Ethylene Scrubbing Offers No Firmness and Scald Benefits to 'Golden Delicious,' 'Delicious,' and 'Spartan' Apples in Low-Oxygen Storage
British Columbia-grown 'Golden Delicious', 'Delicious', and 'Spartan' apples are tolerant to a 1.0% O2 storage atmosphere. These cultivars store well commercially at 0°C in a rapidly established 1.0%-1.5% O2 + 1.5% CO2 atmosphere. The observation of a firmness benefit with low-ethylene storage of 'McIntosh' has generated considerable interest in the Pacific Northwest in using ethylene scrubbing to extend the storage life of apples. However, most of the previous low-ethylene storage studies involved flow-through systems, fruit from single orchards, and carefully controlled harvest conditions. Results of such experiments are difficult to apply to large commercial operations where fruit lots vary considerably in maturity and quality.
Ethylene scrubbing is a relatively expensive process. The experiments reported herein evaluated whether removal of ethylene in a rapidly established 1.5% or 0.7% O2 + 1.5% CO2 storage atmosphere could improve firmness in 'Golden Delicious', 'Spartan', and 'Delicious', and control scald in 'Delicious' apples from commercial sources.
Materials and Methods
Samples of 'Delicious' (DPA-treated), 'Golden Delicious', and 'Spartan' apples (15 fruit lots per cultivar per year) were randomly selected at commercial CA plants in Oliver, Kelowna, and Vernon, B.C., in the early part of the harvest season. The harvest dates were those recommended by the B.C. Apple Maturity Evaluation Program. Internal ethylene concentration in fruit before storage was determined by gas chromatography using a 1-ml gas sample withdrawn from the seed cavity of each fruit.
The storage samples were cooled in 0°C air for 28 hours and then sealed in 1.7-m3 CA cabinets held at 0°C. Continuous operation of a blower fan (2.8 m3 per minute) inside each cabinet raised the storage temperature from 0°C to 1.5°C during the experimental period. Each low-ethylene cabinet was equipped with an internal ethylene scrubber, with 10 kg of Purafil beads (potassium permanganate-alumina) spread evenly over four trays (25 x 70 x 3 cm); the blower-fan circulated the storage atmosphere through the Purafil beads. The amount of Purafil and air movement employed exceeded those suggested by Blanpied.
Storage ethylene was maintained below 1.0 ppm during the first 3 months and never exceeded 6.3 ppm during subsequent months of storage. Ethylene levels in the high-ethylene cabinets were increased gradually by additions of ethylene at a rate of ~100 ppm per month to simulate accumulation of ethylene in non-ethylene scrubbed CA storage. Storage ethylene was measured weekly by gas chromatography. The desired 1.5% O2 + 1.5% CO2 levels were established within 32 hours (by purging with N2) and 6 days of loading (by respiration and additions of CO2), respectively.
Four replicates of 'Delicious' apples were obtained each year from each of eight random fruit lots at a commercial CA plant. The samples were held in 0°C air for 24 hours and then sealed in 0.2°C cabinets. The desired 1.5% or 0.7% O2 levels were established within 24 or 32 hours after sealing by purging with N2. The 1.5% CO2 levels were established within 4.5 days by fruit respiration and additions of CO2 as required. Each low-ethylene cabinet was equipped with a blower-fan and an internal ethylene scrubber as described above. Storage ethylene was kept below 1 ppm during the first 3 (1986) or 6 (1987) months of storage and never exceeded 3.7 (1986) or 4.7 (1987) ppm during subsequent months of storage. Content in the high-ethylene cabinets (1986 = 0 to 819 ppm; 1987 = 0 to 772 ppm) was increased gradually by adding ethylene at a rate of approximately 100 ppm per month.
After storage and a short holding period in 0°C air plus a 7-day shelf-life test in 20°C air, subsamples of 15 (1983-85) to 40 (1986-87) apples from each storage treatment were assessed for flesh firmness and scald.
Results and Discussion
Removal of ethylene from a static 1.5% O2 + 1.5% CO2 storage atmosphere did not significantly improve the retention of flesh firmness in 'Delicious' (1-2 N) and 'Golden Delicious' (0-3 N) apples. For unknown reasons, ethylene removal led to a small (1-2 N) decrease in firmness in 'Spartan' apples in many instances (Table 1). The lack of firmness response to ethylene scrubbing was evident because 1.5% O2 storage with added ethylene (Table 1) or a non-ethylene scrubbed low-O2 atmosphere was effective in itself in maintaining a satisfactory firmness in the fruit. Low O2 and/or elevated CO2 are known to inhibit the action and production of ethylene. Low-ethylene storage is beneficial in the retention of firmness of 'McIntosh' and 'Spartan' apples held in high O2, but not for those held in low O2 levels. Low ethylene has no effect on the retention of firmness in 'Delicious' from single orchards or in 'McIntosh' apples from commercial sources held in 2.2%-3.0% O2 + 2.5%-5% CO2.
Table 1. Firmness of 'Golden Delicious,' Delicious,' and 'Spartan' applesz held in 1.5% O2 at 1.5 °C with and without ethylene scrubbing (n=15 commercial fruit lots per year).
|1983||Ethylene (ppm)y||Firmness (N)||Ethylene (ppm)||Firmness (N)||Ethylene (ppm)||Firmness (N)|
|1984||Ethylene (ppm)||Firmness (N)||Ethylene (ppm)||Firmness (N)||Ethylene (ppm)||Firmness (N)|
|1985||Ethylene (ppm)||Firmness (N)||Ethylene (ppm)||Firmness (N)||Ethylene (ppm)||Firmness (N)|
concentrations in fruit
before storage were 0.03, 0.7, and 0.3 ppm in 'Golden
Delicious'; 14, 14,
and 3 ppm in 'Delicious'; and 38, 89, and 36 ppm in
'Spartan' apples in
1983, 1984, and 1985, respectively.
DPA-treated 'Delicious' apples were virtually free of scald upon removal from the 1.5% O2 + 1.5% CO2 storage (1983-85) and after a 7-day 20°C shelf-life test (1984-85; Table 2). In 1983, when DPA did not completely control scald, low-ethylene decreased scald in the fruit held 7 days in air at 20°C air (Table 2).
Table 2. Incidence of scald in DPA-treated 'Delicious' applesz after storage in 1.5% O2 +1.5% CO2 at 1.5°C with and without ethylene scrubbing (n=15 commercial fruit lots per year).
|Ethylene (ppm)y||Scald (%)||Ethylene (ppm)||Scald (%)||Ethylene (ppm)||Scald (%)|
concentrations if fruit
before storage were 14, 14, and 3 ppm in 1983, 1984, and
In 1986-87, incidence of scald was high in non-DPA 'Delicious' apples held in 1.5% O2 + 1.5% CO2 but low in fruit held in 0.7% O2 + 1.5% CO2 (Table 3). However, ethylene scrubbing had no effect on scald in fruit held in 0.7% or 1.5% O2 (Table 3). Patterson and Workman found that high ethylene did not increase scald in 'Gallia Beauty' apples over that obtained from constantly renewed air. Dover has found inconsistency in ethylene scrubbing and scald reduction in 'Bramley's Seedling' apples.
Table 3. Incidence of scald in non-DPA 'Delicious' applesz held in 1.5% 02 + 1.5% CO2 at 1.5 with and without ethylene scrubbing (n=8 commercial fruit lots per year).
|1986||Scald (% of fruit)||1987||Scald (% of fruit)|
|Ethylene (ppm)y||1.5% O2||0.7% O2||1.5% O2||0.7% O2||Ethylene (ppm)||1.5% O2||0.7% O2||1.5% O2||0.7% O2|
|Scrubbing X O2||ns||ns||Scrubbing X O2||ns||ns|
concentrations in fruit
before storage were 45 and 7.7 ppm in 1986 and 1987,
In summary, British Columbia-grown 'Golden Delicious', 'Spartan', and 'Delicious' apples stored successfully in 1.5% O2 + 1.5% CO2 storage. Removal of ethylene from the storage atmosphere did not improve flesh firmness of the fruit. Except in one incidence, ethylene scrubbing did not appear to serve a useful function in control of scald in 'Delicious' apples held in 1.5% or 0.7% O2. In regions where apples cannot be kept safely in low-O2 storage because of risks of fruit injury, low-ethylene storage has been developed as a nonchemical means to control scald and as a substitute for low-oxygen storage to retard flesh softening and senescence.
Acknowledgments: Appreciation is extended to R. Yastremski, R. Potter, M. Bacon, L. Ostegaard, F. Illig, and D. Worley for their capable assistance. Special thanks are due to the Summerland Research Station for providing research facilities.
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Industry Research Program
Okanagan Federated Shippers Association, Kelowna
c/o Agriculture and Agri-Food Canada
Pacific Agri-Food Research Centre
Summerland, B.C. Canada V0H 1Z0
Dr. O. L. (Sam) Lau, Postharvest Physiologist
Industry Research Program, Okanogan Federated Shippers Association, Canada
Tree Fruit Postharvest Journal 10(1):15-17