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The biosynthetic pathway of oleuropein (from 7-ketologanin, oleoside-11-methyl ester, 7-β-1-d-glucopyranosyl-11-methyl oleoside, and ligstroside to oleuropein) was investigated in two fruit species of Oleaceae, namely, Arbequina and Hojiblanca. Main oleuropein precursors and their metabolites, produced by the enzymatic hydrolysis mediated by β-glucosidase, were identified and quantified to establish the oleuropein transformation pathway. Changes in the concentration of these compounds were measured by direct control of in vivo fruit tissue during their ripening. High contents of aglycones at the initial stage of the process were caused by the high activity of β-glucosidase, which supports that oleuropein biosynthesis is coupled with enzymatic hydrolysis, producing its aglycone form. The low oleuropein content at this initial stage was caused by the imbalance between catabolic and anabolic pathways, favoring the former ones. Once the main polyphenol synthesis phase was completed, the biosynthetic capacity diminished and the content of all compounds decreased. Mass balance revealed that precursors of oleuropein, which are rapidly transformed by β-glucosidase and esterases, scarcely contributed to the accumulation of oleuropein. The biosynthetic pathway proposed by Damtoft applies for both varieties, but our study reveals that the β-glucosidase enzyme is involved in oleuropein synthesis. This enzyme shows high substrate specificity to oleuropein, which consequently is degraded to its aglycone form, with diminished efficacy of oleuropein biosynthesis. Different enzymatic activities of varieties will result in oleuropein accumulation and metabolic transformation of phenols.

The present study investigates oleuropein metabolism, as well as the involvement of β-glucosidase during the growth, development, and ripening of olive fruit. The results show that in olive fruit the in vivo formation and transformation of oleuropein takes place in three different stages. The first one is characterized by a net accumulation of oleuropein and occurs in the immature fruit. In the second stage, associated with the green and light-green fruits, oleuropein content is maintained practically constant, and finally, a third stage that begins in the green-yellow fruit is characterized by a progressive decline of the oleuropein concentration. Our findings confirm that in the absence of β-glucosidase the Damtoft-proposed pathway is active and that net synthesis of oleuropein is unquestionable. β-Glucosidase activity plays a key role in the oleuropein metabolism catalyzing its in vivo hydrolysis.

This work reports on the composition and bionutritional value of organic virgin olive oil from the Nocellara del Belice variety, one cultivated in the olive areas of the Sicily region, Italy. Destoned oils obtained by processing olives with a destoning-based procedure were compared with conventional oils. This innovative technique, consisting in removing the stone from fruits prior to processing, strongly enhanced the already high-quality level of the conventional product. An in-depth analytical investigation from 2008 to 2010 showed how this innovative olive extraction process led to an excellent peculiar final product, mainly attributable to the improved biophenol and volatile composition, as well as higher concentrations of the lipophilic and vitamin antioxidants (tocopherols and tocotrienols). It had higher levels of oleocanthal (p-HPEA-EDA), a nutraceutical compound exerting actions against COX1 and COX2 (cycloxygenases). Its head-space aroma displayed new volatile phytomolecules and also had higher levels of green volatiles from the lipoxygenase (LOX)-pathway (one having as precursors the polyunsaturated fatty acids containing a cis-cis-1,4-pentadiene system). Among the other bioactives, we highlight its significant levels of trans-β-carotene and xanthophylls (lutein, violaxanthin, neoxanthin and other carotenoids). Its enhanced nutritional value was also attributable to the increased intensity of valuable tasting notes.

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