinus edodes and effect on antimicrobial activity against select food borne pathogens

Abstract

Cranberry pomace is a byproduct of the cranberry processing industry. Solid-state bioprocessing of cranberry pomace using food grade fungus Lentinus edodes improved phenolic profile and antioxidant activity. We investigated whether these phenolic phytochemicals mobilized during bio-processing of the pomace would improve the antimicrobial functionality. Listeria monocytogenes, Vibrio parahaemolyticus and Escherichia coli-O157: H7 are important food borne pathogens. Control of these pathogens using synthetic antimicrobials such as currently approved antibiotics have limitations due to potential development of resistance. We believe a profile of antimicrobials compared to a single compound could be potentially more effective. The objective of this research was to use food grade fungus Lentinus edodes to release phenolic aglycones and relate its antioxidant functionality and ellagic acid mobilization to antimicrobial activity against Listeria monocytogenes, Vibrio parahaemolyticus and Escherichia coli-O157: H7 . Bioprocessing of pomace was done for 20 days with Lentinus edodes. Total phenolics in water extracts were assayed using Folin-Ciocalteu method. The antioxidant potential was measured using a β-carotene oxidation system (APF) and 1,1-diphenyl-2-picrylhydrazyl-radical (DPPH) system. Changes in phenolic profiles were analyzed using HPLC. Antimicrobial activities of the extracts during growth were tested using standard disk assays. Results showed that the antimicrobial activities of the extracts were enriched by bioprocessing. The bioprocessing-based antimicrobial activity depended on different phenolic functional properties of the extracts. Inhibition of L. monocytogenes by the extracts correlated well with the increase in soluble phenolics, antioxidant activity and enrichment of ellagic acid during solid-state bioprocessing. Inhibition of V. parahaemolyticus and E. coli O157: H7 by the extracts correlated with highest ellagic acid and/or APF. Sensitivity towards soluble phenolics and the antioxidant activity measured by DPPH radical inhibition assay suggests inhibition by the disruption of the membrane by localized hyper-acidification and potentially disruption of H +-ATPase. Whereas, APF and ellagic acid dependent antimicrobial activity suggests potential inhibition by membrane-transport and/or electron transport disruption. The variation in sensitivity of pathogens has implications for designing new food-grade antimicrobials. This solid-state bioprocessing strategy is an innovative approach to produce broad-spectrum antimicrobials against important food borne pathogens.