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.
Keywords kiwifruit; Actinidia deliciosa; firmness;
temperature; coefficient; storage
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