COMPARISON OF 4 NEW DEVICES FOR MEASURING KIWIFRUIT FIRMNESS

Four new methods of measuring kiwifruit (Actinidia deliciosa) firmness which have been developed in New Zealand have been compared and evalu ated. They are: (1) ''SoftSense'', developed by HortResearch, Ruakura, using characteristics of a fruit's bounce to calculate ''dwell time'' which varies with fruit firmness; (2) ''Softness Meter'', developed b y Massey University, Palmerston North, using the rate at which the fru it surface is deformed by a known load; (3) ''KIWIPOKE'', a hand-held wand, developed by Industrial Research Limited, Auckland, using charac teristics of a small ballistic collision against the fruit to give a f irmness value calibrated to equate to a penetrometer reading; and (4) ''Massey Twist Tester'', a destructive test, developed by Massey Unive rsity, Palmerston North, measuring the force required to rotate a smal l plate within the fruit flesh. Using prototypes of the three non-dest ructive devices, we repeatedly tested the same fruit as they softened during coolstorage. Additional fruit were used to compare fruit firmne ss measured by the four new devices with results obtained using a stan dard Effegi penetrometer. The ability of the devices to differentiate between different lines of fruit, and the ease of operation are discus sed. Although it is clear that a non-destructive method to measure fru it firmness will have considerable advantages, at present none of the devices tested can be recommended unreservedly for general use. Howeve r, all these devices are undergoing further development as a consequen ce of this and other evaluations.