Antibacterial mechanism of adzuki bean seed coat polyphenols and their potential application in preservation of fresh raw beef

The monomeric phenolic components of adzuki bean seed coat polyphenols (ABSCPs) were analysed, and their antibacterial activity and mechanism against two tested bacteria (Escherichia coli ATCC8797 and Staphylococcus aureus ATCC12600) were evaluated for their potential application in preservation of fresh raw beef. ABSCP contained 13 kinds of monomeric phenols, and the minimum inhibition concentration (MIC) of ABSCP against E. coli and S. aureus was 1250 and 625 mu g ml(-1), respectively. The mechanism of ABSCP against E. coli and S. aureus was associated with increased cell protein and nucleic acid leakage, increased cell membrane potential, decreased intracellular ATP concentration and morphological changes in bacterial cell. In addition, ABSCP with whey protein isolate (WPI) was applied to fresh raw beef and this remarkably retarded microbial growth by maintaining the total microbial quality below the acceptable limit of 6 lg CFU g(-1) for 14 days. Lower pH and total volatile base nitrogen values were observed in the coated samples during refrigerated storage (4 degrees C). As a result, we found that ABSCP, as a natural food bacteriostatic agent, can effectively inhibit the growth of E. coli and S. aureus and combined with WPI to apply to fresh raw beef to extend its shelf life.