Microwave cooking enhances glycaemic potential of rice: An in vitro study

Introduction: Rice is the principle staple and energy source for nearly half the world’s population and has significant nutrition and health implications. Most rice varieties are considered high glycaemic index (GI) foods. With rice being a major contributor to the glycaemic load in Asian populations, there is increasing concern of its impact on the development of type 2 diabetes. Devising ways to reduce the glycaemic impact of rice is therefore imperative. Rice is cooked in a variety of ways, such as over an open fire, electric cooker or microwave. We evaluated the impact of the electric cooker and microwave cooking methods on starch digestibility in a variety of rice commonly consumed in Asia. Methods: Nine rice varieties of varying GIs were cooked in an electric cooker and microwave oven, and the starch digestibility of cooked rice measured using an in vitro digestion method. Results: High GI white rice (WR) had reduced starch digestibility after microwave cooking compared to electric cooker (p<0.05). There was a significant reduction in incremental area under the curves (iAUC) and rapidly digestible starch of WR cooked using microwave rather than electric cooker (p<0.05). Interestingly, even for low GI rice varieties such as iddly rice and extra long basmati rice, microwaving increased slowly digestible starch. Conclusion: The results provide indicative data that the glycaemic impact of rice can be reduced when cooked using a microwave oven. These observations have nutritional implications that need to be substantiated using in vivo studies. Microwaving may provide a simple method of reducing the postprandial glycaemia of high GI rice.