Ethylene Treatment of Bartlett Pears in Transit to Improve Ripening and Quality
Freshly harvested Bartlett pears ripen more uniformly and to better eating quality when treated with ethylene. The recommended treatment has been a 24-hour exposure to 100 ppm ethylene at 68 °F (20 °C). However, it is often difficult to delay fruit shipment by 24 hours early in the season due to high market demand. It is possible to treat fruit with ethylene gas in the transportation vehicle, but treatment at warm temperatures could be risky, as ripening would continue at a rapid pace during transit and storage at the warehouse. For these reasons, a study was undertaken to explore the response of Bartlett pear fruit to ethylene at lower temperatures. Laboratory studies showed that a 72-hour treatment at 45.5 °F (7.5 °C) or a 48-hour treatment at 50 °F (10 °C) gave the same ripening response as a 24-hour treatment at 68 °F (20 °C). A trial truck shipment was conducted in 1999. Fruit were shipped from California to Maryland in 2-1/2; days at 50 °F (10 °C) with 100 to 150 ppm ethylene. The shipped fruit ripened similarly to non-shipped fruit from the same load that were treated with ethylene in the laboratory at the University of California (UC), Davis. An additional trial shipment is planned for 2000.
Treatment of Bartlett pears with ethylene at harvest has been demonstrated to improve fruit ripening and eating quality (Agar et al. 1999; Puig et al. 1996) with positive results on pear marketing. Contrary to earlier beliefs, our recent data indicate that fruit from all growing regions in California can benefit from ethylene treatment, particularly the earliest harvests from each region, when marketed within 2 weeks of harvest. However, for many shippers, particularly with early season fruit, the 24 hours required for ethylene treatment at 68 °F (20 °C) is very difficult to achieve because of the intense demands from the market. Unfortunately, untreated, early season fruit does not move well through marketing channels because of its inability to ripen and, as a consequence, its poor quality. This can have a significant negative effect on later sales.
In response to this issue, we initiated research to determine if the ethylene treatment could be accomplished in the transportation vehicle, thereby eliminating the need for a delay in shipment. While the treatment had previously been conducted at 68 °F (20 °C), we knew that at that temperature, ripening would continue at a rapid pace during transit and following arrival at the warehouse. However, pear ripening is very slow at temperatures of 50 °F (10 °C) and lower. For this reason, we were interested in the fruit's ability to respond to ethylene at colder temperatures.
Our objectives were to test the response to ethylene treatment at 50 °F (10°C), 45.5 °F (7.5 °C), and 41 °F (5 °C). The rate of softening of fruit at 45.5 °F (7.5 °C) or 50 °F (10 °C), after ethylene treatment at the same temperature, was also determined.
Materials and Methods
Effect of Temperature on Response to Ethylene
Bartlett pears were harvested from a Sacramento orchard on July 21, 1998, at the start of the season. Fruit were exposed to ethylene at 68 °F (20 °C), 50 °F (10 °C), or 41 °F (5 °C) for 24 or 48 hours. A second group of fruit was harvested on August 14, 1998 from an orchard in Mendocino County. Fruit were exposed to 100 ppm ethylene at 68 °F (20 °C) for 24 hours; 50 °F (10 °C) for 48, 72, or 96 hours; or 41 °F (5 °C) for 48, 72, or 96 hours. Following the ethylene treatment, fruit were ripened at 68 °F (20 °C), and the progress of ripening was monitored for up to 10 days.
In 1999, Bartlett pears were harvested at the initiation of commercial harvest in Sacramento, Mendocino, and Lake Counties, California. Pears from each growing location were exposed to 100 ppm ethylene at 45 °F (7.5 °C), 50 °F (10 °C), and 68 °F (20 °C) for 24, 48, and 72 hours. Pear ripening was monitored during 7 days at 68 °F (20 °C) following treatment with ethylene. A separate group of fruit was treated with ethylene as described above and then held in air at the ethylene-treatment temperature (45.5 °F [7.5 °C] or 50 °F [10 °C]), and firmness and color were evaluated over a 12-day period.
Trial Truck Shipment
Shipment of a truckload of pears from Stockton, California, to Safeway in Upper Marlboro, Maryland, was arranged. UC Davis personnel monitored the forced-air cooling of the fruit in Stockton and measured fruit temperatures. Our goal was to cool the fruit to 50 °F (10 °C). After cooling, fruit and air temperature probes, relative humidity probes, and ethylene and carbon dioxide detector tubes were placed into three boxes of fruit. These boxes were packed in the center of the top third of three pallets. One pallet was placed in the nose of the trailer, one in the center, and one at the rear of the trailer. An additional two boxes of pears were taken to UC Davis for laboratory ripening. The entire trailer was filled with pears. A Department of Transportation approved cylinder of ethylene gas fitted with a protective case, and a slow-emitting valve was placed in the back of the trailer and turned on just prior to closing the truck doors.
In the laboratory at UC Davis, one box from the pear pallets was treated with 100 ppm ethylene at 50 °F (10 °C) for 48 hours then transferred to 68 °F (20 °C) for ripening. A second box was held for 48 hours in air at 50 °F (10 °C) then transferred to 68 °F (20 °C), where ripening was monitored for 6 days.
The truck shipment to Safeway took 2-1/2; days, and the truck was met by UC Davis personnel. The three boxes containing the temperature, ethylene, and carbon dioxide sensors were collected and transported to the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS), Horticulture Crops Quality Laboratory in Beltsville, Maryland. Fruit ripening was monitored at 68 °F (20 °C) using similar techniques to those used at UC Davis.
Results and Discussion
Effect of Temperature on Response to Ethylene
For pears harvested in Sacramento, fruit not treated with ethylene showed no signs of ripening during the 7 days at 68 °F (20 °C). Treatment with ethylene at 41 °F (5 °C) had little effect on softening, color, or ethylene production. At 50 °F (10 °C), the 48-hour ethylene treatment ripened at a similar rate to the fruit treated with ethylene for 24 hours at 68 °F (20 °C). Fruit treated at 50 °F (10 °C) for 72 hours ripened slightly faster than those treated for 48 hours. Fruit treated for 24-hours at 50 °F (10 °C) did not ripen satisfactorily during an 8-day ripening period. Treatment of fruit with ethylene at 45.5 °F (7.5 °C) for 72 hours was equivalent to treatment for 24 hours at 68 °F (20 °C), but treatment for 24 or 48 hours at 45.5 °F (7.5 °C) was not sufficient.
For pears harvested in Mendocino County, fruit not treated with ethylene showed no signs of ripening during the 7 days at 68 °F (20 °C). Treatment with ethylene at 41 °F (5 °C) for 48 hours had little effect on ripening. However, treatment for 72 or 96 hours significantly increased the rate of softening and development of yellow color. Treatment with ethylene for 96 hours at 41 °F (5 °C) stimulated ripening to the same extent as a 24-hour treatment at 68 °F (20 °C). At 50 °F (10 °C), the 48-hour ethylene treatment ripened faster than the fruit treated with ethylene for 24 hours at 68 °F (20 °C). Fruit treated with ethylene for 72 hours at 50 °F (10 °C) ripened even faster than fruit treated for 48 hours; however, there was no difference between fruit treated with ethylene 72 or 96 hours. At 45.5 °F (7.5 °C), fruit treated for 72 hours ripened similarly to fruit treated for 24 hours at 68 °F (20 °C).
Lake County fruit not treated with ethylene softened partially during the 7 days at 68 °F (20 °C). Fruit treated for 24 hours at 50 °F (10 °C) ripened similarly to fruit treated with ethylene for 24 or 48 hours at 68 °F (20 °C). Fruit treated for 48 hours with ethylene at 45.5 °F (7.5 °C) ripened similarly to fruit treated with ethylene at 68 °F (20 °C) for 24 or 48 hours.
These data indicate that a 48-hour treatment with ethylene gas at 50 °F (10 °C) and a 72-hour treatment with ethylene gas at 45.5 °F (7.5 °C) can substitute for a 24 hour-treatment at 68 °F (20 °C). Fruit from Lake County may only require a 2-day treatment at 45.5 °F (7.5 °C); however, a 3-day treatment would not be harmful. Treatment at 41 °F (5 °C) would require 96 hours, too long a treatment under most circumstances.
Fruit softening at 50 °F (10 °C) following treatment with ethylene at 50 °F (10 °C) was much slower than softening at 68 °F (20 °C), but was much faster than for fruit treated with ethylene and held at 45.5 °F (7.5 °C). The longer the fruit was treated with ethylene, the greater the firmness loss during subsequent holding in air at the same temperature. Very little change in firmness and even less change in color occurred at 45.5 °F (7.5 °C), even after 12 days. These data indicate that for longer transits or for fruit held in the warehouse for a long time after arrival, a 72-hour treatment with ethylene in transit at 45.5 °F (7.5 °C) is preferable to a 48-hour treatment at 50 °F (10 °C); the fruit will soften very little during subsequent holding. For transits up to 5 days, when fruit will be marketed promptly, treatment at 50 °F (10 °C) would be preferred as fruit would require less time to ripen upon warming.
Trial Truck Shipment
Fruit temperature upon truck loading ranged from 43.5 to 48 °F (6.4 to 9 °C). Air temperature within the boxes in the trailer during the 2-1/2 day shipment ranged from 47 to 50 °F (8.3 to 10 °C) at the start to 49.5 to 51 °F (9.7 to 10.6 °C) at the end of the shipment. The relative humidity quickly rose to between 95% and 98% and remained at this level throughout the transit.
The indicator tubes placed in the truck to indicate the carbon dioxide and ethylene concentrations in the trailer showed that carbon dioxide accumulated to 0.4% to 0.5% on average, and ethylene concentration ranged between 100 and 150 ppm.
Fruit arrived at Safeway with firmness in the 19- to 21-lb range with full green color. Fruit were transported to the retail stores within 1 to 2 days. Three boxes were collected from the nose, middle, and rear of the trailer and ripened at the USDA ARS facility in Beltsville, Maryland. The ripening characteristics were compared with fruit held under similar conditions with and without 100 ppm ethylene in the laboratory at UC Davis.
The loss in firmness and change in fruit color from green to yellow occurred most rapidly for fruit treated with ethylene at 50 °F (10 °C) for 48 hours in the laboratory. Fruit were eating-ripe within 3 to 4 days. The softening and color change of fruit treated with ethylene in transit was similar to, but slightly slower, than that of the fruit treated with ethylene in the laboratory. The fruit ripened in the laboratory without an ethylene treatment, after being held for 2-½ days in air at 50 °F (10 °C), ripened the slowest, reaching eating firmness after 5 days. The rate of ripening of the untreated fruit was faster than expected. Upon evaluation of the fruit, cuts, punctures, and scuffs were noted. This damage likely induced wound ethylene production within the packed box, resulting in a reasonable rate of ripening for the untreated fruit.
Overall, the in-transit ethylene treatment was a success. The fruit treated in-transit ripened similarly to those ethylene-treated in the laboratory. However, the speed of ripening of the untreated fruit indicates that the results are not completely conclusive. We plan to repeat this test in 2000. The personnel with Safeway were pleased with the test overall.
Agar, I.T., W.V. Biasi, and E.J. Mitcham. 2000. Temperature and exposure time during ethylene conditioning affect ripening of Bartlett pears. Journal Agriculture Food Chemistry 48:165-170.
Agar, I.T., W.V. Biasi, and E.J. Mitcham. 1999. Exogenous ethylene accelerates ripening responses in Bartlett pears regardless of maturity or growing region. Postharvest Biology Technology 17:67-78.
Puig, L., D.M. Varga, P.M. Chen, and E.A. Mielke. 1996. Synchronizing ripening in individual 'Bartlett' pears with ethylene. HortTechnology 6:24-27.
Elizabeth Mitcham, Tayfun Agar, and Bill Biasi(1) and Ken Gross and Wid Douglas(2)
(1)Department of Pomology, University of California, Davis
Davis, CA 95616
(2)USDA, ARS, Beltsville, MD
16th Annual Postharvest Conference, Yakima, WA
March 14-15, 2000