A refined mechanistic model for swelling kinetics of starch granules

Abstract

This paper investigates the gelatinization of individual starch granules using numerical simulations, validated against experimental microscopy data. We show that the dynamics of starch granule swelling can be captured by a diffusion equation of water into the granule, with the equilibrium water content captured by a Flory-Rehner theory of a crosslinked network that has the fraction of crosslinked chains varying as an empirical function of temperature. Having the crosslink density vary with temperature is vital to capture the swelling behavior at large and small swelling extents (i.e., close 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. In general, 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.