Study On The Preparation And Antioxidant Activity Of Sodium Alginate-based Phenolic Acid Copolymer

Sodium alginate is a by-product of mannitol extracted from brown algae.It has an annual output of 26,500 tons.At present,the degree of deep processing of sodium alginate is relatively low,and high-value resources are awaited.Studies have shown that the oligomers polymannuronic acid（PM）and polyguluronic acid（PG）degraded by sodium alginate have certain antioxidant activity.The carboxyl groups in the molecular structure of PM and PG have the ability to introduce phenolic acid groups with stronger antioxidant activity.Introducing the phenolic acid groupcan can improve the antioxidant activity of PM and PG.Therefore,we use the hydrolyzed oligomers of sodium alginate PM and PG as raw materials.We introduces phenolic acid by a two-step reaction and prepare 16 kinds of sodium alginate-based phenolic acid copolymers with stronger antioxidant activity.We measured the antioxidant activity of the copolymers.We preliminarily discussed the relationship between the structure of the copolymer and the antioxidant activity.The main contents are as follows:Sodium alginate hydrolyzed oligomer PM and PG reacts with ethylene diamine（EDA）respectively.We obtained ethylenediamine-polymannuronic acid（PM-EDA）and ethylenediamine-polyguluronic acid（PG-EDA）.We investigated the influence of reactant ratio,activation time,activator ratio,reaction time and p H of the reaction system on the reaction.The optimal preparation conditions of PG-EDA were as follows:n _PM:n _EDAwas 1:1.5,and the molar ratio of PM to the two activators carbodiimide（EDC）and N-hydroxysuccinimide（NHS）was 1:2:1,and the activation time was 0 h,and the reaction time was 24 h,and the p H of the reaction system is 8.0,and the highest degree of substitution of PM-EDA is 17.27%.FT-IR,XRD,¹H NMR test results confirmed that EDA was successfully introduced into PM and PG molecules.PM-EDA and PG-EDA were grafted and copolymerized with 8 different phenolic acids（gallic acid,pyrocatechin,protocatechuic acid,gentisic acid,syringic acid,vanillic acid,isovanillic acid,salicylic acid）respectively.We prepared sodium alginate-based phenolic acid copolymer.We determined the phenolic acid grafting rate of the copolymer by the Folin-Ciocalteau method.The grafting rate of 16 kinds of copolymers was between 3.026±0.11～10.015±0.42 mg GAE/g.UV-vis,FT-IR,XRD,1H NMR test results confirmed that phenolic acid was successfully introduced into PM-EDA and PG-EDA molecules.We determined the scavenging rate of the sodium alginate-based phenolic acid copolymer phenolic acid-PM/PG-EDA to DPPH,hydroxyl radicals,superoxide anions and the reducing power to iron.Analyze the relationship between copolymer molecular structure and antioxidant activity through Genetic Function Approximation mathematical statistics model.We analyzed the relationship between copolymer molecular structure and antioxidant activity through Genetic Function Approximation mathematical statistics model.The experimental results show that the number of phenolic hydroxyl groups is positively correlated with the antioxidant activity in the phenolic acid in the copolymer of phenolic acid-PM/PG-EDA in the four antioxidant models.The anti-oxidant activity of copolymers with para-phenolic hydroxyl groups is stronger than that with ortho-phenolic hydroxyl groups.The anti-oxidant activity of copolymers with para-phenolic hydroxyl groups is stronger than the ortho-phenolic hydroxyl groups.The antioxidant activity of copolymers with 5’phenolic hydroxyl groups is stronger than the copolymers with 3’phenolic hydroxyls.The antioxidant activity of the methoxy copolymer will be reduced.The antioxidant activity is inversely proportional to the number of methoxy groups.