EFFECTS OF ORGANIC ACIDS ON THE PASTING PROPERTIES OF RICE FLOUR FROM WAXY AND NONWAXY VARIETIES

The objective of this study was to investigate the effects of organic acids on the pasting and textural properties of rice flour. Nonwaxy (Taisen 2 rice, TS2) and waxy (Taisen Waxy 2, TSW2) were selected as rice materials. Organic acids (including acetic acid, lactic acid, malic acid, succinic acid and citric acid) of 0.1 mM, 1 mM and 10 mM were added to the rice flour (v/w, on dry basis) at 0.5% and 2.0% levels and cooked in Rapid Visco Analyser (RVA; RVA-4, Newport Scientific, Pty Ltd, Narrabeen, Australia) at 95C for 12.5 min. Results showed that addition of 0.1 mM of organic acids significantly (P < 0.05) decreased peak viscosity, trough viscosity, final viscosity and setback of TS2 rice flour. The hardness of TS2 rice flour gel was significantly (P < 0.05) decreased by the addition of 1 mM and 10 mM of these organic acids compared with the control. Reduced final viscosity showed that the addition of organic acids were able to retard the tendency of rice flour gel to retrograde. For waxy rice TSW2, addition of these organic acids had not the same tendency on pasting and textural properties, possibly because of the 22% amylose content in nonwaxy rice and 0% amylose in waxy rice. PRACTICAL APPLICATIONS Since rice flour is widely used in the rice food industry, while organic acids are effective for improving flavor and texture of food products, the effects of organic acids on the pasting behaviors and textural properties of rice flour need to be examined. This study is of interest because rice flour is usually used along with other ingredients such as salts, sugar, lipids, emulsifiers and organic acids, etc. The presence of organic acids may influence the rice flour pasting properties differently with waxy and nonwaxy rice. Such investigations are of importance to rice food industries and especially to the rice-consuming peoples.