Thermal degradation of carbohydrate polymers in amorphous states: A physical study including colorimetry

The early stages of the thermal decomposition of dense matrices of maltodextrin are studied as a function of the molecular weight and the water content using colorimetry and near-infrared reflectance (NIR) spectroscopy. Dense matrices of maltodextrin prepared by solvent casting equilibrated at 25 degrees C at various water activities are subjected to elevated temperatures for various time intervals using specifically constructed, hermetically sealed cells. The degradation of the maltodextrins is followed colorimetrically and state of water in the thermally treated samples is investigated using NIR spectroscopy. The results are discussed in terms of kinetic models including matrix viscoelasticity and reaction order. The data show that to a good approximation the color formation can be modelled using an Arrhenius' type activation energy, independent of the physical state of the matrix (rubbery or glassy). The relevance of the results for carbohydrate processing and storage is highlighted. (c) 2005 Elsevier Ltd. All rights reserved.