Preparation,Properties And Application Of Functional Products Based On Sodium Alginate

Sodium alginate?SA?is a kind of natural polysaccharide,which has good film-forming,biocompatibility,biodegradability and other advantages.It is widely used in medicine,food and other fields,especially in the field of food active packaging.However,there are some defects in SA,such as weak oxidation resistance,poor mechanical properties of pure SA film,which limit its application scope in food active packaging.In this paper,functional products based on SA with improved properties were prepared by chemical and physical blending modification.Sodium alginate-gallic acid derivative?GA-SA?was prepared by chemical modification.The changes of its structure and oxidation resistance were investigated,and it was applied preliminarily.Gelatin?GE?,graphene oxide?GO?and SA were blended to prepare the composite films with improved mechanical properties by physical blending modification,and then surfactant and rosemary extract?RE?were further mixed to prepare the composite films with antioxidant function.The effects of the proportion or content of some components on the mechanical properties,barrier properties,structural properties,release properties and the antioxidant activity of the composite films were investigated and they were applied to soybean oil packaging preliminarily.The main conclusions are as follows:?1?GA-SA was synthesized by hydrogen peroxide-ascorbic acid?H2O2-AA?radical grafting,and the effect of initiator addition on GA-SA properties was investigated.The results showed that the characteristic peaks of ester groups appeared in the infrared spectrum and Raman spectrum of GA-SA,indicating that gallic acid?GA?and SA were grafted by esterification.Differential scanning calorimetry and scanning electron microscopy?SEM?analysis indicated that the thermal stability of GA-SA was enhanced after grafting,and its molecular structure was changed.The grafting degree of GA-SA was increased first and then decreased with the increase of the total amount of H₂O₂ and AA.When the total amount of initiator was 5.54 mmol,the grafting degree4.260 mg/g was the best.When GA-SA concentration was 4 mg/mL,its DPPH radical clearance rate reached 92.0%,and its antioxidant activity significantly increased?P<0.05?.Application experiment showed that the cherries coated by GA-SA had lower weight loss rate and corruption rate in storage,which indicated that GA-SA coating treatment could effectively delay the fruit decay and water loss.?2?The sodium alginate-gelatin-graphene oxide?SA-GE-GO?composite film was prepared by physical blending.The effects of SA/GE mass ratio and GO content on the properties of the composite film were investigated.The results showed that with the increase of the GE proportion in SA/GE,the tensile strength?TS?of the film increased first and then decreased,and the elongation at break?EAB?gradually increased.When SA:GE=9:1 or 7:3?mass ratio?,the TS of the film significantly increased?P<0.05?.Adding GE could significantly improve the water vapor barrier property and hydrophobicity of the composite film?P<0.05?.With the increase of GO content,both TS and EAB of the composite film increased first and then decreased.When GO content was 0.5%,the mechanical properties of the film were the best?TS=48.01 MPa,EAB=25.75%?.The higher the GO content,the stronger the light barrier property of the film.The infrared spectra showed that SA interacted with GE and GO,and hydrogen bonds were formed in the film.According to the scanning electron microscopy?SEM?and TGA diagram,the proper addition of GE and GO can make the dense and uniform lamellar structure inside the composite film and improve its thermal stability.It was found that the composite film had the best properties when SA:GE=7:3 and GO content was 0.5%.?3?On the basis of SA-GE-GO composite film,RE was added,and the surfactant sodium lauryl sulfate?SDS?and polyvinylpyrrolidone?PVP?were added respectively,to investigate the influence of SDS or PVP content and RE content on the properties of the composite film.The results showed that:with the SDS or PVP content increased,the TS of the film increased first and then decreased.When the content of SDS or PVP was0.1%,the TS of the film increased significantly?P<0.05?,and the water vapor barrier property of the film was enhanced.The infrared spectra showed that the number of hydrogen bonds in the film increased,and SEM observed that the structure of the film was uniform and dense,which may be related to the fact that SDS or PVP can promote the uniform dispersion of GO to promote the interaction between the substances in the film.With the increase of RE content,the TS of the film decreased significantly?P<0.05?.When the content of RE was more than 0.5%,and water vapor barrier and hydrophobicity of the film reduced significantly?P<0.05?.It was found many gaps in the SEM images of the film,indicating that RE may destroy the interaction between substances in the film.However,the higher the RE content,the stronger the light barrier property and thermal stability of the film.?4?The release and antioxidant activity of active substances in the composite film containing RE based on SA were measured,and soybean oil was encapsulated by the film to explore its effect on the oxidation stability of soybean oil in storage.The results showed that in different food simulation systems?distilled water,50%and 95%ethanol solution?,the higher the polarity of the solution,the higher the release rate of the active substances.The higher the RE content,the higher the initial release rate.The higher the RE content,the stronger the antioxidation of the film.The POV and TBA value of soybean oil were measured and analyzed.Compared with the control group,the POV and TBA value of soybean oil encapsulated with composite films containing RE were relatively low,and the higher the RE content,the lower the POV and TBA value,indicating that the composite film containing RE based on SA could effectively inhibit the oxidation of soybean oil.