Effect Of Modified Starch On Stability Of Set Yogurt

In this study,hydroxypropyl distarch phosphate（HDP）,acetylated distarch phosphate（ADSP）and acetylated distarch adipate（ADA）,are commonly used to add into yogurt,were selected as stabilizers in set yogurt.The gelatinization,freeze stability,dehydration shrinkage and rheological properties of three modified starches were studied.According to the results,ADSP has the highest pasting viscosity of1414cP.The freezing and thawing stability of modified starch NS>ADA>HDP>ADSP.According to the results of microscope observation,it was found that ADSP starch granules after gelatinization were not easy to be broken.The set yoghurt added with ADSP showed higher storage modulus（G’）and loss modulus（G’’）values.The rheological properties,fractal dimension and microstructure of casein composite gels were measured.The rheological test results showed that the addition of ADSP changed the rheological properties of casein acid gel,and the steady shear test showed that the casein/ADSP gel exhibited shear thinning behavior.Power Law and Burgers’equations were used to fit the data of frequency scanning and creep experiment respectively.The results showed that when the ADSP content was 1.5%,the composite gel had the maximum instantaneous elasticity and stiffness and also showed higher G’and G’’values.When the ADSP content was 2.0%,the gel showed an inhibition effect.The fractal dimension decreased with the increase of ADSP,indicating that ADSP enhanced the consistency of mixed gel network structure and reduced the degree of confusion.Scanning electron microscopy（SEM）showed that when the ADSP increased to 1.5%the pores of casein/ADSP composite gel decreased gradually,showing a relatively compact structure.The interaction between casein and ADSP was analyzed.It was found that casein increased the viscosity and gelatinization temperature of ADSP,that improved the binding capacity of casein acid gel to water,and the decomposition temperature of new complex was significantly lower than that of casein and ADSP.In the analysis of FTIR results,it was found that the peak at 1159cm^-11 had displacement and the peak at1723cm^-1（C=O）had disappeared.There was an obvious interaction between casein and ADSP.According to the results of the macromicrostructure,rheological properties and solution stability of casein/ADSP gel,the macroscopic phase separation occurred in the mixture of casein and ADSP.Stress scanning G’and G’’shown different trends at the top and bottom.The top and bottom of the mixed gel presented loose and dense microstructure respectively,and the instability index decreased with the increase of ADSP concentration.The physical and sensory properties of solidified yoghurt changed with ADSP.It was found that when the ADSP content was more than 1.5%,granular texture appeared and the taste decreased.The results shown that ADSP can improve the hardness and breaking force of set yogurt,and improve the deformation resistance of set yogurt.