Polyphenol oxidase enzymes in the sap and skin of mango fruit.
Robinson S. P., Loveys B. R., Chacko E. K.
Author Affiliation: Division of Horticulture, CSIRO, GPO Box 350, Adelaide, SA 5001, Australia.
Australian Journal of Plant Physiology 20 : 99-107
Abstract : The sap and the skin of ripe mango cv. Kensington fruits both contained considerable polyphenol oxidase [catechol oxidase] (PPO) activity. The sap enzyme was not activated by SDS, was inhibited by hexadecyltrimethylammonium bromide and was active on both para- and ortho-diphenol substrates, whereas the skin enzyme was activated by SDS, was inhibited by salicylhydroxamic acid and polyvinylpyrrolidone and was only active on ortho-diphenol substrates. From these properties, is was concluded that the sap PPO is a laccase-type enzyme (EC 1.10.3.2) whereas the skin contained the more common catechol oxidase-type PPO (EC 1.10.3.1). The skin enzyme had a temperature optimum of 30°C, compared with 75°C for the sap enzyme. Both were relatively thermostable, requiring more than 15 min at 80° for 50% loss of activity. It was concluded that sap-induced skin browning (sapburn) is predominantly catalysed by PPO in the skin and that this is unlikely to be prevented by heat treatment of the fruits.