Characterization and modeling of the A- and B-granule starches of wheat, triticale, and barley

Wheat, triticale, and barley starches have large, disc-shaped A-granules and small, spherical B-granules. In this study, A- and B-granules of these three starches were separated, and their structures and properties were analyzed. Absolute amylose contents of wheat, triticale, and barley A-granules were 30.9%, 28.2%, and 28.1%, respectively, and that of the B-granules were 25.5%, 19.7%, and 23.0%, respectively. High-performance anion-exchange chromatography, equipped with an on-line amyloglucosidase reactor and a pulsed amperometric detector (HPAEC-ENZ-PAD), of debranched amylopectins showed that the A-granules had more B2 chains and lesser short chains (A and B1 chains) than did the B-granule counterparts. Structure models of the amylopectins of the A- and B-granule starches were proposed, and the relationships between the structures of amylopectin and the shapes of starch granules were discussed. The B-granules displayed higher peak gelatinization temperatures and broader gelatinization temperature ranges than did the A-granules. The retrogradation rates of the B-granules after being stored at 4 °C for 7 days were less than that of the A-granules. The B-granules had higher pasting temperatures, less peak, breakdown, and setback viscosity than did the A-granule counterparts. The pasting properties of reconstitute wheat starch consisting of different proportions of the A- and the B-granules showed that the chemical composition and structure of the starch, instead of the size of the starch granules, controlled the pasting properties of the starch. The differences in the structure of the A- and B-granules suggested that biosynthesis of the two granules differed.