A Portable Device for the Bioyield Detection to Measure Apple Firmness

The bioyield phenomenon occurs to the apple fruit when it is subjected to compressive loading (i.e., compression or puncture), which causes cell failure without disintegrating the macro tissue structure. Force at the bioyield point is useful for nondestructive evaluation of fruit firmness. A portable device, which consisted of an off-shelf force meter, an actuation driver, and control unit, was developed for detecting bioyield force from apples. Experiments were performed on 'Golden Delicious' and 'Red Delicious' apples to determine the correlation between bioyield force measurement and the standard Magness-Taylor (MT) firmness test, evaluate the sensitivity of bioyield measurement to changes in firmness over time, and quantify firmness variation over the fruit. Bioyield force correlated with MT force with R2 values of 0.835, 0.654, and 0.751 for 'Golden Delicious,' 'Red Delicious,' and the pooled data, respectively. Bioyield force was as sensitive to firmness change over time as MT force (R2 = 0.990) for apples that underwent accelerated softening. The bottom section (the calyx end) of the apple was significantly firmer than the middle and top sections of the fruit. Moreover, the south face or sunny side of the apple was significantly firmer than the north face or shady side of the fruit. Hence, two bioyield measurements should be performed at opposing sides of an apple around the equator to obtain the average firmness value for the fruit. The bioyield device is useful for measuring the firmness of apples in the orchard and during postharvest handling, and for monitoring fruit conditions during storage.