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Abstract
The production of CO2 by apple and pear fruit was measured during and after alternating 12-hr exposures to air and N2 atmospheres. Typical stimulation of CO2 evolution in the absence of O2 was observed. Five or more anaerobic cycles imparted a permanent reduction on the subsequent aerobic respiration rate. The differences between control respiration and aerobic CO2 evolution by fruit exposed to cyclic anaerobiosis indicated that the capacity for aerobic respiration was reduced by the early anaerobic cycles. Suppression of the anaerobic stimulation of CO2 production was observed after several cycles suggesting that the capacity for fermentation was accumulatively impaired. Subsequent measurements of physical characteristics showed that flesh softening and chlorophyll degradation, processes which generally coincide during ripening, were differentially affected by cyclic anaerobiosis. Apple scald was induced by anaerobiosis. Pear fruits subjected to anaerobic cycles or continuous anaerobiosis did not ripen during the 14-day poststorage period at 21°C.
Abstract
The ionic Ca content of expressed apple juice conceivably could be used to estimate the total calcium content of fruit flesh. To evaluate this method, samples of 2 strains of ‘Delicious’ apple (Malus domestica Borkh.) were analyzed at 2- to 3-week intervals, from 4 weeks after full-bloom until full-maturity. Ionic Ca in the juice (juice Ca) was analyzed with a selective electrode, total Ca in the flesh (flesh Ca) with a plasma emission spectrophotometer. The correlation coefficient between calcium concentration in flesh vs. juice was very low during the early stages of fruit development, but increased to +0.758 (significant at P<0.0l) for samples collected 5, 3, and 0 weeks prior to fruit maturity. The correlation was generally significant at P<0.01 when all sampling dates were used (r = 0.734 for ‘Miller Spur’, +0.928 for ‘Starking’, and +0.831 for both strains). The calcium concentration in juice samples taken within 35 days of physiological fruit maturity paralleled the calcium concentration in the flesh on any given date, but was not a reliable predictor of flesh Ca concentration in fruit harvested 2 to 3 weeks thereafter.
Abstract
In a collaborative study at 5 North American locations, treatment with 12% CO2 and 3 to 5% O2 for 2 weeks at 0° to 3°C at the beginning of controlled atmosphere (CA) storage significantly delayed softening of ‘McIntosh’ apples (Malus domestica Borkh.). Softening was retarded further when treatment time and CO2 concentration were increased, and when fruit was harvested less mature. The effect was diminished by treatment at 0°, and was nullified by delayed treatment and slow cooling during treatment. Softening response to CO2 was not influenced by O2 concentration or storage humidification during treatment. CO2 treatment reduced the rates of CO2 and ethylene evolution from the fruit, even after 4 to 5 months of subsequent CA storage, but affected neither soluble solids nor titratable acidity of fruit after storage. When taste panelists could distinguish CO2-treated from nontreated CA apples, they preferred the treated fruit.
These beneficial results were usually accompanied by external CO2 injury, and occasionally by internal CO2 injury; 30 to 50% of the fruit were injured in some tests. Treatment in a non-humidified room reduced CO2 injury without also reducing treatment benefits. We conclude that for ‘McIntosh’, the potential for injury outweighs the benefits obtained from CO2 pre-treatment in CA storage.