CREEP-BEHAVIOR OF TOMATO PERICARP TISSUE AS INFLUENCED BY AMBIENT-TEMPERATURE RIPENING AND CHILLED STORAGE

The influence of normal ripening and chilling stress on viscoelastic p roperties of tomato pericarp tissue were investigated by measuring cre ep behaviour of tissue from fruit stored at 22C (nonchilled) or 5C (ch illed) for 28 days, or at 5C for 16 days prior to transfer to 22C for an additional 12 days (prechilled). Creep compliance of tissue from al l treatments subjected to a constant shear stress of 150 Pa for 5 min was best represented by a 6-element Burgers model containing two discr ete Voigt-Kelvin units characterizing fast and slow rate viscoelastic properties. The magnitude of instantaneous elastic, viscoelastic and s teady-state viscous compliances each increased steadily and contribute d to the overall softening of nonchilled and prechilled tissues during ripening, but remained unchanged during chilling of tomato fruit. Inc reased fluidity of ripening tissues occurred at the expense of elastic ity, consistent with a decrease in molecular weight-size distribution of structural elements contributing to respective viscoelastic propert ies. The physico-mechanical changes in prechilled tissue preceded thos e in nonchilled tissue by several days, and occurred at a faster rate. The 6-element Burgers model defining the creep behaviour of tomato pe ricarp tissue was interpreted with respect to general plant cell wall structure and biochemical changes known to occur during ripening of to mato fruits. Multiple mechanisms of softening were thereby consolidate d into a single physico-mechanical model.