Optimized Preparation And Properties Of Chitooligosaccharide-amino Acid Maillard Reaction Products

Chitosan,widely applied in food,medicine,and other industries,has good antioxidant activity,antibacterial activity,and immune function.The carbonyl groups of chitosan can react with amino groups of amino acids through Maillard reaction.Chitooligosaccharides?COS?is the hydrolysis product of chitosan;compared with chitosan,COS has better water solubility,stronger biological activity,but weaker antibacterial ability.Therefore,in this study,COS-lysine Maillard reaction products?CL-MRPs?and COS-glycine Maillard reaction products?CG-MRPs?were prepared using COS and amino acids?AA?systems,which were collectively called COS-AA-MRPs;their structures were characterized,and their biological activities and effects on the fruit juice preservation were studied.Firstly,the reaction conditions for preparing COS-AA-MRPs were optimized by response surface methodology based on the ferric ion reducing/antioxidant power?FRAP?.After optimization,the FRAP value of CL-MRPs and CG-MRPs were 13.86±0.16 mmol Fe²⁺/L and 32.14±0.66 mmol Fe²⁺/L,respectively.The changes in FTIR,UV-Vis,fluorescence spectra and thermogravimetric analysis showed that the Maillard reaction mainly occurs on the carbonyl group of COS;furaldehyde and Schiff base were formed in the MRPs.Fluorescence compounds were generated in the middle stage of Maillard reaction and polymerized into large molecular polymer at final stage.Then,the antioxidant activity of COS-AA-MRPs was studied,with the increase of concentration,the antioxidant activity of COS-AA-MRPs increased gradually.Compared with COS,the FRAP of CL-MRPs and CG-MRPs increased by 2.82-and 7.62-fold,respectively.The DPPH radical scavenging activity was 1.6-and 5.2-fold,the ABTS radical scavenging activity was 1.7-and 4.14-fold that of COS,both CL-MRPs and CG-MRPs exhibited stronger antioxidant activity,and the antioxidant capacity of CG-MRPs was slightly stronger than CL-MRPs at the same concentration.Afterwards,the antibacterial activity of COS-AA-MRPs was analyzed.The results of inhibition zone experiments showed that COS-AA-MRPs had great antibacterial activity against Escherichia coli,Proteus vulgaris,Pseudomonas aeruginosa,Staphylococcus aureus,Micrococcus luteus and Bacillus subtilis,but had no effect on the growth of Lactobacillus acidophilus and Enterococcus faecalis.The Escherichia coli and Staphylococcus aureus were selected to study the antibacterial mechanism of COS-AA-MRPs;the results showed that adding CL-MRPs and CG-MRPs could obviously extend the lag periods of two bacteria,and the integrity of bacterial cell membranes were destroyed,resulting in the leakage of intracellular substances.Finally,the preservative effects of COS-AA-MRPs on fresh kiwifruit juice were studied.During storage,compared with the control,the juices added CL-MRPs and CG-MRPs showed stronger antioxidant ability,higher organic acids,and reducing sugar contents;both PPO and POD activity decreased,indicating COS-AA-MRPs could inhibit the metabolism and browning of juice,prevent the loss of nutrients,and had good preservative effects on fresh juice.