*2.2. Mayonnaise Preparation*

A schematic overview of the vegan mayonnaise production process is reported in Figure 1. The main ingredients used for the formulation were: soya milk, sunflower oil, lemon juice, salt and phenolic extracts (PE A and PEB). All ingredients were mixed using a lab-scale mixer (Bimby TM31, Vorwerk, Wuppertal, Germany) in a three-step process in order to maintain a closely packed emulsion. 1st step: soya milk and salt were mixed (1.100 <sup>g</sup>·min−1, 1 min, 37 ◦C); 2nd step: sunflower oil and lemon juice was slowly added under continuous mixing (2000 <sup>g</sup>·min−1, 3 min) until a mayonnaise emulsion had been formed; 3rd step: the PE A and PEB amounts corresponding to 100 mg L−<sup>1</sup> of Hydroxytyrosol (respectively, 50 and 45 g) were incorporating to the mixture (300 <sup>g</sup>·min−1, 1 min). Mayonnaise samples were stored in capped containers and refrigerated at 10 ◦C for storage. All analyses were performed at 0, 15, 30 and 45 days of storage. The two

enriched mayonnaises, EMPEA and EMPEB, were compared with a sample without PE, named control.

**Figure 1.** Schematic overview of formulation of mayonnaise.

### *2.3. Antioxidant Characterization of Phenolic Extracts*

The main antioxidant parameters, such as: total phenol content (TPC), ABTS and DPPH assays, were performed spectrophotometrically following the method described by De Bruno et al. [16], with some modifications.

For TPC analysis, 0.1 mL of the phenolic extracts (PEA and PEB), were placed in a 25 mL volumetric flask and mixed with 20 mL of deionized water and 0.625 mL of the Folin Ciocalteau reagent. After 3 min, 2.5 mL of a saturated solution of Na2CO3 (20%) were added. The content was mixed and diluted to volume with deionized water. Thereafter, the mixture was incubated for 12 h at room temperature and in the dark. The absorbance of the samples was measured at 725 nm against a blank using a double-beam ultraviolet-visible spectrophotometer (Agilent 8453 UV–Vis, Germany) and compared with a gallic acid calibration curve (concentration between 1 and 10 mg <sup>L</sup>−1). The results were expressed as mg of GAE 100 mL−1.

For DPPH assay, 10 μL of PE extracts (PEA and PEB) were added to 2990 μL of a 6 × 10−<sup>5</sup> M of methanol solution of DPPH (2.2-diphenyl-1-picrylhydrazyl, Carlo Erba, MI, Italy) in a cuvette and left in the dark for 30 min (till stabilization). The decrement of absorbance was determined by a spectrophotometer at 515 nm against methanol as blank and at the temperature of 20 ◦C.

For ABTS assay, 10 μL of PE extracts (PEA and PEB) were added to 2990 μL of ABTS reaction mixture (2.20-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), and the absorbance was measured after 6 min at 734 nm against ethanol as blank by a spectrophotometer. For both the assays, the radical scavenging activity was plotted against Trolox concentration (from 1.5 to 24 μM) and the results were expressed as μmol Trolox mL−<sup>1</sup> of PE.

The quantification of the main phenolic compounds was carried out following the method described by Romeo et al. [4], through a UHPLC-DAD analysis. 5 μL of PE was injected in a UHPLC system that consisted of an UHPLC PLATINblue (Knauer, Berlin, Germany) equipped with a binary pump system using a Knauer blue orchid column C18 (1.8 μm, 100 × 2 mm) coupled with a PDA-1 (Photo Diode Array Detector) PLATINblue (Knauer, Berlin, Germany). The mobile phases were (A) water acidified with acetic acid (pH 3.10) and (B) acetonitrile; the gradient elution program consisted of 0–3 min, 95% A; 3–15 min, 95–60% A; 15–15.5 min, 60–0% A. Finally, returning to the initial conditions was achieved during analysis keeping the column at 30 ◦C. External standards (concentration between 1 and 100 mg <sup>L</sup>−1) were used for the quantification and the results were expressed as mg 100 mL−1.

### *2.4. Physicochemical, Microbiological and Antioxidant Evaluation of Enriched Mayonnaise Samples (EM)*
