PHYSIOLOGICAL AND MECHANICAL-PROPERTIES OF KIWIFRUIT TISSUE ASSOCIATED WITH TEXTURE CHANGE DURING COOL STORAGE

Kiwifruit [Actinidia deliciosa (A. Chev) C.F. Liang et A.R. Ferguson] flesh firmness can decline by as much as 94% during fruit ripening. Th is phenomenon was investigated at the cellular level, with the aim of characterizing changes in the physiological condition and mechanical p roperties of cells. The tensile strength of kiwifruit outer pericarp t issue was measured, and low-temperature scanning electron microscopy w as used to examine the mode of cell failure at fracture surfaces. The propensity with which cells ruptured was determined by incubating tiss ue 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 be tween neighboring cells. Following tensile tests, an examination of fr acture surfaces indicated that cells from freshly harvested fruit had ruptured, exposing the cell interior. After 6 weeks of storage, neighb oring cells separated from each other without breaking open. With 23 a dditional weeks of storage at OC, 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 increa se in the plasticity of the cell wall.