**1. Introduction**

Food industries and, particularly, the olive oil industry produce large quantities of by-products that can be a serious environmental problem. Olive mill wastewater could be an economic and natural source of antioxidants due to its high content of phenolic compounds with a wide array of biological activities [1,2]. Scientific researches have shown that their recovery is important at the environmental level for the reduction of pollution; and in food technologies for different aims such as: nutritious, functional agents and for shelf life extension. Afkhami et al. [3] have studied the orange juice enriched with encapsulated polyphenolic extract of lime waste; Romeo et al. [4,5] studied the using the phenolic extract obtained by olive mill wastewater for the enrichment of hydrophilic model system and the application of natural antioxidants in a lipid system (oil).

Mayonnaise represents one of the most widely consumed sauces in the world [6]: it is a semisolid oil-in-water emulsion, prepared traditionally with egg yolk and 60–80% of oil. The presence of egg in mayonnaise formulation is important both for emulsion and for the taste and color but it is a critical point for the health aspect due to the cholesterol amount [7]. Nowadays an increasing number of people is following a vegetarian or flexitarian diet to prevent cardiovascular diseases resulting from bad nutrition. Many scientific works have been carried out on the possibility of the egg's removal in mayonnaise and replace them with soya, wheat, and milk proteins [8]. For example, soya milk and sunflower oil are used to formulate a vegan mayonnaise. As for all the foods with a high oil content, mayonnaise is susceptible to deterioration due to autooxidation of the unsaturated fats that can negatively affect physicochemical and sensorial attributes of food [9]. Lipid oxidation in mayonnaise causes the development of potentially toxic reaction products, undesirable off-flavors and, simultaneously, it decreases the shelf life of mayonnaise [10,11]. In order to manage these problems, various strategies can be used for avoiding or reduce oxidative

**Citation:** De Bruno, A.; Romeo, R.; Gattuso, A.; Piscopo, A.; Poiana, M. Functionalization of a Vegan Mayonnaise with High Value Ingredient Derived from the Agro-Industrial Sector. *Foods* **2021**, *10*, 2684. https://doi.org/10.3390/ foods10112684

Academic Editor: Theodoros Varzakas

Received: 24 September 2021 Accepted: 1 November 2021 Published: 3 November 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

processes. One of the common ways to delay lipid oxidation is the use of antioxidants. The efficacy of an antioxidant is influenced by different factors, such as its interaction with other ingredients and its ability to be located at the interface where oxidation takes place.

Generally, synthetic and commercial antioxidants, such as butylated hydroxy toluene (BHT), butylated hydroxy anisole (BHA) and ethylene diamine tetraacetic acid (EDTA), are widely used in mayonnaise to prevent rancidity. However, today the substitution of chemical ingredients with natural ingredients is highly appreciated by the consumer for the health effect and it shows also a grea<sup>t</sup> potential for improving food stability against lipid oxidation. Natural antioxidants can act as retarders, when they protect target lipids from oxidation initiators or hinder the propagation phase, the so-called chain-breaking antioxidants [12,13]. For it, the use of plant extracts, rich in antioxidant constituents, such as polyphenols, is an increasing trend in the food industry because they are an alternative to synthetic compounds with reducing and antimicrobial effect [14,15]. The olive oil production generates a considerable amount of olive oil mill waste, rich in organic compounds, mainly phenols. Only a small fraction of phenolic components is transferred to olive oil (1–2%) while the remaining portion is lost in olive oil by-products [16]. This work aimed to evaluate the effect of phenolic extracts obtained by olive mill wastewater in physicochemical and antioxidant characteristics of a vegan mayonnaise during storage period.
