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 (SMCs) 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.

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