Glass transition-related or crystalline forms in the structural properties of gelatin oxidised starch glucose syrup mixtures

The structural properties of acid pigskin gelatin/oxidised waxy maize starch/glucose syrup mixtures at a 70% total level of solids were investigated. Depending on polymer composition and pH, mixtures form phase-separated gels with a gelatin or an oxidised starch continuous matrix. It was found that the continuous phase determined the mechanical behaviour of a mixture. Thus gelatin/glucose syrup systems or gelatin continuous mixtures show a three-fold transformation in viscoelasticity, namely: from solutions at high temperature (>35 degrees C) and rubbery solids at ambient temperature to high modulus viscoelastic liquids at subzero temperatures (e.g, > 10(6) Pa at 10 Hz and -20 degrees C). In the language of polymer physics a transition was observed from rubber-like to glass-like consistency. By contrast, oxidised starch/glucose syrup systems and oxidised starch continuous mixtures show a transformation from liquid-like to solid-like behaviour at subzero temperatures due to water crystallisation. Concentrated oxidised starch (approximate to 31%) with glucose syrup (approximate to 39%) systems are capable of forming intermolecular amylose-like structures at high temperatures (e.g. 80 degrees C), which remain solid-like throughout the cooling run (down to -20 degrees C). Therefore the development of crystallinity (water/polymeric aggregates) in starch-dominated systems prevents them from exhibiting glass-related viscoelasticity. The investigative approach in general, and this mixture in particular (with its multitude of structures) might provide guidance for development work in the confectionery industry. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.