Rice Starch Isolation from Newly Developed Rice Cultivars by the Improved Alkali Method

Abstract

A rapid and efficient rice starch isolation method was tested on two varieties of newly developed rice, Hoshinishiki (Kanto181) and Saikaimochi227 (a high-amylose and a high-yield waxy rice), and a reference rice variety, Nipponbare. Rice flour was stirred in 0.05 or 0.075 M aqueous sodium hydroxide for 3 h once or three times, neutralized with 1 M hydrochloric acid and washed with water. Isolated rice starch was compared with the starch isolated by the conventional method in terms of chemical and physical properties. The improved method reduced processing time to two days, while the conventional method required one to three weeks. The improved method lowered damaged starch and protein contents, but slightly lowered starch recovery. Non-waxy rice starches isolated by the two methods differed in physical properties upon testing by photopastegraphy and Rapid Visco Analyser (RVA), whereas no difference was observed in waxy rice. The phosphorus content in Nipponbare starch decreased during the isolation process due to degradation of the lysophospholipid, and the phosphorus content was the lowest in the starch isolated by the conventional method. Sodium content was high in the starch isolated by the improved method, although the influence of residual sodium on the viscosity of the paste was small. To reduce residual sodium in the starch isolated by the improved method, washing with water eight times after neutralization was needed. Thus, we propose the improved procedure for rice starch preparation. Rice flour is washed with 0.05 M aqueous sodium hydroxide three times, neutralized and then washed eight times with water. In the case of high-amylose or waxy rice flours, alkali washing can be reduced to once.