Changes in gelatinization and rheological characteristics of japonica rice starch induced by pressure/heat combinations

Rice starch suspensions of 10% dry matter (DM) were treated by heat (0.1 MPa at 20-85 degrees C)or pressure/heat combinations (100-600 MPa at 20, 40 and 50 degrees C) for 15 min to investigate their gelatinization and theological characteristics. The maximum swelling index of about 12 g water per gram of DM was obtained by thermal treatment at 85 degrees C, meanwhile, that of 7.0 g was observed by 600-MPa pressurization at 50 degrees C. The higher temperatures or pressures resulted in the higher degrees of gelatinization. Furthermore, treatments of 0.1 MPa at 85 degrees C, 500 MPa at 50 degrees C and 600 MPa at various temperatures caused complete gelatinization of rice starch. The consistency index (K) and storage modulus (G') dramatically increased from 70 degrees C or 400 MPa. The G' values were higher in pressure-treated samples than those in thermal-treated samples. Therefore, an application of pressure/heat combinations as a processing method to improve the quality of rice starch products would be possible. (C) 2008 Elsevier Ltd. AN rights reserved.