Water sorption isotherms and glass transition in strawberries: influence of pretreatment Original Research Article

Water sorption isotherms and glass transition as a function of moisture content were determined in strawberries as a function of sample pretreatment. Sorption experiments were carried out in chambers at controlled aw, at 30 °C. Samples studied were whole and homogenized tissue, fresh (for the desorption process) and previously freeze-dried (for the adsorption process). Glass transition of samples equilibrated to different moisture contents were analysed by DSC. GAB model was fitted to sorption data and Gordon and Taylor equation was used to model the water plasticization effect. Strawberry pretreatments caused changes in the tissue structure that affected the water binding capacity of the different product phases at equilibrium with a determined aw value. This implied differences in the relationships between the mean equilibrium moisture content of the product and both the aw value (equal for all phases at equilibrium) and glass transition temperature of the amorphous soluble solids.