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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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Clara Pelayo, Betty Hess-Pierce, Susan E. Ebeler, and Adel A. Kader

Elevated CO2 atmospheres reduce decay and extend postharvest life based on appearance of strawberries but flavor quality may be lost faster than appearance quality. California-grown `Aromas', `Diamante,' and `Selva' strawberries were stored at 5 °C in air or 20 kPa CO2 + air for 15 days and evaluated for quality attributes, chemical changes, and flavor. In a “Preference Test”, `Selva” and `Diamante' were more preferred than `Aromas'. This may be related to their higher titratable acidity (TA), total soluble solids (TSS), the concentration of total aroma compounds, a different methyl/ethyl esters ratio, and the presence of C6 aldehydes. The postharvest life in air was 7, 9, and 9 days for `Aromas', `Diamante' and `Selva', respectively and these periods were extended by 30%, 20%, and 45% in the CO2-enriched atmosphere. There were no significant differences in TA or TSS between fruits kept in air or in air + CO2 and panelists could not detect differences in sourness and sweetness after 9 days of storage. In contrast, there was a trend for CO2-stored fruits of the three cultivars to be categorized as more aromatic, and for `Aromas' and `Selva' fruits to be described as more “strawberry like” in flavor compared to the corresponding air-stored fruits. The total aroma concentration decreased to a lesser extent in `Aromas' and `Selva' strawberries kept in air + CO2 than in those stored in air. The CO2-enriched atmosphere stimulated fermentative metabolism only in `Aromas' and `Selva'; the higher concentration of ethanol in these two cultivars favored the synthesis of ethyl esters. The total content of aroma compounds and the methyl/ethyl esters ratio may be two of the multiple factors determining the overall fruit flavor.

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Nigel H. Banks, Donald J. Cleland, Arthur C. Cameron, Randolph M. Beaudry, and Adel A. Kader

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Clara Pelayo-Zaldívar, Jameleddine Ben Abda, Susan E. Ebeler, and Adel A. Kader

Quality and chemical changes associated with flavor were evaluated in ‘Camarosa’ strawberries (Fragaria ×ananassa) that had been kept at 5 °C in air or in air + 20 kPa CO2 for 3 and 6 days to elucidate possible factors contributing to the loss of flavor during storage. The elevated CO2 treatment did not affect flesh firmness, total soluble solids, pH, or titratable acidity. In contrast, decreases in color (as indicated by a higher hue angle value) and in concentrations of sucrose, reducing sugars, and citric acid were detected in fruits exposed to elevated CO2. Fermentative metabolites were present in strawberries stored in air and in higher concentration in those kept in air + 20 kPa CO2. Also, strawberries kept in air + 20 kPa CO2 had higher levels of ethyl esters and a major reduction in the level of methyl esters. Thus, clear differences in the aroma profile of strawberries at harvest and after 3 and 6 days of storage at 5 °C in air or air + 20 kPa CO2 were observed. This change in the volatile aroma profile is probably the primary factor contributing to the loss of strawberry flavor during storage.

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Yong Seo Park, Clara Pelayo, Betty Hess-Pierce, and Adel A. Kader

`Shinko' and `Shinsui' Asian pears were kept in air, 2 kPa O2, 2 kPa O2 + 2.5 kPa CO2, and 2 kPa O2 + 5 kPa CO2 (balance N2 in each treatment) at 0 °C or 5 °C for up to 24 weeks. The three CA treatments reduced respiration (O2 consumption) and ethylene production rates relative to air control pears; these rates were higher at 5 °C than at 0 °C and higher for `Shinsui' than for `Shinko' pears. While `Shinsui' pears had a climacteric pattern of respiration and ethylene production rates, `Shinko' pears produced very small quantities of ethylene and exhibited a non-climacteric respiratory pattern. `Shinko' pears had a much longer postharvest life than `Shinsui' pears (24 weeks vs. 12 weeks at 0 °C). CA treatments had a greater effect on delaying deterioration of `Shinsui' than `Shinko' pears, which were more sensitive to CO2 injury and associated accumulation of fermentative metabolites (acetaldehyde, ethanol, ethyl acetate). `Shinko' pears did not benefit from CA storage and were best kept in air at 0 °C. An atmosphere of 2 kPa O2 with or without up to 5 kPa CO2 delayed flesh breakdown of `Shinsui' pears during storage 0 °C.

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Dangyang Ke, Elhadi Yahia, Betty Hess, Lili Zhou, and Adel A. Kader

`Hass' avocado (Persea americana Mill.) fruit were kept in air, 0.25% O2 (balance N2), 20 % O2 + 80% CO2, or 0.25% O2 + 80% CO2 (balance N2) at 20C for up to 3 days to study the regulation of fermentative metabolism. The 0.25% 02 and 0.25% 02 + 80% CO2 treatments caused accumulations of acetaldehyde and ethanol and increased NADH concentration, but decreased NAD level. The 20% O2 + 80% CO2 treatment slightly increased acetaldehyde and ethanol concentrations without significant effects on NADH and NAD levels. Lactate accumulated in avocadoes kept in 0.25 % 02. The 80% CO, (added to 0.25% O2) did not increase lactate concentration and negated the 0.25% O2-induced lactate accumulation. Activities of PDC and LDH were slightly enhanced and a new isozyme of ADH was induced by 0.25% O2, 20% O2 + 80% CO2, or 0.25 % O2 + 80% CO2; these treatments partly reduced the overall activity of the PDH complex. Fermentative metabolism can be regulated by changes in levels of PDC, ADH, LDH, and PDH enzymes and/or by metabolic control of the functions of these enzymes through changes in pH, ATP, pyruvate, acetaldehyde, NADH, or NAD. Chemical names used: alcohol dehydrogenase (ADH), adenosine triphosphate (ATP), lactate dehydrogenase (LDH), nicotinamide adenine dinucleotide (NAD), reduced NAD (NADH), pyruvate decarboxylase (PDC), pyruvate dehydrogenase (PDH).