The EVOO extracts were prepared as previously reported [17]: the extracts were prepared starting from 5 mL of oil, obtaining a dry weight of 10 mg and 5.7 mg for BUO and OMN, respectively. Their total phenolic content and total hydroxytyrosol and tyrosol were determined applying to validated methods [17].

To evaluate the concentration of oleacein, oleuropein, oleocanthal, and ligstroside aglycone, the 1H NMR spectra of BUO and OMN samples were registered by a 400 MHz instrument Advance 400 (Bruker, Bremen, Germany). The extracts were dissolved in 1 mL of CDCl3, and 1 µL of the solution of the internal standard (maleic acid 30 mg/mL in CH3CN) was added. According to our previous studies [21], to reference guidelines for quantitation by NMR [22], and to Karkoula et al. [23], the evaluation of oleacein, oleocanthal, oleuropein aglycone, and ligstroside aglycone in their monoaldehyde forms was done applying the following formula:

C(%), concentration of each of the four secoiridoid aldehydes.

Imal, integral of 2 protons of the ISTD, maleic acid.

ICHO, integral area of the proton signal of the aldehyde of each secoiridoid.

NCHO, the number of the aldehyde proton of each secoiridoid.

Nmal, the number of the protons of maleic acid.

MWX, the molecular weight of each secoiridoid (oleacein 320 g/moL, oleuropein aglycone 378 g/moL, oleocanthal 304 g/moL, and ligstroside aglycone 362 g/moL).

MWmal, the mw of ISTD maleic acid, 116.1 g/moL.

Wmal, weight in mg of maleic acid.

Wsample, dry weight in mg of BUO or OMN.

Pmal, purity grade of maleic acid.

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