Masako Takada

Interaction between Potato Starch and Sucrose-lipid Monoesters Studied by Differential Scanning Calorimetry

The formation and dissociation of complexes composed of potato starch and sucrose-lipid monoesters (SE: monocaprate, monolaurate, monomyristate, monopalmitate, and monostearate) were studied by differential scanning calorimetry (DSC). The formation and dissociation temperatures of each complex increased as the number of carbon atoms in the alkyl chain of SE increased, and as the content of starch increased, overlapping with the gelatinization temperature. Therefore, the DSC curves for starch gelatinization differed according to the added SE and water content. The completion temperature for the dissociation of each starch-SE complex depended on the water content, similar to that for the gelatinization of starch. The heat of fusion of the starch-SE (monopalmitate) complex obtained from the completion temperature was nearly twice that of the original starch, 140 kJ/mol glucose unit. It is suggested that a stable conformation of each complex was not formed during the gelatinization of the starch granules, but during cooling from a temperature higher than the dissociation temperature of the complex which had formed during the gelatinization process.

Bound Water of Six Kinds of Sugar by Pulsed NMR and Sorption Isotherm

The magnetic relaxation times were determined at 32 •Ž by pulsed NMR on aqueous solutions of six kinds of sugar, i.e. glucose, galactose, fructose, maltose, sucrose and lactose, and the amounts of bound water were calculated. Above 1.0 gH2O/gDM of the water content, regardless of the kinds of sugar, the amount of bound water of these sugars was almost constant and was as low as 0.01 gH2O/gDM, which was remarkably lower than the value obtained on rice starch. The amount of monolayer sorption water at 35•Ž was estimated as practical zero, independently of the kinds of sugar. Therefore, the amount of the bound water estimated from the magnetic relaxation times seemed to correspond virtually the monolayer sorption water.