Effects of Time and Temperature of Annealing on Rheological and Thermal Properties of Rice Starch Suspensions during Gelatinization.

Abstract

Effects of annealing time, t a , and annealing temperature on the rheological and thermal properties of rice starch suspensions during the gelatinization were studied by dynamic viscoelasticity, steady shear viscosity, η, and differential scanning calorimetry measurements. When t a increased, for the sample which was annealed at almost the same temperature as the gelatinization temperature (= T gel ; 62C), 58 or 62C, the onset temperatures at which the storage and loss moduli, G' and G″, started to increase shifted to higher temperatures, and G' and G″ decreased in the temperature range from 65 to about 75C. Further, G' and G″ of the sample annealed at higher T than T gel , 65C, increased in the temperature range from 50 to 75C. The amorphous and thermally unstable portion in the starch decreased with increasing t a . Effects of annealing on the temperature dependence of η were found to be almost the same as those of G' and G″. The annealing tended to prevent starch sample from shear thinning. PRACTICAL APPLICATIONS: This article shows the effects of annealing time, t a , and annealing temperature on the rheological and thermal properties of rice starch suspensions. When t a increased, the storage and loss moduli, G' and G″, of rice starch decreased in the temperature range from 65 to about 75C and the gelatinization temperature increased due to the increase of the amount of leached-out amylose. For the sample annealed at 62C for 15 min, it was observed that the annealing tended to prevent starch sample from shear thinning. These findings are helpful to control rheological and thermal properties during cooking of starch-based foods.