Rice starch

Starch is the most abundant composition in the rice grain, and constitutes approximately 90% of milled rice grain. This chapter summarizes the current advances made in the starch structure, starch function, and starch biosynthesis in the past decade. Knowledge of all the three aspects of starch may provide deeper understanding of the "genetics (biosynthesis)-structure-function" relation in rice starch and starch-based food. Starch is mainly composed of amylose and amylopectin, and amylose content is the most important determinant of rice eating and cooking quality. Both amylose content and amylopectin fine structure contribute to the physicochemical and functional properties of rice starch. Functions of major genes and enzymes involved in the starch biosynthesis pathway in rice endosperm have been well characterized. The waxy encoding granule starch synthase 1 (GBSS1) and SSIIa encoding starch synthase IIa (SSIIa) are very useful in breeding for desired eating and cooking quality, whereas the mutations in SSIIIa and branching enzyme IIb (BEIIb) may be useful in breeding for high resistant starch with great health benefit.