Demethyloleuropein and β‐glucosidase activity in olive fruits

Abstract

Demethyloleuropein plays a major role in the defense mechanism of olive fruits. To understand how this molecule is metabolized during different stages of maturation of olive fruits, a biomolecular approach to identify the demethyloleuropein chemistry was employed. The beta-glucosidase activity in crude extracts was assayed spectrophotometrically using the chromogenic substrate p-nitrophenyl-beta-D-glucopyranoside. Demethyloleuropein was extracted and identified by HPLC-MS from both infected and uninfected olive fruits at different physiological stages. The release of more functionally relevant dialdehydes in uninfected fruits was investigated using ESIMS/ MS. In fruits harvested in October, the activity of beta-glucosidase was significantly enhanced in uninfected fruits when compared to the infected fruits. Quantitative differences in the demethyloleuropein content from uninfected fruits showed the highest values (5.09 mg/g) in October, whereas lower levels (4.44 mg/g) were found in infected fruits. The results demonstrated that demethyloleuropein derivatives could be influenced by beta-glucosidase activity to improve the quality of the olive products with the best dialdehyde nutraceutical content.

Olive phenolic compounds: metabolic and transcriptional profiling during fruit development

“…These profiles are similar to those observed for transcripts putatively involved in secoiridoid synthesis. These results confirm the role of these enzymes in processes that lead to the decrease in phenolic concentration observed at 90 and 165 DAF, and their expression might be down-regulated whenever a lower availability of oleuropein, their main substrate, occurs [69]. A similar mechanism might explain the lower expression observed for both types of transcripts in the LP cultivar, where the lack of oleuropein could be due to differences in the regulation of enzymes involved in its biosynthesis rather than in its degradation.…”

Soft-MS and Computational Mapping of Oleuropein

“…However, the rate of cyclization depends on their substituents. For instance, the lack C11-carboxymethyl in oleacein from demethyloleuropein or the π-bond on C9 shifted to C8 in oleuroside slows down the overall dynamics to elenolate ring formation, since the electron withdrawn exerted by the C11-carboxymethyl lessens the nucleophilic attitude of C3-enol [2,6,60,61]. Therefore, the acetal hydrolysis of oleuropein at its seco-site is easy and rapid exclusively when activated by its native β-glucosidase [62].…”

“…They are characterized by a chimeric structure with two chiral centers, C1 and C5 in the secoiridoid moiety. Their glucoside functionality is released via specific enzyme action by native β-glucosidase but is resistant to acidic environment [5,6]. This could result from the extended delocalization of molecular orbitals, which decreases the basicity of the glucosidic oxygen against its protonation and the facile aglycone release.…”

The Role of Polyphenoloxidase, Peroxidase, and β-Glucosidase in Phenolics Accumulation in Olea europaea L. Fruits under Different Water Regimes

“…During fruit growth, oleuropein progressively decreases concomitantly with the increase of 3,4-DHPEA-EDA. Some cultivars are also able to synthesize demethyloleuropein, which increases during ripening (Sivakumar et al, 2007; Alagna et al, 2012). Other secoiridoids, such as ligstroside ( p -HPEA-EDA), hydroxytyrosol (3,4-DHPEA), and tyrosol ( p -HPEA) follow the same decreasing trend as oleuropein during fruit maturation and ripening (Servili et al, 1999, 2004; Morelló et al, 2004), whereas the verbascoside content does not follow an unequivocal pattern (Amiot et al, 1986; Ryan et al, 2002; Alagna et al, 2012).…”