Controlled Reduction of Water Activity in Celery: Effect on Membrane Integrity and Biophysical Properties

Experiments were designed and executed to identify the mechanism responsible for irreversible texture changes in dehydrated and rehydrated celery tissue. Results showed that these changes remained reversible as long as dehydration did not reduce water activity (a w ) below 0.987. Water removal below this level resulted in a partial irreversible loss of rigidity as measured by modulus of elasticity. Correlation of chemical and physical data with electron‐micrographs of tissue ultrastructure suggested that expansion‐ induced lysis of the plasma and tonoplast membranes during rehydration was the responsible mechanism when tissue samples were dehydrated to a w between 0.920 and 0.987. At very low a w (0.25), samples showed a total loss of rigidity that correlated with observed damage to cell walls.