TOMATO COLOR DEVELOPMENT FOLLOWING EXPOSURE TO ETHYLENE AT HIGH TEMPERATURES

Tomato (Lycopersicon esculentum L. Mill.) fruit ripen ing is reversibly inhibited at high temperatures (30C and above). In this study, the ability of tomatoes to respond to ethylene treatment at high temperatures in terms of red color de velopment was investigated. Mature green (MG) Agriset 761 tomato fruit were exposed to 100 ppm ethylene at 20,25,30,35, or 40C and 95% relative humidity (RH) for 24,48, or 72 hr, then transferred to air at 20C for ripening. Tomatoes exposed to eth ylene at high temperatures for 24 hr showed little difference in color development compared to those exposed to ethylene at lower temperatures. Increasing the duration of ethylene/high temperature treatment to 48 and 72 hr at 35 or 40C inhibited subsequent red color development at 20C while prior exposure to 30C stimulated color development. These results suggest that tomatoes can perceive ethylene at high temperatures, but are slow to respond in terms of color development until trans ferred to a lower temperature. Tomatoes are produced in Florida over about a ninemonth season from late September through June, with the ar eas of production moving from northern Florida in the early fall to southern Florida in the winter, and the reverse occur ring in the spring. Tomato is the highest valued vegetable Florida Agricultural Experiment Station Journal Series No. N-01185. grown in Florida, accounting for about 30 percent of the total production value among major Florida vegetables during the 1993-1994 season (Freie and Pugh, 1995). The average value of the Florida fresh market tomato crop for the years 19891994 was $574.3 million (Freie and Pugh, 1995). About 85% of the tomatoes produced in Florida are har vested when green and ripened after harvest (Fla. Tomato Comm., 1995). The harvest operation usually begins in midmorning, and harvested tomatoes are accumulated in field bins or gondolas before transport to the packinghouse. Har vested tomatoes are usually held under shade cover until they are run over the packingline. The packinghouse operations are typically begun in the afternoon and continue until that day's harvest has been processed. The first step in the pack inghouse operation is the dumping of tomatoes from the field bins or gondolas into a heated, chlorinated water receiv ing tank. The water in the receiving tank is maintained 5C higher than the highest fruit pulp temperatures to avoid infil tration of decay organisms into the tomatoes (Sherman et al., 1981). The tomatoes are then washed, treated with waxes or other food grade coatings, graded, sized, packed in shipping containers, and the containers stacked on pallets. Mature green tomatoes are commonly treated with sup plementary ethylene at about 20 to 21C and 85 to 95 percent RH in ripening rooms to provide for faster and more uniform ripening (Hardenburg et al., 1986). Tomatoes are typically held in the ripening rooms for 1 to 3 days, with daily inspec tions to determine when almost all the fruit have begun to de velop red color. Although the ripening rooms used to treat MG tomatoes with ethylene are maintained at 20 to 21C, the pulp temperature of fruit placed in these rooms may be well over 30C (Brecht and Sargent, unpublished). Tomato ripen ing rooms are generally not designed for efficient cooling of the tomatoes (Sherman and Talbot, 1986). Thus, it is likely that tomatoes may remain above 30C for a substantial time while being treated with ethylene in ripening rooms. After re moval from ripening rooms, tomatoes are usually shipped to market in refrigerated trucks at about 12 to 15C. Tomato color development during ripening and posthar vest storage is influenced by many factors. Under normal dis268 Proc. Fla. State Hort. Soc. 108: 1995. tribution and storage circumstances, however, color development depends for the most part on temperature, ini tial maturity and storage duration (Tijskens and Evelo, 1994). Tomato fruit ripening, as indicated by red color (lycopene) development, is reversibly inhibited at temperatures above 30C (Atta-Aly, 1992; Cheng et al., 1988). For example, 'Sun ny' tomato fruit at the breaker stage were held at 30, 35, or 40C and then transferred to a ripening room at 20C. After transfer, increasing delays in red color development were ob served that corresponded to the temperature and time of ex posure to high temperatures (Atta-Aly and Brecht, 1995). When Cheng et al. (1988) treated MG tomato fruit with ethylene, stored them at 37C for 3 or 7 days, then ripened them at 21C, red color development was delayed by the high tem perature treatment, but developed rapidly when the tomatoes were transferred to 21C. The delay in color development at high temperatures is thought to be caused by inhibition of ly copene biosynthesis or that of its precursors phytofluene and phytoene (Yakir et al., 1984). Incubation of 'Rutgers' tomato fruit at 34C or above also resulted in a marked decrease in rip ening-associated ethylene production (Biggs et al., 1988). Florida often experiences temperatures greater than 30C during parts of the tomato harvest season, especially early and late in the season. When harvested fruit are left in the field or outside the packinghouse, they may warm substantially. Tem peratures up to 49C have been measured in tomato fruit that were exposed to sunlight for 1 hr (Bartz, 1995). High temper ature exposure also occurs when tomato fruit are attached to the plant. Midsummer, field-grown tomatoes in warm grow ing regions are often subjected to high temperatures during portions of the day, resulting in inhibition of lycopene devel opment, but lower temperatures at night permit lycopene for mation during part of the 24 hours on most days (MacGillivray, 1934). In Japan, undesirable color changes from green to yellow (abnormal coloring) on the surface of 'Momotaro' tomato fruit were observed after harvest due to high temperatures (Maezawa et al., 1993). Yakir et al. (1984) also reported that processing tomatoes left to ripen at high temperatures had undesirable quality as indicated by poor color development. High temperature exposure of fruits and vegetables can also have beneficial effects. Postharvest heat treatments have been developed or proposed for insect disinfestation or dis ease control of several fruits, including mangoes, papayas and tomatoes (Couey, 1989). For example, holding inoculated MG and pink tomatoes for 3 days at 38C completely inhibited decay caused by Botrytis cinerea, one of the main postharvest pathogens of tomatoes in Israel (Fallik et al., 1993). Heat treatments have also been reported to protect against physio logical disorders such as chilling injury and to be useful for regulation of ripening (Klein and Lurie, 1992; Paull, 1990). Mature green tomatoes held for 3 days at 36, 38 or 40C, then exposed to 2C for 3 weeks did not develop chilling injury, but ripened more slowly than freshly picked fruit (Lurie and Klein, 1991, 1992). Considering the potential positive and negative effects of high temperature exposure on tomato fruit, we wondered how lack of efficient cooling prior to being placed in ripening rooms might be affecting the response of MG tomatoes to ethylene treatment. The ripening response of tomatoes in terms of color development following exposure of MG fruit to ethylene at high temperatures has not previously been inves tigated. Therefore, the objective of this study was to investi gate the influence of high temperatures on the effectiveness of exogenous ethylene in promoting MG tomato fruit ripen ing as measured by color development. Materials and Methods Mature green, large size 'Agriset 761' and 'Sunny' tomato fruit were obtained from a commercial packinghouse in the Ruskin area on the day of harvest, or picked from plots at the IFAS NFREC, Quincy, transported to Gainesville, and stored overnight at 8C. The tomatoes were re-graded, and fruit that were wounded or showing red color development were dis carded. Three buckets, each containing 30 fruit, were placed at each of the following five temperatures: 20, 25, 30, 35 or 40C at 95% RH and treated with 100 ppm ethylene. Ethylene was applied by mixing air and ethylene at constant pressure in a flow through system via a gas mixing board utilizing nee dle valve flowmeters. High RH was maintained by bubbling the gas mixtures through water before entering the storage chambers. After 24, 48 or 72 hr, the fruit were moved to air at 20C and 95% RH for ripening. While at the ripening temperature (i.e. 20C), the color of three, 10-fruit replicates of tomato fruit per time-temperature combination was measured daily for up to 11 days using a Hunterlab Color Quest colorimeter (Hunter Assoc, Reston, Virginia) fitted with a 2.5-cm viewing port and aided by a Ze nith 286 computer. Light reflected by the specimen is picked up by a three-element optical sensor in the colorimeter, the output from which is converted into color specifications which are presented in alphanumeric form as three parame ters: L*, a measure of lightness on a scale of 0 (black) to 100 (white); a*, which denotes greenness when negative and red ness when positive; and b*, denoting blueness when negative and yellowness when positive (Hobson et al., 1983). The hue was calculated from a* and b* values as follows: hue = tan]b*/ a*, representing the shade of color. Chroma was calculated as follows: chroma = (a*2+b*2)1/2, representing the purity of col or of a specific hue. The surface color of the tomatoes was measured at random spots near the blossom end of each fruit (Hobson et al., 1983). The results of these experiments were analyzed as a completely randomized design using Analysis of Variance (ANOVA) and Least Significant Difference (LSD) values calculated at the 5% level using the Statistical Analysis System (SAS, 1986). The results presented here are for 'Agriset' fruit; results obtained with 'Sunny' fruit were similar.