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. 2018 Sep 23;19(10):2892.
doi: 10.3390/ijms19102892.

Probing Downstream Olive Biophenol Secoiridoids

Ganapathy Sivakumar  1 , Nicola A Uccella  2   3 , Luigi Gentile  4   5
Affiliations

Probing Downstream Olive Biophenol Secoiridoids

Ganapathy Sivakumar et al. Int J Mol Sci. .

Abstract

Numerous bioactive biophenol secoiridoids (BPsecos) are found in the fruit, leaves, and oil of olives. These BPsecos play important roles in both the taste of food and human health. The main BPseco bioactive from green olive fruits, leaves, and table olives is oleuropein, while olive oil is rich in oleuropein downstream pathway molecules. The aim of this study was to probe olive BPseco downstream molecular pathways that are alike in biological and olive processing systems at different pHs and reaction times. The downstream molecular pathway were analyzed by high performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI/MS) and typed neglected of different overlap (TNDO) computational methods. Our study showed oleuropein highest occupied molecular orbital (HOMO) and HOMO-1 triggered the free radical processes, while HOMO-2 and lowest unoccupied molecular orbital (LUMO) were polar reactions of glucoside and ester groups. Olive BPsecos were found to be stable under acid and base catalylic experiments. Oleuropein aglycone opened to diales and rearranged to hydroxytyrosil-elenolate under strong reaction conditions. The results suggest that competition among olive BPseco HOMOs could induce glucoside hydrolysis during olive milling due to native olive β-glucosidases. The underlined olive BPsecos downstream molecular mechanism herein could provide new insights into the olive milling process to improve BPseco bioactives in olive oil and table olives, which would enhance both the functional food and the nutraceuticals that are produced from olives.

Keywords: TNDO; antioxidant; biophenols; hydroxytyrosol; oleuropein; olive oil; tyrosol.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Molecular pre-equilibrium of olive biophenol secoiridoids (BPsecos) and H3O+.
Figure 2
Figure 2
Collision activated dissociations (CAD) unimolecular reactions of oleuropein pseudo-molecular ions, m/z 539.
Figure 3
Figure 3
Olive BPseco HPLC/UV profiles; initial stage: a, λ = 240 nm and a′, λ = 280 nm; b and b′: pH = 4.2; t = 120 min; T = 25 °C; c and c′: pH = 1.5; t = 240 min; T = 37 °C; d and d′: pH = 6.0 and 8.0; t = 120 and 120 min; T = 37 °C, under experimental simulations of human digestive and olive processing conditions. Peak 1: oleuropein; peak 2: isomer unidentified; peak 3: oleuroside.
Figure 4
Figure 4
Frontier molecular orbital (FMO) interactions of oleuropein lowest unoccupied molecular orbital (LUMO) and OH− highest occupied molecular orbital (HOMO).
Figure 5
Figure 5
Oleuropein excess of charge on C7, δ = 0.391; C11, δ = 0.386; C4, δ = −0.126; C3, δ = 0.180; O2, δ = −0.212; C1, δ = −0.036.
Figure 6
Figure 6
Olive BPseco molecular dynamic sequence under basic and enzymatic catalysis.
Figure 7
Figure 7
Olive BPseco + H+ isomers: oleuropein O2 + H+; oleuropein GluO + H+; oleuropein C11=O + H+. Arrows indicate the position of the positive charges.
Figure 8
Figure 8
(A) Orbital surfaces and energy for HOMO/LUMO of oleuropein + H+ isomers, calculated at typed neglected of different overlap (TNDO) level; (B) Oleuropein O2 + H+; oleuropein GluO + H+; oleuropein C11=O + H+ excess charges.
Figure 9
Figure 9
Oleuropein HOMO/LUMO and OLE + H+ isomers and H2O correlation diagram of their FMO energies.
See this image and copyright information in PMC

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