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New Zealand Journal of Crop and Horticultural Science abstracts

Short communication
Firmness-temperature coefficient of kiwifruit

PETER B. JEFFERY
NIGEL H. BANKS

Department of Plant Science
Massey University
Palmerston North, New Zealand

Abstract Changes in flesh firmness of kiwifruit (Actinidia deliciosa) in response to fruit temperature were characterised for fruit removed from storage at 0deg.C at a range of levels of firmness generated by the normal softening associated with fruit ripening. Firmness was less after 24 h equilibration to 20deg.C (f2) than when measured immediately after removal from coolstorage (f1). Fruit regained firmness upon recooling to 0deg.C (f3) which, as a proportion of f1, occurred to greater extent in soft fruit than firmer fruit which were in the rapid phase of fruit softening. Thus, the firmness temperature coefficient (kfT, %/deg.C, a measure of the percentage change in firmness caused by a given temperature change) of kiwifruit was itself shown to be a function of flesh firmness. It is suggested this resulted from contributions from two processes: a direct, reversible, physical effect that was a linear function of temperature; and in the phase of rapid fruit softening, an irreversible, physiological loss of firmness associated with stimulated fruit ripening at elevated temperature. Fitted functions relating kfT to f1 and f2 were used to develop expressions which permit approximate calculation of f2 given f1 and vice versa. These expressions could be used to link more effectively research data obtained at 20deg.C with commercial assessments of fruit firmness made on fruit at 0deg.C e.g., by correcting estimates of time required for fruit to soften to commercially important firmness thresholds.