Effects of Milling Ratio on Properties of Endosperm Starches and Rice Flours from Milled Japanese Rice Grains

Abstract

Flour and endosperm starch prepared from rice grains of three Japanese rice cultivars milled from 90 to 30% of their original weight were subjected to physicochemical/structural analysis in order to examine the relationship between milling ratio and physicochemical/starch structural properties. The peak viscosity of the rice flours was found to increase with decreasing milling ratio, while that of the purified starches did not change significantly. The gelatinization peak temperature of the rice flours was found to decrease while enthalpy changes increased with decreasing milling ratio. The gelatinization peak temperature of the purified starches was not found to change significantly with different milling ratios. Differences in structural properties of purified starches were examined by gel-filtration chromatography of isoamylase debranched starch. The FI (percentage of amylose) and FIIb/FIIa (ratio of short-to-long chain amylopectin) were found to be constant for all three cultivars for milling ratios ranging from brown rice to 30%. 精米歩合と物理化学的およびデンプン構造特性との関連性を調べるために，清酒醸造に使用される日本の3品種の米を，玄米から精米歩合90-30%に搗精し，米粉と精製デンプンを調製した．ラピッド・ビスコ・アナライザーで測定した粘度特性においては，米粉で精米歩合が低くなるに伴い，最高粘度が増加したが，精製デンプンでは顕著な変化はみられなかった．示差走査熱量計による糊化特性の解析では，精米歩合が低くなるに伴い，米粉では糊化ピーク温度が低下し吸熱エンタルピー変化量は増加したが，精製デンプンではこれらのパラメータの変化は小さかった．イソアミラーゼで枝切りしたデンプンのゲルろ過HPLCを行い，デンプンの組成・構造を解析した．FI(アミロースの割合)，FIIb/FIIa(アミロペクチンの短鎖/長鎖比)は，品種間に差異がみられたものの，同一品種では精米歩合90-30%で差異はみられなかった．