On the applicability of Flory–Huggins theory to ternary starch–water–solute systems

The effects of glucose and glycerol on gelatinization of highly concentrated starch mixtures were investigated with wide-angle X-ray scattering and differential scanning calorimetry. The gelatinization/melting of starch was found to be a two step process. In the first step the granule swells at low temperatures (i.e., 30–50 °C), which is followed by a solvent–temperature cooperative step that induces loss of crystallinity. The results were interpreted with an extended form of the adapted Flory equation. The values of the model parameters (Tm0, ΔHu, χ12, χ13, and χ23) obtained were similar to the values reported in the literature. Ternary phase diagrams were constructed with melting lines representing fully gelatinized starch. The crystalline region of starch with glucose was larger than with glycerol. This could be understood from the differences in χ13 (solute–solvent interaction). The extended form of Flory–Huggins model somewhat under predicts the experimental values of the gelatinization process. Comparing the Flory–Huggins model with experiments led to the conclusion that Flory equation is a useful tool to interpret and predict the gelatinization and melting behaviour of ternary starch-based systems. But the experiments are complex, the systems are often not in true equilibrium and other disturbing effects are easily encountered. Therefore one should be cautious in the translation of experimental results to the thermodynamics of gelatinization in multicomponent systems.