Postharvest Variation in Cell Wall-Degrading Enzymes of Papaya (Carica papaya L.) during Fruit Ripening

Abstract

Pectin methylesterase (PME), polygalacturonase (PG), xylanase, cellulase, and proteinase activity were determined and related to respiration, ethylene evolution, and changes in skin color of papaya (Carica papaya L.) fruit from harvest through to the start of fruit breakdown. PME gradually increased from the start of the climacteric rise reaching a peak 2 days after the respiratory peak. PG and xylanase were not detectable in the preclimacteric stage but increased during the climacteric: during the post climacteric stage, the PG declined to a level one-quarter of peak activity with xylanase activity returning to zero. Cellulase activity gradually increased 3-fold after harvest to peak at the same time as PME, 2 days after the edible stage. Proteinase declined throughout the climacteric and postclimacteric phases. A close relationship exists between PG and xylanase and the rise in respiration, ethylene evolution, and softening. Cultivar differences in postclimacteric levels of enzymic activity were not detected.