Some Advantages and Disadvantages of Low-Oxygen Storage of Red Delicious Apples
Studies of low-oxygen storage of Red Delicious apple fruit were conducted in Oregon, Washington and British Columbia. The first test in Oregon was conducted at 30°F (-1 °C) in metal chambers (12 cu ft) with a constant gas mixture passing over the fruit. In 3 chambers the carbon dioxide was held to a minimum with lime and the oxygen levels were 0.5, 1.0 and 1.5%. Another 3 chambers were given the same oxygen levels, but the carbon dioxide produced by the fruit was allowed to equilibrate with the gas flow, which resulted in approximately 1% carbon dioxide. The last chamber had 1% oxygen and 3% carbon dioxide. Nitrogen made up the balance in all chambers. Control fruit were held in regular air storage at the same temperature. The following examinations were made.
After 7 months of storage, 10% of the fruit in 0.5% oxygen with equilibrated carbon dioxide showed ribbon like depressed skin browning, whereas fruit in other treatments were free from this disorder (Table 1). After 9 months of storage, a substantial number of fruit stored in all low-oxygen levels with carbon dioxide had developed the skin browning disorder. Fruit stored in 1.0% and 1.5% oxygen with equilibrated carbon dioxide and 3.0% carbon dioxide, however, were free from this type of disorder (Table 1). Since equilibrated carbon dioxide averaged about 1.0% throughout 9 months of storage, carbon dioxide seemed to suppress the development of this type of skin browning on fruit stored at 1.0% to 1.5% oxygen. The symptom of ribbon like, depressed skin browning was quite similar to low-oxygen injury. The storage temperature in this study was 30°F (-1°C). It is possible that the low temperature might enhance the occurrence of ribbon like, depressed skin browning of fruit under low-oxygen.
The development of storage scald was negligible on all apples stored at all levels of low-oxygen for 7 months. Eighty-seven percent of the air-stored fruit had developed storage scald after 7 months. After 9 months of storage, 25% of fruit stored in 1.5% oxygen with carbon dioxide below 0.03% had developed storage scald. However, only 8% of the fruit stored in the same oxygen levels (1.5%) with equilibrated carbon dioxide below 0.03% had developed storage scald. Other fruit stored in 0.5% to 1.0% oxygen, irrespective of carbon dioxide levels, had only 6% or less of fruit with storage scald. All fruit stored in air for 9 months had scald. It appears that storage in low-oxygen levels can protect apples against storage scald.
Firmness, Soluble Solids, Acidity
Fruit stored in low-oxygen atmospheres were about 2.2 pounds firmer than those stored in air after 7 ~ 9 months. Average flesh firmness values for the different low-oxygen treatments ranged from 14.4 pounds to 16.5 pounds after 7 months, and from 14.4 pounds to 15 pounds after 9 months. The soluble solids content of fruit from different low-oxygen conditions ranged 13.3% and 13.9%, with the lowest soluble solids (12.7%) being in fruit stored in air for 9 months. The titratable acidity was higher in low-oxygen stored fruit than those stored in air. The titratable acidity in fruit stored for 9 months was significantly less than that in fruits stored for 7 months (Table 1).
Apples stored at 1.0% and 1.5% oxygen with equilibrated carbon dioxide were ranked as having the best quality; apples stored at the same oxygen concentrations but with less than 0.03% carbon dioxide were next best (Table 1). Other fruit were ranked lower due to lack of flavor and/or the development of an alcoholic taste. All fruit stored in air for 7 and 9 months were mealy, dry and flavorless.
Small CA Room Experiment
In 1982 a small CA room was used and operated comparable to a commercial storage. Lime was used in the room to remove the carbon dioxide and the temperature was kept at 32°F (0°C). After 9 months of storage in 1% oxygen, 4% to 9% of fruit from Orchard 1 developed storage scald; fruit from other orchards were essentially free from storage scald in 1% oxygen (Table 2). All fruit in air storage developed storage scald after 9 months. ribbon like, depressed skin browning on fruit was not found in any of the Delicious strains in either 1% oxygen or air storage. Fruit stored in 1% oxygen were firmer and had higher soluble solids and titratable acidity than air-stored apples. Similar results were found the next year with the same conditions except the carbon dioxide level was maintained at 1%.
Although the development of storage scald on apples could be reduced effectively by 1% oxygen with or without carbon dioxide, fruit maturity and growing location can influence the effectiveness of storage scald control by low-oxygen. A detailed study of factors that may influence the development of low-oxygen injury and storage scald is essential prior to the commercial storage of apples in 1% oxygen.
Dr. Paul M. Chen
Mid-Columbia Agricultural Research and Extension Center, Oregon State University
3005 Experiment Station Dr., Hood River, OR 97031
FAX: (541) 386-1905
Post Harvest Pomology Newsletter, 3(1): 10-13