Biochemical markers for low glycemic index and approaches to alter starch digestibility in rice

Abstract

Recent studies indicate that dietary fibre rich wholegrain foods exhibit low starch digestibility. Hence, resistant starch (RS) content could be an important biochemical marker for slow starch digestibility and hence of low glycemic index (GI) and glycemic load (GL). Rice is a starch rich grain. People consuming milled rice as a staple diet and leading sedentary life are likely to develop type-II diabetes in the long run. With rise in the number of diabetics worldwide, one possible approach is to develop rice based low GI foods with high RS content rice, as these show slow starch digestibility and hence would cause only slow rise in postprandial glucose level. In addition to amylose, the linear chains of amylopectin also influence starch digestibility. Starch debranching enzyme pullulanase (PUL) action releases a mixture of linear amylose-like chains that facilitate retrogradation of starch and synthesis of type 3 RS resulting in reduced starch digestibility. Besides mechanical processing, modern technologies like CRISPR have been used to increase amylose and RS (type 5 and type 3) content in rice making it more suitable for diabetics. Phytic acid (PA) chelates Ca++ ions required by intestinal alpha amylase and hence lowers starch digestibility.