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- Author or Editor: R.E. Bir x
- Journal of the American Society for Horticultural Science x
Abstract
Intact, mature apple (Malus pumila, Mill. cv. Richared Delicious) fruit exhibited 2 exotherms, at −2.1 ± 0.1°C and at −4.7 ± 0.3° during freezing. Freezing only through Exotherm 1 caused fruit softening. Freezing to inception of Exotherm 2 caused increased softening, and also slightly increased ion leakage. Freezing to termination of Exotherm 2 produced a 3rd increment of softening, greatly increased ion leakage, and reduced respiration. Only with freezing through termination of Exotherm 2 did visual injury symptoms occur; these symptoms were evident several hours after thawing, and apparently reflected lethal injury to the fruit. Injury was no greater after 3 months than after 1 month of storage at 0° following freezing.
Abstract
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.