Fruit firmness measurement techniques- a new approach
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Department of Agricultural Engineering, Massey University, Palmerston North, New Zealand
Publication date: 2021-08-20
Int. Agrophys. 1994, 8(3): 461–466
The Massey University Twist Tester is a device for testing fruit. It is a possible replacement for the traditional penetrometer. The device measures the moment (torque) required to shear fruit tissue, and this can be converted to an estimate of the crushing strength of the tissue. It is capable of measuring properties as a function of radial depth, and does not require prior specimen preparation, such as peeling the skin from the test area. Typical results of experiments on apples and kiwifruit are presented, including measurements on kiwifruit columella in situ during storage. The output from the Twist Tester was related to the results obtained from conventional penetrometer measurements. The question of whether or not the Twist Tester would be an improvement on the conventional test is discussed, and the basis for making this decision is considered briefly. It is argued that a comparison of standard errors is not an adequate method, and that an alternative statistical method is required. In addition, further refinements of the system are in progress and some of these are also discussed. In particular, new developments are described to remove the operator effect, and to enable the shape of the load-time curve to be established, so that an estimate can be made of the 'bioyield' of the fruit. Examples of the resulting curves are presented. For Granny Smith apples the stored for 130 days Crush Strength values were 490 ±10 kPa, while the Bioyield was 422±9 kPa.