Gelatinisation related structural aspects of small and large wheat starch granules

Abstract

Wheat starches from four European varieties (Charger, Estica, Skirlou and Soissons), and their small and large granule fractions were characterised on a structural level. Gelatinisation properties of starches and fractions thereof were compared. Isoamylase debranching revealed only limited differences between amylopectin chain lengths of the various starches and their fractions. Wide-angle X-ray diffraction, which showed predominant A-type crystallinity for all starches, revealed that large granules had systematically higher B-type and total crystallinity than small granules. Small-angle X-ray scattering (SAXS) indicated structural differences between amylopectins of distinct granule classes. At 42% moisture, the SAXS patterns of small granules were more intense than those of large granules, which, along with their higher gelatinisation peak temperature, suggested denser crystalline lamellae. Upon hydration from 42 to 66% moisture, small granules showed decreased lamellar repeat distances. As small granules displayed narrower helix–coil transition endotherms than large granules, shorter single stranded chains are envisaged to connect longer double helices to the amylopectin backbone in small wheat granules.