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.

One economic issue that arises from the procedures used to produce dyes from naturally occurring phenolic chemicals that enzymes have oxidized is called "enzymatic browning". Polyphenol oxidase's existence in most fruits and vegetables is in charge of this problem.  Adding antioxidants is one of the most crucial strategies for halting this process. We used spectrophotometry to examine the antioxidant effects of Maillard reaction products on this enzyme. Five hours of heating at 100 °C was used to study the properties and antioxidant activity of model systems including spermine and monosaccharides (glucose, fructose, and ribose). Vitamin C was used as a control to compare the DPPH radical scavenging activity of the MRP spermine-sugar model systems. Intermediate products at A294 and a browning intensity at A420 nm were increased with heating time. This increase was associated with a decrease in reduced sugar and free amino group contents. Polyphenol oxidase from Mirabelle plum (Prunus domestica subsp. syriaca) was fractionated by ammonium sulfate precipitation, dialysis, and ion exchange chromatography.  A single peak was obtained with specific activity 11292.6 U/mg protein. The MRPs exhibited inhibitory effects on purified Mirabelle plum PPO from (42.6- 70.2%) compared with vitamin C which was 57.9%. Furthermore, the Lineweaver-Burk plots discovered the inhibition modes noncompetitive by the strongest system, spermine-glucose.