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Christian Chervin, Janyce K. Truett, and Jim Speirs

Regulation of alcohol dehydrogenase (ADH), activity of pyruvate decarboxylase (PDC) and accumulation of acetaldehyde and ethanol in `Packham's Triumph' pears (Pyrus communis, L.) subsequent to different storage regimes were investigated. Pears were stored for two months at -1 °C either in air (Air) or under hypoxia at 3 kPa O2 (Hyp) and subsequently warmed and allowed to ripen in air at 20 °C. One set of fruit stored in air at -1 °C was subjected to 3 days of hypoxia at -1 °C (Air+Hyp) before ripening in air. Acetaldehyde, ethanol and methanol levels increased in all fruit in a similar fashion during ripening and did not reflect differences in storage treatments. During ripening, ADH activities in posthypoxic samples were generally twice that of air samples. PDC activities increased for ≈6 days during ripening then declined slightly but did not differ significantly among treatments. Upon transfer to 20 °C in air, slightly higher levels of Adh mRNA were observed in samples treated with hypoxia than in air controls. Over the following 2 days at 20 °C, the Adh transcription was markedly induced in Air and Air+Hyp samples. Although all Adh mRNAs returned to control levels within 4 days, ADH activities remained higher in hypoxia-treated fruit than in controls for up to 18 days. These results suggest that, in ripening pears, ADH does not limit ethanol production, and that the expression of this enzyme comprises post-transcriptional regulations. GenBank accession numbers of the Adh cDNAs are AFO 31899 and AFO 31900.

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Hisashi Kato-Noguchi and Alley E. Watada

Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or in air for 7 days at 5 and 15 °C to study the regulation of ethanolic fermentation metabolism. Low-O2 atmospheres of 0.5% and 2% caused increases in ethanol and acetaldehyde concentrations and the activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) compared to air. By day 3, ethanol increased 38-, 25-, 13-, and 9.5-fold; acetaldehyde increased 20-, 13-, 7.7-, and 5.6-fold; ADH increased 7.6-, 6.3-, 3.8-, and 2.7-fold; and PDC increased 4.2-, 3.9-, 2.3-, and 2.2-fold in samples at 0.5% O2 at 15 or 5 °C and at 2% O2 at 15 or 5 °C, respectively, compared with corresponding samples in air. These results indicate that ethanolic fermentation was accelerated more in the 0.5% than in the 2% O2 atmosphere and more at 15 °C than at 5 °C. The acceleration of ethanolic fermentation may allow production of some ATP, which may permit the carrot tissues to survive.

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J. Pablo Fernández-Trujillo, Jacqueline F. Nock, and Christopher B. Watkins

Effects of 20 kPa CO2 treatments on concentrations of fermentation products, organic acids, and activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH), were measured in fruit of selected strawberry cultivars (Fragaria ×ananassa Duch. `Annapolis', `Cavendish', `Honeoye', `Kent', `Jewell', `Lateglow', and `NorthEast'). Acetaldehyde, ethanol, and ethyl acetate concentrations accumulated in CO2-treated fruit of `Honeoye' and `Kent', but not in `Cavendish' or `Annapolis'. The former two cultivars were classified as intolerant to high CO2 and the latter two as tolerant to high CO2. Activities of PDC and ADH were higher in CO2-treated than in air-treated fruit of the tolerant cultivars but not in the intolerant cultivars. Succinate accumulated in fruit of all cultivars, but concentrations were higher in the tolerant than in the intolerant cultivars. Results are discussed in relation to tolerance of fruit to CO2.

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Jennifer R. DeEll and Peter M.A. Toivonen

The objective of this study was to determine if chlorophyll fluorescence could be used as an indicator of anaerobic respiration in broccoli (Brassica oleracea L., Italica group) during modified-atmosphere packaging (MAP). Two types of packages were used, PD-941 bags, which provided optimum MAP conditions for broccoli (≈3 kPa O2 plus 5 kPa CO2), and PD-961EZ bags, which allowed the CO2 to accumulate (≈11 kPa CO2). After 28 days in MAP at 1 °C, the broccoli from both types of bag had similar appearances and weight losses. However, broccoli held in the PD-961EZ bags had developed slight to moderate alcoholic off-odors and had higher ethanol, acetaldehyde, and ethyl acetate content, as compared with broccoli in PD-941 bags. Chlorophyll fluorescence parameters (Fv/Fm, T1/2, Fmd, and ΦPSII) were lower for broccoli held in the PD-961EZ bags than in PD-941 bags, and these differences increased with storage duration. These results indicate that chlorophyll fluorescence is a reliable, rapid, nondestructive indicator of broccoli quality during MAP, and that it could be used to determine if broccoli has developed off-odors without opening the bag and disrupting the package atmosphere.

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Edna Pesis, Rosa Ben Arie, Oleg Feygenberg, and Fanny Villamizar

Bananas have a short shelf life after ethylene treatment and there is a high commercial demand to increase the storage life of individual clusters at the retail stage. To extend the shelf life of ethylene-pretreated banana, two different forms of modified atmosphere packaging (MAP) were used. In the first, individual clusters of ethylene-pretreated bananas were stored in a range of microperforated polyethylene (PE) bags (25 μm) creating various MAPs. Storage in PE bags with low microperforation (PE8) that created an atmosphere with 11% CO2 and 12% O2 was the most effective treatment for delaying banana ripening. The banana clusters kept firmer with nice peel color after 1 week at 20 °C, but the humidity inside the bags caused some decay development on the crown cut. In the second type of MAP individual clusters of ethylene-pretreated bananas were stored in air-evacuated PE bags (80 μm) under light vacuum (550 mm Hg) for short periods of 24 to 48 hours followed by storage in the same PE bags after releasing the vacuum. Storing bananas in air-evacuated bags for 24 to 48 hours reduced O2 levels to 1% and increased the production of CO2 up to 30%, but perforating the bags dramatically reduced the CO2 level to around 9% and increased the O2 level to 12%. Storing ethylene-pretreated banana clusters under vacuum for a limited time (24 to 48 hours), did not cause any damage, although the levels of acetaldehyde (AA) and ethanol increased dramatically. The AA and ethanol levels of 150 and 300 μL·L–1, respectively, that accumulated in the PE bags did not cause any off-flavors; on the contrary, the taste panelists preferred these bananas. Adding ethylene absorbents (EAs) to the air-evacuated PE bags reduced the ethylene levels as well as the AA and ethanol levels in the bags, which indicate that EAs also absorbed the AA and ethanol volatiles. Storing ethylene-pretreated banana clusters under vacuum for 24 to 48 hours was the most effective treatment for delaying ripening and senescence in yellow bananas (stage 3 to 4).

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Richard K. Volz, William V. Biasi, and Elizabeth J. Mitcham

Apple (Malux ×domestica Borkh., cv. Fuji) fruit were harvested from two California orchards 190 and 210 days after full bloom and from an additional three orchards at 190 days after full bloom. Fruit were immediately exposed to 20 or 50 kPa CO2 in air at 20 °C. Area of flesh browning and tissue ethanol, acetaldehyde, and ethyl acetate concentrations for individual fruit were determined immediately before exposure and after 3 and 7 days (20 kPa) or 1 and 3 days (50 kPa) exposure to CO2. Area of flesh browning and concentrations of all compounds increased with increasing duration of exposure to high CO2, were greater in response to 50 kPa than to 20 kPa CO2, and were greater for fruit harvested later in the season. For individual orchards and for individual fruit within most orchards, greater flesh browning was associated with higher acetaldehyde concentrations after 7 days exposure to 20 kPa CO2 or 3 days exposure to 50 kPa CO2. Similarly, flesh browning was positively correlated with ethanol concentrations after 7 days at 20 kPa CO2, but was not related to tissue ethyl acetate concentrations at either CO2 partial pressure. However, higher production of ethanol, acetaldehyde, or ethyl acetate relative to flesh browning occurred during exposure to 50 kPa than to 20 kPa CO2. This suggests that the relationship between accumulation of these compounds and CO2-induced flesh browning in `Fuji' is not simply causal.

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Giancarlo Colelli, F. Gordon Mitchell, and Adel A. Kader

Good quality of fresh `Mission' figs (Ficus carica L.) was maintained for up to 4 weeks when kept at 0, 2.2, or 5C in atmospheres enriched with 15% or 20% CO2. The visible benefits of exposure to high CO2 levels were reduction of decay incidence and maintenance of bright external appearance. Ethylene production was lower, and fruit softening (as measured with a deformation tester) was slower in the high-CO2-stored figs than in those kept in air. Ethanol content of the CO2-treated fruit increased slightly during the first 3 weeks and moderately during the 4th week, while acetaldehyde concentration increased during the first week, then decreased. The results may be applicable to the transport and storage of fresh `Mission' figs, as high CO2 extended their postharvest life, especially near 0C.

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George D. Nanos, Roger J. Romani, and Adel A. Kader

`Bartlett' pears (Pyrus communis L.) that had been stored for either 2 or 8 weeks in air at 0C were placed under an atmosphere of 0.25% 0, (balance N2) at 20C for 4 days then returned to air. Control pears were kept in air at 20C. Suspension-cultured `Passe Crassane' pear fruit cells in aging medium were treated similarly. During exposure of the fruit to 0.25% O2, loss of greenness and ethylene production were inhibited and CO2 production substantially decreased. Pears that had been stored for 2 weeks at 0C ripened normally, while those that had been stored for 8 weeks at 0C failed to recover normal ethylene and CO2 production upon transfer to air after a 4-day exposure to 0.25% O2 at 20C. Most of the latter fruit were injured as indicated by skin browning. Acetaldehyde and ethanol content increased considerably with ripening of control fruit. Although 0.25% O2-treated fruit developed yet higher acetaldehyde and ethanol contents during treatment, the concentrations returned to or below normal during subsequent exposure to air. Pears exposed to 0.25% 0, had increased pyruvate decarboxylase (PDC; EC and alcohol dehydrogenase (ADH; EC activities that remained high after ripening in air for 6 days. Three ADH isozymes were discernible in the 0.25% O2-treated pears, whereas only one, ADHZ, was found in control fruit. These observations imply that preclimacteric pears are both less stressed during hypoxia and have greater potential for posthypoxia repair than pears of a more advanced physiological age. Increased posthypoxia respiratory and enzymatic activity and the elaboration of new ADH isoenzymes appear to be part of the repair response. Suspension-cultured pear fruit cells responded to the atmospheric changes very much like the S-week stored fruit and likely is a good model system to further study the effects of hypoxia on pear metabolism.

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Jeffrey A. Anderson

`Early Calwonder' pepper (Capsicum annuum L.) and `Jubilee' corn (Zea mays L.) leaf disks exposed to high temperature stress produced ethylene, ethane, methanol, acetaldehyde, and ethanol based on comparison of retention times during gas chromatography to authentic standards. Methanol, ethanol, and acetaldehyde were also identified by mass spectroscopy. Corn leaf disks produced lower levels of ethylene, ethane, and methanol, but more acetaldehyde and ethanol than pepper. Production of ethane, a by-product of lipid peroxidation, coincided with an increase in electrolyte leakage (EL) in pepper but not in corn. Compared with controls, pepper leaf disks infiltrated with linolenic acid evolved significantly greater amounts of ethane, acetaldehyde, and methanol and similar levels of ethanol. EL and volatile hydrocarbon production were not affected by fatty acid infiltration in corn. Infiltration of pepper leaves with buffers increasing in pH from 5.5 to 9.5 increased methanol production.

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Dangyang Ke, Hendrik van Gorsel, and Adel A. Kader

`Bartlett' pears (Pyrus communis L.) tolerated up to 10 days of exposure to atmospheres containing 1.0%, 0.5%, or 0.25% O2 at 0, 5, or 10C without any detrimental effects on their quality attributes. The fruits also tolerated 4 to 6 days of exposure to air enriched with 20%, 50%, or 80% CO2 at the three temperatures. The beneficial effects of exposures to the O2-reduced or CO2-enriched atmospheres included reduction of respiration and ethylene production rates and retardation of skin yellowing and flesh softening. While 1.0% or 0.5% O2 and 20% CO2 did not increase ethanol and acetaldehyde contents, 0.25% O2 slightly increased and 50% or 80% CO2 dramatically increased the contents of these two volatiles in juice of the fruits. The effects of low O2 or high CO2 on the above attributes generally became more pronounced at the higher temperatures. The low O2 or high CO2 treatments did not significantly affect either soluble solids content or titratable acidity. Low O2 did not influence, but high CO2 slightly increased pH of the fruits.