ANTIMICROBIAL SYNERGISM OF PARTIALLY-DENATURED LYSOZYME WITH GLYCINE - EFFECT OF SUCROSE AND SODIUM-CHLORIDE

Previously we reported that heat-treatment of lysozyme at 80 degrees C for 20min in pH6.0 (HL80/6) greatly promoted its antimicrobial action to Gram-negative bacteria without detrimental effects on its inherent action to Gram-positive ones. In this study the effects of sucrose an d NaCl on the promoted antimicrobial activity of HL80/6 and synergy wi th glycine were investigated. This potent antimicrobial lysozyme (HL80 /6) retained 54% of the native enzymatic activity. The enhanced bacter icidal action of HL80/6 against Escherichia coli K12 was gradually dec reased with increasing sucrose and NaCl concentration in the medium, w here complete suppression was observed at 2% sucrose and 0.1% NaCl. On the other hand, 1% NaCl concentration was required to suppress the an timicrobial activity against Staphylococcus aureus of either native ly sozyme (NLz) or HL80/6, while sucrose up to 8% had no detectable inhib itory effect on this strain. However, similar doses of sucrose or NaCl had no effect on the enzymatic activity of both NLz and HL80/6, indic ating that the antimicrobial action of HL80/6 is independent of its mu ramidase activity. HL80/6 lysozyme, but not NLz, exhibited good synerg y with glycine against Gram-negative bacteria even in the presence of the inhibitory doses of sucrose or NaCl, suggesting a possible applica tion in food industry as a food preservative. Thus, the results introd uce an interesting finding that partial denaturation of lysozyme can i nduce its antimicrobial specificity to include the food-borne Gram-neg ative pathogens and heralded fascinating opportunities for application of HL80/6 with glycine in formulated food systems. (C) 1997 Canadian Institute of Food Science and Technology. Published by Elsevier Scienc e Ltd.