THE EFFECT OF ANNEALING ON THE PHYSICOCHEMICAL PROPERTIES OF WHEAT, OAT, POTATO AND LENTIL STARCHES

Abstract

Native wheat, oat, potato and lentil starches were annealed at various starch/water ratios at 50C for time intervals ranging from 0.5 to 72 h. Annealing did not change granule size and shape. Oat starch granules were less compactly packed after annealing. X-ray diffraction patterns remained unchanged and X-ray intensities changed only marginally in all starches. The swelling factor (SF), amylose leaching (AML) and the gelatinization temperature range (GTR) decreased on annealing. The extent of decrease in SF and AML followed the order: lentil > wheat > potato > oat, while the corresponding order for GTR was: wheat > lentil > oat > potato. The gelatinization transition temperatures (GTT) and enthalpy (ΔH) increased on annealing. However, the increases in GTT and ΔH did not begin concurrently during the time course of annealing. Increases in ΔH were slower and were evident only after 1, 2, 6 and 48 h, respectively, in lentil, potato, oat and wheat starches. The extent and rate of increase in GTT and ΔH followed the order: potato > lentil > wheat > oat. The magnitude of changes in GTT and ΔH increased with increase in annealing moisture content. The susceptibility of oat starch to enzyme and acid hydrolysis increased on annealing. However, decreases occurred in the other starches (lentil > wheat > potato). Thermal and shear stability of starch granules increased on annealing (potato > lentil > wheat > oat). The results showed that the above changes in physicochemical properties were due to increased interaction between starch components during annealing.