Nonlinear Rheological Properties Of Wheat Starch Gel

The processing and sensory properties of wheat starch gel foods are closely related to their rheological properties.However,the actual processing and consumption scenarios of starch gel foods involve large deformation processes such as stirring and shearing,which belong to the category of nonlinear rheology.Linear rheological properties cannot accurately reflect the rheological properties of starch gels in real application scenarios.Therefore,the study of nonlinear rheological properties of wheat starch gels can better reflect the changes in the properties of gel foods under real processing conditions,which is important for the development,processing,and quality improvement of starch gel foods.1.The study compared the differences in the rheological properties of wheat starch（WSS）gels and cold skin（Liangpi,LPS）gels at different concentrations and explored the effect of non-starch fractions in the cool skin system on the rheological properties of wheat starch gels.At lower concentrations（20%）,the pasting behaviors of LPS and WSS were similar,but at higher concentrations（25%,30%）,the peak pasting viscosity of LPS was significantly higher than that of WSS,which was related to the non-starch fraction in LPS.The results of rheological tests showed that the elastic modulus（G’）and viscous modulus（G’’）of LPS gels at different concentrations were higher than those of WSS gels.In addition,the non-starch components induced more complex rheological behavior of the starch gels in large deformation,which showed that the elastic Lissajous curve evolved into a bowtie shape and the viscous Lissajous curve evolved into a self-intersecting ring structure,and was accompanied by higher strain hardening coefficients and shear thinning characteristics as well as higher harmonic ratios than those of the WSS gels.2.The effect of pentosan on the gel properties of wheat starch was investigated at different system concentrations（5%to 30%,w/w）.It was found that at low concentrations（5%and 10%）,pentosan decreased the peak starch pasting viscosity as well as the gel G’;at high concentrations（20%and 30%）,pentosan instead increased the peak starch pasting viscosity and the gel G’and G’’and caused the gel to develop a nonlinear rheological behavior similar to that of LPS gels（bowtie like elastic Lissajous curve with self-intersecting loop-like viscous Lissajous curves and elevated higher harmonic ratios）.NMR relaxation tests,on the other hand,showed that pentosan shifted the T₂ distribution peak to the left at all system concentrations,enhancing the binding of the gel network to water.3.The effects of lipid addition and cooling rate on the properties of starch gels and starch-pentosan gels were investigated,respectively.The results showed that the lipid addition significantly decreased the G’and G’’of the gels.The starch-lipid complex index（CI）was highest（56.3%）at a cooling rate of 30^oC/min,and the addition of pentosan reduced the CI of starch-lipid composite gels（53.3%）.Both gels reached the maximum long and short-range order at this cooling rates.The linear rheological properties of the gels were less affected by the cooling rate,but their nonlinear rheological properties showed different viscoelastic stress evolution patterns at different cooling rates.4.The changes in the rheological properties of starch gels of different composite systems during storage were investigated.The results showed that retrogradation led to viscous and elastic energy dissipation of the gels at smaller strains.In short-term aging（0 d～3 d）,the nonlinear parameters of the gels varied depending on the gel system;in long-term aging（7 d～14d）,the nonlinear behavior of strain hardening and shear thinning of the gels was enhanced and the higher harmonic ratios increased,and these changes were related to the aging crystallization of branched chain starch.