A refined mechanistic model for swelling kinetics of starch granules

This paper investigates the gelatinization of individual starch granules using numerical simulations, validated against experimental microscopy data from a ParCS apparatus. We show that the dynamics of starch-granule swelling can be captured by a diffusion equation for mass transfer of water into the granule, with the equilibrium water content captured by a Flory-Rehner theory of a cross-linked network in which the fraction of cross-linked chains is made to vary as an empirical function of temperature. Having the cross-link density vary with temperature is vital to capture the swelling behavior at large and small swelling extents (i.e., close to and far away from the gelatinization temperature). The theory produces excellent agreement with both equilibrium swelling data and dynamic swelling data for red bean starch. Further, we show that the model is able to reproduce a previous experimental finding that swelling data from different granules from red bean, chickpea, green lentil, and yellow pea starches can be collapsed onto a universal curve with only two empirical parameters. The simulations are then used to predict the relationship between the empirical parameters in the master curve and the true material properties. The modified theory presented here is a major step forward in the fundamental understanding of starch gelatinization and the ability to use predictive models for optimization of industrial manufacturing processes.