Physiological responses of apple fruits to oxygen concentrations

SUMMARY The effects of oxygen concentration on respiration and ripening processes in apple fruits at storage temperatures have been investigated. The response of carbon dioxide production to a change in O2 concentration occurred after a delay of 1–4 days, depending upon the time and direction of change. When apples were stored in flowing streams of oxygen/nitrogen mixtures the time of onset of ethylene production was inversely related to oxygen concentration and the maximum rate of production was directly related to oxygen. However when apples were stored in product‐generated atmospheres low ventilation caused rapid accumulation of ethylene. The retardation of ripening processes by low oxygen concentrations observed under these conditions was not, therefore, a result of inhibition of ethylene synthesis. When permanganate was present in the storage container the build up of ethylene was delayed, especially at low oxygen concentrations. In these conditions there was sometimes a further retardation of softening and soluble polyuronide formation. Rates of chlorophyll degradation in peel and cortex, flesh softening and soluble polyuronide formation were all half maximal at 2.5–4.0% O2.