Histochemical localization and developmental expression of peroxidase and polyphenol oxidase in strawberries

Levels and histochemical localization of pc I oxidase and polyphenol oxidas e, and levels of anthocyanins and (+)-catechin, were studied in fruit of tw o strawberry (Fragaria xananassa ouch,) cultivars ('Oso Grande' and 'Chandl er'), which show different degrees of susceptibility to enzymatic browning after processing. Although the levels of anthocyanins at the processing-rip e stage may be important in determining pigment stability, and therefore ma rket suitability, the color stability of 'Chandler' is apparently determine d hy the lon:er endogenous levels of peroxidase and polyphenol oxidase in t he processing-ripe stage, which are also accompanied by a lower (+)-catechi n content. Polyphenol oxidase was localized almost exclusively in the corte x and to a lesser extent in the pith, showing a complementary pattern to th at shown hy peroxidase, which was localized in the vascular bundles. Since peroxidase and polyphenol oxidase showed a complementary localization patte rn in the fruit, these results strongly suggest a synergic role for these t wo oxidative enzymes in pigment decay and the associated browning reaction, which occurs in processed strawberry fruit and their derived foods.