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 dimethylsulfoxide (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 min and finally an isothermal step of 20 min at 75 degrees C. The profiles were characterised by an initial peak (at 75 degrees C) followed by a trough, much as is the case with profiles of such starch in water. Increasing the DMSO concentration in the DMSO-water mixture from 70-97.5% (by weight), without changing the starch concentration, resulted in lower end-viscosities. The RVA pasting profiles of a series of sodium 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 viscosity increased with the degree of cross-linking. At lower starch concentrations (>6% d.m.), the more highly cross-linked starches yielded lower peak- and end-viscosities than starches with lower degrees of cross-linking. The solubilisation of the starches in 92.5% DMSO was complete for the native starch and decreased considerably for the highly cross-linked starches. Light microscopy showed that the cross-linked starches, upon heating in DMSO-water, were converted to a biphasic system consisting of insoluble granule remnants and a starch solution. (C) 1995 Academic Press Limited