Factors Influencing The Stabilization Of Different Milk Proteins By Soluble Soybean Polysaccharides Under Acidic Conditions

Acidified milk drinks are popular among consumers because of their unique taste and nutritional value.However,the problem of milk protein precipitation and whey separation under acidic conditions is always a challenge for the development of new products.In recent years,soluble soybean polysaccharides(SSPS),has attracted much attention due to its good acid and heat resistance as well as its low viscosity,refreshing taste,and excellent protein stabilizing ability under low p H conditions.However,there are few studies on the mechanism and influencing factors of the ability of SSPS to stabilize protein,especially the inconsistent study results of the effects of molecular weight(Mw)and degree of esterification(DE).Moreover,the studies on the effects of fermentation,formulation and sterilization on the stabilizing ability of SSPS on protein is still lacking.All these factors make it difficult to solve the technical difficulties and apply SSPS to the acidified milk drinks.Therefore,in this study,casein,whey protein and skimmed milk protein were studied through the contents of complexes,instability index of LUMi Sizer,particle size,zeta potential and storage stability,to explore the combining and stabilizing ability of SSPS on milk protein under acidic conditions,and the effects of molecular weight(Mw),degree of esterification(DE)and processing methods so as to provide a foundation for elucidating the mechanism and influencing factors of the stabilizing ability of SSPS on milk proteins and improving the application level of SSPS.Firstly,in order to investigate the differences between SSPS and pectin in combining and stability ability on three types of milk proteins under acidic conditions.The results showed that the ability of SSPS to bind milk protein was casein > skim milk protein > whey protein,and the ability to stabilize milk protein was whey protein > casein > skim milk protein.The results above combined with the storage stability indicated that the number of complexes formed by polysaccharides and milk proteins was an important factor to affect the stability of milk proteinsIn order to further investigate the effect of SSPS structure on its ability to stabilize different milk proteins,nine kinds of SSPS with different Mw and DE were extracted.The effects of SSPS structure on its stabilization of different milk proteins under acidic conditions were investigated thoroughly.The results showed that the ability of SSPS to stabilize milk protein was related to the content of SSPS-protein complexes and the stability of the complexes themselves.De-esterification improved the ability of SSPS to from complexes.Compared with casein,lower DE made it better for SSPS to combine skim milk proteins.The SSPS with medium Mw was more likely to combine casein and skim milk protein.The LUMi Sizer results showed that the complexes formed by SSPS with large Mw and milk protein had larger steric hindrance,better stabilization ability.The results of average particle size and zeta potential showed that the complex stabilized milk proteins mainly through steric repulsion,thereby reducing the average particle size.Overall,the results above combined with the storage stability results showed that the SSPS with high Mw and medium or low DE,medium Mw and medium or low DE had better ability to stabilize casein,the SSPS with medium Mw and low DE had better ability to stabilize whey protein,and the SSPS with high Mw and low DE,medium Mw and low DE had better ability to stabilize skim milk protein.Based on the study of Mw and DE,SSPS with medium Mw and low DE was selected due to its excellent stabilizing ability.This part aimed at exploring the effects of different acidification methods,pasteurization temperature and centrifugation rate on the ability of SSPS to stabilize casein,whey protein and skim milk protein,and pectin was used as the contrast.The results of fermentation and artificial acidification showed that the contents of complexes formed by SSPS or pectin and milk protein decreased significantly,and the instability index increased after fermentation.Overall,SSPS and pectin had different mechanisms to stabilize acidified milk drinks under different acidification methods,and the particle size of milk proteins was one of the factors affecting the formation of polysaccharide-protein complexes.The results of different sterilization temperature showed heat treatment promoted the binding between polysaccharide and milk protein,the complex formed by SSPS and whey protein increased,and the instability index of SSPS-stabilized whey protein decreased,but the instability index of casein and skim milk protein did not change significantly.These results indicated that the steric hindrance of SSPS can stabilize the protein well at high temperature.Different from SSPS,the ability of pectin to stabilize the protein was decreased.The results of different centrifugal forces indicated that except for SSPS-casein system,the combination of other polysaccharide with proteins will be destroyed to a certain extent under the centrifugal effect,resulting in the decrease of complex content and the increase of precipitation rate.In summary,the results above also showed that the centrifugal precipitation rate,which was commonly used in industry to predict the ability of hydrophilic colloid to stabilize protein or to long-term stability of acidified milk drinks,should be investigated comprehensively with other factors.