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Zhenyong Wang and David R. Dilley

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Dangyang Ke, Leonor Rodriguez-Sinobas, and Adel A. Kader

Fruits of `Granny Smith' and `Yellow Newtown' apples (Malus domestica Borkh), `20th Century' pear (Pyrus serotina L.), and `Angeleno' plum (Prunus domestica L.) were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10C for 3, 7, 14, 25, or 35 days to study the effects of low-O2 atmospheres on their postharvest physiology and quality attributes. Soluble solids content (SSC), pH, and external appearance were not significantly influenced, but resistance to CO2 diffusion was increased by the low-O2 treatments. Exposures to the low-O2 atmospheres inhibited ripening, including reduction in ethylene production rate, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. The most important detrimental effect of the low-O2 treatments was development of an alcoholic off-flavor that had a logarithmic relation with ethanol content of the fruits. The ethanol content causing slight off-flavor (Eo) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula: (Log Eo)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (VE) from each low-O2 treatment, the tolerance limit (Tl) of fruits to low-O2 atmospheres could be predicted as follows: Tl = Eo/VE = (100.228SSC)/VE.

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Dangyang Ke and Adel A. Kader

Fruits of peach (Prunus persica L., cv. `Fairtime') and plum (Prunus domestica L., cv. `Angeleno') were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10°C for 3 to 40 days to study the effects of temperatures and insecticidal low O2 atmospheres on their physiological responses and quality attributes. Exposure to low O2 atmospheres reduced respiration and ethylene production rates of the stone fruits. The low O2 treatments retarded color change and flesh softening of plums and maintained acidity of peaches. Exposure to the low O2 atmospheres also delayed incidence and reduced severity of internal breakdown (chilling injury) and decay of the peaches at 5°C and, therefore, maintained both external and internal appearance qualities of the fruits longer than those kept in air. The most important limiting factor for fruit tolerance to insecticidal low O2 atmospheres was development of alcoholic off-flavor which was associated with accumulation of ethanol and acetaldehyde in the fruits. The peaches and plums could tolerate exposures to the low O2 atmospheres for 9 to 40 days, depending on the temperature and O2 level used. These results suggest that stone fruits are quite tolerant to insecticidal low O2 atmospheres.

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Edna Pesis, Rosa Marinansky, Giora Zauberman, and Yoram Fuchs

Prestorage treatment of avocado fruit (Persea americana Mill. cv. Fuerte) with a low-O2 atmosphere (3% O2 + 97% N2) for 24 hours at 17C, significantly reduced chilling injury (CI) symptoms after storage at 2C for 3 weeks. Fruit softening was also delayed by this treatment. The treated fruit had lower respiration and ethylene production rates during storage at 2C and subsequently at 17C. Electrolyte leakage was significantly lower in peel disks from treated fruit. Reducing power, expressed as total sulfhydryl groups, was higher in the peel and pulp of low-O2-treated fruit. The amount of peel chlorophyll was inversely correlated with the severity of CI symptoms.

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Nathanee P. Ko, Alley E. Watada, Donald V. Schlimm G., and John C Bouwkamp

The extinction point (EP) of spinach cultivars was determined to identify the minimum O2 concentration that can be used for modified-atmosphere storage of spinach. EP was based on respiratory quotient (RQ) and appearance quality during storage. Oxygen consumption decreased as O2 concentration was lowered from 2.0% to 0.1%; whereas CO2 production decreased as O2 concentration was lowered from 2.0% to 0.5%, but not below 0.5%. The RQ was close to 1 in oxygen atmospheres of 2.0% to 0.4% and exceeded 1 at 0.2% or less. No alcohol production was noted at 0.2% or less O2, but deterioration of leaves occurred at these low-O2 atmospheres. Since the EP is slightly below 0.4% O2, the concentration of O2, should not be allowed to go below 0.5% for successful modified-atmosphere storage of spinach.

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Elhadi M. Yahia and Martin Tiznado Hernandez

`Keitt' mangoes (Mangifera indica L.) were stored for 0 to 5 days at 20C in a continuous flow of an insecticidal low-O2 atmosphere (0.2% to to 0.3%, balance N2). Fruit were evaluated every day after exposure to a low-O2 atmosphere and again after being held in air at 20C for 5 days. There was no fruit injury, organoleptic fruit quality was not lowered due to the low-O2 atmosphere, and fruit ripened normally. These results indicate that applying low-O2 atmospheres postharvest can be used to control insects in mangoes.

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Abd. Shukor Rahman

Controlled-atmosphere (CA) storage of fruits employing low O2 and/or elevated CO2 have been used to reduce respiration and other associated metabolic activities. Papaya fruit cv. Eksofika were exposed to 2%, 5%, and 21% (air) O2 for 4 weeks at 12C. The CO2 production rates of fruit previously stored in 2% and 5% O2 were suppressed during storage, but increased upon transfer to air at 20C. Carbon dioxide production rates of low-oxygen stored fruits were slightly lower than the air-stored fruit during transfer to air, indicating a slight residual effect of low O2 on the respiratory activity of the fruit. This was highly evident in fruit stored in 2% O2 for 4 weeks. Ethylene production rates were not affected by prior storage of fruit in low-O2 atmosphere. Anaerobic metabolism did not occur in fruit stored in 2% O2 for 4 weeks, as evidenced by the RQ values close to unity and the absence of ethanol from the headspace of the respired gas. The total sugar content of ripe fruit at color score 5, previously stored in low-O2 atmosphere for 4 weeks, were not significantly different from the air-stored fruit.

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Hisashi Kato-Noguchi

Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or air at 5 °C to investigate the effect of low O2 atmosphere on respiratory metabolism, particularly on lactate dehydrogenase (LDH) activity and its isozyme composition. Low O2 atmospheres caused a decrease in CO2 production and an increase in lactate concentration and LDH activity compared to air. By day 2, CO2 production rate decreased 0.4- and 0.5-fold, lactate increased 3.5- and 2.2-fold, and LDH activity increased 2.3- and 1.7-fold in carrot shreds stored in 0.5% and 2% O2, respectively, compared to samples in air. Based on nondenaturing electrophoresis, LDH isozyme composition analysis revealed five bands consisting of a tetrameric enzyme with subunits encoded by two different Ldh genes. Changes in staining intensity of the isozymes indicated that the increase in LDH activity in carrots under low O2 atmospheres resulted from increased enzyme synthesis and that there was preferential induction of one Ldh gene. These results suggest that lactic acid fermentation may be accelerated more under 0.5% than 2% O2 atmospheres due to greater expression of the Ldh genes.

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Abd-Shukor A. Rahman, Donald J. Huber, and Jeffrey K. Brecht

Bell pepper (Capsicum annuum L., var. `Jupiter') fruit stored in 1.5%, 5%, or 10% O2, or in air at 20C for24 hours were compared to determine the residual effect of low-O, storage on respiration after transfer to air. The lowest O2 concentration (1.5%) exerted the greatest residual effect on bell pepper fruit CO2 production and O2, uptake. No ethanol was detected in the headspace gas of fruit stored in 1.5% O2. Carbon dioxide production continued to be suppressed for ≈ 24 hours after transfer from 1.5% O2 to air. Exposure to 5% O2, for 24 hours resulted in less suppression of CO, production and O2 uptake upon transfer to air, while 10% O2 exerted no residual effect. Extending the storage period in 1.5% O2 to 72 hours extended the residual effect from 24 to 48 hours. Ethylene production was not affected by storage in 1.5% or 4% O2 for 24 or 72 hours. The residual effect exhibited in whole fruit was not apparent in mitochondria isolated from bell pepper stored in 1.5% or 4% O2.