3.2.3. Sensory Parameters

The enrichment with PE, leads to a variation of sensory parameters compared to the control sample (Figure 4). In general, all the tested samples showed differences for descriptors among them, except for saltness. Flavour, bitterness, spreadability were affected by the addition of PE; in particular, the increase of the perception of bitterness meant such as acid and pungen<sup>t</sup> taste, was linked probably to the high acidity of the PEB extract (pH 2), as well as to the amount of oleuropein occurred in the enriched samples, acknowledged as responsible of bitter tasting. The natural proteins present in soya milk, determine the formation of the emulsion. Enriched Mayonnaise resulted less consistent than the control sample, probably due to the partial substitution of soya milk with PE. As described by Giacintucci et al. [32], the incorporation of PE in fact modifies the dispersion degree of emulsion with consequences on hardness, consistency end elasticity of samples. Overall, although the sensory evaluation reveals that the addition of PE interferes with the main sensorial attributes, the overall acceptability of EMPEB can be considered good compared to the control sample.

**Figure 4.** Spider plot of sensory attributes of mayonnaise samples.

3.2.4. Oxidative Stability and Antioxidant Activity of EM

The rate of lipid oxidation in an emulsion is influenced by several factors, including the molecular structure of lipids, heat, light, physical characteristics of emulsion droplets and processing conditions [33]. As it can see in Figure 5, at 1st day of production, enriched samples showed the longer induction period (EMPE A: 25:15 h and EMPEB: 23:57 h) compared to the control sample (13:05 h). Although, after 45 days of storage lower induction periods were observed in all samples, PEs seems to exert a protective role on thermal oxidative stability of emulsions. At the end of storage, the resistance to rancidity was found to be of 33% and 58% higher rather than the Control for EMPE A and EMPEB, respectively.

**Figure 5.** Oxidation curves at 1st and 45th day of storage: red (EMPEA), dark grey (EMPEB), yellow (Control).

Likewise, Raikos, [34], showed that the addition of natural antioxidant can be a reliable strategy to improve the resistance to lipid oxidation of fat emulsion. In a previous article written by Paradiso et al. [35], it was reported that the catechol structure characterizing, e.g., hydroxytyrosol and oleuropein exerts a marked inhibiting activity towards oxidation in emulsion. To verify the actual formulation effect on the inhibition of rancidity processes, chromatographic quantification and antioxidant evaluation were performed. UHPLC analysis showed that the main compounds were transferred from extracts to emulsion. The highest content of hydroxytyrosol was detected in EMPEA (82.75 mg kg−1) while similar content of tyrosol was quantified in the two EMPE (EMPEA 19.28 and EMPEB 18.12 ± 0.16 mg kg−1). Even though, after 45 days, a significant decrease of Hydroxytyrosol was detected equal to 46% for EMPEA sample and 41% for EMPEB. It is conceivable that the concentration of bioactive compounds was still relevant in term of antioxidant efficiency. However, it is important to point out that mayonnaise is a multiphase system. In this regard, the polarity antioxidant of different compounds which in turn affects their partition into the different phases, play a key role in antioxidant real effectiveness [36].

In view of the above, multiple assays, TPC, DPPH, and ABTS were performed to allow a full insight into the antioxidant capacity of extracts. As reported in Table 3, the scavenging effect of PEB extracts against ABTS radical cation showed the same trend of TPC. Either way, no significant variations were observed during storage (*p* > 0.05). Only a decrease of 9% in ABTS+ results were observed for samples enriched with PEA extract. The addition of PEB extract had a radical scavenging potential against DPPH radical: 134 μmol TE 100 g<sup>−</sup><sup>1</sup> after 1st day while. 78 μmol TE 100 g<sup>−</sup><sup>1</sup> were instead measured in MPEA at the same storage time. Nevertheless, ANOVA data elaboration reveals a significant effect of storage time on EMPEB. After 45 days a decrement of 25% of antioxidant activity was detected for EMPEB while no significant variation was observed for EMPEA. The highest results of antioxidant activity were showed by ABTS assay, particularly in EMPEB samples with values greater than 610 μmol TE 100 g<sup>−</sup>1. The results obtained from different assays can be correlated to the polarity of compounds present in the food matrix (hydrophilic or lipophilic) for this reason, the antioxidant efficiency has responded better with ABTS test.


**Table 3.** Variation of the mayonnaise antioxidant parameters at 1st and 45th day of storage.

**Note:** The data are presented as means ± SD. Abbreviation: ns, not significant. \*\* Significance at *p* < 0.01; \* Significance at *p* < 0.05. μmol TE 100 g<sup>−</sup><sup>1</sup> PE for ABTS and DPPH and mg kg−<sup>1</sup> for TPC and single phenolics.
