Glycation of Nisin with Glucose, Lactose and Dextran and investigation of its inhibitory effect on Escherichia coli and Salmonella typhimurium

Nisin is an antimicrobial peptide used in food industry as preservative. However, this peptide has no considerable effect on gram negative bacteria. In this study the effect of glycation on antimicrobial activity of gram negative bacteria was elucidated against gram negative bacteria. Solution of nisin and fivefold concentration of glucose, lactose and dextran and solution of nisin without any sugar were prepared in phosphate buffer and were lyophilized. The lyophilized powder was exposed to 60°C temperature and 70% humidity for 7 days. Every 24 hours, one sample was collected and dissolved in distilled. Equal molar concentration of native and conjugated nisin were made. Percent of glycation was measured by OPA (ortho-phthalaldehyde) method. MIC50 of nisin was assayed by microdilution method against Escherichia coli and Salmonella typhimurium. The result of this study has revealed that percentage of glycation is conversely related to the size of carbohydrates in which nisin-glucose had the highest and nisin-dextran had the least percentage of glycation. Glycation of nisin increased the MIC50 of nisin against E. coli after seven days. MIC50 of native nisin and glycated nisin had no difference against S. typhimurium. From this study it was concluded that conjugation of nisin with carbohydrates is not able to extend the antimicrobial activity of nisin to gram negative bacteria.