Physicochemical properties of commercial starch hydrolyzates in the frozenstate

The physical properties of commercial starch hydrolyzate (varying in dextro se equivalent values, DE, from 0.5 to 42) solutions in the frozen state wer e related to their composition. At 20% (w/v) hydrolyzate concentration, an inverse linear relationship between DE and apparent glass transition temper ature (T-g') of the unfrozen solute matrix was observed. The T-g' temperatu res remained relatively constant for solute concentrations below 40% (w/v); above this concentration the T-g' was depressed, possibly due to the plast icizing effect of additional water entrapped in the glassy state during non -equilibrium freezing. Simple predictive models (based on the Flory-Fox equ ation; 1/T-g = Sigma{w(i)/T-gi}) were found to predict reasonably well the T-g' value of 'binary' monodisperse and polydisperse hydrolyzate mixtures o f varying proportions between the two components. Linear relationships were also found between T-g'(measured) (by calorimetry) and T-g'(predicted) (ba sed on the Flory-Fox model, and using the oligosaccharide composition of th e hydrolyzates and the respective T-g' values of the pure components). The rate of oxidation of ascorbic acid has been measured in the presence of sta rch hydrolyzates at temperatures between -4 and -16 degrees C. Both the Arr henius and WLF (Williams-Landel-Ferry) kinetic models were found to describ e the temperature dependence of reaction rate constants reasonably well. Ho wever, knowing the T-g' value of the amorphous maltodextrin was not suffici ent to predict its cryostabilization behavior. (C) 1999 Elsevier Science Lt d. All rights reserved.