STUDIES ON MOISTURE SORPTION ISOTHERMS FOR OSMOTICALLY PRETREATED AND AIR-DRIED POMEGRANATE ARILS

Moisture sorption isotherms of unosmosed and osmosed convectively dehydrated pomegranate arils were determined at 25, 40 and 50C using standard gravimetric static method over a range of relative humidity from 10 to 95%. Among the applied models, the modified Smith model was found to describe the moisture sorption isotherms of unosmosed and osmosed pomegranate arils. The net isosteric heat of sorption of unosmosed arils varied between 54.12 and 63.31 kJ/mol and that of osmosed arils between 67.34 and 73.00 kJ/mol at moisture levels varying between 10 and 12% (d.b.). Heat of vaporization of unosmosed and osmosed dehydrated pomegranate arils increased with decrease in moisture content and storage temperature. The heat of vaporization is more for osmosed pomegranate arils as compared with unosmosed ones for given moisture content. PRACTICAL APPLICATIONS The process of osmotic dehydration can be used for the preparation of high-quality shelf-stable product for the purpose of use during off-season. The moisture sorption isotherms are extremely important in modeling the drying process, in design and optimization of drying equipment, in predicting shelf stability, in calculating moisture changes that may occur during storage and in selecting appropriate packaging material.