Study On The Synthesis And Properties Of EGCG Grafted Bio-based Raw Materials

Epigallocatechin gallate(EGCG)is one of the most important active substances in green tea.Although it has excellent biological activity,its chemical and color instability limit its application scope.EGCG grafted bio-based raw materials can not only keep EGCG excellent biological activity and improve its stability,but also improve bio-based raw materials physicochemical properties and biological activity.It can even bring new functional properties to EGCG grafted bio-based raw materials,thus expanding the application of grafted copolymers in cosmetics,food and biological medicine,etc.In this paper,in order to obtain new materials with high functional properties,EGCG grafted carboxymethyl yeast?-glucan(CMG),EGCG grafted carboxymethyl curdlan(CMCD)and EGCG grafted?-polylysine(?-PL)were prepared by chemical coupling method and free radical mediated grafting method.The main research contents and conclusions are as follows:(1)EGCG grafted CMG(named CMG-EGCG)was synthesized in two steps based on 1-ethyl-3-(3-dimethylaminopropyl)carbodiimidehydrochloride(EDC)/4-dimethylaminopyridine(DMAP)chemical coupling method.The physicochemical properties of CMG-EGCG were characterized by UV-Vis Spectrophotometer(UV-Vis),Fourier transform infrared spectroscopy(FT-IR),thermogravimetry(TGA)and scanning electron microscopy(SEM).The grafting rate of EGCG in CMG-EGCG was determined by Folin-Ciocalteu method.The antioxidant activities of CMG-EGCG and CMG were compared.The color stability of CMG-EGCG aqueous solution was investigated.The results showed that EGCG was first succinylated and then grafted with the hydroxyl group of CMG,which protected the carboxyl group of CMG and increased the solubility of the reactant,thus improving the grafting rate of EGCG.The grafting rate of EGCG in CMG-EGCG was 100.25 mg/g.Compared with CMG,CMG-EGCG had better antioxidant activity.When the concentration was 0.4 mg/m L,the scavenging percentages of DPPH radical by CMG-EGCG was 92.22±1.45%;when the concentration was 0.16 mg/m L,the scavenging rate of ABTS radical by CMG-EGCG was99.17±0.30%,which were close to the activity of EGCG.Moreover,when the concentration was 1.0 mg/m L,the reducing ability and ferrous ion chelating ability of CMG-EGCG were1.65±0.13 and 9.13±0.64%,respectively.In addition,CMG-EGCG aqueous solution had good color stability.(2)Three groups of EGCG grafted CMCD(respectively named CMCD-1-EGCG,CMCD-2-EGCG and CMCD-3-EGCG)were prepared by EDC/DMAP coupling method,and the effects of substitution degree of CMCD on the grafting rate of EGCG and the physicochemical properties and biological activities of EGCG grafted CMCD were further investigated.The physicochemical properties of EGCG grafted CMCD and the grafting rate of EGCG were evaluated by FT-IR,UV-Vis and TGA,etc.The antioxidant activity and color stability of EGCG grafted CMCD were analyzed.The results showed that the higher the substitution degree of CMCD,the higher the grafting rate of EGCG and the better the water solubility of grafted copolymer,that is,CMCD-3-EGCG had the highest EGCG grafting rate(132.01 mg/g)and the best water solubility(23.14 mg/m L).The DPPH radical scavenging activity,ABTS radical scavenging activity,reducing ability and ferrous ion chelating ability of EGCG grafted CMCD were positively correlated with the grafting rate of EGCG,that is,CMCD-3-EGCG had the best antioxidant activity.When the concentration was 0.2 mg/m L,the scavenging rate of DPPH radical by CMCD-3-EGCG was 94.41±2.66%;when the concentration was 0.06 mg/m L,the scavenging rate of ABTS radical by CMCD-3-EGCG was 96.91±1.65%;when the concentration was 1.0 mg/m L,the reducing ability was 3.08±0.13,which were close to the activity of EGCG.Moreover,the ferrous ion chelating ability of CMCD-3-EGCG was37.07±1.07%at the concentration of 1.0 mg/m L.In addition,the color stability of EGCG grafted CMCD aqueous solution was good.(3)With ascorbic acid/hydrogen peroxide(H₂O₂)as redox initiator,EGCG grafted?-PL(respectively named?-PL-EGCG-0.1,?-PL-EGCG-0.3,?-PL-EGCG-0.5,?-PL-EGCG-0.7 and?-PL-EGCG-1.0)were prepared by free radical mediated grafting method.The effects of the molar ratio between?-PL and EGCG on the grafting rate of EGCG and the physicochemical properties,antioxidant and antibacterial activities of EGCG grafted?-PL were studied.The physicochemical properties of EGCG grafted?-PL and the grafting rate of EGCG were evaluated by FT-IR,UV-Vis and TGA,etc.The antioxidant activity of EGCG grafted?-PL and their inhibitory effects on Gram-positive(Staphylococcus aureus)and Gram-negative(Escherichia coli)bacteria were investigated.The results showed that when the molar ratio of EGCG was relatively large,the dimer of EGCG appeared during the reaction,which affected the grafting rate of EGCG and the chemical structure of EGCG grafted?-PL.?-PL-EGCG-1.0had the best antioxidant activity.When the concentration was 0.8 mg/m L,the DPPH radical scavenging activity of?-PL-EGCG-1.0 was 94.03±1.10%;when the concentration was 0.4mg/m L,the ABTS radical scavenging activity of?-PL-EGCG-1.0 was 98.86±2.94%;when the concentration was 1.2 mg/m L,the reducing power and ferrous ion chelating ability of?-PL-EGCG-1.0 were 2.06±0.10 and 65.99±2.01%,respectively.In addition,the antibacterial activity of EGCG grafted ?-PL was slightly lower than that of ?-PL.