A Reassessment of the Chemical Structure of Barley and Wheat Starch Granules

Barley starch exists in two clearly defined populations of large (ca. 25 μ diameter) and small (ca. 5, μ diameter) granules, whilst in wheat there is a range of granule sizes with no similar bimodal distribution. The small granules of barley represent about 90% of the total starch granules by number, but account for only about 10% of the total starch in weight. Fractions containing only large or only small granules have been isolated from both barley and wheat. The small granules from barley have a higher amylose content than the large granules, a higher gelatinisation temperature, and are usually associated with more protein. In contrast, large and small granules from wheat differ only slightly in their respective amylose contents but, like barley differ in gelatinisation temperatures and amounts of associated protein. It is proposed that starch synthesis in the small starch granules of barley is under different genetic control from that in the large granules.