Analytical Approaches for the Characterization and Identification of Olive (Olea europaea) Oil Proteins

Abstract

Proteins in olive oil have been scarcely investigated probably due to the difficulty of working with such a lipidic matrix and the dramatically low abundance of proteins in this biological material. Additionally, this scarce information has generated contradictory results, thus requiring further investigations. This work treats this subject from a comprehensive point of view and proposes the use of different analytical approaches to delve into the characterization and identification of proteins in olive oil. Different extraction methodologies, including capture via combinational hexapeptide ligand libraries (CPLLs), were tried. A sequence of methodologies, starting with off-gel isoelectric focusing (IEF) followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) or high-performance liquid chromatography (HPLC) using an ultraperformance liquid chromatography (UPLC) column, was applied to profile proteins from olive seed, pulp, and oil. Besides this, and for the first time, a tentative identification of oil proteins by mass spectrometry has been attempted.

Antihypertensive Effects of Virgin Olive Oil (Unfiltered) Low Molecular Weight Peptides with ACE Inhibitory Activity in Spontaneously Hypertensive Rats

“…A later study showed the presence of olive oil proteins with molecular weight above 30 kDa, without finding any evidence of the 4.6 kDa protein [26]. In a recent article [41], the authors showed that the 4.6 kDa protein was an artefact from the filter paper used to clarify the extracts and they only found proteins of molecular weights higher than 10 kDa. Using a protein extraction method with acetone:hexane, which showed the best extraction results and the lowest interference problems, the concentration of proteins in virgin olive oil was reported to range 0.2-0.6 mg/kg [26,27].…”

Olive oil

“…A tentative identification to characterize protein species has been attempted by Esteve et al (2013), who used very sophisticated methods including sodium dodecyl sulphate−polyacrylamide gel electrophoresis (SDS−PAGE), high-performance liquid chromatography (HPLC) in an ultra performance liquid chromatography (UPLC), and mass spectrometry. A tentative identification to characterize protein species has been attempted by Esteve et al (2013), who used very sophisticated methods including sodium dodecyl sulphate−polyacrylamide gel electrophoresis (SDS−PAGE), high-performance liquid chromatography (HPLC) in an ultra performance liquid chromatography (UPLC), and mass spectrometry.…”

Use of protein profiles established by CZE to predict the cultivar of olive leaves and pulps

“…Different protocols to determine olive leaf and pulp proteins have been published in literature. SDS‐PAGE , ultra‐HPLC (UHPLC) , nLC‐MS/MS , MALDI‐TOF , CZE , and CGE techniques have been proposed to carry out leaf and pulp protein separation. Garcia et al compared by SDS‐PAGE the protein composition of juvenile and adult olive leaf, bark, and bud tissues, founding that the proteins observed in each sample were highly dependent on the maturation stage of the tissue.…”

“…After SDS‐PAGE protein separation and nLC‐MS/MS determination, a quite large number of compounds have been identified . On the other hand, olive pulp and seed proteins have been also examined by IEF‐SDS‐PAGE . The same combinatorial peptide ligand libraries were also applied to the determination of olive oil proteins ; however, when the electrophoretic profiles obtained with the olive oil and those corresponding to the olive seed and pulp were compared, only the smaller proteins in the seed and the pulp seem to pass to the oil while the bigger proteins probably remain in the pellet resulting from the oil extraction.…”

“…On the other hand, olive pulp and seed proteins have been also examined by IEF‐SDS‐PAGE . The same combinatorial peptide ligand libraries were also applied to the determination of olive oil proteins ; however, when the electrophoretic profiles obtained with the olive oil and those corresponding to the olive seed and pulp were compared, only the smaller proteins in the seed and the pulp seem to pass to the oil while the bigger proteins probably remain in the pellet resulting from the oil extraction. On the other hand, Montealegre et al separated proteins from olive fruits of different cultivar and geographical origin using CGE.…”