A high throughput in vitro digestibility assay for rapidly predicting glycaemic index of rice varieties

The aim of this study was to construct the high throughput needs of rice breeding programs for rapidly predicting the glycaemic index (GI) of rice varieties. Milled rice grains from varieties (Opus, Koshihikari, Reziq, Topaz, Doongara, YRL127, Sherpa, Illabong, Langi and Waxy) differed by GI were subjected to an in vitro enzymatic digestion by a mixture of pancreatic α-amylase and amyloglucosidase (Aspergillus niger). An aliquot of digesta was pipetted at each time points, of which the generated glucose concentration measured through Megazyme GOPOD assay and calculated into the starch digested percentage. Digestion curves were generated by plotting starch digestion percentages vs. time and the first order kinetic parameters of starch digestion were obtained through the combined techniques of logarithm-of-slope analysis and non-linear least-squares fitting method, which allow for an accurate determination of critical parameters including predicted GI, areas under curves and/or digestion rate coefficients. This in vitro digestibility assay allows for a rapid prediction of the GI to screen large number of rice lines within tight timeframes, and has the potential to assist in the delivery of new low GI rice cultivars.