Physicochemical properties of commercial starch hydrolyzates in the frozen state

The physical properties of commercial starch hydrolyzate (varying in dextrose equivalent values, DE, from 0.5 to 42) solutions in the frozen state were related to their composition. At 20% (w/v) hydrolyzate concentration, an inverse linear relationship between DE and apparent glass transition temperature (Tg′) of the unfrozen solute matrix was observed. The Tg′ temperatures remained relatively constant for solute concentrations below 40% (w/v); above this concentration the Tg′ was depressed, possibly due to the plasticizing effect of additional water entrapped in the glassy state during non-equilibrium freezing. Simple predictive models (based on the Flory–Fox equation; 1/Tg=∑{wi/Tgi}) were found to predict reasonably well the Tg′ value of ‘binary’ monodisperse and polydisperse hydrolyzate mixtures of varying proportions between the two components. Linear relationships were also found between Tg′measured (by calorimetry) and Tg′predicted (based on the Flory–Fox model, and using the oligosaccharide composition of the hydrolyzates and the respective Tg′ values of the pure components). The rate of oxidation of ascorbic acid has been measured in the presence of starch hydrolyzates at temperatures between −4 and −16°C. Both the Arrhenius and WLF (Williams–Landel–Ferry) kinetic models were found to describe the temperature dependence of reaction rate constants reasonably well. However, knowing the Tg′ value of the amorphous maltodextrin was not sufficient to predict its cryostabilization behavior.