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Impact of Rice Flour Cold-Water-Soluble Fraction Removal on Gelatinization and Pasting Properties

¹China National Center for Rice Improvement/State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, Zhejiang 310006, China. ²Corresponding authors. Phone/Fax (Hu): +86 571 63370221. E-mail: hupeisong@caas.cn. Phone/Fax (Tang): +86 571 63370381. E-mail: sqtang@126.com

The influence of the cold-water-soluble fraction on gelatinization and pasting properties of rice flour was investigated. The cold-water-soluble fraction was removed by water extraction under room temperature. The gelatinization properties of untreated and treated flour were analyzed with a differential scanning calorimeter, and pasting profiles were measured with a rapid viscosity analyzer. The removal of the cold-water-soluble fraction resulted in the formation of a loosened starch granule structure, a morphological alteration of protein bodies, a markedly lower gelatinization temperature, and a significantly higher pasting enthalpy. The impact on paste viscosity followed different trends. In some cultivars that had lower endogenous amylase activity, the paste viscosity was greatly reduced by the removal of the cold-water-soluble fraction. In others, the higher level of endogenous amylase activity led to more soluble saccharides being released through starch hydrolysis. Removing the soluble fraction caused a remarkable increase in peak viscosity. The overall effect on paste viscosity of removing the cold-water-soluble fraction was attributed to multiple factors, involving loosening of the starch granule structure, alteration of morphology of protein bodies, and the release of saccharides by endogenous amylase activity.