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T. Vilasachandran and Steven A. Sargent

Pericarp browning, weight loss, and the associated quality deterioration are the unsolved postharvest problems of lychee (Litchi chinensis Sonn.). Freshly harvested fruits (`Brewster') were stored ± plastic wrap (99% and 84% relative humidity, RH, respectively) and ± panicle at 5°C for 18 days to simulate commercial handling scenarios. There were no significant losses in pericarp color (L*, hue angle, chroma value), total soluble solids, and total sugars from initial values for wrapped fruits. Wrapped lychees were 100% marketable, compared to 17% for unwrapped fruits. The former retained higher weight, moisture content and total titratable acidity (TTA, pulp), and lower pulp pH. Colletotrichum sp., Cladosporium sp., and Alternaria sp. caused decay in 56% of unwrapped fruits, whereas wrapped fruits were free of decay. Fruits with panicles had significantly higher weight loss (3%) than clipped fruits for both wrapped and unwrapped fruits. Pulp TTA tended to decrease and pH to increase more in fruits with panicle. Postharvest quality of lychee fruits was significantly extended by removing the panicle and maintaining nearly saturated RH during handling and storage.

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Steven A. Sargent and Jeffrey K. Brecht

Carambolas (Averrhoa carambola L., cv. Arkin) ware harvested at colorbreak (CB) and light green (LG) ripeness stages, commercially packed and cooled. The next day the fruit were treated as: Control (ungassed): CB, LG; Ethylene pretreatment (ETH) @100ppm: LC for 1, 2 or 3 days at 20°C or 25°. After pretreatment the fruit were stored at 5°. After 1, 2, 3, 4 weeks, 10 fruit from each treatment ware removed from storage and placed at 20°. Fruit color and decay were rated daily until 80% of the fruit in each treatment reached the yellow ripeness stage, at which time external color, total soluble solids (TSS), pH and total titratable acidity (TTA) were determined. Carambolas harvested at the LG stage can be ripened to good quality with ETH pretreatment. For two weeks storage at 5°, 2 days ETH are necessary at 20° or 25° to initiate ripening. For three weeks storage, 3 days ETH are required at 20°, and 2 or 3 days ETH are required at 25°. Fruit stored four weeks were of fair quality. LG with slower ripening initiation developed chilling injury during storage; the fastest initiation had the best color but the shortest marketing life. Fruit harvested CB had slightly higher TSS than ETH-treated LG but pH and TTA were similar.

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Fernando Maul, Steven A. Sargent, Elizabeth A. Baldwin and Charles Sims

`Agriset-761' and `CPT-5' tomato fruits were harvested at green stage and subsequently exposed to a postharvest exogenous ethylene-air mixture (100 ppm C2H4 at 20°C). Tomatoes with visual symptoms of ripening (breaker stage = <10% red coloration) were removed from ethylene treatment after 1, 3, and 5 days and were transferred to 20°C and 85% RH. At “table-ripe” stage (full red coloration and 4-mm fruit deformation after 5 sec@9.8N), whole fruit samples were analyzed for difference/discrimination sensory evaluations, aroma volatile profiles, and chemical composition. Flavor of fruits gassed for 1 day was rated significantly different than that of fruits gassed for 3 or 5 days (n = 25 panelists) for both cultivars. Several panelists noted the perception of “rancid” and “metallic” tastes, and “lingering” aftertaste in fruits gassed for 5 days. Chemical composition assays showed that flavor differences could be partially due to a significant increase in pH values between fruits gassed for 1 and 5 days (4.23 and 4.34, respectively for `Agriset-761') and a significant decrease in titratable acidity (0.91% and 0.73%, respectively, for `Agriset-761'; 1.04% and 0.86%, respectively, for `CPT-5'). No significant differences in soluble solids content or total sugars were found in any treatments for either cultivar. `Agriset-761' showed significant increases in the concentrations of acetone, hexanal, 2+3 methylbutanol, and a decrease in 2-isobutylthiazole, whereas, `CPT-5' fruits showed significant increases in hexanal, 2+3 methylbutanol, trans-2-heptenal, 6-methyl-5-hepten-2-one, 2-isobutylthiazole, β-ionone, geranylacetone, and a decrease is ethanol concentration. In both cultivars, these significant differences in important aroma volatile compounds could be of enormous relevance in the perception of off-flavor/off-odors.

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Jiwon Jeong, Donald J. Huber and Steven A. Sargent

Ethylene is integrally involved in the ripening of climacteric fruit. The ability to prevent ethylene action, or manipulate fruit sensitivity to ethylene, would provide a powerful means of extending postharvest storage life of these fruit, particularly for those that ripen rapidly and/or that are not tolerant of low-temperature storage. In this study, 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, was used to investigate ripening, respiration, and ethylene production in avocado fruit. `Monroe' avocados were treated with 1-MCP (Ethylbloc®) for 24 h at 20 °C. The fruit were subsequently stored at 13 or 20 °C. Some fruit were exposed to 100 ppm ethylene at 13 and 20 °C before or after MCP treatment. As evaluated by flesh firmness, respiration rate, and ethylene evolution, 1-MCP completely inhibited the ripening of avocado fruit stored at 13 and 20 °C and 85% relative humidity. Ethylene evolution and respiration rates were dramatically depressed, greater than 95% and 52%, respectively, by 1-MCP. Whereas firmness of control fruit decreased from over 100 N to 10 N in as few as 7 days, fruit treated with 1-MCP remained firm (>45 N) for periods of up to 3 weeks at 13 °C. Treatment of avocado fruit with 100 ppm ethylene at 20 °C for 12 h did not overcome the influence of MCP treatment. Similarly, treatment with ethylene before MCP exposure did not circumvent the effects of the cyclic olefin on ripening. Current studies are addressing the effects of MCP concentration and exposure time on avocado ripening.

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Jiwon Jeong, Donald J. Huber and Steven A. Sargent

1-Methylcyclopropene (1-MCP), an inhibitor of ethylene action, has been shown to extend the storage life of avocado fruit. Waxing is also known to extend the storage life of avocado by reducing water loss and modifying the fruit internal atmosphere. In this study, 1-MCP and waxing were used to investigate their effects on ripening characteristics in avocado fruit. Preclimacteric `Tower II' and `Booth 7' avocados were treated with 1-MCP (Ethylbloc®) for 12 h at 20 °C. Half of the fruit were waxed (Sta-Fresh 819F®, FMC Co.) after 1-MCP treatment. The fruit were subsequently stored at 13 °C or 20 °C at 85% RH. As evaluated by fruit firmness, ethylene evolution, and respiration rate, 1-MCP and waxing delayed the ripening of `Tower II' avocados stored at 20 °C. Fruit treated with both 1-MCP and wax had better retention of green peel color and fruit firmness, and the delayed climacteric pattern of ethylene evolution and respiration rates. Waxing reduced weight loss and retarded softening, but did not delay climacteric ethylene evolution and respiration rates. Whereas firmness of control fruit decreased from >100 N to 20 N in as few as 7 days at 20 °C, fruit treated with both 1-MCP and wax reached 20 N over 11 days at 20 °C. The firmness of `Booth 7' avocados treated with both 1-MCP and wax decreased from >170 N to 20 N over a 5-week period at 13 °C. Current studies are addressing the nature of the dramatic decrease in firmness of MCP-treated fruit.

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Michael T. Masarirambi, Jeffrey K. Brecht and Steven A. Sargent

Mature green fruit of `Agriset 761', `Colonial', `Sunny' and `Sunbeam' tomatoes were exposed to 100 ppm ethylene at 20, 25, 30, 35, or 40°C around 95% relative humidity (RH) for 24, 48, or 72 hours, then transferred to air at 20°C and 95% RH for ripening. There were few differences in ripening behavior in tomatoes exposed to ethylene at high temperatures (>30°C) for 24 hours compared to those treated at lower temperatures. However, increasing the duration of ethylene treatment at 35 or 40°C to 48 or 72 hours inhibited subsequent red color development, but prior exposure to ethylene at 30°C stimulated red color development. Ethylene production was inhibited after 48 or 72 hours at 40°C, but was stimulated by exposure to lower temperatures in the order shown: 35 > 30 > 25. During ripening, conversion of ACC to ethylene increased in fruit exposed to ethylene at 20 or 25°C but did not change in fruit from 30 or 35°C. ACC oxidase activity was lowest after exposure to 40°C. Untreated fruit ripened slowly and nonuniformly compared to those previously treated with 100 ppm ethylene. Increasing the ethylene treatment concentration to 1000 ppm did not alter the responses to high temperatures described above.

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Steven A. Sargent, Peter J. Stoffella and Donald N. Maynard

Short-day onions (Allium cepa L.) grown under humid, subtropical conditions at two locations were evaluated for bulb size and yield at five harvest dates (H1 to H5) ranging from 94 to 132 days after transplanting (DAT) for `Granex 33' and from 115 to 153 DAT for `Texas Grano 1015Y'. Maximum yields were attained by H4 for both cultivars and were attributed to increased bulb size rather than differences in plant (bulb) population. Nondried, large bulbs (>7.6 cm diameter) from each harvest were trimmed and stored at 1 or 10 °C and 80% relative humidity (RH) for 2 weeks plus 2 weeks at 20 °C and 80% RH to simulate commercial storage and handling. Initial respiration rates of bulbs of both cultivars decreased >60% between H1 and H4. Bulbs also retained higher fresh weight during storage as harvest was delayed. Storage for 2 weeks at 1 °C suppressed sprouting of immature (H1) `Texas Grano 1015Y' bulbs, but not of `Granex 33' bulbs from one location. Storage at 10 °C did not suppress sprouting of either cultivar. Decay became more prevalent with delayed harvest, but `Granex 33' was more resistant to decay than was `Texas Grano 1015Y', which developed up to 40% decay after 2 weeks at 20 °C. Harvest at 115 and 132 DAT resulted in acceptable yields for `Granex 33' and `Texas Grano 1015', respectively, and satisfactory postharvest quality of nondried bulbs following 2 weeks of storage at 1 °C and 80% RH plus 2 weeks at 20 °C.

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Eunkyung Lee, Steven A. Sargent and Donald J. Huber

Roma tomatoes (‘BHN 467’) were hand-harvested at mature-green color stage and treated with ethylene (100 μL·L−1 at 20 °C and 90% relative humidity) until reaching breaker (<10% red), pink (30%–60% red), or light-red ripeness stage (60%–90% red). Individual fruit at each ripeness stage were subjected to double impacts over the locule using a pendulum-impact device with a force equivalent to two 40-cm drops, followed by ripening at 20 °C. Fruit exhibited most noticeable increases in respiration and ethylene production within 1 hour and 1 day after impact, respectively. After 24 hours, respiration rates increased 40%–60% regardless of ripeness stage, while ethylene production in impacted breaker-stage fruit increased 3-fold (to 6.7 μL·kg−1·h−1). Fruit impacted at breaker stage softened 2 days earlier compared with non-impacted breaker fruit. Fruit impacted at all ripeness stages had higher electrolyte leakage and polygalacturonase (PG) activity during ripening than non-impacted fruit. After 6 days, electrolyte leakage in fruit impacted at light-red ripeness stage was 23% higher than non-impacted fruit; PG activity in breaker fruit increased 40% at 10 days over non-impacted fruit. No changes were observed for soluble solids content, total titratable acidity, pH, or sugar/acid ratio from impacts, independent of ripeness stage.

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Steven A. Sargent, Jeffrey K. Brecht and Judith J. Zoellner

Internal bruising (IB) caused by handling impacts results in disruption of normal ripening in tomato (Lycopersicon esculentum Mill.) locular gel. It was selected as an injury indicator to investigate the effect of drop height (O, 10, 20, 30 cm) onto an unpadded surface and number of impacts (one or two) for three tomato cultivars. For mature-green (MG) tomatoes, significant incidence of IB (5% to 45%) was found in all cultivars for single drops on opposite sides of fruits from 20 cm; two drops on the same location from 20 cm caused 20% to 30% IB. Breaker-stage (BR) tomatoes were more sensitive to impacts than MG. Single drops from 10 cm on opposite sides of BR fruits caused 15% to 73% IB, depending on cultivar. Two drops on a single location from 10 cm caused 50% to 68% IB. `Sunny' was less susceptible to IB than `Solar Set' or `Cobia' (formerly NVH-4459).

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Eunkyung Lee, Steven A. Sargent and Donald J. Huber

Roma tomatoes (`Sunoma') were hand-harvested at the mature-green color stage and treated with 100 μL·L-1 ethylene for 60 h at 20 °C and 90% RH. Tomatoes at breaker ripeness stage (<10% red coloration) were sorted by weight (about 100 g) and half of the fruits were treated with 1-methylcyclopropene (1-MCP; 1 μL·L-1 for 24 h at 22 °C). After 1-MCP treatment, individual fruits were subjected to double impacts over the marked locular surface with force equivalent to a 40-cm height drop using a pendulum impactor. In non-1-MCP treated fruit, impacts increased the maximum respiration rate by 27% (to 39.1 mL·kg-1 per h) and ethylene production by 24% (to 5.5 μL·kg-1 per h). Treatment with 1-MCP decreased relative production of both CO2 (56%) and ethylene (54%) over non-1-MCP treated fruit, while the ripening period (as measured by softening and color development) was extended 2.5 times, to about 8 d. Fruits treated with 1-MCP had increased TTA (about 40%; 0.58% citric acid equivalent), decreased pH (5%), and no difference in soluble solids content (3.7 °Brix); double impacts did not affect these values. Double impacts accelerated the onset of polygalacturonase (PG) activity by about 100% (to 99.8 mol·kg-1 per min*10-5 D-galacturonic acid) at day 6 over non-impacted control fruit. 1-MCP treatment delayed the onset of increased PG activity by 10 d over non-1-MCP treated fruit. Although 1-MCP alleviated the impact-induced increase in PG activity, PG activity recovered to rates similar to those of non-1-MCP treated fruit during the final 4 d of ripening.