*Article* **Oleic Acid Is not the Only Relevant Mono-Unsaturated Fatty Ester in Olive Oil**

**Archimede Rotondo 1,\*, Giovanna Loredana La Torre 1, Giacomo Dugo 1, Nicola Cicero 1, Antonello Santini 2 and Andrea Salvo 3**


Received: 26 February 2020; Accepted: 19 March 2020; Published: 26 March 2020

**Abstract:** (1) Background: Extra-virgin olive oil (EVOO) is a precious and universally studied food matrix. Recently, the quantitative chemical composition was investigated by an innovative processing method for the nuclear magnetic resonance (NMR) experiments called Multi-Assignment Recovered Analysis (MARA)-NMR. (2) Methods: Any EVOO 13-carbon NMR (13C-NMR) profile displayed inconsistent signals. This mismatch was resolved by comparing NMR data to the official gas-chromatographic flame ionization detection (GC-FID) experiments: the analyses concerned many EVOOs but also the "exotic" *Capparis spinosa* oil (CSO). (3) Results: NMR and GC-FID evidenced the overwhelming presence of *cis*-vaccenic esters in the CSO and, more importantly, *cis*-vaccenic 13C-NMR resonances unequivocally matched the misunderstood 13C-NMR signals of EVOOs. The updated assignment revealed the unexpected relevant presence of *cis*-vaccenic ester (around 3%) in EVOOs; it was neglected, so far, because routine and official GC-FID profiles did not resolve oleic and *cis*-vaccenic signals leading to the total quantification of both monounsaturated fatty esters. (4) Conclusions: The rebuilt MARA-NMR and GC-FID interpretations consistently show a meaningful presence of *cis*-vaccenic esters in EVOOs, whose content could be a discrimination factor featuring specific cultivar or geographical origin. The study paves the way toward new quantification panels and scientific research concerning vegetable oils.

**Keywords:** *cis*-vaccenic; monounsaturated fatty; glycerols; NMR analysis; olive oil; *Capparis spinosa*; 13C-NMR; MARA-NMR
