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Renar J. Bender, Jeffrey K. Brecht, Steven A. Sargent and Donald J. Huber

`Haden' and `Tommy Atkins' mangoes (Mangifera indica L.) were stored in air, 2, 3, 4 or 5 kPa O2 plus N2, or 25 kPa CO2 plus air for 14 days at 15 °C or 21 days at 12 °C, respectively, then in air for 5 days at 20 °C to determine their tolerance to reduced O2 levels for storage times encountered in typical marine shipments. All low O2 treatments reduced mature green mango respiration (CO2 production), however, elevated ethanol production occurred in 2 and 3 kPa O2 storage, with the levels two to three times higher in `Tommy Atkins' than `Haden'. In contrast, `Haden' fruit at the onset of the climacteric also accumulated ethanol in 4 kPa O2 and produced 10 to 20-fold more ethanol in 2 and 3 kPa O2 than preclimacteric fruit. While there were no visible injury symptoms, off flavor developed in mature green fruit at 2 kPa O2 and in ripening initiated fruit at 2 and 3 kPa O2. Ethanol production was not affected by storage in 25 kPa CO2. Ethylene production was reduced slightly by low O2, however, `Haden' fruit also showed a residual inhibitory effect on ethylene production after 2 or 3 kPa O2 storage, while `Tommy Atkins' fruit stored in 2 kPa O2 produced a burst of ethylene upon transfer to air at 20 °C. Fruit firmness, total sugars, and starch levels did not differ among the treatments, but 2, 3 or 4 kPa O2 and 25 kPa CO2 maintained significantly higher acidity than 5 kPa O2 or air. The epidermal ground color responded differently to low O2 and high CO2 in the two mango cultivars. Only 2 kPa O2 maintained `Haden' color better than air, while all low O2 levels maintained `Tommy Atkins' color equally well and better than air. High CO2 was more effective than low O2 in maintaining `Haden' color, but had about the same effect as low O2 on `Tommy Atkins'. Results indicate that preclimacteric `Haden' and `Tommy Atkins' mango fruit are able to tolerate 3 kPa O2 for 2 or 3 weeks at 12 to 15 °C and that tolerance to low O2 decreases as mangoes ripen. Results also show that low O2 and high CO2 affect mango ripening differentially.

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Jiwon Jeong, Jeffrey K. Brecht, Donald J. Huber and Steven A. Sargent

A study was conducted to determine the effect of 1-methylcyclopropene (1-MCP) on textural changes in fresh-cut tomato (Lycopersicon esculentum, Mill.) slices during storage at 5 °C. The relationship between fruit developmental stage and tissue watersoaking development was also determined. Fresh-cut tomato slices prepared from light-red fruit that had been exposed to 1-MCP (1 μL·L-1 for 24 h at 5 °C) retained significantly higher pericarp firmness during storage at 5 °C for 10 d than slices from nontreated fruit or slices stored at 10 or 15 °C and they also had a significantly higher ethylene production maximum. 1-MCP (1 or 10 μL·L-1 for 24 h at 5 °C) had no affect on the firmness of fresh-cut, red tomato slices at 5 °C or on slices prepared from 5 °C-stored, intact red tomatoes. Nor did 1-MCP treatment have a significant effect on electrolyte leakage of tomato slices or intact fruit stored at 5 °C. Slices from fruit of the same developmental stage but with higher initial firmness values had less watersoaking development and responded better to 1-MCP treatment during 8 d storage at 5 °C. 1-MCP (1 μL·L-1) was more effective in reducing watersoaking in light red stage tomato slices when applied at 5 °C for 24 h compared with 1-MCP applied at 10 or 15 °C. Watersoaking development was also more rapid in fresh-cut tomato slices as initial fruit ripeness advanced from breaker to red stage. Our results suggest that watersoaking development in fresh-cut tomato slices is an ethylene-mediated symptom of senescence and not a symptom of chilling injury as had previously been proposed.

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Peiyan Li, Xiaolin Zheng, Md. Golam Ferdous Chowdhury, Kim Cordasco and Jeffrey K. Brecht

Effects of postharvest oxalic acid (OA) application on chilling injury (CI) in harvested mango fruit (Mangifera indica L.) were investigated using ‘Tommy Atkins’ fruit from Florida and ‘Zill’ fruit from Panzhihua. The OA was applied to harvested fruit as a 5 or 10 mm drench for 10 or 15 minutes at 25 °C. ‘Tommy Atkins’ fruit typically develop external CI symptoms while ‘Zill’ develops internal symptoms. Development of CI symptoms was significantly reduced in OA-treated ‘Tommy Atkins’ fruit stored for 18 days at 5 °C as was the rate of softening upon transfer to 25 °C for 4 days. However, OA treatment did not substantially control fruit decay. For ‘Zill’, CI development was significantly reduced in OA-treated fruit during storage at 10 °C for 49 days and subsequently for 4 days at 25 °C. In addition, membrane integrity was enhanced and the activities of the antioxidant system enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were elevated, although there were decreases in both hydrogen peroxide (H2O2) content and superoxide radical production in OA-treated fruit. The activities of some enzymes of the energy cycle were also elevated in the OA-treated fruit, including succinate dehydrogenase (SDH), cytochrome C oxidase (CCO), H+-adenosine triphosphatase (H+-ATPase), and Ca2+-adenosine triphosphatase (Ca2+-ATPase). Thus, OA may enhance CI tolerance in mango fruit by maintaining membrane integrity associated with enhanced antioxidant activity and regulation of energy metabolism. Application of 5 mm OA appears to be beneficial in controlling postharvest CI in mango fruit.

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Jiwon Jeong, Jeffrey K. Brecht, Donald J. Huber and Steven A. Sargent

A study was conducted to determine the influence of the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), on the shelf life and deterioration during storage at 5 °C of intact netted muskmelon (Cucumis melo L. var. reticulatus) fruit and fresh-cut cubes prepared from those fruit. ‘Durango’, ‘Magellan’, and ‘7920’ fruit (3/4 to full-slip stage) were treated with 1-MCP (1.0 μL·L−1) for 24 h at 20 °C. Preliminary research with ‘Athena’ muskmelon had shown that the more physiologically advanced distal pericarp tissue developed significantly more watersoaking than the less advanced proximal and center portions during 5 °C storage; therefore, after treatment with 1-MCP and cooling to 5 °C, the center portions of the fruit were used to prepare the fresh-cut samples. Fresh-cut cubes and intact fruit were stored for 12 d at 5 °C. Intact fruit of all tested cultivars responded to 1-MCP application with improved firmness retention during storage, but no watersoaking was observed in intact fruit. The effect of 1-MCP treatment on the firmness retention and watersoaking of fresh-cut cubes from the different cultivars was inconsistent. Exposure of muskmelon fruit to 1-MCP did not significantly influence the flesh color or soluble solid contents of either intact fruit or fresh-cut cubes during storage at 5 °C.

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Ernesto A. Brovelli, Jeffrey K. Brecht, Wayne B. Sherman and Charles A. Sims

The notion that ethylene production levels in nonmelting-flesh (NMF) peach (Prunus persica L.) fruit are normally lower than those in melting-flesh (MF) fruit is refuted in our study. In fact, NMF fruit (`Oro A' and FL 86-28C) usually produced higher levels of ethylene than did MF fruit (FL 90-20 and `TropicBeauty'). In both MF and NMF peaches, the rate of ethylene production, rather than the respiration rate, provided a good indication of the developmental stage of the fruit at harvest. Ethylene content in fruit on the tree followed a climacteric pattern, with the level in `Oro A' (NMF) and FL 90-20 (MF) peaking at 50 and 12 μL·L–1, respectively. The respiratory climacteric was not apparent in either `Oro A' or FL 90-20, and levels of CO2 were similar in both genotypes.

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Ernesto A. Brovelli, Jeffrey K. Brecht, Wayne B. Sherman and Charles A. Sims

Potential maturity indices were determined for two melting-flesh (FL 90-20 and `TropicBeauty') and two nonmelting-flesh (`Oro A'and Fl 86-28C) peach [Prunus persica (L.) Batsch.] genotypes. A range of developmental stages was obtained by conducting two harvests and separating the fruit based on diameter. Fruit in each category were divided into two groups. One group was used to determine potential maturity indices: soluble solids, titratable acidity, soluble solids to titratable acidity ratio, peel and flesh color on the cheeks and blossom end, cheek and blossom-end firmness, ethylene production, and respiration rate. The other group was stored at 0 °C for 1 week and ripened at 20 °C for 2 days to simulate handling conditions and presented to a trained sensory panel, which rated the fruit for three textural aspects (hardness, rubberiness, and juiciness) and six flavor aspects (sweetness, sourness, bitterness, and green, peachy, and overripe character). Principal component (PC) analysis was used to consolidate the results of the descriptive sensory evaluation into a single variable that could be correlated with the objective measurements at harvest. The attributes that best correlated with the first sensory PC of each genotype, and thus are promising maturity indices, were as follows: for FL 90-20, peel hue, peel L, and cheek firmness; for `TropicBeauty', peel L, cheek firmness, and blossom-end firmness; for `Oro A', cheek firmness, blossom-end firmness, and cheek chroma; and for 86-28C, blossom-end firmness, cheek hue, and cheek firmness.

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Ernesto A. Brovelli, Jeffrey K. Brecht, Wayne B. Sherman and Charles A. Sims

A study to compare the response to postharvest chilling (4 °C) for up to 3 weeks of melting-flesh (MF)—FL 90-20, FL 90-21W, and FL 91-16—and nonmelting-flesh (NMF)—`Oro A', FL 90-35C, and FL 90-47C—peach (Prunus persica L.) genotypes revealed that MF fruit were notably more susceptible to the development of mealiness than NMF types. Cell separation in mealy fruit was demonstrated by the release of mesocarp cells to an aqueous medium, allowing determination of mealiness severity. At a histological level, chilling brought about an impressive expansion of the intercellular spaces in MF mesocarp tissue but did not affect NMF fruit. A decrease in flesh electrical resistance after 1 week of chilling was observed only in MF fruit. However, electrical resistance increased in MF and NMF fruit following 2 and 3 weeks at 4 °C. Electrical resistance also decreased with ripening of MF fruit but did not change when NMF fruit were ripened. Unlike NMF fruit, the MF genotypes FL 90-21W and FL 91-16 showed an increase in respiration rate due to chilling. The rate of ethylene production decreased after 1 week at 4 °C in MF and NMF genotypes. However, two MF and two NMF genotypes exhibited rising ethylene levels after the second week of storage at 4 °C, while ethylene production in one MF and one NMF genotype continued to decline.

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Jeffrey K. Brecht, Robert L. Shewfelt, Joseph C. Garner and E.W. Tollner

Cross-sectional X-ray-computed tomography (X-ray CT) images through the equator of tomato fruit (Lycopersicon esculentum Mill., cv. Sunny) ranging in maturity from immature (Ml) to advanced mature green (M4) revealed localized differences in X-ray absorption related to the formation of locular gel during maturation of the fruit. While maturity stage was poorly correlated with average X-ray absorbance and standard deviation or with average fruit density and water content, significant relationships' existed between maturity stage “and the number of image pixels with absorbance values >10 (Ml vs. M2 vs. M3) or 20 (M3 vs. M4) Hounsfield units. Using discriminant analysis, a relationship was developed that correctly identified the maturity class of 77% of the fruit and placed 96% of the tomatoes into the correct or an adjacent class.

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Jinhe Bai, Elizabeth A. Baldwin, Kevin L. Goodner, James P. Mattheis and Jeffrey K. Brecht

Apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf. (`Gala', `Delicious', `Granny Smith' and `Fuji')], pretreated or nontreated with 1-methylcyclopropene (1-MCP, 0.6 to 1.0 μL·L–1 for 18 hours at 20 °C), were stored in controlled atmosphere (CA, 1 to 1.5 kPa O2; 1 to 2 kPa CO2) or in regular atmosphere (RA) for up to 8 months at 1 °C. Firmness, titratable acidity (TA), soluble solids content (SSC), and volatile abundance were analyzed every month directly or after transfer to air at 20 °C for 1 week to determine effect of 1-MCP, storage atmosphere and storage time on apple quality immediately after cold storage and after simulated marketing conditions at 20 °C. The 1-MCP ± CA treatments delayed ripening and prolonged storage life as indicated by delayed loss of firmness and TA in all four cultivars during storage. The 1-MCP ± CA also slightly delayed loss of SSC for `Gala' but had no effect on SSC levels for the other cultivars. There were differences among treatments for firmness and TA content [(1-MCP + RA) > CA] for `Gala', `Delicious', and `Granny Smith' apples, but not for `Fuji'. These differences were generally exacerbated after transfer of fruit to 20 °C for 1 week. A combination of 1-MCP + CA was generally best [(1-MCP + CA) > (1-MCP + RA) or CA] for maintaining `Delicious' firmness and TA. However, the treatments that were most effective at retaining TA and firmness also retained the least volatiles. The results indicate that the efficacy of 1-MCP and CA in maintaining apple quality factors is cultivar dependent and that 1-MCP + RA may be a viable alternative to CA for optimal eating quality for some cultivars.

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Ernesto A. Brovelli, Jeffrey K. Brecht, Wayne B. Sherman and Jay M. Harrison

Potential maturity indices were determined for two melting-flesh (FL 90-20 and Tropic Beauty) and two nonmelting-flesh (Oro A and Fl 86-28 C) peach cultivars. A range of developmental stages was obtained by conducting two harvests and separating fruit based on their diameter. Fruit in each category were divided into two groups. One group was used for determining potential maturity indices: soluble solids, titratable acidity, soluble solids: titratable acidity, peel and flesh color on the cheeks (CH) and blossom end (BE), CH and BE texture, ethylene production, and respiration rate. The other group was stored at 0°C for 1 week and ripened at 20°C for 2 days to simulate actual handling conditions, and were presented to a trained sensory panel, which rated the fruit for three textural (hardness, rubberiness, and juiciness) and three flavor aspects (sweetness; sourness; bitterness; and green, peachy, and overripe character). Principal component (PC) analysis was used to consolidate the results of the descriptive sensory evaluation into a single variable that could be correlated with the objective measurements at harvest. The first overall PC explained 40% of the total variation. Following are the attributes that best correlated with PC 1 and, thus, are promising maturity indices: for FL 90-20, peel hue, peel L, and CH texture; for Tropic Beauty, peel L, CH texture, and BE texture; for Oro A, CH texture, BE texture, and CH chroma; for 86-28C, BE texture, CH hue, and CH texture.