Water activity and glass transition effect on the physical properties and bioactive compounds of persimmon peel powder

Summary Persimmon peel is an agro‐industrial by‐product that could be valorised as a potential powdered functional ingredient. However, powdered products exhibit quality and stability problems associated with the water activity and the glass transition. In this work, hot‐air drying was used to produce a persimmon peel powder, which was conditioned at 20 °C at different relative humidity (11.3%–75.5%). The changes in physical properties (water sorption, glass transition, mechanical properties), structure (light microscopy) and bioactive compounds (soluble tannin content, total carotenoid content) were evaluated. By combining the GAB sorption model and the Gordon and Taylor equation, the critical values of water activity ( a w = 0.211) and water content (0.029 g water g −1 product), related to the glass transition, were obtained. These values were critical for the production of a free‐flowing powder rich in bioactive compounds and high antioxidant capacity.