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Dana F. Faubion and Adel A. Kader

California-grown `Hass' avocado fruit were stored at 5C, in air or a controlled atmosphere (CA) of 2% oxygen and 5% carbon dioxide. Fruit were evaluated at 0, 2, 4, 6, 8, 10, and 12 weeks, both immediately upon removal from storage and after ripening at 20C. Severe chilling injury (flesh browning) developed in the airstored fruit after 6 weeks, while only moderate symptoms were observed in CA-stored avocado fruit after 12 weeks. Lipid peroxidation breakdown products increased during storage and ripening in both air and CA treatments. Sterols, steryl esters, steryl glycosides, glycolipids, and phospholipids were analyzed. Quantity of acylated steryl glycoside in ripe fruit changed from 34 nmoles initially, to 51 or 27 nmoles after 6 weeks at 5C in air or CA, respectively. Glycolipid fatty acid unsaturation in air-stored fruit decreased with the development of chilling injury. Fatty acid unsaturation in phospholipids (phosphatidylinositol, phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine) of air-stored avocados decreased with the development of chilling injury. CA storage delayed the development of chilling injury and the loss of fatty acid unsaturation.

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James R. Gorny and Adel A. Kader

The optimal `Bartlett' pear ripeness stage for fresh-cut processing based on flesh firmness ranges between 44.5 and 58 N (10 and 13 lbf). Use of softer pears reduces postcutting life due to flesh browning. Firmer pears may have longer postcutting life but lack good flavor. Dipping pear slices in a mixture of 2% (w/v) ascorbic acid + 1% (w/v) calcium lactate + 0.5 (w/v) cysteine (pH 7) for 5 min at 20 °C extended their shelf-life by inhibiting flesh softening and surface browning during storage at 0 °C for 10 days. After 3 days at 0 °C, ascorbic acid and cysteine residues dropped below detectable levels, while calcium content was double that of untreated slices. Preliminary sensory evaluation indicate no negative impact on flavor from this dip treatment. Exposure of intact pears to heat (35 or 40 °C) or controlled atmospheres (0.25 kPa O2 and/or 40 kPa CO2) for 24 or 48 h did not influence postcutting cut surface browning of pear slices. Storage of `Bartlett' pears at -1 °C in 2 kPa O2 (balance N2) resulted in longer postcutting life of the slices as compared to those made from air-stored pears at -1 °C. The longer the storage duration of whole pears, the shorter the shelf-life of their slices was. Fruit size did not affect the postcutting life of the pear slices, provided that they were treated with the ascorbic acid + calcium lactate + cysteine mixture. Untreated slices made from small pears exhibited surface browning faster than those made from large pears.

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Diana Dostal Lange and Adel A. Kader

Stress levels of carbon dioxide can be effective in the retardation of ripening and control of decay-causing pathogens and insect infestation of some horticultural perishables. Our objective has been to identify key mitochondrial enzymes and pathways that regulate the fruit's response to CO2 actions. Oxygen uptake of fruit stored in air + 20% CO2 (16.8% O2) was depressed compared to the airstored fruit, whereas the fruit stored in air + 40% CO2 (12.6% O2) had an elevated respiration rate. Climacteric fruit treated with 20% CO2 at 10C had increased pyruvate dehydrogenase (PDH) activity, decreased cytochrome oxidase (CytOx) activity, and double the alternative oxidase (AltOx) activity compared to air-stored fruit. Air + 40% CO2-stored fruit had reduced PDH and CytOx activities, and 50% more AltOx activity than the control fruit. Mitochondria were treated directly with the same CO2-enriched atmospheres to measure the catalytic effects of CO2. Total O2 uptake was decreased in both CO2 atmospheres and the cytochrome/alternative pathway ratio was greater than with mitochondria held in air. Nuclear magnetic resonance analysis of whole fruit confirmed that these CO2 atmospheres decrease the intracellular pH several 0.1 pH units with 2 h.

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Dana F. Faubion and Adel A. Kader

California grown `Hass' avocado fruit were stored at 5C, in air or a controlled atmosphere (CA) of 2% oxygen and 5% carbon dioxide. Fruit were evaluated at 0, 3, 6, and 10 weeks, both immediately upon removal from storage and after 5 days at 20C. Severe chilling injury developed in the air-stored fruit after six weeks, while only moderate symptoms were observed in CA stored avocado fruit after 10 weeks. Lipid peroxidation breakdown products increased during storage and ripening in both air and CA treatments. Sterols, sterol esters, glycolipids, and phospholipids were analyzed. There was a shift in composition during storage towards increasingly saturated fatty acids. The fatty acid shift was greater in air, than in CA stored fruit. Results will be discussed concerning their relevance to chilling injury development.

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Diana L. Lange and Adel A. Kader

Changes in cytosolic and vacuolar pH, ATP, ADP, and the ATP : ADP ratio were measured in whole fruit or mesocarp disks of avocado [Persea americana (Mill.) cv. Hass] during brief exposures to elevated CO2. Intact climacteric fruit exposed to air (21% O2), 20% CO2 (17% O2, balance N2), or 40% CO2 (13% O2, balance N2) had cytosolic pH values of 7.0, 6.6, and 6.4, respectively, while mesocarp disks had cytosolic pH values of 6.9, 6.7, and 6.4, respectively. The ß-ATP levels of intact climacteric fruit exposed to 20% CO2 or 40% CO2 for 2 h were reduced by 25% or 43%, respectively, relative to air-exposed fruit. HPLC analysis of nucleotide phosphates from preclimacteric avocados revealed that ATP levels and the ATP : ADP ratio increased in 40% compared to the air-stored fruit. However, 1 day after transfer to air, the effects of elevated CO2 had dissipated. These modifications in cellular state could alter the activity of respiratory enzymes in fruit exposed to elevated CO2 atmospheres.

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Diana Dostal Lange and Adel A. Kader

Carbon dioxide-enriched atmospheres can be effective in the retardation of ripening and in the reduction of decay of horticultural commodities. However, concentrations in excess of the tolerance level may cause physiological damage. The goal of our research is to elucidate the specific regulatory mechanisms of CO2 actions. Cytochrome oxidase (CytOx) in vitro activity in preclimacteric avocado fruit stored in air or 40% CO2 + 12.6% O2 was evaluated at 20C. Activities were determined during treatment and also after a transfer to air. Fruit treated with 40% CO2 + 12.6% O2 had elevated CytOx in vitro activity when compared to air-stored fruit. Immunoblot analysis was performed to determine if the increase in CytOx activity could be due to an increase in enzyme concentration. The decline in respiration rate of CO,-treated fruit was most likely due to the decrease in intracellular pH and its effect on the activities of important respiratory enzymes, including CytOx. The regulatory mechanisms of other mitochondrial respiratory enzymes in `Hass' avocados exposed to elevated CO2 atmospheres are also under investigation.

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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.

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Keri L. Morrelli, Betty M. Hess-Pierce, and Adel A. Kader

The variation in chilling sensitivity of mature-green specialty bananas (Musa paradisiaca var. sapientum) and plantains (Musa paradisiaca var. paradisiaca) was examined using four cultivars of bananas and one plantain cultivar stored under various time and temperature combinations. Cold storage for 1 day at 5.0, 7.2, or 10.0 °C (41, 45, or 50 °F) resulted in acceptable fruit quality for up to 8 days at 20.0 °C (68 °F) for `Petite' and `Red Macabu' bananas and `Dominico Harton' plantains. `Grand Nain' and `Yangambi' bananas were considered unmarketable due to moderate to severe graying after 8 days at 20.0 °C when fruit were previously stored for 1 day at 5.0 or 7.2 °C. Storage for 3 days at 10.0 °C was acceptable for all cultivars tested, however 5 days at 10.0 °C resulted in moderate to severe browning and graying of the `Grand Nain' fruit. The traditional Cavendish-type, `Grand Nain', as well as `Petite' and `Yangambi', required temperatures greater than 10.0 °C for a 7-day storage duration while `Red Macabu' bananas could be safely stored for 7 days at 10.0 °C. Plantains could be stored at 7.2 °C for 7 days without visible chilling injury symptoms. The storage of specialty bananas and plantains at or above their minimum safe temperatures resulted in improved uniformity of ripening and overall quality of the fruit due to a decrease in chilling injury symptoms.

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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.