Résumé :
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Effects of cooking temperature (70, 75, 80, 85, 90, 95 °C) and stirring speed (60, 160, 260 rpm) on the gel/paste properties of cornstarch and oat flour were investigated. Pasting properties during cooking were evaluated using an Rapid Visco-Analyser-4 (RVA). Rheological properties and microstructure of cooled gels/pastes were evaluated using dynamic mechanical analysis (DMA) and stress relaxation and scanning electron microscopy (SEM). For both cornstarch and oat flour, the storage modulus (G') of gels measured at 25 °C increased with cooking temperature up to about 85 °C at 160 rpm and 260 rpm and up to about 90 °C at 60 rpm and decreased dramatically thereafter for all stirring speeds. G' values for oat flour gels were lower than those for cornstarch gels at all temperatures, but particularly at 85 °C and 90 °C. Higher G' values of the cornstarch gels at these temperatures were associated with a composite gel structure containing collapsed starch granules. This phenomenon was not as apparent for the oat flour gels. The scanning electron micrographs of cornstarch and oat flour gels prepared at the different cook temperatures highlighted the importance of changes in the starch granules on both the pasting curves and rheological properties of the corresponding gels.
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