Water sorption isotherm and glass transition temperature of freeze-dried Syzygium cumini fruit (jambolan)

The sorption isotherms analysis and glass transition temperature should provide important information about the role of water in food. Sorption/desorption isotherms of freeze-dried jambolan (FDJ) were determined at 15, 25 and 35 °C temperatures. The determination of glass transition temperature is also performed in order to establish packaging and storage conditions. The hygroscopic behavior of jambolan pulp after freeze-dried process was studied through sorption isotherms and models fit to experimental data. The freeze-dried material was highly hygroscopic and Peleg’s model showed the highest coefficient of determination and lower values of average deviation and relative average error estimated, therefore the best fit sorption isotherms. The lowest value of monolayer was 7.64 gH2O·100gdb−1 to 25 °C. At temperature higher than 17 °C (Tg), the material become more amorphous and the site of interaction with water molecules becomes available. As conclusion, the material must be storage at temperatures below Tg and low relative humidity.