Richared Delicious’ apple (Malus pumila, Mill.) fruit tissues exhibited 2 distinct freezing points (exotherms) during freezing. Exotherm 1 occurred at −1.5° to −2.2°C and Exotherm 2 occurred between −4.2° and −7.7°C. The inception temperature of Exotherm 2 varied considerably both within a fruit and among different fruits. During fruit maturation from August to October, no significant change in freezing pattern occurred, although soluble solids increased 55% during the period tested. Inception of Exotherm 1 caused no distinct change in physical properties of cortex tissue. Inception of Exotherm 2 was associated with significant softening and increased ion leakage from the tissue. Just beyond termination of Exotherm 2, the tissue lost its capacity to exhibit multiple exotherms on thawing and refreezing, and underwent massive changes in firmness, ion leakage, and respiration; it was concluded that freezing to this point was lethal to the tissue. The concept that tissue injury is related to specific points on the freezing curve of apples is presented.
Received for publication September 8, 1972.
Present address: Extension Horticulturist, Pinellas County Agricultural Department, Largo, Florida.