The Properties of Extruded Pregelatinized Starch and the Effect of Its Addition on the Quality of Steamed Brown Rice Cakes

Pregelatinized rice starch was prepared by extruding rice starch with different moisture content (45%, 25% and 18%), and its molecular weight, crystallinity, gelatinization degree, water absorption index, water solubility index and cold paste viscosity were determined. Meanwhile, the effects of pregelatinized starch addition on the pasting characteristics of brown rice flour and the quality of steamed brown rice cakes were investigated. The results showed that compared with the native rice starch, pregelatinized rice starch prepared by extrusion of 45%, 25% and 18% moisture content decreased in crystallinity by 51.93%, 58.93% and 59.04%, the water absorption index increased by 1.56, 4.69 and 6.11 times, the water solubility index improved by 7.21, 16.64 and 28.21 times, the cold paste viscosity increased by 2.00, 21.44 and 14.67 times, respectively. Extrusion also degraded rice starch molecules, producing more small chain molecules. The changes in the properties of pregelatinized rice starch were related to the moisture content of the starch during the extrusion process. The quality of steamed brown rice cake was significantly improved with the addition of pregelatinized rice starch. The high cold paste viscosity and low molecular weight (18% moisture extrusion) were more conducive to the preparation of steamed brown rice cakes with large specific volume (1.64 cm³/g), fine and uniform pores, low hardness (338.59 g) and elasticity.