Water sorption and glass transition in freeze-dried persimmon slices. Effect on physical properties and bioactive compounds

Abstract

The use of persimmon variety “Rojo Brillante”, has seen a great expansion in recent years. Its production is associated with substantial amounts of post-harvest waste, therefore, development of products that allow its valorisation are of great interest. In this study, a freeze-drying technique was used to obtain a high quality product. Freeze-dried samples were conditioned in a range of water activities (0.113–0.680) at 20 °C at equilibrium, allowing for products of different water content. Water sorption isotherms were determined from persimmon slices, with BET (Brunauer, Emmett, and Teller) and GAB (Guggenheim, Anderson, and de Boer) models applied to the sorption data. The glass transition was analysed using differential scanning calorimetry (DSC); the Gordon & Taylor equation modelled the water plasticisation effect. Results confirmed a critical water activity (CWA) of 0.165 and a critical water content (CWC) of 0.0312 g water/g product. Below these critical values, the glassy state of the amorphous matrix and the crispness were guaranteed. This consequently avoids an increase in the rate of deterioration reactions, texture and colour changes, and the loss of the fruit bioactive compounds.