Effect of different oxygen levels on the metabolic activity and quality of apple fruits during storage

Oxygen serves as a critical regulator of metabolic processes in stored apple fruits. Reducing oxygen concentrations to the minimum permissible level—which prevents metabolic disorders while maximally suppressing metabolic activity—is of paramount interest driven by rising consumer demands for product quality and environmental safety. The present study aimed to determine the effect of atmospheric oxygen levels during storage on the physiological status, fruit quality, and storage potential of various apple cultivars. Conducted in 2023–2024, the study analyzed apple fruits of five commercial cultivars (Gala, Granny Smith, Jeromine, Red Delicious, and Fuji) grown in the North Caucasus Federal District (Stavropol Krai, Sady Stavropolya). Apple fruits of each cultivar were stored for eight months at a constant temperature of 1°C using three storage technologies with different oxygen levels: regular atmosphere (21.0% O2; 0.03% CO2); ultra-low-oxygen controlled atmosphere (1.2 ± 0.1% O2; 1.0 ± 0.1% CO2); dynamic controlled atmosphere (< 0.8% O2 depending on the cultivar; 0.8 ± 0.1% CO2). After the eight-month storage period, the oxygen concentration was found to significantly affect the physiological status and biochemical parameters of all studied cultivars, including endogenous ethylene levels, α-farnesene oxidation products (CT281), flesh firmness, soluble solids content, titratable acidity, and the development of physiological disorders and fungal diseases. The minimum permissible oxygen level under a dynamic controlled atmosphere was found to enable significantly more effective control over numerous physiological disorders in fruits, while preserving their quality (flesh firmness, juiciness, flavor, and aroma), compared to an ultra-low-oxygen controlled atmosphere and especially a regular atmosphere. The dynamic controlled atmosphere storage, based on maintaining the lowest possible yet safe oxygen level for the fruit, is becoming of particular importance for enhancing storage efficiency and extending shelf life in the absence of, or with limited, postharvest chemical treatments.

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