Changes in ethylene production, carbohydrase activity and antioxidant status in pepper fruits during ripening

Abstract

The aim of the present study was to evaluate the changes in ethylene production, carbohydrase activities and antioxidant status in pepper Kulai at different ripening stages. This cultivar of pepper fruits exhibits a peak in ethylene production during stage 3 of ripening. The production of 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC oxidase activity also peaked during stage 3, whereas ACC synthase activity increased gradually during ripening. In the carbohydrase activity study, the β-galactosidase activity increased significantly, whereas the α-mannosidase and α-galactosidase activities remained low and fairly constant throughout the ripening process. The lipoxygenase (LOX) activity, lipid peroxidation level and hydrogen peroxide content were also examined to evaluate changes in oxidation status. The LOX activity and hydrogen peroxide concentration decreased during ripening, whereas lipid peroxidation increased. However, the total antioxidant potential also increased, most likely as a defensive response towards oxidative stress. The activities of ascorbate peroxidase (APX) and glutathione reductase (GR) and the total phenolic content significantly increased during ripening. Furthermore, ascorbic acid levels greatly increased, and the ratio of reduced glutathione (GSH) to oxidised glutathione (GSSG) remained constant. However, the activities of superoxide dismutase (SOD) and catalase (CAT) declined. The overall results indicated that pepper Kulai is a climacteric fruit and that β-galactosidase activity increases as the fruit ripens and softens, suggesting a role for this enzyme in cell wall modification. In addition, the results presented here also revealed that the antioxidant capacity is enhanced during the ripening process and is accompanied by an increase in oxidative stress.