Effect of Ripening on the Phenolic Composition and Mineral Content of Three Varieties of Olive Fruits

Abstract

The phenolic composition and mineral content of Cornezuelo, Cornicabra and Picual olive fruit varieties were investigated during olive ripening in two different harvesting seasons (2017/2018 and 2018/2019). Phytochemical profiles were evaluated by high-performance liquid chromatography (HPLC) with diode-array and mass spectrometry detection. Mineral contents were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Twenty-five compounds were characterized and the main ones quantified. These compounds corresponded mostly to secoiridoids, the main ones being oleuropein, oleoside/secologanoside, oleoside-11-methylester, and oleuropein and comselogoside isomers. Total phenolic contents reached the highest values between December and January, coinciding with the usual harvesting date. This trend was observed in both harvesting seasons, although higher phenolic contents were recorded in season 2018/2019. This was due to the different weather conditions, which caused a lower olive production in season 2017/2018. No clear tendency was observed between mineral content and harvest time in any of the studied seasons. The highest concentration of total phenolics was obtained in Cornezuelo variety (840 mg/100 g) in January 2019 (season 2018/2019). Picual and Cornicabra varieties reached concentrations of 670 mg/100 g and 530 mg/100 g, respectively, also in the last harvesting dates of season 2018/2019.

Exploring the Isomeric Precursors of Olive Oil Major Secoiridoids: An Insight into Olive Leaves and Drupes by Liquid-Chromatography and Fourier-Transform Tandem Mass Spectrometry

“…Minor chromatographic peaks were emphasized by magnifications reported in insets to panels b, c, d, e, and f of the figure. In agreement with previous findings [ 22 , 24 , 26 , 27 , 28 , 31 ], peaks related to isomeric forms were detected not only for oleuropein, but also for ligstroside and for demethylated oleuropein and ligstroside. Normalization Levels (NL) referred to the respective XIC traces suggested that demethylated forms were present at much lower concentrations ( vide infra ).…”

“…Based on the similarity of the MS/MS fragmentation pathways, an additional peak, closer to that of oleuropein, was assigned as "oleuropein isomer" in three studies [25][26][27]. The presence of an isomeric form of oleuropein in extracts of drupes from different Spanish olive cultivars was recently reported also by Fernandez-Poyatos et al [31]. Additionally, some differences in the profiles of product ions obtained for oleuropein (and its putative isomer) and oleuroside were evidenced by Quirantes-Piné et al [27] after MS/MS analysis, yet an interpretation for this finding was not reported.…”

“…Accordingly, two oleuroside-related chromatographic peaks should be detected in XIC traces obtained for the m / z value 539.1770, along with that of oleuropein (see Table 1 ). Although previous studies tentatively referred the second peak detected in XIC traces obtained for that m / z ratio to a not better clarified “oleuropein isomer” [ 26 , 27 , 28 , 31 ], a single isomeric form can be predicted for oleuropein. A careful interpretation of HCD-MS/MS spectra averaged under each chromatographic peak detected during this study helped us to clarify this issue.…”

“…The close similarity of fragmentation patterns inferred for the three compounds despite the potential presence of structural differences recalled that observed for the different isomeric forms related to the aglycones of oleuropein and ligstroside [ 17 , 18 ]. The interpretation of MS/MS profiles was undertaken by considering the occurrence of oleuropein, as the prevailing species, and oleuroside, as already proposed in the literature [ 22 , 24 , 26 , 27 , 28 , 31 ]. As explained before, the displacement of the exocyclic C=C bond makes the C 9 atom a stereogenic center in the case of oleuroside (see Figure 1 ).…”

“…Notably, several papers have been published in the last two decades on the analysis of secoiridoids in olive leaves and/or drupes using mass spectrometry coupled to liquid chromatography [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. In some cases, the occurrence of oleuroside in olive leaves or drupes extracts was explicitly indicated, based on the presence of a peak eluting later than that of oleuropein in the RPLC extracted ion current chromatogram referred to the [M-H] − ion with nominal m / z ratio 539 [ 22 , 24 , 26 , 27 , 28 ].…”