Aim: Obesity is associated with insulin resistance which results in hyperglycemia when food that is rapidly digested to glucose is consumed. The aim was to measure the effect of rice product, storage and particle size on in vitro glucose release over 180 minutes and the changes in proportions of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS).
Methods: A 5x rice product 2x storage time 2x particle size experimental design investigated glucose release over 180 minutes (dinitrosalicylic colorimetry) and the digestibility of starch (Megazyme™). The five rice products: medium grain white, medium grain brown, basmati, long grain brown, and parboiled, were boiled to gelatinization then either left intact or minced to 2.5mm , and digested at 65°C (T0) or after 24-hr storage at 4°C then reheated to 65°C (T24). Digestibility profiles (proportion of SDS, RS, and RDS) and glucose release (area under the curve for 180min) by treatment were compared using repeated-measures-ANOVA.
Results: Digested at T0 and T24 intact parboiled rice had the least RDS (20.8%[18.4%,23.2%]) and minced medium grain white rice the most (58.7%[53.5%,63.9%]). On average cold storage for 24h increased RS by 8.0%[9.5%,6.5%] and reduced the area under the curve by 9.5%[2.6%,15.2%] compared to freshly prepared rice. At T24 the starch profile of intact parboiled rice (RDS:SDS:RS = 1:2.2:1.6) compared with intact medium grain white rice of 1:0.3:0.2. Mincing increased RDS by 17.8% and reduced the SDS by 13.3% and the RDS by 4.5%.
Conclusion: At a population level for those who eat freshly prepared medium grain white rice regularly, consuming cooked parboiled rice that has been stored for 24 hours at 4ºC then reheated may be a way to improve postprandial blood glucose control. In vivo testing is required to explore this further.
There is no conflict of interest in this study.