Effect of the degree of milling on the physicochemical properties, pasting properties and in vitro digestibility of Simiao rice

Simiao rice is a variety of long-grain Indica rice popular in South China. However, researches on the milling technology of Simiao rice are limited. The effect of different degrees of milling (DOMs) of Simiao rice (0–12%) were evaluated in terms of the physicochemical properties and in vitro starch digestibility of the rice. The results showed that, as the DOM increased from 0 to 12%, the head rice yield (HRY) and the content of protein, lipid, dietary fiber, vitamin B₁, vitamin E and niacin nonlinearly decreased, while the content of total starch and amylose and paste viscosity parameters nonlinearly increased. The differences in chemical constituents between the brown and milled Simiao rice with different DOMs lead to the variation in their pasting properties and in vitro digestibility. Because of lower content of slowly digestible starch (SDS) and resistant starch (RS), milled Simiao rice exhibited greater digestibility and a higher estimated glycaemic index (EGI). The EGI of Simiao rice ranged from 77.98 to 85.55, and remained almost constant (approximately 84) when the DOM was above 4%. Correlation analysis indicated that the EGI had strong negative correlations with lipid, protein, dietary fiber and RS, but a positive correlation with amylose. These results provide theoretical guidance for the production of Simiao rice with desired physicochemical properties and digestibility by adjusting the DOM.