Wendy C. Schotsmans

Determination of the optimal pre-storage delayed cooling regime to control disorders and maintain quality in ‘Honeycrisp’TM apples

Summary Several pre-storage time (0, 1, 2, 4, and 6 d) and temperature (3.5º, 10º, 15º, 20º, 25º, and 30ºC) delayed cooling (DC) treatments were tested on harvested ‘Honeycrisp’TM apples to determine which combination was optimal for reducing soft scald and low temperature breakdown (LTB), while maintaining the highest fruit quality [i.e., firmness, minimal mass loss, titratable acidity (TA), soluble solids content (SSC), absence of rot, and minimal skin greasiness] after 4 months of refrigerated air (RA) storage. Fruit were harvested from three separate Annapolis Valley (Nova Scotia) orchard sites in 2006 and in 2007. Multiple linear regression and surface response curves showed that fruit firmness and SSC generally increased throughout the DC treatment, but were affected curvilinearly by temperature, reaching a maximum at approx. 15ºC, then declining. Loss of fruit mass was positively related to a (day temperature2) interaction, indicating that it increased synergistically the longer and the warmer the DC treatment. Fruit acidity was affected only by temperature, with the highest TA values at approx. 15ºC, then declining at higher DC temperatures. Multiple logistic regression and surface responses demonstrated that the incidence of soft scald declined curvilinearly the longer and the warmer the DC treatment, while LTB declined curvilinearly with increasing DC temperature only. A positive (day2 temperature2) interaction indicated that fruit greasiness increased non-linearly as the duration and temperature of DC increased. Collectively, these results show that both soft scald and LTB were suppressed or eliminated by a DC regime of 25ºC for 1 – 2 d, or 30ºC for 1 d, without incurring a major reduction in fruit quality.

Temperature kinetics of texture changes in Actinidia chinensis ‘Hort16A’ during storage

Summary Kinetic models describing softening during storage of ‘Hort16A’ kiwifruit at different temperatures are useful tools for the development of pre-conditioning and ripening protocols. Magness-Taylor firmness, compression firmness, and stiffness were assessed for their usefulness as tools to monitor and predict softening of ‘Hort16A’ kiwifruit during storage at six storage temperatures ranging from 1.5°C to 25°C. Softening showed the same general biphasic pattern for all three measures, similar to that for green ‘Hayward’ kiwifruit, and could be described using simple exponential decay models. Magness-Taylor firmness reached an asymptotic minimum rapidly, whereas compression firmness and stiffness still decreased measurably at the end of storage. The rate of softening increased with temperature, and the biphasic pattern of the softening curves became more pronounced with later harvest dates. The effects of orchard, cane, and fruit position on parameter estimates such as rate constant, activation energy, and asymptotic firmness value, were negligible.