Preparation And Characterization Of Acetylated Soluble Soybean Polysaccharides

SSPS is a water-soluble anionic polysaccharide extracted from bean dregs,which is widely used because of its good dispersion stabilities,emulsifying and foaming properties.SSPS can stabilize the emulsion and foam system through the steric hindrance of the side chain and the electrostatic force.However,due to its small molecular weight and short chain length,its stabilities need to be improved.In order to solve the above-mentioned problems,SSPS was used as raw material to prepare acetylated soluble soybean polysaccharide by acetic anhydride method,hoping to improve its emulsifying and foaming properties.In this study,a suitable aqueous solution system was selected for acetylated modification of SSPS and the preparation process was optimized.On this basis,the product was separated by ultrafiltration,and the effects of acetylation on the structure and properties of soybean polysaccharides was discussed.The research contents and results were listed as follows:Firstly,the solvent system which was suitable for acetylated modification of SSPS was selected.The conditions of acetylation of SSPS in formamide and aqueous solutions were optimized through single factor and orthogonal experiments by taking the degree of acetyl substitution as an indicator.The best conditions for preparing Ac-SSPS(F)in formamide were:liquid-to-material ratio of 15:1,reaction temperature of 50°C,reaction time of 4 h,and the relative degree of acetyl substitution(RDS)of Ac-SSPS(F)under these conditions was 0.474.While the best conditions for preparing Ac-SSPS(W)in aqueous solutions were:liquid-to-material ratio of 15:1,reaction temperature of 40°C,reaction time of 1.5 h,and the RDS of Ac-SSPS(W)under these conditions was 1.257.And FT-IR showed that both of them were successfully acetylated.In addition,Ac-SSPS(F)was only completely dissolved in a strong alkaline solution with a p H of 12,while Ac-SSPS(W)could be completely dissolved in aqueous solutions in the range of p H 2?12.Ac-SSPS(W)obtained higher RDS and required lower reaction temperature,shorter reaction time.Therefore,the aqueous solution was selected as the required modification system,and Ac-SSPS(W)was used for subsequent experiments,hereinafter referred to as Ac-SSPS.Secondly,the effects of acetylation on the structure of SSPS were studied.The results of molecular weight and z-average radius of gyration(Rz)showed that the molecular weight of SSPS increased after acetylation,the degree of molecular chain stretch was enhanced,and Ac-SSPS could be effectively divided into high molecular weight components and low molecular weight components by ultrafiltration.Ac-SSPS,Ac-SSPS(H)and Ac-SSPS(L)all showed acetyl ester group C=O and C-O stretching vibration peaks at around 1740 cm^-1 and 1245 cm^-1in FT-IR.And the characteristic peaks of acetyl group were also detected at the?1.2?2.2 ppm of ¹H-NMR at the same time.Thirdly,the effects of acetylation on the properties of SSPS were studied.The viscosities,absolute value of Zeta potentials,foaming properties,emulsifying properties showed the following order:Ac-SSPS(H)>Ac-SSPS>Ac-SSPS(L)>SSPS.And the particle size of Ac-SSPS(H)was about 320 nm,while the particle size of Ac-SSPS(L)was about 100 nm after ultrafiltration.It indicated that the degree of molecular chain stretch of SSPS increased after acetylation,entanglement between molecular chains was more likely to occur,and the addition of acetyl group increased its hydrophobicity.Furthermore,Ac-SSPS(H)showed superior foaming and emulsifying properties due to its high molecular weight,more stretched molecular chain,and high degree of acetylation.Finally,the stability of the emulsions stabilized by SSPS,Ac-SSPS,Ac-SSPS(H)and Ac-SSPS(L)were studied.The particle size of the emulsion stabilized by SSPS increased from500 nm to micron level during storage,and there was obvious oil layer floating phenomenon.The particle size of the emulsion stabilized by Ac-SSPS(H)was about 300 nm,and there were no significant changes during the 28-day storage.In addition,the emulsion stabilized by Ac-SSPS(H)was less affected by temperature and p H.In general,the emulsion stabilities of Ac-SSPS(H)were significantly better than the emulsions stabilized by the others.