synthesis the bioactive conjugates of nisin-xanthan through the maillard reaction at moderate temperature

Nisin is a natural heat resistance preserver with a wide range of applications in food industries. the main drawback of nisin is its weak activity against the most of gram-negative bacteria. in this study, the antibacterial activities of nisin against salmonella typhimurium, klebsiella pneumoniae, citrobacter freundii, and escherichia coli improved via the maillard reaction with xanthan. the nisin-xanthan conjugates analyzed by the ultraviolet, fluorescence, and fourier transform infrared spectroscopies. the results showed temperature, the reaction duration, and the nisin-to-xanthan ratio affected the quality of the obtained conjugates. the antibacterial activity of 100 ppm of the conjugates was increased and reached 88.8, 98.7, and 97.7% respectively against s. aureus, s. typhimurium, and e. coli, when the nisin to xanthan ratio was increased from 1:1 to 4:1. the increase in temperature from 90 °c to 110 °c enhanced the antibacterial effects against all test bacteria, especially for persistent gram-negative cells, namely c. freundii and k. pneumoniae. the longer maillard reaction after 110 min at 110 °c did not improve the antibacterial activity of the conjugates against all test bacteria. the best antibacterial activity was observed at the temperature of 110 °c for 110 min for the nisin-to xanthan ratio of 4:1.