RELATIONSHIP OF SONIC RESONANT-FREQUENCY TO COMPRESSION TESTS AND MAGNESS-TAYLOR FIRMNESS OF APPLES DURING REFRIGERATED STORAGE

Apple growers and packers need to measure the firmness of their fruit to make management decisions, preferably using nondestructive measurem ents so the tested apples remain marketable. 'Delicious', 'Golden Deli cious', and 'York Imperial' apples from Pennsylvania were stored at 0- degree-C in air for 0 to 8 months. The sonic transmission power spectr um, compression force/deformation (F/D) curves, and Magness-Taylor (MT ) firmness were recorded after storage. Resonant frequencies were dete rmined from sonic data and used to calculate stiffness coefficients. R esonant frequencies, stiffness coefficients, compression measurements, and MT firmness decreased during storage. Resonant frequencies and st iffness coefficients were most highly correlated with compression slop e, then area, then maximum force. Correlation coefficients decreased p rogressively from 'Golden Delicious' to 'Delicious' to 'York Imperial' apples, the same progression as their deviation from spherical symmet ry and their characteristic extent of textural change during ripening and storage.