A polymer physico-chemical approach to the study of commercial starch hydrolysis products (SHPs)

Abstract

The behavior of 55 commercial SHPs, of dextrose equivalent (DE) 0·3–100, was studied by a low-temperature differential scanning calorimetry technique. The method, based on derivative thermograms, is used to measure the characteristic sub-zero glass transition temperature, T′ g , of a maximally freeze-concentrated aqueous solution. An inverse linear correlation exists between T′ g and DE. A plot of T′ g vs. number-average molecular weight ( M n ) demonstrated the classical behavior of SHPs as a homologous series of amorphous glucose polymers, and revealed an ‘entanglement coupling’ capability for SHPs of ≤ 6 DE and T′ g ≥ −8°C. The possible relationship between intermolecular entanglement (leading to network formation) and SHP functional behavior as a food ingredient in applications involving gelation, encapsulation, frozen-storage stabilization, thermomechanical stabilization or facilitation of drying processes is discussed. The utility of low-DE SHPs for inhibiting various ‘collapse’-related phenomena, which affect the processing/storage stability of many foods, is described and explained. An example of the inhibition of enzymic activity in a frozen system, stabilized with low-DE maltodextrin, is cited. A generalized mechanism for collapse is proposed, based on the occurrence of a critical structural relaxation transition at T′ g , followed by viscous flow in the rubbery liquid state. The mechanism is derived from Williams-Landel-Ferry free volume theory for amorphous polymers, and leads to a conclusion of the fundamental equivalence of T′ g (or other relevant glass transition temperature, T g ) and the observed collapse temperature and the temperature of recrystallization.