EFFECT OF OSMOTIC AND CONVENTIONAL DEHYDRATION ON QUALITY OF SOME FRUITS AND VEGETABLES

This study deals with the effect of using osmotic  pr-etreatment technology applied to plant materials prior to osmotic dehydration ((O.D)) and the conventional drying((C.D)) on some physicochemical and sensory characteristics of apples , papaya fruits and sweet potatoes . The   osmosis syrups were sucrose ,high fructose corn syrup (HFCS) and a mixture of sucrose + HFCS (1:1) . Physicochemical properties of apples , papaya fruits and sweet potatoes  were evaluated. The quality attributes of osmo –dehydrated ((O.D)) and convectional dried ((C.D)) cubes of  apples , papaya fruits and sweet potatoes  were evaluated just after processing and during storage for 6 months  at ambient temperature . Results indicate that osmo-dried ((O.D)) samples recorded higher values of moisture , sugars , total acidity but lower pectin contents  compared to the convention dried ((C.D))  samples . Also, the retention of ascorbic acid and β–carotene was higher in (O.D) samples which means higher nutritive value . The positive effect of osmotic pretreatment on the physical properties of different dried samples was found . The drying ratio , rehydration ratio (R.R )  , the texture ( firmness ) and drying time were lower in (O.D) samples  compared with the (C.D) samples . The reduction in Hunter color parameters L , a  and  b  was higher in (C.D) samples than the (O.D) ones . The effect of storage on different quality parameters were more evident in the C.D samples than the (O.D) ones . The evaluation of sensory characteristics indicated that the (O.D) samples gained the highest scores while there were high significant differences found between the (O.D) and (C.D) samples . slight significant differences were found between the different used syrups of osmosis .