`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 220.127.116.11) and alcohol dehydrogenase (ADH; EC 18.104.22.168) 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.
George D. Nanos, Roger J. Romani, and Adel A. Kader
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.
George D. Nanos, Roger J. Romani, and Adel A. Kader
`Bartlett' pears (Pyrus communis L.) at two physiological stages, climacteric minimum or approaching the climacteric peak as achieved via storage for 2 or 8 weeks in air at 0C, respectively, were either ripened at 20C in air immediately or after exposure to 0.25% 02 for 4 days at 20C. Fruit stored for 2 weeks had relatively stable phosphofructokinase (PFK), pyrophosphate: fru-6-P phosphotransferase (PFP), and pyruvate kinase (PK) activities but decreasing succinate dehydrogenase (SDH) activities during ripening in air. Similar fruit treated with 0.25% O2 had slightly increased PFK, PFP, and SDH activities and decreased PK activity. Fruit stored for 8 weeks exhibited higher levels of PFK and PFP activity upon transfer to 20C, in accordance with their more advanced physiological state. In general, the enzymic changes in these fruit upon exposure to 0.25% O2 and subsequent ripening in air were similar to those observed in the less-mature counterparts, most notable being an increase in mitochondrial SDH. Exposure of suspension-cultured pear fruit cells to hypoxia resulted in an accentuated rise in phosphoenolpyruvate carboxykinase activity and a dramatic rise in SDH activity upon transfer to air. Taken in concert, the enzymic analysis supports the hypothesis that the rise in succinate levels observed in hypoxic fruit tissues is the result of a partial reductive tricarboxylic acid cycle. Cytochrome oxidase activity did not change during hypoxia whereas soluble peroxidase decreased somewhat, perhaps a reflection of their Michaelis constants for O2.
Eduardo L. Kerbel, Adel A. Kader, and Roger J. Romani
Suspension-cultured `Passe Crassane' pear fruit (Pyrus communis L.) cells in aging media were ventilated with air or air + 20% CO2 for 4 days at 26C. Cells exposed to elevated CO2 exhibited reduced respiration (02 consumption). Ethylene production of both air and CO2-treated cells also declined to barely discernible levels by day 3. Fructose 6-phosphate (F6P) accumulated, while levels of fructose l,6-bisphosphate (F1, 6-P2), and activities of ATP and PPi phosphofructokinases (PFK and PFP) declined in response to elevated CO2. These results indicate an inhibitory effect of CO2 at the site of action of both phosphofructokinases in the glycolytic pathway, which could account, at least in part, for the observed reduction in respiration. The responses to elevated CO2 levels of the cell suspension system and intact pear fruit ventilated with air + 10% CO2 are compared, revealing a close similarity.
George D. Nanos, Roger J. Romani, and Adel A. Kader
The response of pear fruits and suspension-cultured pear fruit cells to 0% or 0.25% O2 is being examined to evaluate the feasibility of using such atmospheres for postharvest insect control. These treatments inhibited ethylene production, had no effect on acetaldehyde content, and increased ethanol production in pears kept at 20C for 10 days. The blossom end area of pear fruits was more prone to anaerobiosis, as indicated by increased alcohol dehydrogenase activity and ethanol content. Pear fruit plugs showed increased respiration and ethylene production rates when skin was present compared to plugs without skin. Methods for measuring activity of alcohol dehydrogenase, pyruvate decarboxylase, and pyruvate kinase have been modified and optimized and will be used to determine changes in pear fruit tissue during low O2 treatment and subsequent recovery in air.
Fairuz. El-Wazir, Dangyang Ke, and Adel A. Kader
The tolerances (based on time before detection of off-flavor) of nectarine and peach cultivars to an insecticidal controlled atmosphere of 0.25% O2 (balance N2) at 20C were 2.8, 4.0, 4.0, 4.4, 5.1, and 5.3 days for `John Henry' peaches, `Fantasia' nectarines, `Five Red' peaches, `O'Henry' peaches, `Royal Giant' nectarines, and `Flamekist' nectarines, respectively. The greater sensitivity of `John Henry' peaches to low O2 stress was associated with a higher respiration rate; faster accumulation rates of acetaldehyde, ethanol, and ethyl acetate; and a more mature and larger fruit. The tolerances of `Fairtime' peaches to 0.21% O2 + 99% CO2 at 20C, 0.21 O2 + 99% CO2 at 0C, and 0.21% O2 at 20C were 3.8, 5.0, and 6.0 days respectively. There was a good correlation between tolerance of nectarines and peaches to insecticidal atmospheres and the accumulation rates of acetaldehyde (r=-0.94, p<0.01) and ethanol (r=-0.88, p,0.01).
Marius Huysamer, John M. Labavitch, and Adel A. Kader
Commercially grown Granny Smith apples were stored at 0°C in air or 1% O2, and 2 sets of samples were taken every 4 weeks over a 28 week period. One set was immediately analysed for weight loss, firmness, color, soluble solids, pH and titratable acidity. Alcohol-insoluble substances were analysed for starch, water-soluble uronides, water-insoluble uronides, cellulose and neutral sugars. The second set of samples was kept in air at 20°C for an additional week, during which respiration and ethylene production rates were measured, prior to the above analyses. Storage in 1% O2 led to the improved maintenance of firmness, reduced respiration and ethylene production rates in ambient air, and a reduced content of water-soluble uronides, suggesting a reduced degree of hydrolysis. The correlation between firmness and water-soluble uronide content was not very strong. The predominant neutral sugars present in the wall were arabinose and galactose, and activities of putative hydrolyses that may be involved in the metabolism of polymers containing these sugars will be discussed.
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.
Deirdre M. Holcroft, Maria I. Gil, and Adel A. Kader
The influence of CO2 on color and anthocyanin concentration in the arils of `Wonderful' pomegranate (Punica granatum L.) was investigated. Pomegranates were placed in jars ventilated continuously with air or air enriched with 10% or 20% CO2 at 10°C for 6 weeks. Samples were taken initially, and after 1, 2, 4, and 6 weeks and anthocyanin concentration was measured by HPLC. The arils of the pomegranates stored in air were deeper red than those stored in CO2-enriched atmospheres. This increase in red color resulted from an increase in anthocyanin concentration. Arils from fruit stored in air+10% CO2 had a lower anthocyanin concentration than air-stored fruit, and atmospheres enriched with 20% CO2 suppressed anthocyanin biosynthesis. Anthocyanin concentration was well-correlated to the activity of phenylalanine ammonia lyase (PAL), but not to glucosyltransferase (GT) activity. Moderate CO2 atmospheres (10%) prolong the storage life and maintain the quality of pomegranates, including an adequate red color of the arils.
Dangyang Ke, Elhadi Yahia, Mila Mateos, and Adel A. Kader
Changes in fermentation volatiles and enzymes were studied in preclimacteric and postclimacteric `Bartlett' pears (Pyrus communis L.) kept in air, 0.25% O2, 20% O2 + 80% CO2, or 0.25% O2 + 80% CO2 at 20C for 1, 2, or 3 days. All three atmospheres resulted in accumulation of acetaldehyde, ethanol, and ethyl acetate. The postclimacteric pears had higher activity of pyruvate decarboxylase (PDC) and higher concentrations of fermentation volatiles than those of the preclimacteric fruit. For the preclimacteric pears, the 0.25% O2 treatment dramatically increased alcohol dehydrogenase (ADH) activity, which was largely due to the enhancement of one ADH isozyme. Exposure to 20% O2 + 80% CO2 slightly increased ADH activity, but the combination of 0.25% O2 + 80% CO2 resulted in lower ADH activity than 0.25% O2 alone. For the postclimacteric pears, the three atmospheres resulted in higher PDC and ADH activities than those of air control fruit. Ethanolic fermentation in `Bartlett' pears could be induced by low O2 and/or high CO2 via 1) increased amounts of PDC and ADH; 2) PDC and ADH activation caused by decreased cytoplasmic pH; or 3) PDC and ADH activation or more rapid fermentation due to increased concentrations of their substrates (pyruvate, acetaldehyde, or NADH).