| Citrus pectin has good physicochemical properties and biological activity,but its large molecular weight and low solubility limit the practical application of citrus pectin.In order to improve the solubility and utilization value of citrus pectin,the phenolic acid-citrus pectin graft copolymer was prepared by free radical-mediated grafting method with citrus pectin as the research object.The five phenolic acid-citrus pectin graft copolymers reached the maximum grafting rate by single-factor optimization of experimental conditions.Fourier transform infrared spectroscopy,nuclear magnetic resonance,differential scanning calorimetry and other experimental methods Pectin graft copolymers were characterized.The antioxidant activity and immune activity of phenolic acid-citrus pectin graft copolymer were studied by cell experiments.Experimental results show:(1)The maximum graft ratios of the phenolic acid-citrus pectin graft copolymer were:Gallic acid-citrus pectin 68.29 mg/g,Tea polyphenols-citrus pectin 73.24 mg/g,Vanillic acid-citrus pectin 63.70 mg/g g,Syringic acid-citrus pectin 78.32 mg/g,Gentisic acid-citrus pectin 69.51 mg/g.Through Fourier transform infrared spectroscopy,nuclear magnetic resonance and scanning electron microscopy studies,it was found that the phenolic acid was covalently grafted to the citrus pectin chain,its basic structure and sugar type did not change,and its thermal stability was slightly lower than that of citrus pectin,and after graft modification,the microstructure changed from a rough and dense block-like structure to a relatively smooth sheet-like structure.Compared with citrus pectin,the molecular weight distribution of the graft copolymer changed to homogeneity and decreased from(109.98±0.05)k Da to(39.83±0.05)k Da;At the same time,the degree of esterification,galacturonic acid content and solubility of the graft copolymers increased with the decrease of molecular weight,and the maximum increase of Syringic acid-citrus pectin was(72.73±2.18)%,(54.12±1.12)% and(59.87±1.19)%.(2)The antioxidant activity of phenolic acid-citrus pectin graft copolymer was determined by DPPH,ABTS,hydroxyl radical scavenging rate and reducing power.The results showed that Syringic acid-citrus pectin had the strongest antioxidant capacity and the DPPH free radical scavenging rate reached(65.66±0.80)%,followed by Tea polyphenols-citrus pectin(63.27±0.61)% and Gentisic acid-citrus Pectin(61.70±0.74)%,the weakest of citrus pectin(45.83±0.64)%,indicating that grafting phenolic acid can effectively enhance the antioxidant activity of citrus pectin.In cell experiments with antioxidant activity,it was found that compared with citrus pectin,the graft copolymer can significantly reduce the levels of LDH,ROS,and MDA in cells,increase the mitochondrial membrane potential,antioxidant enzyme activities,and maintain intracellular redox balance.Cells play a protective role.This further illustrates the increased antioxidant activity of the graft-modified citrus pectin.(3)The immune activity of the phenolic acid-citrus pectin graft copolymer was determined by cell experiments,and the results showed that high doses of Syringic acid-citrus pectin,Tea polyphenols-citrus pectin and Gentisic acid-citrus pectin could Significantly improved cell viability,respectively:(182±4.1)%,(192±6.7)% and(187±2.6)%.In addition,the graft copolymer can significantly increase the NO release,phagocytic neutral red capacity and cytokine secretion of RAW264.7 cells.Among them,the cells cultured with Tea polyphenol-citrus pectin had the best test indicators at a concentration of 200 μg/m L,with NO release reaching(23.61±0.52)μM,and phagocytosis of neutral red(2.12±0.05)%.It is further explained that the phenolic acid-citrus pectin graft copolymer can regulate the immune function of cells,stimulate and activate macrophages,and enhance the cellular immune activity. |
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