Effect of state transition, drying kinetics and moisture content on Young's modulus variation during thermal drying of hygroscopic food materials

Young's modulus is one measure of texture, an important quality parameter in processed food materials. During thermal drying, the Young's modulus undergoes significant variation due to moisture loss and rubbery-glassy state transitions, and physics-based models help in understanding trade-offs involved in dryer designs. However, studies that establish the relationship among drying kinetics, state transition and Young's modulus changes are lacking in the literature. In this paper, the role of various stages of drying and rubbery–glassy states on Young's modulus variation is presented. A modelling framework is developed to capture the effect of moisture loss on local and effective Young's modulus. Experiments are conducted for measuring local and effective Young's modulus variation with time and moisture content. The model is validated with experiments conducted in this work as well as with those reported earlier in the literature, and the agreement is within 10% on average. The importance of a two-stage model for predicting Young's modulus variation during different drying stages and in case of state transition is discussed. The present work could serve as an initial step towards improved understanding and model development for Young's modulus variations during thermal drying.