717 PB 423 ETHYLENE DEGASSING OF GRAPEFRUIT

Early-season fresh citrus are routinely exposed to ethylene to trigger chlorophyll degradation (degreening) in the peel and thus improve fruit color. Recent questions about whether ethylene is trapped in the fruit by subsequent waxing have sparked interest in characterizing ethylene exchange. Internal gas samples of mature, pesticide-free `White Marsh' grapefruit were taken through septa of silicone rubber on electrical tape affixed 10 the blossom end. Gassing of the fruit in a degreening room (10 ppm ethylene) required about four hours lo reach equilibrium while degassing was completed in less than two hours and was not affected by location of the fruit in a 0.680 m 3 pallet bin. Waxing with a water-soluble wax immediately following ethylene exposure increased the time for complete degassing to over 48 h. Surface gas exchange protiles were prepared by sequentially analyzing the same fruit after: (1) harvest, (2) 22 h exposure to 10 ppm ethylene, (3) exposure to ethylene and washing with an ionic cleaning surfactant, and (4) exposure to ethylene and waxing. Glass cells with interfacing silicone rubber o-rings (23 mm diam.) were strapped to the fruit following each treatment. Ethylene emanation was measured by sampling the cells which were capped 15 m after removal from ethylene. Water and CO 2 were measured by flow-through cells following ethylene analysis. Ethylene emanation following the initial exposure was the same for the stem end and midsection and two fold greater than the blossom end. Washing increased the rate of emanation five fold for the stem end and about 2.5 fold for the midsection and blossom end. Waxing reduced emanation by nearly four fold for the midsection and blossom end, but only 30% for the stem end. Water loss was increased about 40% by washing, reduced about 30% by waxing, and was primarily through the stem end. Stem-end CO 2 exchange doubled upon waxing.