Rice grain quality and starch digestibility- desired traits for evaluating rice varieties

Abstract

Rice grain quality is the most important factor for evaluation of a variety as well as millers, consumers and farmer's point of view. It includes physico-chemical, nutritional and sensory qualities. The consumers of India and other south east Asian countries prefer medium to high amylose content (AC) rice due to their non-stickiness properties of boiled rice but in many Asian countries, waxy rice (having low AC) mainly preferred. The colour of rice grain may be white, purple, red and black; which are mainly associated with pericarp or bran layers of the whole grain. The bran contains most of the phytochemicals like oils, antioxidants, minerals, proteins, vitamins and crude fibers in higher concentration than white endosperm. Pigmented rice is generally rich in nutritional compounds as compared to white one but those are unpopular among the farmers because of many undesirable physiological and agronomic characteristics. Sensory qualities like colour, texture, pasting properties, aroma are essential for consumers as per their preference and acceptance. As rice grain is mainly composed by starch, hydrolyzed by digestive enzymes and converted into glucose which is the major energy source for various metabolic functions. After fulfilling the body energy requirement, extra calories from starch are stored as fats or glycogen for later use. Therefore, overeating food containing rice with sedentary lifestyle potentially leads to some health issues, such as type-II diabetes, obesity and colon diseases in long term particularly in Asian countries. Various biochemical factors affect the starch digestibility and Glycemic index (GI) of a food or its products. These factors are resistant starch, AC and phytic acid which lowers the starch digestibility by various ways and have been negatively correlated with GI value. Now-a-days quality assessment of rice grain in terms of its nutritional as well as physico-chemical parameters is gaining prime importance gradually.