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.