## 2 Materials and Methods  
The raw materials used to prepare O/W emulsions were refined sunflower oil (Jaen, Spain), purchased from a local supermarket, and high purity cellulose powder, obtained from cotton linters (Sigma-Aldrich, St. Louis, MO, USA), to produce the CMF. Chemically unmodified CMF were obtained by soaking in water for at least 24 h before high-pressure homogenization. The homogenization process was carried out at 600 bar and 10 passes using a laboratory homogenizer PANDA PLUS 2000 manufactured by GEA Niro Soavy (Parma, Italy). Chemicals were not used in this process. CMF were characterized by determining the consistency, carboxylic groups, nanofibrillation degree, transmittance, cationic demand, polymerization degree, and CMF diameter distribution according to [PERSON] et al. [39]. The amount of carboxylic groups in the oxidized fibers was determined by conductimertic titration before homogenization. A pulp sample containing 0.15 g of dry CMF was added to 5 mL of 0.01 M NaCl, and deionized water was added to a total volume of 55 mL. pH was adjusted to 2.5-2.8 by adding 0.1 M HCl to protonate all carboxylate groups. 0.05 M NaOH was added to the sample in 0.2 mL increments, and the conductivity was recorded after each addition. The amount of carboxylic groups was calculated from the curve of conductivity vs. NaOH (meq) added [39; 40]. Nanofibrillation degree was determined by centrifugation of 0.1% of dry CMF suspension at 4500\(\times\)\(g\) for 30 min. The nanofibrillated fraction was isolated in the supernatant, and the yield was calculated as the relationship between dry solids in the supernatant and total dry solids [39; 41]. Transmittance readings of 0.1 wt% CMF diluted suspensions were performed at 800 nm on a Cary 50 Conc UV-visible spectrophotometer (Varian Australia PTI LTD, Victoria, Australia), and cationic demand measurements were taken by colloidal titration of 0.1 wt% CMF suspensions with 0.001 N-polyDADMAC on a Mutek PCD04 particle charge detector (BTG Instruments GmbH, Herrsching, Germany). Polymerization degree (PD) was calculated from the limiting viscosity number (intrinsic viscosity) of the CMF suspension, which was determined by the ISO 5351 standard (2010) according to Equation (1) [39; 42; 43]:  
\[\eta=\mathrm{K}\cdot\mathrm{PD}^{\mathrm{a}} \tag{1}\]  
where \(\eta\) is the intrinsic viscosity (mL/g). \(\mathrm{K}\) and \(\mathrm{a}\) have different values according to PD; when PD \(<\) 950, \(\mathrm{K}\) = 0.42 mL/g and a = 1 [42]. Finally, CNF was characterized by scanning electron microscopy (SEM) with a JEOL JSM 6335F microscope (JEOL, Tokyo, Japan). Microscopic analyses were carried out in the National Centre of Electronic Microscopy at the Complutense University of Madrid. To prepare the CMF samples for SEM, a drop of diluted suspension (0.001 wt% and 0.005 wt%) was dried on a carbon tape at room temperature and covered with a thin layer of Au to avoid superficial charge accumulation. Image J software was used as image processing program, and diameter distribution of the CMF suspension was evaluated by measuring the diameter of the fibers located in diagonal line of the images. The O/W **Pickering emulsions** were prepared with O/W ratios from 20/80 to 70/30 (wt%). CMF were added in the aqueous phase with a total concentration of 0.25, 0.5, 0.75, and 1.0 wt%. Emulsions were carried out by mixing sunflower oil and aqueous phase with a high-speed overhead stirrer Heidolph RZR 2051 (Heidolph Instruments, Schwabach, Germany) at 2000 rpm for 60 min. The O/W emulsion samples were prepared in duplicate and stored at 25 \({}^{\circ}\)C.  
Stability over time of the emulsions was assessed by measuring the heights of water, oil, and emulsion phases for 48 h in a 100 mL graduated cylinder at ambient temperature. The emulsifying capacity of CMF and the stability of the emulsions were expressed by the emulsification index (EI).