FIRMNESS MEASUREMENT OF FRESHLY HARVESTED DELICIOUS APPLES BY SENSORY METHODS, SONIC TRANSMISSION, MAGNESS-TAYLOR, AND COMPRESSION

A rapid nondestructive method for measuring apple texture using sonic vibrational characteristics of intact apples was tested on freshly harvested 'Delicious' apples from major U.S. production areas. Sonic transmission spectra and Magness-Taylor (MT) firmness were measured on whole apples and compression measurements were made on excised tissue. Two experienced Agricultural Marketing Service apple inspectors assessed each apple and assigned a ripeness score according to U.S. Dept. of Agriculture grades and standards inspection procedures (based primarily on texture). Sonic functions correlated significantly with ripeness scores, MT firmness, and forces to rupture or crush the tissue in compression. Ripeness scores were more closely correlated with the destructive firmness measurements than with sonic functions. However, sonic measurement has the advantage of being nondestructive, whereas MT and tissue compression are inherently destructive. Further research is needed to modify the Instrumentation and Sensing Laboratory's sonic technique to improve the prediction of apple firmness before it can be adapted for on-line sorting.