Effects Of High Oxygen Atmospheres On Quality Maintenance And Its Mechanisms In Strawberry Fruit

Freshly harvested strawberry (Fragaria ananassa, Duchesne.FengXiang) fruits were placed in jars and continuously ventilated with air or with 40%, 60%, 80 % or 100% O₂ to investigate the effects of high oxygen atmospheres on postharvest physiology, quality, fruit decay and total antioxidantl activity during storage. The results were as follows:1. While the quality parameters of titratable acidity, total soluble solids, surface color measurements were only slightly affected by the superatmospheric O₂ levels, treatments with 60-100% O₂ significantly inhibited decay incidence; there was a decrease in decay with an increase in oxygen concentration, the 100% O₂ treatment was the most effective in controlling fruit decay. The 40% O₂ treatment was ineffective in inhibiting fruit decay. Fruit treated with O₂ concentrations at 60% or higher also exhibited significantly higher fruit firmness value, vitamin C content and less weight loss. These results suggest that high oxygen atmospheres may provide a potential alternative for postharvest decay control on strawberry fruit.2. Compared with the air-treated fruits, treatments with 60% or 100% O₂ maintained significantly higher levels of SOD, CAT and APX activities and Vitamin C content, inhibited the increases in superoxide radical production, MDA content and cellulase activity, and the decrease in fruit firmness. Fruit treated with high oxygen atmospheres also exhibited significantly less decay rate. Data obtained suggest that high oxygen atmospheres may maintain the balance of active oxygen metabolism in strawberries, thereby delaying fruit senescence and inhibiting fruit decay.3. Treatment with 60% or 100%O₂ maintained higher levels of PAL, PPO, chitinase and -l,β-glucanase activities and total phenolic content during cold storage at 5℃. When the fruits were removed from the high oxygen atmospheres and held for additional 1 day in air at 20 ℃, fruits treated with 60% or 100%O₂ also had significantly less decay rate and higher levels of PAL, PPO activities and total phenolic content. These results suggest the inhibition of fruit decay by high oxygen was related to the induction of defensive enzyme activities. The induced disease resistance may be involved in the mechanisms by which high oxygen treatment inhibited fruit decay in strawberry fruit.4. Treatment with 60%O₂ or 100%O₂ inhibited the decrease of vitamine C content, promoted the increase of total phenolic and anthocyanin contents and DPPH scavenging activity, thereby improving the antioxidant activity of strawberry fruit. Statistical analysis showed a positive linear relationship between total phenolic or anthocyanin content and antioxidant activity. The correlation coefficient for total phenolic content and total antioxidant activity was 0.8454 and that for total anthocyanin content and total antioxidant activity was 0.8997. Therefore, the increase of total antioxidant activity in strawberry fruit subjected to high oxygen treatments maybe attributed to the increase of total phenolic as well as total anthocyanin contents.