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Low temperature conditioning prevents loss of aroma-related esters from ‘Nanguo’ pears during ripening at room temperature

Zhou, Xin, Dong, Ling, Li, Rui, Zhou, Qian, Wang, Jun-wei, Ji, Shu-juan
Postharvest biology and technology 2015 v.100 pp. 23-32
1-aminocyclopropane-1-carboxylic acid, Pyrus ussuriensis, alcohol dehydrogenase, alcohols, ambient temperature, aminocyclopropanecarboxylate oxidase, chilling injury, esters, ethylene, ethylene production, gene expression, linolenic acid, lipoxygenase, odors, pears, refrigeration, ripening, shelf life, signal transduction
Refrigeration delays ripening and reduces decay of pear fruit, but this benefit is offset by a loss of aroma when the fruit is then ripened at room temperature. Low temperature conditioning (LTC) has been used to alleviate chilling injury (CI) of fruit, however, its effect on aroma remains unknown. Pear fruit cv. ‘Nanguo’ (Pyrus ussuriensis Maxim.) were subjected to LTC (namely, exposed to 10°C, decreased by 1°C every 3 days to 5°C, then decreased by 1°C per day to 0±0.5°C) and changes in aroma-related esters, levels of fatty acids, the activity and gene expression of alcohol acyltransferase (AAT), lipoxygenase (LOX), and alcohol dehydrogenase (ADH) were investigated. Changes in the activity and gene expression of enzymes involved in ethylene biosynthesis and the expression of genes involved in ethylene signal transduction were also studied. Significantly higher ester contents and levels of linoleic and linolenic acids were found in LTC-treated fruit. Levels of PuAAT1, PuLOX1, and PuADH3 transcripts were promoted by LTC treatment and the activity of AAT, LOX and ADH was higher in LTC-treated fruit during the shelf-life at room temperature. The increased levels of the expression and activity of 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO) contributed to the elevated ethylene levels in LTC-treated fruit. The expression of genes involved in ethylene signal transduction (PuETR1 and PuCTR1) was also promoted by LTC treatment. Treatment with LTC effectively prevented the loss of aroma-related esters from refrigerated ‘Nanguo’ pears and possible mechanisms were discussed.