Structure And Properties Of Phenolic Acid Soybean Polysaccharide Films

The application range of soybean polysaccharide(SSPS)films has been limited due to the problems of easy moisture,insufficient mechanical properties,and low biological activity.Therefore,current researches are looking for safe and non-toxic active substances that can significantly improve the antioxidant and antibacterial activity of the film,and can effectively improve the mechanical properties of the film and low cost to improve the properties of soybean polysaccharide films.Natural phenolic acid is an active substance from plants.It has broad-spectrum bactericidal effect and strong antioxidant properties.It has been used to improve different types of polysaccharide films.At present,research on phenolic acid-soybean polysaccharide films is relatively rare.Therefore,soybean polysaccharide copolymers of phenolic acids(such as gallic acid,protocatechuic acid,etc.)are prepared by graft copolymerization to improve the functional properties of soybean polysaccharides.Further,a phenolic acid-soybean polysaccharide copolymer film will be prepared to improve the properties of the soybean polysaccharide film,especially the antioxidant activity and antibacterial properties.The effects of graft copolymerization and blending on the properties of soybean polysaccharide films were also investigated.PPA-g-SSPS,PA-g-SSPS,GA-g-SSPS with similar grafting degrees were synthesized by carbodiimide-mediated method,and the grafting degrees of the copolymers were 29.45,31.76 and 30.74 mg/g.The three phenolic acid-soybean polysaccharide copolymers appeared obvious new absorption peaks near 1739 cm-1in the infrared spectra,which were attributed to the ester bond formed between the phenolic acid and SSPS.In the UV spectra,the absorption peaks of the three copolymers at 200-300 nm are caused by the unsaturated groups of the benzene ring.In the NMR spectrum,there are signal peaks between chemical shifts δ6.90 and 8.00 ppm,which can be attributed to the aromatic protons of the three phenolic acids.The DPPH free radical scavenging ability,reducing ability,antibacterial activity and physiological activity of three phenolic acid-soybean polysaccharide copolymers and soybean polysaccharide were evaluated.GA-g-SSPS showed the best DPPH free radical scavenging ability,reducing ability,antibacterial and physiological activities.PPA-g-SSPS,PA-g-SSPS and GA-g-SSPS were prepared into films with glycerol and gelatin,and the phenolic acid-soybean polysaccharide blend films with the same phenolic acid content were prepared.The effect of the combination of phenolic acid and soybean polysaccharide on the film properties was analyzed.The results showed that the effect of the two binding modes of phenolic acid and soybean polysaccharide on the physical properties of the film was not clear.The combination of graft copolymerization will reduce the mechanical properties and water vapor transmission rate of the film,and improve the biological activity of the film.Three protocatechuic soybean polysaccharide graft copolymers(PA-g-SSPS 1,PAg-SSPS 2 and PA-g-SSPS 3)were synthesized by controlling the reaction conditions,and the grafting degrees were 19.56,31.76,48.03 mg/g.The three copolymers showed obvious absorption peaks around 1739 cm-1,which were attributed to the formation of ester bonds between soybean polysaccharide and protocatechuic acid;the three copolymers showed absorption peaks of phenolic acid benzene ring around256 nm.The signal peaks between δ6.90 and 8.00 ppm in the hydrogen spectrum were attributed to aromatic protons on phenolic acids,and the intensity of the signal peaks increased with the increase of grafting degree.The DPPH free radical scavenging ability,reducing ability,antibacterial activity and physiological activity of the three copolymers were investigated.Studies have shown that PA-g-SSPS 3 has the highest DPPH free radical scavenging ability,reducing ability and physiological activity.Three protocatechuic acid soybean polysaccharide graft copolymers were prepared into films(PA-g-SSPS 1,PA-g-SSPS 2 and PA-g-SSPS 3 film),and phenolic acidsoybean polysaccharide blend films(PA-SSPS 1,PA-SSPS 2 and PA-SSPS 3 film)with the same protocatechuic acid content were prepared at the same time.).To explore the effect of the combination of protocatechuic acid and soybean polysaccharide on film properties.The results showed that with the increase of protocatechuic acid content,the mechanical properties,water solubility and water vapor transmission rate showed a decreasing trend,but enhanced the bioactivity of the film,while graft copolymerization decreased the mechanical properties and water vapor transmission rate of the film.Vapor transmission rate,enhance the biological activity of the film.Among them,the antioxidant activity was significantly improved,and the DPPH free radical scavenging rate of PA-g-SSPS 3 film reached 81.47±1.78%.