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A special low oxygen controlled atmosphere combination and its effect on controlling apple superficial scald
Abstract
The efficacy of low oxygen controlled atmosphere (CA) treatment combinations (2% O2 + 3, 7.5 or 12% CO2) in controlling superficial scald in apple cv. Meiguihong, a strain of Delicious, stored at 0 and 10°C, was investigated. Fruits stored at 2% O2 + 7.5% CO2 were firmer and had a higher chlorophyll content compared with those stored under control (0°C, air) conditions. However, the contents of α-farnesene and conjugated trienes of fruits stored under this CA treatment were lower than those stored under control conditions after 121 days. Thereafter, fruits stored at 10°C + 2% O2 + 7.5% CO2 were scald-free after storage in air at 20°C for 7 days or at 5-7°C for 122 days. Fruits stored at 0°C + 2% O2 + 7.5% CO2 were also scald-free after storage in air at 5-7°C for 30 days. The results indicate that suitable low oxygen CA treatment can control superficial scald of apples for a longer period after low oxygen CA storage.
Based on a successful experiment of a special low oxygen CA combination storage, 2394kg apples were treated in a chamber enclosed by 0.12mm thickness of PE film, gas composition was adjusted by nitrigen gas during the first 4 months; then the PE chamber was sealed and the apples were in MA storage during next 2 months. The results indicted that the oxygen level in the PE chamber could be adjusted to 2% low oxygen level and carbon dioxide could be maintained in the ideal range during the first 4 months. Then, when gas composition was not adjusted, it could still be mainrained at 6.6%-10.6% O2 and 8.6-9% CO2 during next 2 months. After 6 months of storage, the treated apples kept good fresh appearance, low scald incidence (1.7%) , low decay rate, high flesh firmness and high chlorophyll level. Furthermore, the apple scald incidence was only 5.9% after another 51 days of cold storage.
The physiological basis of post - storage effects of low - oxygen CA treatment which can control superficial scald of apples for a longer period was studied, using Starkrimson apple as experimental material. The results showed that the α- farnesene and conjugated trienes contents of special CA - treated apples were significantly low ,its fruit firmness , soluble solids and peel chlorophyll levels were almost the same as those of standard CA ,equal to or higher than those of cold storage in air after 4 months. When special CA - treated apples were stored in cold air ,α- farnesene and conjugated trienes contents of special CA - treated apples were high ,but apples were still scald - free during 2 months of post - storage periods. The formations of α- farnesene and conjugated trienes were significantly inhibited by special CA treatment during CA storage and the accumulation peak of conjugated trienes was delayed to appear after a longer post - storage period ,this may be the reason why no scald fruit was observed among special CA - treated apples during a longer post - storage period.
We formerly reported a special lowoxygen CA combination (2 %O2 + 7. 5 %CO2) , which can control superficial scald of apples for a longer period after 4 months of treatment . Now , a further experiment of Starkrimson apples was conducted to study the effects of delayed and shortened treatment . The results showed that the scald incidence of apples of control (0 ℃, air) and conventional CA treatment (0 ℃, 3 %O2 + 3 %CO2) were 25. 6 % and 1. 02 % respectively , and their flesh firmness were 5. 79 and 6. 52 kg/ cm2 respectively after 123 days of storage. The apples of special CA treatment (10 ℃, 2 %O2 + 7. 5 %CO2) was scald2free after 123 days of storage , its flesh firmness (6. 63 kg/ cm2) was the same as that of conventional CA treatment and significantly higher than that of control . The apples of delayed treatment developed scald (6. 67 %) after 15 days of storage at 10 ℃in air and 108 days of special CA treatment , its flesh firmness (4. 8 kg/ cm2) was significantly lower than those of control and conventional CA treatment . These results indicted that it is necessary to treat apples with special CA combination on time. The scald incidence of apples of control , conventional CA treatment and special CA treatment were 46. 9 % , 36. 4 % and 0 respectively after 123 days of storage plus another 58 days of cold storage in air , their flesh firmness were 5. 28 , 5. 21 and 4. 5 kg/ cm2 respectively. The apples of special CA treatment was also scald-free after 96 days of storage plus another 50 days of cold storage in air , its flesh firmness was 4. 67 kg/ cm2 . Based on the consideration of both scald incidence and flesh firmness , it is possible to change the duration of special CA treatment from 4 months to 3. 3 months if we want to store apples for about 5 months. The formations of α-farnesene and conjugated trienes in the peels of apple fruits were significantly inhibited by special CA treatment during CA storage.
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