Glycemic index of starchy crops and factors affecting its digestibility: A review

The starchy crops which normally form the staple diet of people are rich in carbohydrates. People leading a sedentary lifestyle and consuming high amounts of carbohydrate-rich food normally invite obesity and type-II diabetes. Upon digestion of starchy food, postprandial blood glucose level rises rapidly and sharply, which reflects a high glycemic index (GI) value. Various factors affect starch digestibility and the GI of a food or its products. The internal factors such as amylose, lipid, protein, phytic acid, dietary fibre and resistant starch (RS) have been correlated with lower GI value. The external factors which affect GI and starch digestibility include cooking, processing, retrogradation, soaking and germination. Various food matrices are also responsible for alteration in the GI value. Moreover, changes in the environmental conditions including abiotic and biotic stresses are also responsible for the change in starch structure and composition which ultimately affects GI of starchy crops. The GI and starch digestibility of foods are affected by intrinsic and extrinsic factors which affect strategies for management of sugar level to ensure better human health. High amylose, RS, lipid and protein in the food were found to reduce starch hydrolysis. Further, retrogradation, various cooking methods and modification of starch by physical and chemical means resulted in lower GI and increased RS considerably. Analysis and management of postprandial blood glucose level while eating starchy crops would help to understand the risk of diabetes and other lifestyle-related diseases.