Purification and characterization of a basic peroxidase isoenzyme from strawberries

Canned syrup strawberries (Fragaria ananassa var. Oso Grande, Tudla and Chandler) after appertization showed significant signs of red pigment decay and the appearance of visible browning reactions. Even after this industrial processing, residual peroxidase activity may be measured in drained (syrup-free) canned strawberries, suggesting that a partially thermostable peroxidase activity may be involved in these browning reactions. Strawberries contain a peroxidase isoenzyme of basic pI, which is the only component of peroxidase polymorphism in the whole fruit. For this reason, this isoenzyme was purified by preparative isoelectric focusing in glycerol-stabilized 3.5–10.0 pH gradients and by liquid chromatography on CM-cellulose, and characterized as regards its catalytic properties against several phenols. The results showed that this isoenzyme is capable of oxidizing phenols only in the presence of H2O2, lacking oxidase (catecholase, cresolase, and laccase) activities. These results, and the previous observation that its homologous isoenzyme in other plant species may play a role in anthocyanin turnover and degradation, suggest that a participation of this peroxidase isoenzyme in browning reactions in canned syrup strawberries should be taken into account.