Physiological responses and quality attributes of Japanese pear 'Kosui' fruit kept in low oxygen atmospheres

Japanese pear 'Kosui' fruits were stored under a continuous flow of 0 %, 1 %, 3 %, 5 % and 10 % O-2 (balance N-2) or air for 7 d at 20degreesC to study the effects of low O-2 on their physiological responses and quality attributes. Low O-2 treatments did not significantly influence changes in skin colour and soluble solids content. However, weak off-flavours were detected in the fruits stored at 0 % O-2 on day 3, and the intensity of these off-flavours increased as storage progressed. The concentrations of acetaldehyde in fruit increased throughout the storage period. The ethanol concentration was greatly increased in fruits stored at 0 % O-2. Moreover, ethanol concentrations were much higher than those of acetaldehyde and remained very low during storage in air, but their concentration were just slightly increased in fruits exposed to 1 %, 3 %, 5 % and 10 % O-2, Pyruvate decarboxylase activity was greatly increased in fruits exposed to 1 % and 3 % O-2, while its activity in fruits exposed to 5 % and 10 % O-2 were only slightly higher than that of the control and at 0 % O-2 at the same level as the control. Alcohol dehydrogenase (ADH) activity greatly increased in fruit exposed to 0 %, 1 %, 3 % and 5 % O-2, while at 10 % O-2, ADH was only slightly higher than the control. Changes in ADH isozymes correlated well with changes in ADH activity. The homogenate pH of fruits exposed to 1 %, 3 %, 5 % and 10 % O-2 and air remained constant, while in fruit stored at 0 % O-2 their pH increased. The potential for using low O-2 atmospheres to help in maintaining the quality of Japanese pear 'Kosui' is discussed.