Synthesis the Bioactive Conjugates of Nisin-Xanthan through the Maillard Reaction at Moderate Temperature

Nisin is a natural heat resistance preserver with wide applications in food industries. The main drawback of nisin is its weak activity against most 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, reaction duration, and nisin-to-xanthan ratio affected the quality of the obtained conjugates. In relevant to the results, the antibacterial activity of 100 mg L-1 of the conjugates was increased against S. aureus, S. typhimurium, and E. coli when the nisin to xanthan ratio was increased from 1:1 to 4:1 and reached 88.8, 98.7, and 97.7%, respectively. The increase in temperature from 90 ᵒC to 110 ᵒC 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 ᵒC did not improve the antibacterial activity of the conjugates against all test bacteria. The best antibacterial activity was observed at a temperature of 110 ᵒC for 110 min for a nisin-to-xanthan ratio of 4:1.