Properties of Damaged Starch Granules. V. Composition and Swelling of Fractions of Wheat Starch in Water at Various Temperatures

Abstract

Abstract Wheat starch was ball milled to obtain various levels of damaged starch (4·6-93·7%). On hydration in excess water below the gelatinisation temperature of the original starch, damaged starch gave soluble material comprising low molecular weight fragments of amylopectin (LMWAP) with a little lipid-free amylose (FAM), and a gel derived from disordered (amorphous) amylopectin (AP), LMWAP, FAM and lipid-complexed amylose (LAM). The ungelatinised material comprised undamaged granules and some birefringent remnants of partially damaged granules. On hydration above the gelatinisation temperature, all starch was converted either into a gel of AP, FAM and LAM, with little or no LMWAP, or into soluble material. The swelling factors of the starches ranged from 1 to 6·7 at 20°C, and from 10·0 to 9·4 at 80°C with increasing levels of damaged starch. The swelling factors calculated for the gel fraction alone (the main component responsible for swelling and water uptake) ranged from 1 to 10·0 at 20°C, and from 11·8 to 18·5 at 80°C. It was concluded that the swelling of undamaged granules and remnants was probably inhibited by LAM, as reported before. The swelling of damaged starch appeared to be unaffected by its LAM content, however, but depended greatly on its damaged starch content and on the extent to which structural order in the gel-forming components had been 'loosened' during the creation of damaged starch. Roller-dried starch (which contained no LMWAP) had the properties of damaged starch gel, with slightly greater swelling power at all temperatures.