Oleuropein Degradation Research Articles

Cell and tissue localization of β-glucosidase during the ripening of olive fruit ( Olea europaea) by in situ activity assay

Olea europaea is an endemic tree in the Mediterrranean basin of large economic interest for both oil and fruits production. One of the main problems to solve for improving the fruit quality is olive debittering. Thus we aimed to study, at cytological level, the β-glucosidases involved in the enzymatic degradation of oleuropein, a bitter defence phenol glucoside. This work represents the first insight on the in situ localization of β-glucosidase activity in the mesocarp tissue of olive during fruit ripening. The cytological localization is performed by the hydrolysis of X-Glc, a chromogenic synthetic substrate developing an insoluble blue precipitate in the cells. A strong reaction is detected within nucleus, chloroplasts and cytoplasm oil droplets. The enzymes kept in chloroplasts and oil droplets showed high specificity for the exogenous oleuropein respect to those toward X-Glc in the in situ competitive assay, thus indicating that two different oleuropein-degradative-β-glucosidases are present in these cell compartments. Following the fruit ripening, significant variations in the number and distribution of reactive cells in mesocarp tissues are observed. In fact in immature fruits the reactive cells are very few and located in the inner mesocarp zone; thereafter, in green mature fruits a great number of reactive cells are found distributed in the whole mesocarp. Finally in black fruits numerous reactive cells are located only in the inner mesocarp close by the woody endocarp, whereas the outer mesocarp cells are devoted to polymeric anthocyanins accumulation. These results clearly showed that the variations of oleuropein-degradative-β-glucosidases activity during ripening are due to changes in the competence of single mesocarp cells to synthesize the enzyme isoforms.

Changes in phenolic and enzymatic activities content during fruit ripening in two Italian cultivars of Olea europaea L.

During the ripening of two Italian cultivars of Olea europaea L. ( Ascolana Tenera and Frantoio Seedling no. 17 ( FS17)) we have identified a β-glucosidase activity that contributes to the oleuropein degradation during maturation as well as an esterase activity, whose trend during the ripening is hypothesised to be linked to the fatty acid biosynthesis involved later in the maturation of fruits. This activity, in fact, is involved in the estereolysis of C 3 and C 4 esters that supply acetyl-CoA as the basic unit for fatty acid biosynthesis. The data obtained during the ripening indicate that polyphenol content and composition, in particular the oleuropein concentration, and their correlation with the recovered enzymatic activities, will be useful for a biochemical characterisation of different O. europaea L. varieties as important parameters in testing the quality of the obtainable oils.

Oleuropein Site Selective Hydrolysis by Technomimetic Nuclear Magnetic Resonance Experiments

Technomimetic NMR experiments were performed in accordance with the lye treatment adopted during table olive industrial procedures for the debittering process causing oleuropein degradation. The site selective hydrolysis of the two ester groups, characterizing the biophenolic secoiridoid molecule, was shown to be dependent on the different reactivities of these functionalities. The process is controlled by the experimental conditions exerted on the olive pulp and determined by the buffering capacity of the olive mesocarp and by the epicarp molecular components influencing the reactant penetration into the fruit pulp. The overall hydrolytic process of oleuropein, the bitter principle of olives, using the technomimetic experimental mode, gave rise to its catabolic derivatives, hydroxytyrosol, 11-methyloleoside, and the monoterpene glucoside, technomimetically produced, isolated, and structurally characterized by (1)H, (13)C, and COSY spectroscopy as the oleoside.