Osmodehydrofreezing of apples: structural and textural effects
1996
Tregunno, N.B. | Goff, H.D.
Osmodehydrofreezing refers to the combined process of partial drying in a concentrated solution (osmotic dehydration) followed by freezing. The physical properties of osmodehydrofrozen apple slices were determined. 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 deformation) indicated that the presence of sugars increased firmness of thawed/rehydrated tissue compared with apples treated in the same manner without sugar, however, untreated frozen controls were firmer than osmodehydrofrozen samples after thawing/rehydration, indicating that conditions used during osmotic dehydration (50 degrees C for 40 min) were 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 apple tissue indicated that much of the damage done to osmodehydrofrozen fruit membranes was done during pre-freezing treatment.
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