Effects of Cooking Methods and Starch Structures on Starch Hydrolysis Rates of Rice

Abstract

This study aimed to understand effects of different cooking methods, including steamed, pilaf, and traditional stir-fried, on starch hydrolysis rates of rice. Rice grains of 3 varieties, japonica, indica, and waxy, were used for the study. Rice starch was isolated from the grain and characterized. Amylose contents of starches from japonica, indica, and waxy rice were 13.5%, 18.0%, and 0.9%, respectively. The onset gelatinization temperature of indica starch (71.6 °C) was higher than that of the japonica and waxy starch (56.0 and 56.8 °C, respectively). The difference was attributed to longer amylopectin branch chains of the indica starch. Starch hydrolysis rates and resistant starch (RS) contents of the rice varieties differed after they were cooked using different methods. Stir-fried rice displayed the least starch hydrolysis rate followed by pilaf rice and steamed rice for each rice variety. RS contents of freshly steamed japonica, indica, and waxy rice were 0.7%, 6.6%, and 1.3%, respectively; those of rice pilaf were 12.1%, 13.2%, and 3.4%, respectively; and the stir-fried rice displayed the largest RS contents of 15.8%, 16.6%, and 12.1%, respectively. Mechanisms of the large RS contents of the stir-fried rice were studied. With the least starch hydrolysis rate and the largest RS content, stir-fried rice would be a desirable way of preparing rice for food to reduce postprandial blood glucose and insulin responses and to improve colon health of humans.

The Glycemic Potential of White and Red Rice Affected by Oil Type and Time of Addition

“…The amount of starch left undigested for white rice was highest for the “before” addition time and lowest for the “after” addition (Figure ). This was a similar finding in another study where a larger resistant starch content was reported in pilaf white rice (addition time “before”) compared with steamed white rice suggesting the presence of amylose–lipid complex formation during cooking ( Reed and others ). Oil type had no effect on the IDS content of white rice when compared with the control ( P = 0.603).…”

“…The addition time “after” was significantly different to "during" ( P = 0.0004) and "before" for SDS content of red rice ( P = 0.002). A study by Reed and others () showed no significant impact of stir‐frying with corn oil on SDS content of cooked white rice. Our study showed that the addition time of oil “after” that is stir‐frying, to white rice or red rice has the potential of increasing SDS content, and thus its glycemic impact.…”

Physicochemical, antioxidant properties and in vitro digestibility of wheat–purple rice flour mixtures

“…In addition, it is possible that starch digestibility is related to granule size. Larger granules tend to have a lower digestibility (Reed et al ., ). The correlation between the antioxidant compounds and in vitro starch digestibility is also reported in this study.…”

Addition of defatted green‐lipped mussel powder and mixed spices to wheat–purple rice flour biscuits: Physicochemical, in vitro digestibility and sensory evaluation

“…Total carbohydrate was calculated by difference (AOAC, ) and total dietary fiber (TDF) was measured using a total dietary fiber assay kit (Sigma‐Aldrich, MO, USA). The total starch content was determined using a Megazyme starch assay kit (Megazyme International Ireland Ltd., Wicklow, Ireland), using approved method 76–13 (Reed, Ai, Leutcher, & Jane, ).…”