Mechanical Stress Stimulates Peroxidase Activity in Cucumber Fruit

Abstract

Abstract Peroxidase activity was determined in cucumber fruit (37 to 55 mm in diameter) subjected to mechanical stress followed by storage at 25C and 100% RH. Compared to unstressed, unstored control fruit, severe mechanical stress stimulated total extractable peroxidase activity after 24 and 48 hr of storage. Moderate mechanical stress or storage alone stimulated peroxidase activity to lesser degrees. Peroxidase isozyme analysis by native polyacrylamide gel electrophoresis showed that cucumber anodic peroxidases could be separated into slow-, moderate-, and fast-migrating groups. Both moderate and severe mechanical stress caused the appearance of a new slow-migrating peroxidase isozyme immediately after treatment. This slow-migrating isozyme disappeared after 24 hr of storage, then reappeared after 48 hr. Severe stress induced the appearance of two additional moderate-migrating peroxidases 24 hr after treatment. The same fast-migrating isozymes were also present in unstressed and moderately stressed fruits stored for 48 hr. Hence, using peroxidase as an indicator, it appears that mechanical stress induces an accelerated aging of processing cucumber fruit.