Differences of biochemical components between the skin tissues of normal and black-speckled 'd'Anjou' pears after prolonged low-oxygen storage

A proportion of 'd'Anjou' pear fruit (Pyrus communis L.) developed a disorder, "black speck" or "skin speckling", after prolonged controlled atmosphere (CA) storage (1% O2, -0.5C). A comparative study of biochemical components revealed that there was no significant difference in succinic, citric, fumaric, and pyruvic acids between the speckled and normal skin tissues. The content of malic acid in the affected tissue was almost three times lower than that in the normal tissue. The specific activity of NADP-malic enzyme (EC 1.1.1.40) in the affected tissue was also lower, but the total activities were similar. The affected tissue contained higher percentages of dry matter and soluble proteins than the normal tissue. Two-dimensional gel electrophoresis of proteins showed that two groups of novel polypeptides appeared only in the affected skin tissue. This study indicated that a certain proportion of 'd'Anjou' pear fruit might have been exposed to unfavorable preharvest environmental stresses, and, therefore, could no longer tolerate the subsequent semi-anaerobic and chilling stresses during prolonged CA storage