OSMODEHYDROFREEZING OF APPLES - STRUCTURAL AND TEXTURAL EFFECTS

Osmodehydrofreezing refers to the combined process of partial drying i n a concentrated solution (osmotic dehydration) followed by freezing. The physical properties of osmodehydrofrozen apple slices were determi ned. Granny Smith apples slices were dehydrated to the point of a 50% weight reduction using concentrated sugar solutions (sucrose, sorbitol , or 42 DE corn syrup solids [CSS]) and were frozen at -35 degrees C. Rheological testing (force deformation and small scale oscillatory def ormation) indicated that the presence of sugars increased firmness of thawed/rehydrated tissue compared with apples treated in the same mann er without sugar, however, untreated frozen controls were firmer than osmodehydrofrozen samples after thawing/rehydration, indicating that c onditions used during osmotic dehydration (50 degrees C for 40 min) we re too severe. Cryo-scanning electron microscopy revealed a smoothness of the middle lamella of cryoprotected cells and cracking in that of untreated, frozen cells. Conductivity measurements of rehydrating appl e tissue indicated that much of the damage done to osmodehydrofrozen f ruit membranes was done during pre-freezing treatment. Copyright (C) 1 996 Published by Elsevier Science Ltd on behalf of the Canadian Instit ute of Food Science and Technology