study on the effect of osmotic pretreatment on the structural and microstructural properties of air-dried tomato

tomatoes (roma cultivar) picked up for the study were obtained from varaminelocal market. each tomato was divided into four portions. quarter portions of tomato were placed in osmotic solutions that were different in levels of sucrose and nacl (30 and 40% for sucrose, and 5, 10 and 15% for nacl). osmotic dehydration was carried out for varied time durations from 15 up to 240 min. temperature of dehydration process was kept constant at 30?2°c. ratio of tomato to solution was 1:10. the mixture was agitated by use of an agitating system of 150 rpm. two osmotic solutions of specified concentration and treatment times were chosen, following a determination of water loss vs solid gain for all the treatments. samples dehydrated with these (5% nacl+40% sucrose or 10% nacl+40% sucrose) solutions were then dried in a hot air dryer. finally, dried samples were analyzed for their texture and microstructure by employing instron and scanning electron microscope (sem) respectively. comparing the osmosis treated samples with non-osmosed ones demonstrated that applying osmotic pretreatment caused a softening of structure. it reduced the shrinkage of dried product by restraining the rupture of product's cellular structure.