Glycaemic index values and physicochemical properties of five brown rice varieties cooked by different domestic cooking methods

Background: The prevalence of diabetes has increased dramatically in recent decades in the regions where people excessively consume white rice. Due to higher nutritional values and bioactive components, low to medium glycaemic index (GI) brown rice could be a potential alternative to white rice in these regions. Methods: Five varieties, Chiang (CH), Sungyod (SY), Lepnok (LP) from Thailand, Long grain specialty 1 (LS1) and Long grain specialty 2 (LS2) from Malaysia were tested for GI. Ten test foods were prepared from 5 varieties by 2 cooking techniques (pressure cooker, PC and rice cooker, RC). Overnight fasted 10 healthy subjects were fed with 25 g glucose as a reference food (RF) on 3 occasions and amount equivalent to 25 g available carbohydrate portion of test food (TF) on 1 occasion in separate days. Fasting and post-prandial capillary blood glucose was measured via finger-prick methods at 0, 15, 30, 45, 60, 90 and 120 min, and the incremental area under curve (iAUC) was determined. The GI of each TF was calculated as percentage of incremental area under curve (iAUC) of TF over RF. Results: The mean GI values of SY (72 -81, high), CH and LP (59 -65, medium) and LS1 and LS2 (64 -73, medium to high) for cooking were discovered by PC and RC methods. The GI did not vary significantly (p>0.05) among varieties as well as between cooking methods. GI showed a significant negative correlation with the amylose content (r = -0.70, p<0.05) and significant positive correlation with cold peak viscosity (r = 0.80, p<0.01). Conclusions: All five rice varieties irrespectively of the cooking method used are classified as medium to high GI foods. Medium GI varieties could have potential of being used in diabetic diet. Cooking methods did not significantly alter the glycaemic characteristics of the studied varieties. Amylose content and pasting properties can be used for predicting GI of brown rice. It is urgent to explore low GI brown rice varieties in these regions.