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The relationships between cellular characteristics of cortical tissue from `Braeburn' apple fruit (Malus domestica Borkh.) that had been harvested at two maturities and changes in texture that occurred during storage at 0C were studied. Tensile tests were used to measure adhesion between neighboring cells, and turgor pressure was manipulated to determine the pressures required to burst cells. Apples of advanced maturity became mealy during cool storage, while those of less advanced maturity did not. Mealiness was associated with low adhesion between neighboring cells, and a relatively high resistance to cell rupture.
Kiwifruit [Actinidia deliciosa (A. Chev) C.F. Liang et A.R. Ferguson] flesh firmness can decline by as much as 94% during fruit ripening. This phenomenon was investigated at the cellular level, with the aim of characterizing changes in the physiological condition and mechanical properties of cells. The tensile strength of kiwifruit outer pericarp tissue was measured, and low-temperature scanning electron microscopy was used to examine the mode of cell failure at fracture surfaces. The propensity with which cells ruptured was determined by incubating tissue discs in hypertonic and hypotonic solutions, and water potentials, osmotic potentials, turgor pressures, and tissue density were measured. An initial rapid reduction in flesh firmness—from 80 to 27 N during 6 weeks of storage at 0C—was related to a reduction in the adhesion between neighboring cells. Following tensile tests, an examination of fracture surfaces indicated that cells from freshly harvested fruit had ruptured, exposing the cell interior. After 6 weeks of storage, neighboring cells separated from each other without breaking open. With 23 additional weeks of storage at 0C, flesh firmness decreased from 27 to 5 N. The final softening stage was associated with an increase in the proportion of cells that separated at the middle lamella and an increase in the plasticity of the cell wall.