Calculating the cost of citrus degreening

Unlike most fruits, the color of the citrus fruit skin does not correspond with internal ripeness, but more with the climatic conditions. Lemons are often picked when they have a minimum of 20% juice and reach 58 mm diameter. The fruits are mature but still green at this stage. Leaving fruit on the tree, growers would have to wait up to two months longer before the desired consumer color is achieved. This can reduce time available for transport, increase the likelihood of bruising, and cut profits. Hence, citrus is harvested early, while it is still green, and degreened artificially. When left on trees to ripen naturally, lemons typically turn yellow—and grapefruits reddish-yellow—by the end of October or mid-November. In Spain, 40% of the lemons (Citrus macrophylla) are mature enough for harvest by mid-September. Fruits harvested at this time, the beginning of the season, must be artificially degreened. In contrast, fruits harvested later in the season are already developing their characteristic colors, and need little help achieving consumer-desired traits. Degreening advantages and disadvantagesDuring degreening, ethylene gas is used to break down chlorophyll and encourage the synthesis of carotenoids, which make the peels yellow and orange. However, ethylene, a phytohormone, triggers many other ripening processes besides a change in color. Changes in texture, flavor, and taste are common. The rate of alterations will depend on environmental conditions such as temperature, relative humidity, and concentrations of CO2 and O2. Some of the changes that occur due to ethylene are an increase in respiration and senescence, which can lower fruit quality. In citrus fruits, degreening impacts quality by increasing the susceptibility of fruits to stem end rot. The calyx and rind can also senesce faster, and the fruit can suffer weight loss. However, the benefits of degreening outweigh its disadvantages, so the practice continues. Surprisingly, the costs of degreening are seldom included in market analysis. Thus, the financial benefits of degreening postharvest citrus are not clear. Quantifying benefits of degreening postharvest citrusTo shed more light on the costs and underlying biological reasons of degreening, a team of Spanish scientists from different backgrounds such as agriculture, horticulture, microbiology, and economics came together to analyze the process of degreening lemon and grapefruit. The multi-disciplinary team of Conesa, Brotons, Manerac, and Porras examined the changes to rind color, the rate of change, the duration of treatment necessary, and the costs involved based on harvesting dates. The scientists also tested the natural degreening of fruits on trees to compare it with the rind color changes that took place in the ethylene chamber. The lemon cultivars studied were ‘Eureka’, ‘Fino 49’ and ‘Lisbon’ and the grapefruit cultivars were ‘Marsh’, ‘Red Blush’. Each lot remained in the ethylene chamber for 7 days, and the colour coordinates were measured every 2 days to obtain the Colour Index (CI*) of the fruit for each harvesting date. The data showed that the greener the fruit when they entered the ethylene chamber, the greater the degreening rate. The different costs of degreening were estimated for each harvesting date and cultivar. The findings showed that the costs involved in degreening the grapefruit cultivars ‘Red Blush’ and ‘Rio Red’ were three times greater than the costs associated with ‘Marsh’ and ‘Star Ruby’. The costs of degreening lemon did not differ during the first half of the harvesting period and fell gradually during the second half. The findings provide a useful tool for calculating the cost of degreening as a function of harvesting date for each cultivar. Gas analyzers for regulating the atmosphere during degreeningThere are gas analyzers on the market that are specifically made for regulating the atmosphere during degreening, such as the F-901D10 and F-901D200 AccuRipe, which are part of the F-901 AccuStore & AccuRipe - Precision Atmosphere Control series. These tools not only take CO2 and ethylene measurements, but also have a controller to regulate the flow of ethylene for degreening. Others, such as the portable gas analyzer F-960 Ripen It!, manufactured by FELIX INSTRUMENTS, can assist in this process by providing rapid, on site CO2 and ethylene measurements.