ALTERNATIVE FIRMNESS TESTING METHODS FOR FRUIT AND VEGETABLES

摘要

This paper describes a new method of determining firmness, and presents results of tissue crush strength for kiwifruit. For over sixty years the fruit penetrometer has been used as the standard for assessing the firmness of fruit, despite serious misgivings about its repeatability, variability between operators, and its correlation with textural properties. Recently an alternative mechanical test, known as the Massey Twist Tester, has been developed in which a blade is inserted into the fruit and rotated. The test can measure tissue crush strength at any depth, and does not require removal of the skin prior to testing. It is as fast as the penetrometer and damages a smaller area of the fruit, so that several measurements can be conducted on the samefruit to assess variation within individual fruit. The tester can be used on a range of fruit and vegetables, including apples, potatoes, and kiwifruit, throughout the growth and post-harvest lifetime of the crop. Results of measurements on kiwifruit harvested from two orchards are presented. The flesh and columella strengths were measured throughout storage. These showed that the tester can be used to measure changes in the firmness of the tissue from harvest to the end of the storage life. For thirtysamples, typical values ranged from 402 ± 12 kPa and 211 ± 3 kPa at harvest for the columella and flesh respectively, falling to 14.7 ± 0.6 kPa and 25.0 ± 0.5 kPa after 194 days storage at 1°C. In comparison penetrometer values fell from 82.5 ± 1.5 N (8.38 ± 0.15 kg) to 3.8 ± 0.3 N (0.39 ± 0.03 kg). The error in the penetrometer reading was considerably greater than the twist tester at low firmness values. The twist tester is therefore a low cost alternative to the penetrometer, which offers researchers and growers a useful tool to enhance their assessment of the state of fruit and vegetables, and a commercial model is currently under development.