Preparation,Functional Properties And Preservation Effect Of Chitosan-gallic Acid Derivatives Of Saimaiti Apricot

Chitosan（CS）,a deacetylated product of chitin,has a variety of biological activities and is often used as a novel material in food and pharmaceutical applications.However,its special spatial structure makes its solubility and antioxidant properties insignificant,and these drawbacks limit the application of CS.Therefore,in order to improve its inherent physical structure and chemical properties,such biopolymers are needed to introduce external functional groups through certain chemical modifications.In this study,chitosan was modified by introducing gallic acid（GA）via H₂O₂/Vc radical-induced grafting reaction to synthesize chitosan-gallic acid derivatives（CS-GA）.The effect of different reaction conditions on the grafting amount of CS-GA derivatives was compared using single-factor and response surface experiments to determine the grafting reaction conditions and analyze its structural and functional properties.Then it was applied to the preservation of Saibati apricots to investigate the effects of chitosan and CS-GA derivatives on the quality of apricot fruits during refrigeration.To provide a theoretical basis for the storage and preservation technology of Xinjiang specialty fruit apricot.The results of this experiment were as follows:1.Gallic acid was covalently grafted with chitosan through graft modification to form CS-GA derivatives.The effect of reaction conditions on the grafting amount of gallic acid was investigated by one-way and response surface experiments on reaction time,ascorbic acid concentration,hydrogen peroxide concentration and gallic acid/chitosan ratio.The reaction time was 12 h,the ratio of chitosan/gallate was 1:1,the concentration of ascorbic acid was 0.3 m M,and the concentration of hydrogen peroxide was 800 m M.The amount of gallic acid grafted was 163.19 mg GAE/g.2.The structural analysis of the chitosan-gallate derivatives yielded no significant UV absorption peaks in the range of 200-500 nm for the CS solution,while the CS-GA derivative retained the characteristic chitosan absorption peak and showed a gallic acid benzene ring absorption peak at 261 nm.In addition,the infrared spectrum of the CS-GA derivative has polysaccharide features and the amide band is overloaded from primary to secondary,indicating that a covalent coupling reaction occurs.x-diffraction spectrum of the CS-GA derivative disrupts the hydrogen bonding structure of CS,resulting in its low crystallinity.The analysis of the NMR hydrogen and carbon spectra showed that the CS-GA derivative retained the structural absorption peaks of CS,while new signal peaks appeared around 7.00ppm and 145 ppm,corresponding to the aromatic proton and C=C double bond of GA,while the thermal scan analysis showed that the thermal stability of CS-GA derivative was lower than that of CS;the antioxidant capacity experiment obtained that the modified CS-GA derivative The antioxidant capacity of CS-GA derivatives was higher than that of CS,and the scavenging rate of DPPH radicals was 93.52%at a concentration of 1.0 mg/m L,which was not significantly different from that of ascorbic acid at the same concentration;the inhibition test showed that CS-GA had the largest inhibition circle diameter against Staphylococcus aureus,and its minimum inhibition concentration was 1.0 mg/m L,which was lower than that of chitosan.3.CS-GA derivative coated film could effectively reduce the quality loss of Saibati apricot fruits and maintain the higher hardness and good color of the fruits.At 35 d of storage,the soluble solids content and titratable acid content of the CS-GA-0.5%treated group were 1.12 and 1.25 times higher than those of the control fruit,respectively.The relative conductivity of the control group（49.53±0.58%）was 1.97 times higher than that of the CS-GA-0.5%treated group（25.20±0.28%）.The peak respiration and ethylene release of the blank control group were reached at day 14,while the peak respiration of the CS-GA-0.5%treated group was delayed at day 28 and the peak ethylene release was delayed until day 21,indicating that the CS-GA treatment could slow down the respiration rate and ethylene production thus delaying the peak respiration and ethylene release and maintaining a higher quality of appearance.