*2.1. Sample Preparation*

For this preliminary study, a total of 65 extra virgin olive oil samples were collected from the Maltese islands over four harvest seasons from 2013–2016 and from other neighboring Mediterranean countries. The cultivars used in this study and their country of origin can be seen in Table S1. The samples were all taken from different oil producers to cover a representative sample of the Maltese islands in terms of pedological and microclimatic conditions, whilst also accounting for manufacturing techniques and the different presses employed. Foreign olive oils obtained were bought with a protected designation of origin in order to ensure traceability of the product. All the samples were stored at 4 ◦C in the absence of light prior to the analysis. The samples were preheated to 35 ◦C in a water bath for 1 h and mixed to ensure homogeneity. For 1H NMR, 20 μL of the EVOO were placed in 5 mm NMR tubes and dissolved in 700 μL of deuterated chloroform, followed by the addition of 20 μL

of deuterated DMSO and vortex mixing for 20 s. For 13C NMR, 440 μL of sample was dissolved in 420 μL of deuterated chloroform without the addition of DMSO [23].
