The purposes of this symposium are to focus attention on the subject of ripening, to consider the nature of the ripening process, to reveal developments concerning morphology and mechanisms, and to promote thinking covering control of ripening.
The control of enzymatic browning of apple slices with papain is presented. Fresh apple slices dipped in a 1% Papain solution for 2 min did not brown for more than 12 hours at room temperature. Papain also gave good browning control of sliced pears. Further study indicated that polyphenoloxidase, a key enzyme involved in browning, was inactivated by this treatment.
‘Delicious’ apples (Malus domestica Borkh.) were transferred from commercial controlled atmosphere (CA) storage after 7 months into a factorial series of CO2 (0%, 3%, 6%, and 12%) and O2 (0.0%, 0.5%, and 1.0%) concentration mixtures at 0.5°C for up to 14 weeks. Fruit tolerance to specific atmospheres that yielded anaerobic products was determined. Tissue ethanol levels ranged from about 2700 to 5800 µl·liter–1 in apples stored in 12:0 (CO2:O2) and 0:0 atmospheres, respectively, indicating CO2 inhibition of ethanol accumulation in the absence of O2. Less than 360 µl ethanol/liter was produced in the 0.5% and 1.0% O2 treatments, No CO2 inhibition of ethanol or acetaldehyde production occurred in the 0.5% and 1.0% O2 treatments. Tissue acetaldehyde concentrations ranged from 6 to 14 µl·liter–1 in fruit held in 0.0% O2 and 3 to 9 µl·liter–1 in fruit held in 0.5% O2. No visible injury developed from the high CO2 and low O2 concentrations used in any of the storage treatments. After a week in air at 20°, following 0.0% O2 storage, the fruit tissue ethanol content decreased while the acetaldehyde content increased.
‘Delicious’ apples (Malus domestica Borkh.) harvested on two dates and stored in controlled atmospheres (CA) from 0.0% to 1.5% O2 were analyzed biweekly during a 14-week storage period for tissue ethanol and other quality parameters. After 14 weeks, ‘Delicious’ fruit stored in 0.0% O2 was significantly firmer, lower in soluble solids, and had 10 times more ethanol than fruit stored in 0.5% to 1.5% O2. Upon return to ambient air for 7 days following low-O2 storage, up to 50% of the ethanol accumulated was lost. The first external symptoms of low-O2 injury appeared after 8 weeks in 0.0% O2 followed by a week in air. Symptoms were associated with ethanol contents >2500 μg·liter−1. Fruit harvested 7 Oct. produced more ethanol than fruit harvested 23 Sept. (i.e., greater concentration and faster rate). There were no differences in firmness, soluble solids, and titratable acidity due to harvest date.
`Delicious' apple (Malus domestica Borkh.) trees received regulated deficit irrigation (RDI) early in the growing season to determine if fruit quality and storage life would he altered compared to well-watered trees. Soil moisture and leaf water potential were lower in RDI trees than in those that did not receive RDI most of the season. Internal ethylene concentration increased logarithmically earlier in RDI apples. At harvest, RDI fruit were smaller and had a higher soluble solids concentration (SSC) and lower titratable acidity. Starch degradation was delayed in RDI fruit, and their color was not affected. Firmness was not affected when the effect of size on firmness was removed. The SSC of RDI apples remained higher during storage, but starch content, titratable acidity, firmness, and color were similar.
Walla Walla Sweet onions (Allium cepa L.) have a short storage and marketing season. Studies to determine viable shelf life and to extend post-harvest life with controlled atmosphere (CA) storage were conducted. Onions were exposed to various CA gas mixtures in combination with heat curing (35°C) and/or chlorine dioxide (ClO2) fumigation, to control disease. Preliminary results indicated Botrytis was the primary cause of post-harvest losses. A 1% O2, 5% CO2 atmosphere appeared to maintain onion quality better than other gas mixtures tested during 15 weeks of CA storage (0°C). Carbon dioxide series above 5% show promise in reducing the 35% storage loss that occurred with the 5% CO2 treatment. Curing for at least 72 hours followed by a 1-hour ClO2 fumigation resulted in the least bulb decay and after 15 weeks of storage (1% O2, 5% CO2), 75% of the bulbs were in marketable condition. Onions stored 15 weeks in air (0°C, 70% RH) were unmarketable. Shelf life of freshly harvested onions was 18 days, after which the onions rapidly decayed. After CA storage, shelf life was reduced to 10-14 days due to rapid sprouting. To enjoy a 30-day market window, disease control is necessary for freshly harvested onions and sprouting must be controlled in post-storage onions.