Steady Shear Flow Behavior and Thixotropy of Wheat Starch Gel: Impact of Chemical Modification, Concentration and Saliva Addition

Abstract The rheological properties of native wheat starch ( NWS ), cross‐linked wheat starch ( CLWS ) and hydroxypropylated wheat starch ( HPWS ) gels at two concentrations (8 and 12%) and in the presence and absence of saliva at 37C were investigated. More decrease in viscosity was observed for the HPWS (83.33%) gel samples at simulated mouth conditions ( SMC s) compared to the NWS (32.05%) and CLWS (23.88%) gel samples. In the absence of saliva, the Herschel–Bulkley and Sisko models were the best ones to describe viscous flow behavior of all starch gels. The highest thixotropy extent was obtained for the HPWS (1.98–9.26) while no statistically significant difference was observed for that between the NWS and CLWS gel samples ( P > 0.05). The first‐order stress decay model predicted the closest data in the SMC . The results suggested that chemical modification such as hydroxypropylation and cross‐linking can be used to manipulate or modify the rheological behavior of starch in the mouth conditions. Practical Applications Because of many nutritional, technological and textural advantages of starch in food and pharmaceutical systems, it is receiving much more attention. Investigation of the changes in such bioactive carbohydrates in gastrointestinal tract has recently been considered. Study of the rheological parameters is one of the ways to find the influence of each digestion process on the structural properties of starch samples. In this work, steady shear flow behavior and thixotropy of wheat starch gel affected by the type of wheat starch (native, cross‐linked and hydroxypropylated), concentration and saliva addition (SMCs) were studied. Investigation of rheological properties in a SMC allows a better understanding of food structure in the mastication condition, which can be used to develop a food product with special mouthfeel or for special consumers like people with dysphagia.