**1. Introduction**

Nowadays, the increasing amount of attention being paid to health and wellbeing has modified consumer choices toward foods that, besides meeting nutritional requirements and providing hedonistic gratification, may also guarantee benefits by exerting desired functional properties. Mayonnaise is a traditional sauce prepared by the gentle mixing of oil with egg yolk, vinegar, salt, and spices to form an oil-in-water emulsion with a dispersed lipid phase ranging between 60 and 80%. It represents one of the most consumed sauces worldwide and is highly appreciated for its special flavor and creamy mouthfeel.

The words "functional" and "mayonnaise" do not seem to get along; however, if such a combination of words is considered from another point of view, it could lead to an innovative and challenging functional food [1]. Several strategies have been proposed to make mayonnaise a healthier product: along with the reduction of fat, which is the most widespread approach used up to now, a more recent approach is based on the enrichment of emulsified sauces with beneficial ingredients that can respond to the health-related needs of people (antioxidant, prebiotics, and probiotics). Moreover, from a food science point of view, functional ingredients, such as natural antioxidants, are known to improve the oxidative stability of the product and allow the replacement of synthetic and debated antioxidants. The interest in the use of natural ingredients is often associated with the opportunity of recovering

functional and bioactive compounds from food waste and by-products, such as those derived from the olive oil chain. Recently, several studies have proposed the enrichment of different food products with an olive leaf phenolic extract (OLE), as in the case of vegetable oils, due to their antioxidant activity (i.e., sunflower, soybean, maize, and frying oils) [2], or meat products against oxidative [3] and microbial spoilage [4]. Moreover, the use of OLE was also tested in cereal [5] and dairy products [6]. Apart from having healthy, antioxidant, and antimicrobial properties, olive polyphenols have been proven to exert important technological functionality, such as a water/oil holding capacity and emulsifying activity [7], and can represent a useful multifunctional ingredient that can help in the production and stabilization of complex food products such as emulsions. However, consumers' willingness to accept foods produced with olive by-product ingredients depends on the perception of different factors, mainly related to the general attitude of the consumer, rather than a product-specific choice. Indeed, information about the characteristics of olive by-products and the perception of the benefits from sustainable consumption can possibly offset the consumers' choice with a positive association between the use of vegetable by-products and sustainable production and environmental responsibility [8].

One main barrier to a large usage in food manufacturing is that phenolic-rich extracts are characterized by chemical and physical instability under conditions commonly encountered in processing and storage (temperature, oxygen, and light) [9], as well as by an unpleasant bitter and pungent taste [10].

Therefore, encapsulation could represent a valid strategy for overcoming all of these drawbacks and various investigations have been carried out in this field by using different technologies and approaches [11–14]. Nonetheless, up to now, few works have reported the use of encapsulated OLE in foodstuffs: In one study, an OLE encapsulated by nano-emulsions was added in soybean oil, increasing the solubility and controlling the release of olive leaf phenolic compounds, as well as enhancing its antioxidant activity when compared to non-encapsulated OLE and synthetic antioxidants [15]. In another study, OLE encapsulated in water-in-oil-in-water double emulsions (W1/O/W2) was used in meat systems, improving the oxidative stability of the product, while providing a healthier lipid profile with respect to the free extract [16]. Furthermore, the enrichment of cereal, dairy, beverages, and spreadable products with OLE encapsulated with different techniques was assessed, in order to improve their shelf-lives [17–20], but additional studies are needed, in order to widen the knowledge on the qualitative properties of OLE-enriched formulated products.

Therefore, the aim of this research was to study the physical, structural, and sensory properties of a full-fat mayonnaise (≈ 80% oil) enriched with an olive leaf phenolic extract (OLE), encapsulated in alginate/pectin microparticles. The physical characterization of the mayonnaise samples after preparation was investigated by measuring the particle size, viscosity, tribology, and color; a sensory profile was also developed by a quantitative descriptive analysis. For comparison purposes, samples enriched with pure OLE and without OLE (control) were prepared. The results will provide a new formulation and technological insights on the effect of the enrichment of a full-fat mayonnaise with encapsulated OLE on its physical and structural properties and, at the same time, evaluate the effect of encapsulation on OLE performances.
