Tolerance of plum (Prunus domestica L.) fruits stored in low-oxygen atmosphere

Plum fruits of the cultivars Stanley and Valjevka picked at the beginning of climacteric were stored in different storage atmospheres for 31 days at 3°C. The relations between the O2 and CO2 content during this period and after removal from the gas mixture to ethanol, acetaldehyde, non-volatile compounds and some textural values of fruits were investigated. Concentrations of ethanol in the flesh were related to levels of oxygen and CO2 in ambient atmosphere. In anaerobic conditions (< 0.2% O2) ethanol reached 1,109 mg/l for the cultivar Valjevka and 628 mg/l for Stanley. The results of single fruit analysis showed a steeply increasing concave curve of ethanol production in the period of anaerobic conditions, followed by the phase of a drop of the production rate in air stored fruit. The concentration of oxygen at a level of 0.9% (ultra low oxygen - ULO) does not physiologically harm the tissues of plums by producing mostly negligible content of ethanol and acetaldehyde, but an ethanol increase to half concentration after 31 days was observed to compare with anaerobic conditions in the cultivar Valjevka. From this aspect plums seem to be relatively sensitive to low oxygen. The post-storage period was extended up to 53 to 63 days, respectively. The senescence caused an increase in ethanol production rate that was exponentially increased after 20 days of cold storage atmosphere. The final concentration after 53 days was still higher for cv. Valjevka than for cv. Stanley at the respective content of 828 mg/land 498 mg/l. Skin firmness was differentiated for both cultivars, and softness was higher for the cultivar Valjevka.