Postharvest ripening and ethylene biosynthesis in purple passion fruit

A study was undertaken to investigate the pattern of changes in some chemical constituents, ethylene biosynthesis, and the effect of ethylene treatment during postharvest ripening in purple passion fruit (Passiflora edulis Sims.). During ripening, sucrose content decreased while fructose and glucose contents increased. Citric and malic acid contents slightly increased during the early stage of ripening and decreased thereafter. Amino acids did not change significantly, except for proline, which increased rapidly towards the late stage of ripening. While 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC synthase activity increased in parallel with ethylene production, ACC oxidase activity was already high when harvested at the turning stage and further increased during ripening. Application of 1000 ppm ethylene for 24 h did not induce earlier onset of ethylene production when applied on harvest day, but was effective when applied one day or five days after harvest. The results indicate that purple passion fruit produces ethylene with the same biosynthetic pathway as other tissues in higher plants; its ethylene biosynthesis is regulated mainly by ACC synthase activity, and the sensitivity to ethylene might have changed after harvest as the fruit ripened.