The Application And Mechanism Of Cross-linked Acetylated Starch In The Set Yoghurt System

This topic researches the application and mechanism of the modified starch in theset yoghurt system. The first, cross-linked acetylated starch was prepared byacetylating and cross-linking from tapioca starch. The cross-linked acetylated starchwas determined the physical and chemical properties. Then, the cross-linked acetylatedstarch was added to the set yoghurt system, which was the stabilizer agent. The effectof the addition of cross-linked acetylated starch on the flow, the viscoelasticity, theZeta potential, the conductivity and the microscopic observation of set yoghurt systemwas studied. This study could provide a structure and stability for casein micelles of setyoghurt system with addition of cross-linked acetylated starch. In the present work, wehave used dynamic rheometer, particle-size analysis and microscopy (SEM) to explorethe effect of different concentrations of cross-linked acetylated starch (0,0.5,1,1.5,2and2.5wt%) on its structure and stability. All samples, which used in this study,exhibited shear-thinning behavior. The evident properties of the set yoghurt systemswere time dependent flow behavior. In the range of experimental (the0.1-100Pa ofshear stress), the addition of cross-linked acetylated starch of the set yoghurt systemshowed pseudoplastic fluid to exhibiting yield stress. At room temperature (25℃),withthe increasing of the cross-linked acetylated starch concentrations, the elastic modulus(G’) and viscous modulus (G") of set yoghurt system increased. All samples of the setyoghurt systems showed pseudoplastic behavior under experiment environment, whichwere consistent with power law fluid. When the shear rate increased greater than80r/min, set yoghurt system was fall short of the law of rheology, which indicated thatin this state of shear, the natural structure of set yoghurt had been destroyedpermanently and could not the creep recovery. In the set yoghurt systems, with theaddition of cross-linked acetylated starches, the measureresults of conductivity andparticle size became larger. Microstructures of set yoghurt were found to be composedof network of casein. The samples of the set yoghurt systems showed that the networkwas stronger by adding cross-linked acetylated starch. The granules of the set yoghurtsystem were accrescent. We considered the cross-linked acetylated starch preventedflocculation of casein particles by electrostatic adhesion, steric stabilization and osmotic ef fect, forming a thick adsorption layer to the surface of the particles.