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Jiwon Jeong and Donald J. Huber

Pre-ripe `Booth 7' avocado (Persea americana Mill.) fruit, a cross of West Indian and Guatemalan strains, were treated with 0.9 μL·L-1 1-methylcyclopropene (1-MCP) for 12 hours at 20 °C. After storage for 18 days in air at 13 °C, at which time whole fruit firmness values averaged about 83 N, half of the 1-MCP-treated fruit were treated with 100 μL·L-1 ethylene for 12 hours and then transferred to 20 °C. 1-MCP delayed softening, and fruit treated with 1-MCP retained more green color than air-treated fruit when full ripe (firmness 10 to 15 N). 1-MCP affected the activities of pectinmethylesterase (EC 3.2.1.11), α-(EC 3.2.1.22) and β-galactosidases (EC 3.2.1.23), and endo-β-1,4-glucanase (EC 3.2.1.4). The appearance of polygalacturonase (EC 3.2.1.15) activity was completely suppressed in 1-MCP-treated fruit for up to 24 days, at which time the firmness of 1-MCP-treated fruit had declined nearly 80% compared with initial values. The effect of exogenous ethylene applied to partially ripened 1-MCP-treated fruit differed for different ripening parameters. Ethylene applied to mid-ripe avocado exerted no effect on the on-going rate or final extent of softening of 1-MCP-treated fruit, even though polygalacturonase and endo-1,4-β-glucanase activities increased in response to ethylene. β-galactosidase decreased in 1-MCP-treated fruit in response to ethylene treatment. 1-MCP delayed the increase in solubility and depolymerization of water- and CDTA (1,2-cyclohexylenedinitrilotetraacetic acid)-soluble polyuronides, likely due to reduced polygalacturonase activity. At the full-ripe stage, the levels of arabinose, galactose, glucose, mannose, rhamnose, and xylose associated with the CDTA-soluble polyuronide fraction were similar among all treatments. In contrast, the galactose levels of water-soluble polyuronides declined 40% and 17% in control and 1-MCP treated fruit, respectively. Hemicellulose neutral sugar composition was unaffected by 1-MCP or ethylene treatment. The data indicate that the capacity of avocado fruit to recover from 1-MCP-mediated suppression of ripening can be only partially amended through short-term ethylene application and differs significantly for different ripening parameters.

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Gene E. Lester and Michael A. Grusak

Commercially grown honey dew fruit [Cucumis melo (Inodorus group)] typically are harvested before abscission because fruit cut unripe have a longer storage life than fully ripe fruit. However, because fully ripe fruit contain higher concentrations of soluble solids (predominantly as sugars), an attribute that increases their preference among consumers, methods are being explored to extend the storage life of fully ripe fruit. In this study, fully abscised honey dew fruit were evaluated for tissue attributes and consumer preference following postharvest dipping in either chelated or nonchelated calcium (Ca) solutions. Calcium sources were an amino acid-chelated Ca, ethylene-diamine tetraacetic acid (EDTA)-chelated Ca, or calcium chloride (CaCl2), with each provided at three different rates. Fruit were evaluated at harvest, and after 14 or 22 days commercial storage. Evaluations were peel surface changes (color and disorders), hypodermal-mesocarp tissue Ca concentration, flesh firmness, soluble solids concentration, and consumer preference of the edible flesh. Peel color became yellowed and lighter during storage for all fruit, with higher Ca rates resulting in more intensely yellowed fruit. Hypodermal-mesocarp tissue Ca concentration was 0.90 mg·g-1 of fresh weight (900 ppm) at harvest, and declined in all fruit by 22 days storage. Peel disorders (disease and spotting) were none to slight for all fruit by 14 days storage, but by 22 days storage disease incidence ranged from none to severe, depending on the Ca source and rate. Fruit firmness declined in all fruit throughout storage, with the smallest declines measured in fruit treated with the amino acid-chelated Ca. Soluble solids concentration of fully ripe fruit was 12.3% at harvest, and showed either no decline or slight declines with storage among the treatments. Consumer preference was highest for freshly harvested fruit, but fruit were desirable even after 22 days storage across all treatments. Postharvest application of Ca at ≤0.16 m Ca in an amino acid-chelated form, versus EDTA-chelated Ca or CaCl2, slowed honey dew melon senescence so that after 22 days of commercial and retail storage the fruit were of high marketable quality, and there was no detrimental effect on consumer preference for the edible flesh.

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Angela R. Davis, Amnon Levi, Sungil Kim, Stephen R. King, and Alvaro Hernandez

RNA isolation from ripe fruit can be complicated by high concentrations of sugar and water. These sugars interfere with RNA extraction often resulting in low RNA quality and quantities, and high water concentrations dilute the RNA, making isolation difficult. We report a simple but novel method by which the majority of the excess sugar and water in mature fruit of tomato (Lycopersicon esculentum Mill.), watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], and muskmelon (Cucumis melo L.) can be easily removed from tissue before RNA extraction. This method produced quality RNA in a shorter time than the currently accepted method for fruit tissue RNA isolation and does not require liquid nitrogen or a freeze dryer.

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Georges T. Dodds and Pamela M. Ludford

Chilling-injury symptoms on the surface of eight cultivars or lines of tomato (Lycopersicon esculentum Mill.) fruit were mapped with respect to subtending locules. Mature-green (MG) fruit were chilled at SC for 10 to 25 days and then ripened to red ripe at 20C. Mature-green fruit showed a major portion of injury over subtending locules and on the stem end. The location of injury corresponded with the regions that were the last to ripen. The injuries of immature-green (IG) fruit treated in a similar manner were different from those of MG fruit both in appearance and in distribution.

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P. Perkins-Veazie, J.K. Collins, and J.R. Clark

Promising white peach and nectarine selections, many with nonmelting flesh, from the Univ. of Arkansas breeding program were evaluated for fruit quality and flavor. About 20 kg of fruit, consisting of mature ripe and ripe stages, were harvested from 4- to 7-year-old trees in Arkansas and transported to Lane, Okla. Fruit were divided into two boxes per selection. One box was held at 5 °C for 8 days, then transferred to 20 °C for 4 days to induce chilling injury and was evaluated for storage quality. The other box was held at 20 °C for 4 days and fruit used for taste panels. Of the 14 nectarine and 12 white peach selections evaluated, one nectarine and four white peach selections had slight chilling injury. Flesh firmness of selections after storage ranged from 6 to 50 N. Taste panelist scores indicated that sweetness was associated with peach flavor in both nectarines and white peaches and that overall acceptability was dependent on sweetness, peach flavor, and low tartness. Ten of the white peach selections were equal to or better in overall acceptability compared to `Summer Pearl' and `Carolina Belle' cultivars included in the study. Panelists did not consider firm texture to be detrimental to overall acceptability. Results indicate that many of the breeding lines used in this study had fruit equal to or better than currently available cultivars in storage life, firmness, and sweetness.

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R.E. McDonald, T.G. McCollum, and E.A. Baldwin

Mature green `Sunbeam' tomato fruit (Lycopersicon esculentum Mill.) were treated in water for 1 hr at 27 (ambient), 39, 42, 45, or 48°C, and then either ripened at 20°C (nonchilled) or stored at 2°C (chilled) for 14 days before ripening at 20°C. The most-effective heat treatment was 42°C, which reduced decay 67% in chilled fruit and 53% in nonchilled fruit. Heat treatment had no effect on time required to ripen the fruit. Red-ripe tomatoes had higher respiration rates and evolved more ethylene following nonchilling storage, but heat treatment had no effect on respiration or ethylene evolution. Red color development was enhanced by heat treatment, and inhibited by chilling. At red ripe, fruit were firmer as a result of storage at the chilling temperature, while heat treatment had no effect on firmness. Heat-treated fruit were preferred in terms of taste and texture over nontreated fruit in informal taste tests, with the exception of the 45°C treatment. With increasing temperature of heat treatment, there was increased electrolyte leakage following chilling storage. Of the 15 flavor volatiles analyzed, the levels of five were decreased with increasing temperature of heat treatment. Storage at the chilling temperature reduced the levels of six flavor volatiles. Prestorage heat treatments can reduce decay with only minimal adverse effects on tomato fruit quality.

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P. Perkins-Veazie, J.K. Collins, and W. Roberts

Reports on the lycopene content of tomatoes vary widely with country and source of fruit (field, greenhouse, retail). This study was done to compare the lycopene content of organically grown tomatoes, and to compare fully red fruit to those ripened after harvest. Thirteen tomato cultivars (12 beefsteak and one Roma type) were planted in land designated as transitional organic and fertilized with organic poultry litter. No additional fertilizer was applied. Pesticides approved for organic use were applied as necessary. Fruit at the turning to firm red stages were harvested and held at 20 to 28 °C until the soft red stage was reached (about 2 to 8 days). Day 0 fruit at pink to soft red stages was harvested at the same time. Multiple harvests were made for 6 weeks, until 10 fruit per cultivar and ripeness stage and storage treatment were obtained. Lycopene content of firm red and soft red fruit were similar, and was 50 to 65 mg·kg–1 for all the round fruit types, and 115 mg·kg–1 for the Roma type. Fruit ripened after harvest without ethylene were able to obtain similar levels of lycopene, even in those fruit harvested with just a trace of color. `Sunmaster' and `Solar Set' tomatoes grown organically were similar in lycopene content to those grown in previous years in a conventional production system. These results show that organically grown tomatoes can achieve normal to high levels of lycopene. Tomatoes ripened after harvest without ethylene can achieve the lycopene content of fruit harvested fully ripe.

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Kanjana Mahattanatawee, Elizabeth Baldwin, Kevin Goodner, John Manthey, and Gary Luzio

Fourteen tropical fruits from southern Florida [red guava, white guava, carambola, red pitaya (red dragon), white pitaya (white dragon), mamey, sapodilla, lychee, longan, green mango, ripe mango, green papaya and ripe papaya] were evaluated for antioxidant activity, ascorbic acid (vitamin C), total fiber and pectin. ORAC (oxygen radical absorbance capacity) and DPPH (1,1-diphenyl-2-picrylhydrazyl, radical scavenging activity) assays were used to determine antioxidant activity. The total soluble phenolics (TSP), ORAC, and DPPH ranged from 205.4 to 2316.7 μg gallic acid equivalent/g puree, 0.03 to 16.7 μmole Trolox equivalent/g puree and 2.1 to 620.2 μg gallic acid equivalent/g puree, respectively. Total ascorbic acid (TAA), total dietary fiber (TDF) and pectin ranged from 13.6 to 159.6 mg/100 g, 0.88 to 7.25 g/100 g and 0.2 to 1.04 g/100 g, respectively. The antioxidant activities, TSP, TAA, TDF and pectin appeared to be influenced by cultivar (papaya, guava and dragon fruit) and ripening stage (papaya and/or mango). Data demonstrate the potential benefits of several of these fruits for human health.

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Donna A. Marshall, J.M. Spiers, K.J. Curry, and S.J. Stringer

Fruit splitting takes place in rabbiteye and southern highbush blueberries when a preharvest rainfall occurs and when fruit are fully ripe or approaching full ripeness. This study was initiated to develop a laboratory method to identify the rain-related incidence of splitting in cultivated blueberries. Multi-year field surveys of select rabbiteye and southern highbush cultivars show that the incidence of rain-related splitting is strongly cultivar dependent. Year to year variations within cultivars reflected yearly differences in ripening times and amounts and timing of rainfall. Laboratory values of forced splitting and field splitting data of three years show a strong correlation indicating that the incidence of fruit splitting can be accurately estimated by laboratory methods. Soaking the berries in distilled water 14 hours at room temperature gives a confident determination of splitting tendencies. Blueberry breeders can use this method to evaluate new potential blueberry cultivars for splitting tendencies. This laboratory method could also be used by geneticists to test selections accurately for splitting tendencies as part of routine screening. This can lead to a long-term goal of reducing splitting susceptible blueberries in commercial plantings.

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John L. Maas, Shiow Y. Wang, and Gene J. Galletta

Ellagic acid in tissue extracts of green and red-ripe strawberries (Fragaria × ananassa Duch.) was detected and quantified by HPLC. Ellagic acid content of green fruit pulp ranged from 1.32 to 8.43 mg·g-1 of tissue dry weight (mean 3.36 mg·g-l) and in achenes of green fruit from 1.32 to 20.73 mg·g-1 (mean 7.24). Ellagic acid content of red fruit pulp at one location for 35 cultivars and selections ranged from 0.43 to 4.64 mg·g-1 of dry weight (mean 1.55) and from 0.43 to 3.47 mg·g-l (mean 1.45) for 15 clones at another location. Achenes from red-ripe fruit ranged from 1.37 to 21.65 mg·g-1 (mean 8.46) for 34 clones at one location and from 2.81 to 18.37 mg·g-1 (mean 8.93) for 15 clones at another location. Leaf ellagic acid content ranged from 8.08 to 32.30 mg·g-1 of dry weight (mean 14.71) for 13 clones examined. Large differences in ellagic acid content were found among cultivars, but tissue values were not consistent within cultivars. Values from one tissue type did not correlate consistently with values of the other tissues. Sufficient variation was found among cultivars to suggest that increased ellagic acid levels may be achieved in progeny from crosses with selected parental material.