Comparison of a non-destructive acoustic method with an intrusive method for firmness measurement of kiwifruit

A non-destructive acoustic measurement and an intrusive method for determining tissue firmness were compared to assess the textural properties of kiwifruit (Actinidin deliciosa (A. Chev.) Liang et Ferguson, cv 'Hayward'). Kiwifruit were treated with ethylene to initiate development and thereby provide a range of tissue textures. Individual fruit were subjected to pulsed sound, generated by a function synthesizer. The elapsed time for sound transmission through fruit tissues, which was measured by a storage oscilloscope (non-destructive method), increased as a function of the duration of ethylene treatment. Transverse slices of comparable kiwifruit tissue (2 cm in thickness) were placed on a stage and a conical probe attached to a load sensor was inserted to a depth of 5 mm. Tissue firmness was related to the maximum force required to achieve the constant strain (intrusive method). The results obtained by acoustic measurements were in good agreement with those achieved by the more conventional intrusive method, demonstrating that sound can be applied for the evaluation of firmness of intact kiwifruit. (C) 1997 Elsevier Science B.V.