Development of Ethylene Biosynthesis and Ethylene-induced Ripening in ‘d'Anjou’ Pears during the Cold Requirement for Ripening

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Abstract
Forty-six days at –1°C were required to stimulate ethylene synthesis in harvested ‘d'Anjou’ pears (Pyrus communis L.). The effect of exogenous ethylene on changes in quality parameters and organoleptic properties, and the effect of cold temperature on the development of ethylene production, were studied during the 46 days at –1°. Pears were held in 10 or 50 ppm exogenous ethylene at 20° after 30 or less days at –1°. Respiration increased from 8 to about 19 mg CO2·kg-1·hr-1 in fruit held in ethylene over a 12-day period, whereas fruit held in air showed only a slight increase. Firmness of fruit held in ethylene decreased from 66 to 12 N over 12 days at 20°. No significant change in firmness occurred in fruit held in air at 20°. The volume of extractable juice was unchanged in fruit held in air, but declined in fruit held in ethylene. The soluble solids content was not affected by ethylene treatment. Taste panel evaluation determined that fruit held 30 days at –1° then held 10 days in ethylene at 20° were ripe, sweet, and juicy, but fruit held in air were comparable to fruit never held at 20°. Pear flesh disks cut from fruit held 21 days at –1° did not convert exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, but did so when cut from fruit held 41 or 50 days at –1°. Only with the onset of ethylene production was endogenous ACC detectable in pear flesh. During the 46 days at –1° required for initiation of ethylene production, the capacity to convert ACC to ethylene developed first, followed by production of ACC and ethylene.

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