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Refrigeration reduces the glycemic index of cooked rice

Several studies highlight the benefits of refrigeration on the glycaemic index of rice, which is important in the control of chronic diseases such as diabetes.

Rice (Oryza sativa L.) is a major staple food for nearly half the world's population in Asia, Latin America and the Caribbean, and increasingly in Africa. According to the OECD-FAO Agricultural Outlook report, world rice consumption for food is expected to increase from about 420 million tonnes in 2019 to over 470 million tonnes by 2030, due to population growth.[1]

 

Rice contains about 80% starch and is generally considered a high glycaemic index (GI) food. [2, 3] GI is a measure of glucose uptake upon digestion (or postprandial glucose), resulting in a sudden spike in blood glucose content.[3] Numerous studies have demonstrated that white/milled rice after cooking induces a high postprandial glucose level, as it is digested rapidly. Studies indicate that rice consumption may increase the risk of hyperglycaemia and diabetes over time.[4] Therefore, it is important to investigate ways to slow down the rate of starch digestion in cooked rice.

 

In a recent study published in Foods, the estimated baseline GI of freshly cooked rice was 91.08. After chilling at 4°C or frozen storage at −20°C, −40°C, and −80°C, the estimated GI values were above 84 for all storage times and temperatures. Their results indicated that after storage, the digestibility of the cooked rice declined, namely, the rapidly digestible starch content and estimated glycaemic index (GI) decreased, whereas the slowly digestible starch and resistant starch content increased.[4] Other studies have shown that chilling cooked rice at 4°C for 24 hours resulted in a reduction in digestibility and estimated GI for both brown and milled rice.[2] In a study on instant rice, the rice was first cooked, then either frozen at −20°C or cooled to 4°C for 24 hours, and finally dried to prepare instant rice. The GI of the rice that was frozen before being dried was found to be lower. The authors suggest that freezing rice may be a beneficial pretreatment in the production of instant rice.[5]

 

According to a review article by Sivakamasundari et al., during the cooling of cooked rice, the amorphous structure of the starch takes on a crystalline form that can resist enzymatic digestion in the small intestine for up to three hours.[5] Overall, cooling appears to be a simple and effective intervention to reduce the GI of rice.[2] Furthermore, Sivakamasundari et al. recommended that cooked rice be stored at low temperatures overnight for diabetic patients.[5]

 

 

Sources

[1] OECD/FAO (2022), OECD-FAO Agricultural Outlook 2022-2031, OECD Publishing, Paris, https://doi.org/10.1787/f1b0b29c-en

[2] Kaur, B., Ranawana, V., & Henry, J. (2016). The glycemic index of rice and rice products: a review, and table of GI values. Critical reviews in food science and nutrition, 56(2), 215-236. https://doi.org/10.1080/10408398.2020.1865259

[3] Jukanti, A. K., Pautong, P. A., Liu, Q., & Sreenivasulu, N. (2020). Low glycemic index rice—a desired trait in starchy staples. Trends in Food Science & Technology, 106, 132-149. https://doi.org/10.1016/j.tifs.2020.10.006

[4] Li H, Liu B, Bess K, Wang Z, Liang M, Zhang Y, Wu Q, Yang L. Impact of Low-Temperature Storage on the Microstructure, Digestibility, and Absorption Capacity of Cooked Rice. Foods. 2022; 11(11):1642. Article available in FRIDOC thanks to an agreement with MDPI

[5] Sivakamasundari, S. K., Priyanga, S., Moses, J. A., & Anandharamakrishnan, C. (2022). Impact of processing techniques on the glycemic index of rice. Critical Reviews in Food Science and Nutrition, 62(12), 3323-3344. https://doi.org/10.1080/10408398.2020.1865259