Thixotropic properties of normal potato starch depending on the degree of the granules pasting

• Rheologically unstable properties of normal potato starch (NPS) pastes were presented.
• In the 2 and 3% samples pasted at 80 °C the swelling of the granules prevailed their destruction.
• In the other cases the inverse phenomenon was observed—the destruction predominated the swelling.
• The samples pasted at 121 °C were the most stable and those pasted at 95 °C—the most unstable.
• Rheologically unstable (thixo- or antithixotropic) behavior took place mainly when the pasting of starch was partial.

The aim of this paper was the study of the rheological instability (thixotropy and/or antithixotropy) of normal potato starch (NPS) pastes depending on their concentration (2–5%) and degree of pasting. Flow curves with hysteresis loops, apparent viscosity at constant shear rate and in-shear structural recovery tests were carried out. Granule size profiles, the pasting characteristic of corresponding starch suspensions and the transmittance of the pastes, the molecular weights and polydispersity of granular starch and its pastes prepared at 80, 95 and 121 °C were also studied.The degree of pasting was dependent on the temperature and the concentration and influenced strongly the rheological behavior of the pastes. All pastes belonged to the non-Newtonian liquids thinned by shear and were rheologically unstable to the various extent. Thixotropic properties were connected to the size and the number of the starch granules in the pastes as well as depended on the measuring method used. In the 2 and 3% samples pasted at 80 °C the swelling of the granules prevailed their destruction (thixotropy was observed). In the other samples the destruction predominated the swelling (antithixotropy observed).