## 2 Materials and Methods  
Sample collection: A set of commercial oils with differing fatty acid compositions was selected: olive oil, sunflower oil, linseed oil, sesame oil, and soybean oil. All samples were obtained exclusively from the first cold-pressing process and were purchased in opaque glass containers from a local market to minimize light-induced oxidation. Sample analysis: MRI, NMR, and TD-NMR studies were performed at the BioImaC node of the ICTS ReDIB (ICTS BioImagen Complutense, Madrid, Spain; [[https://www.redib.net/](https://www.redib.net/)]([https://www.redib.net/](https://www.redib.net/)), accessed on 5 December 2024). MRI analysis: All MRI measurements were performed using an ICON-1T spectrometer (Bruker GmbH, Ettlingen, Germany) operating at 1 T (42.58 MHz) equipped with a shielded imaging gradient capable of reaching 450 mT/m along all of the axes. Each edible oil, in 1 mL Eppendorf tubes, was randomly placed in triplicate in a sample holder. For the calculation of T1 and T2 values, and following methodologies from previous studies [19], spin-echo sequences were acquired. The following parameters were used to obtain the images: a field of view of 24 mm \(\times\) 12 mm, a slice thickness of 2 mm, and a slice number of 1, always maintaining an in-plane resolution of 250 \(\upmu\)m\({}^{2}\). The experiments were performed in triplicate. For T2 measurements, separate images were acquired with 50 echo times (TE) that varied constantly from 6.5 ms to 325 ms, with a constant repetition time of 5000 ms. The data were then fitted to a single-exponential decay, according to the equation \(S(TE)=S_{0}\times e^{-TE/T2}\), where S(TE) is the signal at this TE and S\({}_{0}\) is the image signal when TE is equal to zero. For T1 values, separate experiments were acquired with 10 repetition times (TR = 50, 75, 150, 300, 600, 1000, 2000, 3000, 5000, and 7500 ms) and a constant TE of 7 ms. The data were then fitted to an exponential equation \(S(TR)=S_{0}\times\left(1-e^{-\frac{TR}{T1}}\right)\), where S(TR) is the signal at this recovery time and S\({}_{0}\) is the image signal when TR is equal to zero. Image acquisition and processing were performed using ParaVision 6.0.1.pl3 software (Bruker BioSpin Group, Bruker Corporation, Ettlingen, Germany). To obtain representative T1 and T2 values, a central region of interest (ROI) was selected in each of the vials. TD-NMR analysis: The analysis was performed directly on the edible oil inside its commercial glass container. TD-NMR measurements were performed on a Bruker minispec LP90 II TD-NMR analyzer (Bruker Biospin, Ettlingen, Germany) with a magnetic field strength of 0.146 T corresponding to a proton resonance frequency of 6.2336 MHz at a magnet temperature of 36 \({}^{\circ}\)C. Transversal (T2) relaxation was measured using a standard multi-echo Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The T2 measurements were conducted with a time delay between the 90\({}^{\circ}\) and 180\({}^{\circ}\) pulses (t) of 0.20176 ms. Data from 4096 echoes were acquired and 16 scans were averaged; the TR was set to \(\sim\)2 s. The T2 relaxation data calculation was performed by fitting the decay signal to the equation \(S=A\times e^{(-TE/T2)}+offset\). For the T1 calculation, a spin-echo sequence with a variable repetition time (TR) was selected. TR values varied from 50 ms to 1000 ms and 20 different TR values were acquired. For each TR, 4 scans were averaged. The signal curve was fitted to the equation \(S=A\times\left(1-e^{(-TR/T1)}\right)+offset\). Iodine value (IV): The \({}^{1}\)H-NMR spectra were acquired and processed following the procedure described in previous works (20,21). A Bruker DPX 300 MHz NMR spectrometer was employed for NMR data acquisition, and MestReNova 11.0.4 (Mestrelab Research SL, Santiago de Compostela, Spain) was used for spectra processing.