Comparison of starch physicochemical properties from medium-grain rice cultivars grown in California and Arkansas

The starch molecular structure and physicochemical properties of two medium-grain rice cultivars from Arkansas (Bengal, Medark) and from California (M202, M204) were determined and compared when they were grown in their respective locations and grown together in Arkansas to better understand the impacts of genetics and environment on starch characteristics. Both M202 and M204 contained significantly higher amylose contents (13.2-15.3%) compared with the Arkansas cultivars (11.6-12.4%). Starch from the Arkansas rice cultivars exhibited higher pasting and gelatinization temperatures and higher enthalpy values. Rice amylopectin from the California cultivars consisted of a smaller proportion of intermediate chains (DP 13-24), and had a lower molecular weight and a smaller radius of gyration. When the four cultivars; were grown together in Arkansas, the ranges for amylose content narrowed (10.6-12.4%), their differences in thermal and pasting properties became smaller, and the molecular characteristics of amylose and amylopectin changed for all four cultivars. This study demonstrated that genetics, location, and crop year all contributed to variations in rice starch fine structure and physicochemical properties.