Effect of amylose content and rice type on dynamic viscoelasticity of a composite rice starch gel

Amylose content is an important indicator to determine the utility of raw milled rice. Indica type rice with high amylose content is usually used for manufacturing rice noodles, while Japonica rice may be mixed partially to adjust the noodle texture. The effect of amylose and rice type on dynamic viscoelasticity of rice starch gel was investigated using a model starch composite in this study. The information will be helpful to control and obtain the required noodle texture by combination of different rice types. The results show that nonwaxy Indica and waxy Japonica rice starches in a composite mixture were incompatible and demonstrated their individual gelatinization behavior during heating. High amylose starch showed higher moduli and lower loss tangent values, as well as higher retrogradation rate. The starch gel made from Japonica rice starch showed a slow retrogradation rate even containing a similar amount of amylose to Indica starch. The storage modulus of the gel made from higher amylose rice was shown to be more independent of frequency. Not only amylose content but also chain length distribution in amylopectin affected the dynamic viscoelasticity of rice gel. Japonica rice starch, with fewer super-long chains in amylopectin, retrograded slower after gelatinization than Indica rice, thus the paste is too sticky for production of rice noodles.