STIFFNESS-TEMPERATURE COEFFICIENT FOR 'HORT16A' KIWIFRUIT MEASURED BY ACOUSTIC FIRMNESS

A fruit’s textural properties are influenced by its temperature at the time of measurement. Texture assessment therefore requires either equilibrating the fruit to a constant temperature, or recalibrating the measurement to account for the temperature effect. In this work the firmness of kiwifruit flesh (Actinidia chinensis cultivar ‘Hort16A’) measured as acoustic stiffness was characterised as a function of storage time and fruit temperature at measurement. Seven grower lines of fruit (5 conventional and 2 organic) were stored for 12 weeks at 1.5°C. At two week intervals fruit stiffness within each grower line was assessed at the storage temperature (s₁), then at 20°C (s₂) and on return to storage at 1.5°C (s₃) allowing 24 hours after each temperature change for the fruit temperature to equilibrate. The initial measurement (s₁) indicated changes in stiffness due to ripening in storage, while the difference (s₂ – s₁) represented the change in texture as a result of both the temperature change and the more rapid ripening at the higher temperature. The differences (s₂ – s₃) and (s₁ – s₃) provided further information on these dual effects of temperature. The data obtained permitted the formulation of a temperature correction model to estimate stiffness measurement at 1.5°C as a function of fruit temperature at the time of measurement. Fruit measured at temperatures intermediate to 1.5 and 20°C were used to validate the correction model.