A New Bioyield Tester for Measuring Apple Fruit Firmness

The objective of this research was to evaluate a newly developed bioyield tester for measuring fruit firmness and its measurement variability within individual fruit. The specially designed soft tip bioyield probe was coupled to a handheld digital force gauge that was mounted on a tabletop motor-driven stand. Bioyield force (or Fbyst = force to cause bioyield by the soft tip probe) and Magness-Taylor (MT) firmness were measured on Delicious and Golden Delicious apples under different storage conditions and/or treatments. The correlation between MT firmness and Fbyst ranged from 0.62 to 0.81 with a standard error between 5.2 N and 6.7 N. Bioyield force decreased at about the same rate as that for MT firmness when apples were stored in refrigerated air at 5.C. When fruits were kept at room temperature (24.C), the percent decline in Fbyst over the test time period was less than that in MT firmness. Bioyield force measurements within individual apples were 42.6% to 46.8% more variable than MT firmness, as measured by the coefficient of variation. Since the bioyield tester does not degrade apple fruit, it will be useful for measuring and monitoring fruit firmness during growth, harvest, and postharvest operations.