PASTING PROFILES AND SOLUBILITY OF NATIVE AND CROSS-LINKED CORN STARCH IN DIMETHYLSULFOXIDE-WATER MIXTURES

The pasting profiles of native and cross-linked corn starch in dimethy lsulfoxide (DMSO)-water mixtures were investigated with a Rapid Visco Analyser. The temperature profile included an isothermal step of 1 min at 30 degrees C, followed by a linear gradient to 75 degrees C in 3 m in and finally an isothermal step of 20 min at 75 degrees C. The profi les were characterised by an initial peak (at 75 degrees C) followed b y a trough, much as is the case with profiles of such starch in water. Increasing the DMSO concentration in the DMSO-water mixture from 70-9 7.5% (by weight), without changing the starch concentration, resulted in lower end-viscosities. The RVA pasting profiles of a series of sodi um trimetaphosphate (STMP) and epichlorohydrin (ECH) cross-linked corn starches were investigated in 92.5% DMSO at different dry matter (d.m .) contents. At high starch concentrations (>60% d.m.), the end viscos ity increased with the degree of cross-linking. At lower starch concen trations (>6% d.m.), the more highly cross-linked starches yielded low er peak- and end-viscosities than starches with lower degrees of cross -linking. The solubilisation of the starches in 92.5% DMSO was complet e for the native starch and decreased considerably for the highly cros s-linked starches. Light microscopy showed that the cross-linked starc hes, upon heating in DMSO-water, were converted to a biphasic system c onsisting of insoluble granule remnants and a starch solution. (C) 199 5 Academic Press Limited