Effect of heat- moisture treatment on starch properties and digestibility of brown red rice

Abstract

Starch extracted from heat-moisture treated brown red rice flour was used to determine physicochemical properties and digestibility. Heat-moisture treatments at different conditions (20, 25, 30% of moisture level at 100oC and at 120oC) contributed significant changes to the results of this study. Heat moisture treatment resulted in increased pasting temperature and decreased breakdown of brown red rice starch. This physical modification also reduced significantly swelling power of isolated starch as compared to the non-treated one. The A-type crystalline structure of starch was determined by X-ray diffraction method remained unchanged after heat-moisture treatment. After heat-moisture treatment, granule morphology of starch remained almost unchanged, nevertheless, a significant difference in the format and degree of agglomeration from 30%-100oC and 30%-120oC starch samples was easily observed. Notably, heat moisture treatment had positive impact on enhancing the resistant starch content of all treated starch samples according to in vitro digestibility examination, thus, reducing both the released glucose concentration and glycemic index after ingestion in mice. Among all treated starch samples, 30%-120oC starch sample obtained the highest amount of resistant starch, which was 49.06%, correspondingly, the released glucose level and glycemic index were also lowest as compared with these of others. Key words: Resistant starch; Glycemic index; Heat moisture treatment; Brown red rice