Effects of viscoelasticity on moisture sorption of maltodextrins

By means of a physically-based drying model we argue that hysteresis in moisture sorption of food materials can be explained by viscoelastic relaxation effects. The model is applied to maltodextrins, for which we have recently determined their rheology for conditions approaching the glassy state, as well as their moisture diffusion coefficients (which is shown to follow our earlier model for moisture diffusion). For these maltodextrins moisture sorption has been performed using the Dynamic Vapour Sorption (DVS) method. After an update of the earlier (sub)model for moisture diffusion with insights from aerosol drying, the model is shown to give reasonable predictions of the DVS experiments, which clearly exhibit the hysteresis in moisture sorption. The model was fitted to DVS data of four maltodextrins, differing in their DE-values. The independently determined fitting parameters showed a high degree consistency amongst the four maltodextrins, and they were close to some parameter values determined experimentally with rheology measurements. Via a parameter study we have performed a rough sensitivity study, showing significant effects of all model parameter. All the results of this study together makes us quite confident that viscoelastic relaxation effects is indeed the cause of hysteresis in moisture sorption, as has been argued earlier for solvent sorption of synthetic polymers.