Oleuropein, the main phenolic compound of olive fruit, has important antioxidant properties that are responsible for some of the nutritional properties of fruits and the defence mechanism of leaves. Polyphenol oxidase (PPO) activity changes during fruit ripening in many plants. We studied the kinetics and molecular properties of PPO in fruits and leaves of olive (Olea europaea L.) cv. 'Picual' trees and the relationship between PPO and oleuropein concentration during fruit ripening. Polyphenol oxidase showed hyperbolic kinetics in fruits and leaves. Significant increases in PPO specific activity, V(max), K(m )and catalytic efficiency occurred during fruit ripening. Based on SDS-PAGE under partially denaturing conditions and in-gel staining with DL-3,4-dihydroxyphenylalanine, PPO activity was found in one major protein of 55 and 50 kDA in fruits and leaves, respectively. During the last stages of fruit maturation, a second 36 kDa protein was observed in fruits but not in leaves, indicating that this protein could serve as a marker of the final phase of fruit maturation. Under fully denaturing conditions, only one 27.7 kDa immunoreactive band was detected in fruits. Both the amount of PPO activity and the amount of PPO protein increased significantly during fruit maturation. Immunohistochemical studies indicated that PPO is located in the epidermis, parenchyma and companion vascular cells of leaves as well as in the epidermis of fruit. During fruit maturation, oleuropein concentration measured by HPLC significantly decreased in fruits and increased in leaves.

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Pentacyclic triterpenoids are plant secondary metabolites of great interest for health and disease prevention. HPLC-UV/vis was used to determine the concentration of the pentacyclic triterpenoids present in fruits and leaves of Picual and Cornezuelo olive tree cultivars. Maslinic acid (MA) and oleanolic acid (OA) are the only two compounds present in fruits, MA being the more abundant. In leaves, in addition to MA and OA, uvaol (UO), and erythrodiol (EO) are found, with OA being the most abundant. In this work, the changes in the concentrations of these compounds during ripening as well as the effect of Jaén-style table-olive processing are reported. The amount of MA and OA found in Picual and Cornezuelo olives after processing was 1.26 ± 0.06, 1.30 ± 0.06, 0.31 ± 0.02, and 0.23 ± 0.01 mg per fruit, respectively. These results enable us to calculate the average intake of pentacyclic triterpenoids and reinforce the importance of table olives as a source of healthy compounds.