PURIFICATION AND CHARACTERIZATION OF A BASIC PEROXIDASE ISOENZYME FROM STRAWBERRIES

Canned syrup strawberries (Fragaria ananassa var. Oso Grande, Tudla an d Chandler) after appertization showed significant signs of red pigmen t decay and the appearance of visible browning reactions. Even after t his industrial processing, residual peroxidase activity may be measure d in drained (syrup-free) canned strawberries, suggesting that a parti ally thermostable peroxidase activity may be involved in these brownin g reactions. Strawberries contain a peroxidase isoenzyme of basic pi, which is the only component of peroxidase polymorphism in the whole fr uit. For this reason, this isoenzyme was purified by preparative isoel ectric focusing in glycerol-stabilized 3.5-10.0 pH gradients and by li quid 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) activitie s. These results, and the previous observation that its homologous iso enzyme in other plant species may play a role in anthocyanin turnover and degradation, suggest that a participation of this peroxidase isoen zyme in browning reactions in canned syrup strawberries should be take n into account.