Effects of Ethylene on the Ouality of Fruits and Vegetables

Use of Ethylene As described by Abeles (1973), interest in ethylene dates back to at least 1864, when Girarden reported that gas from gas lamps caused injuries and defoliation of trees. In 1901, Neljubov identified ethylene as a component of the illuminating gas. Crocker and Knight reported in 1908 that ethylene and illurninating gas induced same physiological responses in flowers. In 1912, Sievers and True showed that color development of lemon was induced by the gaseous product of a kerosene heater. Gane (1934) showed that the gaseous product from the heater contained ethylene, and Denny (1924) demonstrated that coloration of lemons can be induced with ethylene. Harvey (1925; 1928) conducted a comprehensive study on the use of ethylene to blanch celery and to ripen bananas, pineapples, dates, persimmons, tomatoes, hard pears (probably winter pears), apples, muskmelons, honeydew melons, casaba melons, mangoes, avocados, papayas, custard apples, and jujubes. Harvey indicated that loss of chlorophyll, development of ripening color, softening of tissue, removal of tannins, development of flavor, increase in sweetness, and early proteoclastic enzyme activity occurred when these fruits were exposed to ethylene. The amount of endogenous ethylene produced by plant tissue generally increases autocatalytically at a specific stage of growth or development to initiate a physiological response. Application of exogenous or supplemental ethylene to a plant tissue prior to the autocatalytic increase will generally initiate the physiological response as well as the increase in ethylene production. Today, supplemental ethylene is commonly used to induce ripening of avocado, bananas, mangoes, tomatoes, and honeydew melons; degreen citrus fruits (except lime) for fresh market; and induce softening of freestone peaches and pears destined for processing. Mature-green tomatoes are treated at shipping point with 100 ppm, and in some instances 1,000 ppm, ethylene for 24-48 hr at 20-25oC and 85-909" relative humidity (Gull, 1981). Although 1-10 ppm ethylene is sufficient to induce ripening, higher concentrations are used to ensure treatment of fruits located in the center of the container and pallets, and to compensate for leakage of ethylene out of the treatment rooms. Because high levels of cariron dioxide inhibit ethylene action on ripening, the recommended treatment procedure is to keep the CO2 from accumulating beyond 49'o during treatment, and to keep it below 2 9o after the treatment. Honeydew melons will ripen with 10 ppm ethylene, but commercially they are treated with 1,000 ppm ethylene for 18-24 hr (Redit, 1969). The fruits are generally examined after 24 hr of ethylene treatment and, if adequate ripening is not noted, may be given a reoeated ethvlene treatment.