Characterization of Pregelatinized and Heat Moisture Treated Rice Flours

Abstract

Three rice varieties; Chai Nat 1, Khao Dawk Mali 105 and RD 6 (28.72, 16.46 and 5.54% amylose content, respectively) were modified by pregelatinization (pregel) and heat moisture treatment (HMT) method. Pregelatinized flour was prepared by passing 40% rice flour solution through drum dryer, which conditions were set at 20 lb/inch² of steam pressure, 0.25 rpm of drum dryer speed and 0.01 inches of drum dryer gap. The modification of rice flour by HMT method was prepared by adjusting rice flour initial moisture to 30% and then incubating at 100^oC for 16 hr. When compared the pasting properties between native and pregel flours, the results were significantly different (p ≤ 0.05). For all three pregel rice flours, they show that the pasting temperature (49.90-51.47 ^oC), peak viscosity (198.41-281.42 RVU), breakdown (48.20-175.67 RVU) and final viscosity (156.75-306.83 RVU) decreased significantly. In addition, the degrees of syneresis or freeze thaw stability of three pregel flours (1.06-47.65 %) increased (p≤0.05) as compared with the native flours (0.12-39.93 %). The pasting properties of native and three HMT rice flours were observed and the results were significantly different (p≤0.05). For all three HMT rice flours, they show that the pasting temperature (80.18-88.64 ^oC) increased significantly; while peak viscosity (95.59-167.17 RVU), breakdown (12.50-22 RVU) and final viscosity (101.82-259.17 RVU) decreased siginificantly (p≤0.05). In addition, swelling power and solubility of HMT flours decreased (p≤0.05); whereas the freeze-thaw stability (1.06-37.36 %) increased (p≤0.05).