Physical and Sensory Properties of Mayonnaise Enriched with Encapsulated Olive Leaf Phenolic Extracts

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Article Physical and Sensory Properties of Mayonnaise Enriched with Encapsulated Olive Leaf Phenolic Extracts

Federica Flamminii , Carla Daniela Di Mattia *, Giampiero Sacchetti , Lilia Neri, Dino Mastrocola and Paola Pittia

Faculty of Bioscience and Technology for Agriculture, Food and Environment, University of Teramo, Via Balzarini 1, 64100 Teramo, Italy; ﬄ[email protected] (F.F.); [email protected] (G.S.); [email protected] (L.N.); [email protected] (D.M.); [email protected] (P.P.) * Correspondence: [email protected]; Tel.: +39-0861-266947

Received: 1 July 2020; Accepted: 22 July 2020; Published: 24 July 2020

Abstract: This work aimed to study the physical, structural, and sensory properties of a traditional full-fat mayonnaise ( 80% oil) enriched with an olive leaf phenolic extract, added as either free extract ≈ or encapsulated in alginate/pectin microparticles. Physical characterization of the mayonnaise samples was investigated by particle size, viscosity, lubricant properties, and color; a sensory profile was also developed by a quantitative descriptive analysis. The addition of the extract improved the dispersion degree of samples, especially when the olive leaf extract-loaded alginate/pectin microparticles were used. The encapsulated extract affected, in turn, the viscosity and lubricant properties. In particular, both of the enriched samples showed a lower spreadability and a higher salty and bitter perception, leading to a reduced overall acceptability. The results of this study could contribute to understanding the effects of the enrichment of emulsified food systems with olive by-product phenolic extracts, both as free and encapsulated forms, in order to enhance real applications of research outcomes for the design and development of healthy and functional formulated foods.

Keywords: olive leaf polyphenols; encapsulation; functional food; mayonnaise; alginate/pectin beads; phenolic extract; food enrichment

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.

Foods 2020, 9, 997; doi:10.3390/foods9080997 www.mdpi.com/journal/foods Foods 2020, 9, 997 2 of 12

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.

2. Materials and Methods

2.1. Materials A dried olive leaf extract (OLE) with a standardized concentration of oleuropein (40%) was kindly donated by Oleaﬁt srl (Isola del Gran Sasso, Teramo, Italy) Dried OLE-loaded alginate/pectin microcapsules (Alg/Pec) with an average volume weighted mean diameter (D ) of 62.6 0.2 µm 4,3 ± were obtained by applying an emulsion/internal gelation technique [11]. Sunﬂower oil, eggs, salt, vinegar, and lemon juice were purchased in a local supermarket. All of the reagents used were of analytical grade. Foods 2020, 9, 997 3 of 12

2.2. Mayonnaise Preparation Mayonnaise samples were prepared according to a reference recipe with the following formulation: Oil (500 g 78%), five egg yolks (27 g 12%), vinegar (10 g 2%), salt (5 g 1%), lemon juice ≈ ≈ ≈ ≈ (37.5 g 7%), and sodium azide 0.05% (w/w). The samples were prepared using a lab-scale mixer ≈ (Bimby TM31, Vorwerk, Wuppertal, Germany) in a two-step standardized process: Eggs, vinegar, salt, and lemon juice were preliminary mixed (100 g min, 1 min), and oil was then slowly added under · vigorous mixing (from 500 up to 1000 g min) for 20 min, allowing complete oil incorporation. In order · to evaluate the exploitability of pure OLE and Alg/Pec + OLE beads as functional ingredients, a final concentration of 200 mg of total phenolic compounds per kg of product was added to mayonnaise. In particular, 1 g/kg ( 0.09%) of OLE and 4 g/kg ( 0.32%) of Alg/Pec + OLE, both in a dried form, ≈ ≈ ≈ ≈ were added to the water phase during the preliminary mixing (first step). Three following series of samples were thus prepared: A control (without phenolic extract added), Mayo + OLE (enriched with pure OLE), and Mayo + Alg/Pec (enriched with Alg-Pec + OLE microspheres). Just after preparation, the following evaluations were carried out on the samples: Particle size distribution, microstructure, color, viscosity, tribology, and sensory profile evaluations.

2.3. Particle Size Particle size distribution was measured by laser diffraction analysis and the use of a particle size analyzer (Mastersizer Hydro 3000, Malvern Instruments Ltd., Worcestershire, UK). Mayonnaise samples (0.2 g) were diluted with 20 mL of a 1% (w/v) sodium dodecyl sulphate (SDS) solution, gently stirred with a magnetic stirrer until complete dispersion [21], and thereafter added to the Hydro 2000S dispersion unit containing distilled water at 2500 rpm until an obscuration of 5–6% was reached. Each sample was analysed in triplicate and five records for each measurement were collected. The optical properties of the sample were defined as follows: Refractive index of 1.46 and absorption of 0.00. Droplet size measurements are reported as particle size distribution curves (PSD), the surface mean diameter (D3,2), and the volume mean diameter (D4,3).

2.4. Microstructure An Olympus BX53F optical microscope (Olympus, Tokyo, Japan) was used to evaluate the mayonnaise’s microstructure. An amount of each sample was deposited until a very thin and homogeneous layer developed on the slide and images were obtained with 100 magniﬁcation and × acquired with a QCAM fast 1934 (QImaging, Surrey, BC, Canada), equipped with a 55 mm objective. Images were elaborated through the Software “Image Pro Plus 7.0” (Media cybernetic, Inc., Rockville, MD, USA).

2.5. Color Evaluation The color of the mayonnaise was evaluated with a CHROMA METER CR5 instrument (Konica Minolta, Osaka, Japan), illuminant D65; each sample was homogeneously distributed into a glass vessel and the color was recorded at five different points. The average of the five measurements was assessed for all the colorimetric parameters (L*, a*, and b*). In the CIE Lab colour space, L* represents the lightness within the range of 0 (black) to 100 (white); a* is the redness, from green ( a*) to red − (+a*); and b* is the yellowness, from blue ( b*) to yellow (+b*). The a* and b* parameters were used to − calculate the tonality angle (Hue angle, h◦) according to Equation (1): ! 1 b∗ h◦ = tan− (1) a∗ Foods 2020, 9, 997 4 of 12

2.6. Flow Behavior and Tribological Measurements

Mayonnaise rheological measurements were performed at 25 ◦C by a controlled stress–strain rheometer (MCR 302, Anton Paar, Graz, Austria) connected to a circulating water bath for temperature control. The flow behavior of the samples was evaluated by using a parallel plate configuration (50 mm) and a gap distance of 1 mm, and excess sample protruding from the edge of the sensor was carefully trimmed off with a thin blade. Flow curves were measured by recording viscosity values 1 shearing the samples at logarithmic increasing shear rates from 3 to 300 s− . Flow curves were built for all of the tested samples and fitted to the Herschel–Bulkley model by using Excel’s solver software to obtain the yield stress (τ0), consistency index (k), and flow index (n). The friction and lubricant properties of model-like mayonnaise samples were evaluated using a tribology apparatus (Anton Paar, Graz, Austria) fitted to the rheometer. The measuring cell consisted of a ball-on-three-plates geometry consisting of a rotating glass ball and three stationary cylindrical polydimethylsiloxane (PDMS) pins fixed to the sample holder. The ball measured 12.7 mm in diameter and the pins measured 6 mm in diameter and height. The friction and lubricating properties of mayonnaise samples in between two surfaces were recorded at 30 ◦C with a normal force (FN) of 1 N. The Stribeck curves for each sample were shaped by plotting the friction factor ( ) versus the sliding velocity (Vs). − 2.7. Sensory Evaluation Sensory evaluation was carried out through quantitative descriptive analysis (QDA) by a panel consisting of 15 assessors. The panelists were students and technical staff of the Faculty of Bioscience and Technology for Agriculture, Food and Environment (University of Teramo, Teramo, Italy). Before analysis, brief training was carried out, in order to verify and discuss the vocabulary and to explain the scales being used. The following attributes were evaluated: Spreadability, consistency, and color uniformity for the appearance and structure; saltiness, bitterness, sourness, and astringency for flavor and taste; creaminess and grittiness for texture and mouthfeel; and then the overall acceptability. The ranking was defined as follows: 1 = lowest intensity and 10 = highest intensity. The samples (about 10 g) were served at room temperature in white plastic dishes with teaspoons. Judges were asked to first observe all of the samples, in order to evaluate the appearance and structure, and then, to put the mayonnaise into their mouth and evaluate the other attributes (flavor, taste, texture, and overall acceptability). Water was used for cleaning the mouth between tasting different samples. Data were normalized to the average score given by each panelist, for each attribute. Then, data were recalculated using the calibration curve obtained by plotting each attribute’s raw data (y-axis) versus normalized data (x-axis). Through this approach, differences in the scale of values of each non-calibrated panel member were avoided. The average scores for each attribute were determined and reported as spider plots.

2.8. Statistical Analysis All of the data are the average of at least three measurements and reported as the mean and corresponding standard deviation; for the viscosity parameters, the median was considered. One-way ANOVA analysis was applied to experimental data. Linear regression analyses were carried out on data and the goodness of fit of the models was checked by the determination coefficient R2. Tukey’s test was used to establish the significance of differences among the mean values at the 0.05 significance level. Data were processed with XLSTAT software (Addinsoft SARL, New York, NY, USA).

3. Results and Discussion The effect of the enrichment with Alg/Pec + OLE microparticles was studied by evaluating several physical properties of the mayonnaise samples just after preparation. In particular, the particle size, viscosity, tribology, and color were determined for their effect on the structural properties and stability of the emulsified structure and the sensory attributes. Foods 2020, 9, 997 5 of 12

Foods 2020, 9, x FOR PEER REVIEW 5 of 13 3.1. Particle Size and Microstructure In Table 1, the particle size of the mayonnaise samples, expressed as both D4,3 and D3,2, which In Table1, the particle size of the mayonnaise samples, expressed as both D 4,3 and D3,2, which are are related to the size of the bulk of the droplets constituting the mayonnaise and the size of small related to the size of the bulk of the droplets constituting the mayonnaise and the size of small droplets [22], respectively, are reported together with the specific surface area (SSA). droplets [22], respectively, are reported together with the speciﬁc surface area (SSA).

Table 1. Particle size parameters of mayonnaise samples after preparation, as affected by olive leaf Table 1. Particle size parameters of mayonnaise samples after preparation, as affected by olive leaf phenolic extract (OLE) and alginate/pectin (Alg/Pec) + OLE enrichment. phenolic extract (OLE) and alginate/pectin (Alg/Pec) + OLE enrichment. D [4;3] D [3;2] SSA D [4;3] D [3;2] SSA 2 µμmm µμmm m2//kgkg a a c ControlControl 2.72.7 ±0.7 0.7a 1.91.9 ±0.2 0.2a 3270 ± 408408c ± ± ± Mayo+ + OLEOLE 2.12.1 ±0.0 0.0b b 1.71.7 ±0.0 0.0b b 3663 ± 5959b b ± ± ± Mayo ++ AlgAlg/Pec/Pec 1.81.8 ±0.0 0.0b b 1.51.5 ±0.0 0.0c c 4272 ± 99a a ± ± ± ValuesValues are means are means ± SD.SD. Different Different superscript superscript letters letters in thethe samesame column column indicate indicate significant significant differences differences (p < 0.05). (p < 0.05). ± The results showed a reduction of the volume mean diameter (D ) and the surface mean diameter The results showed a reduction of the volume mean diameter4,3 (D4,3) and the surface mean (D ) values for both of the enriched samples (Mayo + Alg/Pec and Mayo + OLE), with respect to the diameter3,2 (D3,2) values for both of the enriched samples (Mayo + Alg/Pec and Mayo + OLE), with respectcontrol, to and the a correspondingcontrol, and a increasecorresponding of the specific increase surface of the areaspecific with surface values ofarea 4272, with 3663, values and of 3270 4272, for 3663Mayo, and+ Alg 3270/Pec, for Mayo Mayo+ + OLE,Alg/Pec, and Mayo the control, + OLE, respectively. and the control, In general, respectively. the particle In general, size distributionthe particle sizecurves distribution of the samples curves showed of the asamples polymodal showed distribution a polymodal with two distribution main populations with two and main a shiftpopulations towards anda lower a shift size towards in both a of lower the enriched size in both systems, of the whichenriched was systems, more evident which inwas the more Mayo evident+ Alg in/Pec the sample Mayo (Figure+ Alg/Pec1). sample (Figure 1).

Figure 1. 1. ParticleParticle size size distribution distribution curves curves of the of thedifferently diﬀerently enriched enriched mayonnaise mayonnaise samples samples after preparatiafter preparation.on.

The decrease of the particle size in both of the enriched systems can be associated with the presence of of olive olive leaf lea amphiphilicf amphiphilic phenolic phenolic compounds, compounds which, which have beenhave proven been proven to lower to the lower oil/water the oil/waterinterfacial interfacial tension and tension exert emulsifying and exert properties, emulsifying especially properties, when espe testedcially in acidic when conditions tested in (acetate acidic conditionsbuffer, pH 4.5)(acetate [7]. Inbuffer, the case pH of4.5) Mayo [7]. In+ Algthe /casePec, of the Mayo presence + Alg/Pec, of microparticles the presence could of microparticles have further couldimproved have the further formation improved and stabilization the formation of the and emulsified stabilization structure, of the likely emulsified due to a structure Pickering, stabilizinglikely due tomechanism. a Pickering Indeed, stabilizing particles mechanism. are able to Indeed, stabilize particles oil/water are interfaces, able to stabilize making oil/water them mechanically interfaces, makingstronger, them and mechanically are able to provide stronger a, su andfficient are able steric to repulsion provide a force sufficient to inhibit steric droplet repulsion coalescence force to inhibitduring droplet emulsification coalescence [23]. during The positive emulsification effect of [23] OLE. The on thepositive dispersion effect degreeof OLE ofon the the oil dispersion droplets degreeis in accordance of the oil withdroplets other is authorsin accordance who prepared with other mayonnaise authors who samples prepared enriched mayonnaise with increasing samples enrichedamounts of with olive increasing phenolic extract amounts [24 ].of In olive particular, phenolic the mayonnaise extract [24]. prepared In particular, with sunflower the mayonnaise oil (SO) prepared with sunflower oil (SO) with an amount of oil (≈ 80%) comparable to the systems under investigation in this study, showed quite similar values of D4,3 with respect to the control samples. However, when the enrichment was carried out at a similar concentration (200 ppm) to the one used

Foods 2020, 9, 997 6 of 12

Foodswith 2020 an amount, 9, x FOR PEER of oil REVIEW ( 80%) comparable to the systems under investigation in this study, showed6 of 13 ≈ quite similar values of D4,3 with respect to the control samples. However, when the enrichment was incarried this work, out at aa less similar broad concentration particle distribution (200 ppm) with to thea lower one useddegree in of this polydispersity work, a less broadwas obtained. particle Moreover,distribution in with the same a lower study, degree olive of oil polydispersity mayonnaise was-likeobtained. emulsions Moreover, formulated in thewith same different study, naturally olive oil phenolicmayonnaise-like-rich extra emulsions virgin olive formulated oils displayed with di ffsimilarerent naturally results when phenolic-rich a low phenolic extra virgin olive olive oil (270 oils mgdisplayed/kg) was similar used results as the when source a low of phenolicphenolic olivecompounds. oil (270 mg Therefore,/kg) was usedsuch as results the source strength of phenolicen the argumentcompounds. for Therefore,the use, for such the results formulation strengthen of high the argumentoil content for emulsions, the use, for of thea phenolic formulation-rich ofextract high recoveredoil content by emulsions, olive by of-products, a phenolic-rich with respect extract to recovered a more byexpensive olive by-products, ingredient with, such respect as extra to avirgin more oliveexpensive oil. ingredient, such as extra virgin olive oil. Optical microphotographs were were captu capturedred to characteri characterizeze the microstructural fe featuresatures of the samples (Figure 22aa–c).–c). InIn general,general, aa well-dispersedwell-dispersed oil phase could be observed in all of the systems, in agreement with the particle size results.results. While While the the presence presence of of larger larger droplets droplets was evident in samples a and b b,, defining defining a higher degree of polydispersity, a more finely finely dispersed structure and a closely packed distribution of oil droplets were visible in the mayonnaise enriched with OLE OLE-loaded-loaded alginate/pectinalginate/pectin microparticles.

Figure 2. 2. OpticalOptical micrograph micrograph images images of mayonnaise of mayonnaise samples samples just after just afterpreparation. preparation. Control Control (a), Mayo (a), +Mayo OLE +(bOLE), and (b Mayo), and + Mayo Alg/Pec+ Alg (c)./Pec (c). 3.2. Color Properties 3.2. Color Properties Color has a main impact on consumers’ choice, as it is one of the most important sensory features Color has a main impact on consumers’ choice, as it is one of the most important sensory features that affect the willingness to purchase or taste a food. In general, the typical pale yellow color of that affect the willingness to purchase or taste a food. In general, the typical pale yellow color of mayonnaise originates from the egg yolk and oil and may be further influenced by the addition mayonnaise originates from the egg yolk and oil and may be further influenced by the addition of of mustard, additives, or some other spices with coloring effects (i.e., Annatto E160 and Turmeric). mustard, additives, or some other spices with coloring effects (i.e., Annatto E160 and Turmeric). The The enrichment of mayonnaise with unconventional ingredients, which are different with respect to enrichment of mayonnaise with unconventional ingredients, which are different with respect to those those used in a standard recipe, could lead to physical and chemical changes that may affect, in turn, used in a standard recipe, could lead to physical and chemical changes that may affect, in turn, the the color of the final products. In Figure3, the chromatic indices of lightness and hue angle (L* and h◦, color of the final products. In Figure 3, the chromatic indices of lightness and hue angle (L* and h°, respectively) of mayonnaise samples, prepared with the addition of free OLE or OLE encapsulated in respectively) of mayonnaise samples, prepared with the addition of free OLE or OLE encapsulated alginate/pectin microparticles, are reported, along with the control sample. in alginate/pectin microparticles, are reported, along with the control sample.

Foods 2020, 9, 997 7 of 12 Foods 2020, 9, x FOR PEER REVIEW 7 of 13

Figure 3. Color properties in terms of the lightness (L*) and hue angle (h◦) of the mayonnaise samples underFigure investigation. 3. Color properties Different in terms letters of the for lightness parameters (L*) are and significantly hue angle ( dih°ff) oferent the bymayonnaise Tukey’s HSD samples test (underp < 0.05). investigation. Different letters for parameters are significantly different by Tukey’s HSD test (p < 0.05). The lightness value (L*), which is the colorimetric parameter referring to the ability of the system to reflect and scatter the light, was, in general, similar to data reported in the literature for The lightness value (L*), which is the colorimetric parameter referring to the ability of the system p full-fatto reflect mayonnaise and scatter [25 the–27 light,]. Significant was, in general, differences similar ( < 0.05)to data between reported the in L* the value literature of the control for full and-fat Mayomayonnaise+ Alg/ Pec[25–sample27]. Significant with respect differences to that of(p < the 0.05) Mayo between+ OLE the sample L* value were of observed the control and and this Mayo result + mayAlg/Pec reflect sample the di withfferent respect dispersion to that degreesof the Mayo of the + systems.OLE sample In particular, were observed the Mayo and +thisOLE result product may displayedreflect the a different significantly dispersion lower lightness degrees due of tothe the systems. color of In the particular, added OLE the extract, Mayo which, + OLE in theproduct case ofdisplayed Mayo + aAlg significant/Pec samples,ly lower was lightness mitigated due by to the the encapsulation. color of the added OLE extract, which, in the case of MayoOn the+ Alg/Pec contrary, samples, the results was mitigated of the hue by angle the encapsulation. were close to 90◦, confirming the yellow color, p withoutOn significantthe contrary, di fftheerences results ( >of 0.05)the hue among angle the were samples. close Overall,to 90°, confirming these results the highlight yellow color, that thewithout addition significant of the olivedifferences leaf extract, (p > 0.05) either among as a the pure samples. or encapsulated Overall, these form, results did not highlight alter the that visual the appearanceaddition of ofthe the olive emulsion. leaf extract, either as a pure or encapsulated form, did not alter the visual 3.3.appearance Effect of OLEof the Enrichment emulsion. on Flow Behavior and Lubricant Properties

3.3. EffectThe viscosity of OLE E propertiesnrichment on of concentratedFlow Behavior emulsions,and Lubricant such Properties as mayonnaise, are strictly related to the close packing of the dispersed oil droplets as they interact with one another in the matrix: The closer The viscosity properties of concentrated emulsions, such as mayonnaise, are strictly related to the droplets, the higher the viscosity, as a consequence of the higher droplet–droplet interaction [24]. the close packing of the dispersed oil droplets as they interact with one another in the matrix: The The flow curves of mayonnaise samples are reported in Figure4. In general, all of the mayonnaise closer the droplets, the higher the viscosity, as a consequence of the higher droplet–droplet samples exhibited a non-Newtonian shear-thinning behavior and a yield point related to the initial interaction [24]. resistance of the systems to flow. Control and Mayo + OLE samples are both characterized by a The flow curves of mayonnaise samples are reported in Figure 4. In general, all of the similar trend, with a tendency to break-down at a higher shear rate (300 s 1). At a similar shear rate, mayonnaise samples exhibited a non-Newtonian shear-thinning behavior− and a yield point related OLE-enriched mayonnaise displayed lower shear stress values with respect to the control, while the to the initial resistance of the systems to flow. Control and Mayo + OLE samples are both Alg/Pec mayonnaise samples showed higher yield stress and shear stress values. This latter behavior characterized by a similar trend, with a tendency to break-down at a higher shear rate (300 s−1). At a may be related to several factors, including the higher packing degree of the lower size oil droplets similar shear rate, OLE-enriched mayonnaise displayed lower shear stress values with respect to the (Figure2c) and the thickening e ffect of beads swelling due to the presence of alginate and pectin in the control, while the Alg/Pec mayonnaise samples showed higher yield stress and shear stress values. aqueous continuous phase. Recent studies observed an increase in viscosity for mayonnaise enriched This latter behavior may be related to several factors, including the higher packing degree of the with carbohydrate-based capsules due to the thickening effect of the polymers (i.e., dextran, pullulan, lower size oil droplets (Figure 2c) and the thickening effect of beads swelling due to the presence of glucose syrup, and zein) used as shell material upon their disintegration [28,29]. Moreover, it must alginate and pectin in the aqueous continuous phase. Recent studies observed an increase in viscosity be pointed out that the pH values of the samples were 3.87 0.06, 3.92 0.01, and 3.89 0.01 for for mayonnaise enriched with carbohydrate-based capsules± due to the± thickening effect± of the the control, Mayo + OLE, and Mayo + Alg/Pec, respectively, which are values close to the average polymers (i.e., dextran, pullulan, glucose syrup, and zein) used as shell material upon their isoelectric point of egg yolk proteins, when the protein charge is minimized and both the viscoelasticity disintegration [28,29]. Moreover, it must be pointed out that the pH values of the samples were 3.87 and stability of mayonnaise are generally enhanced [30]. ± 0.06, 3.92 ± 0.01, and 3.89 ± 0.01 for the control, Mayo + OLE, and Mayo + Alg/Pec, respectively, which are values close to the average isoelectric point of egg yolk proteins, when the protein charge is minimized and both the viscoelasticity and stability of mayonnaise are generally enhanced [30].

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Figure 4. FlowFlow curves of the mayonnaise after preparation.

Mayonnaise flow flow curves were fitted fitted with the Herschel Herschel–Bulkley–Bulkley model,model, which is commonly used to describe the flow flow properties of concentrated emulsified emulsified systems such as as mayonnaise mayonnaise [31] [31];; the flow flow n parameters yield stress τ0 (Pa),(Pa), consistency consistency index index K K (Pa (Pa s n)),, and and flow flow index index nn of the samples after preparation are listed in Table2 2..

Table 2. HersHerschel–Bulkleychel–Bulkley viscosity parameters of the mayonnaise samples. τ n τ0 (Pa)0 (Pa) nn K (PaK s (Pa) sn) ControlControl 78.878.8 b b 0.3 b b 71.3 a71.3 a a,b a,b b Mayo +Mayo OLE+ OLE 136.1136.1 a,b 0.50.5 a,b 21 21 b Mayo + Alg/Pec 171.4 a 0.7 a 11.4 c Mayo + Alg/Pec 171.4 a 0.7 a 11.4 c n Values are the median SD. The flow parameters are the yield stress τ0 (Pa), consistency index K (Pa s ), and flow indexValuesn. are Diff erentthe median superscript± ± SD. letters The inflow the sameparameters column are indicate the yield significant stress di ffτ0erences (Pa), consistency (p < 0.05). index K (Pa sn), and flow index n. Different superscript letters in the same column indicate significant differences (Whenp < 0.05). compared to the control, both of the enriched samples were statistically different (p < 0.05) in terms of K, τ0, and n, with Mayo + Alg/Pec showing the highest τ0 and n values. As reported in theWhen literature, compared yield to stress the control, values both are an of indexthe enriched of the strength samples ofwere the statistically attractive forces different between (p < 0.05) the inoil terms droplets of K [,24 τ0,,32 and] and n, with this isMayo in agreement + Alg/Pec withshowing the resultsthe highest related τ0 and to the n values. Mayo +AsAlg reported/Pec sample, in the whichliterature exhibited, yield thestress finest values oil dispersion are an index (Table of 1 the). strength of the attractive forces between the oil dropletsMoreover, [24,32] and all of this the is mayonnaises in agreement presentedwith the results a flow related index to (n the)—the Mayo parameter + Alg/Pec that sample describes, which a pseudoplasticexhibited the finest shear oil thinning dispersion behavior—lower (Table 1). than 1. It is interesting to note that the flow index tendedMoreover, to increase all from of the the mayonnaises control to the presented enriched samples, a flow index with Mayo(n)—the+ Alg parameter/Pec mayonnaise that describes showing a pseudoplasticthe highest value, shear corresponding thinning behavior to a lower—lower pseudoplastic than 1. It is behavior. interesting A shear-thinningto note that the profile flow index in an tendoil-in-watered to increase emulsion from is an the indication control to that the the enrich systemed flowssamples, more with readily Mayo as + the Alg/Pec dispersed mayonnaise particles showingalign with the the highestdirection value of flow;, correspond the enrichmenting to with a lower alginate pseudoplastic/pectin OLE-loaded behavior. beads, A whichshear-thinning undergo profileswelling in uponan oil hydration,-in-water emulsion caused an is increasean indication of solids that inthe the system dispersing flows phasemore readily that likely as the hindered dispersed the particlesalignment align of the with oil droplets.the direction of flow; the enrichment with alginate/pectin OLE-loaded beads, whichIt undergo is known swelling that flow upon behavior hydration, can aff causedect the mouthfeelan increase of of food solids emulsions, in the dispersing while other phase sensory that likelyattributes, hindered such the as creaminess,alignment ofcan the beoil correlateddroplets. with the lubrication properties of the emulsified structure.It is known Overall, that the flow perception behavior of can a food affect emulsion the mouthfeel in the mouth of food is emulsions initially dominated, while other by thesensory bulk viscosityattributes, at such the front as creaminess, of the oral can cavity, be wherecorrelated the gapwith between the lubrication the tongue properties and palate of the israther emulsified large (structure.>10 µm) [Overall,33]; upon the chewing, perception the productof a food mixed emulsion with in the the saliva mouth is squeezed is initially between domina movingted by the surfaces, bulk viscositysuch as the at tonguethe front and of palatethe oral (or cavity food, substratewhere the and gap palate), between and the the ton oralgue perception and palate dependsis rather onlarge its (>thin10 film μm) rheological [33]; upon behavior. chewing To, the better product analyse mixed the rheological with the salipropertiesva is squeezed of the mayonnaise between samplesmoving surfacesin the form, such of thin as the films, tongue tribological and palate investigations (or food were substrate carried and out. palate) The lubrication, and the properties oral perception of the depends on its thin film rheological behavior. To better analyse the rheological properties of the mayonnaise samples in the form of thin films, tribological investigations were carried out. The

Foods 2020, 9, x FOR PEER REVIEW 9 of 13 Foods 2020, 9, 997 9 of 12 lubrication properties of the control and differently enriched mayonnaise samples were represented incontrol the form and diofﬀ aerently Stribeck enriched curve (Figure mayonnaise 5), where samples the werefriction represented coefficient in ( the−) was form plotted of a Stribeck against curve the sliding velocity (mm s−1) in the regions from 1 mm s−1, generally associated with mouth1 -like (Figure5), where the friction coe ﬃcient ( ) was plotted against the sliding velocity (mm s− ) in the conditions during food1 consumption, up to− 200 mm s−1, which is the maximum speed that the human regions from 1 mm s− , generally associated with mouth-like conditions during food consumption, tongue can move1 [34]. up to 200 mm s− , which is the maximum speed that the human tongue can move [34].

FigureFigure 5. 5. StribeckStribeck curves curves of of m mayonnaiseayonnaise samples. samples.

ForFor all all samples samples,, it it is is possible possible to to observe observe the the occurrence occurrence of of a a typical typical Stribeck Stribeck curve curve where where the the differentdifferent regimes can be distinguished distinguished:: In In particular, particular, the the boundary boundary regime, regime, at at low low sliding sliding speeds speeds,, withwith surface–surfacesurface–surface interactionsinteractions dominating dominating the the friction friction response response with with high high friction friction factors; factors; the mixed the mixedregime, regime, at mid-speeds, at mid- whenspeeds the, when sample the starts sample to separate starts fromto separate the contact from surfaces, the contact decreasing surfaces, the decreasingfriction; and, the finally, friction the; hydrodynamicand, finally, the regime, hydrodynamic where the surfacesregime, arewhere completely the surfaces separated are completely by the fluid switheparated an increase by the of fluid the frictionwith an values. increase For of all the of thefriction mayonnaise values. samples,For all of a the similar mayonnaise behavior samples against the, a similarentertainment behavior speed against was the noticed, entertainment with some speed differences was noticed in the friction, with some factor differences values with in the the following friction factorranking: values Mayo with+ Alg the/Pec following< Mayo + rankingOLE < control,: Mayo and+ Alg/Pec a clear discrimination< Mayo + OLE among < control samples., and Witha clear the discriminationexception of the among highest samples. sliding speeds, With the where exception all of the of samples the highest present sliding similar speeds, trends, where the mayonnaise all of the samplesenriched present with Alg similar/Pec microparticles trends, the mayonnaise showed the enriched lowest friction with Alg/Pec values, microparticles probably associated showed with the a lowesthigher friction content values of solids, pro inbably the formulation associated andwith the a higher finest oilcontent droplet of solids dispersion, in the with formulation a corresponding and the finestbetter oil lubricant droplet behavior. dispersion The, with highest a corresponding lubricant properties better oflubricant Mayo + behavior.Alg/Pec could The highest also be attributedlubricant propertiesto the swelling of Mayo of the + Alg/Pec hydrogel could particles, also be which attributed made to them the swelling more deformable, of the hydrogel allowing particles a decrease, which in madethe friction them [more35]. Another deformable, interesting allowing result a decrease is related in to the the friction fact that [35] Mayo. Another+ Alg/Pec interesting sample exhibitedresult is relateda shift oftothe the transition fact that fromMayo a + mixed Alg/Pec to hydrodynamicsample exhibited regime a shift toward of the a highertransition speed from with a respectmixed to to hydrodynamiccontrol and Mayo regime+ OLE toward samples. a higher speed with respect to control and Mayo + OLE samples. DespiteDespite the the general general effect effect of of the the addition addition of of OLE OLE,, in in both both the the free free form and and e encapsulatedncapsulated in in Alg/PecAlg/Pec beads,beads, on on the the lubricant lubricant properties, properties which, which decreased decreas the frictioned the factorsfriction obtained factors byobtained tribological by tribologicalmeasurements, measurements, additional investigations additional investigations are needed to are describe needed the to behavior describe of the such behavior systems of during such systemsoral processing, during oral where processing, other parameters, where other including parameters, the presence including of salivathe presence and mouth of saliva conditions and mouth (e.g., conditiontemperature),s (e.g. may, temperature), play a key role.may play a key role. 3.4. Effect of OLE Enrichment on the Sensory Profile 3.4. Effect of OLE Enrichment on the Sensory Profile Mayonnaises enriched with pure OLE or OLE encapsulated in alginate/pectin microparticles were Mayonnaises enriched with pure OLE or OLE encapsulated in alginate/pectin microparticles assessed by a group of 15 panelists using a quantitative descriptive analysis. Before each session, were assessed by a group of 15 panelists using a quantitative descriptive analysis. Before each session, the assessors were trained on each attribute, the scale used, and how to score the samples. The average the assessors were trained on each attribute, the scale used, and how to score the samples. The scores of each selected attribute are reported in the spider plot shown in Figure6. As expected, average scores of each selected attribute are reported in the spider plot shown in Figure 6. As polyphenols addition, either in a pure or encapsulated form, significantly affected the bitterness expected, polyphenols addition, either in a pure or encapsulated form, significantly affected the perception with respect to the control sample, while no marked differences were reported for the bitterness perception with respect to the control sample, while no marked differences were reported

FoodsFoods 20202020, 9,, x9 ,FOR 997 PEER REVIEW 10 10of 13 of 12 for the two enriched mayonnaise samples, which were both perceived with a medium bitterness intensitytwo enriched (score mayonnaise ≈ 5.8) not appreciated samples, which by the were assessors. both perceived The enrichment with a medium of mayonnaise bitterness did intensity not influence(score the5.8 )color, not appreciated astringency, by consistency, the assessors. creaminess The enrichment, and graininess of mayonnaise parameter dids, which not influence could be the ≈ relatedcolor, to astringency, the presence consistency, of OLE or creaminess, microcapsule and powder. graininess The parameters, saltiness, sourness which could, and bespreadability related to the werepresence partially of OLEinfluenced or microcapsule by the addition powder. of Thealginate/pectin saltiness, sourness, microcapsules. and spreadability It can be hypothesized were partially thatinfluenced the saltiness by the increase addition may of have alginate been/pectin caused microcapsules. by the presence It canof calcium be hypothesized alginate of that the themicrogels saltiness structure;increase m mayoreover, have beenin the caused literature, by the it presenceis reported of that calcium bitter alginate compounds of the microgelssuch as caffein structure; can enhance moreover, thein effect the literature, of salt [36] it. is However, reported thatto the bitter best compounds of the authors’ such knowledge, as caffein can to date enhance, no literature the effect ofdata salt has [36 ]. beenHowever, reported to theon bestthe ofinteraction the authors’ between knowledge, the saltiness to date, and no literaturebitterness data of hasolive been leaf reportedphenolic on compounds.the interaction The betweenenriched thesamples saltiness scored and low bitterness in spreadability of olive leaf with phenolic respect compounds.to the control, The indicating enriched somesamples resistance scored to low spread, in spreadability which is a result with that respect is in to accordance the control, with indicating the higher some values resistance of yield to stress spread, observedwhich isin a the result flow that curves. is in Eventually accordance, the with sensory the higher evaluation values highlighted of yield stress that both observed of the inenriched the flow mayonnaisecurves. Eventually, samples the, but sensory in particular evaluation the highlighted system fortified that both with of the OLE enriched-loaded mayonnaise microparticles, samples, displayedbut in particular the lowest the overall system fortifiedacceptability with from OLE-loaded the panel. microparticles, The results displayedreflect the the low lowest ability overall of algiacceptabilitynate/pectin frommicroparticles the panel. Theto mask results the reflect bitternes thes low of abilityan OLE of extract alginate and/pectin present microparticles new challenges to mask forthe further bitterness investigations, of an OLE extractespecially and in present terms new of alternative challenges forencapsulation further investigations, methods, in especially order to in overcometerms of such alternative issues. encapsulation methods, in order to overcome such issues.

Figure 6. Spider plot of specific sensory attributes of the mayonnaise formulations. Lowercase letters Figure 6. Spider plot of specific sensory attributes of the mayonnaise formulations. Lowercase letters for each attribute indicate significant differences (p < 0.05). for each attribute indicate significant differences (p < 0.05). 4. Conclusions 4. Conclusions The enrichment of mayonnaise with OLE-loaded microparticles (Mayo + Alg/Pec) was effective in improvingThe enrichment its physical of mayonnaise properties in with terms OLE of both-loaded the dispersionmicroparticles degree (Mayo of the + oilAlg droplets/Pec) was and effective lubricant in propertiesimproving of its the physical emulsions; properties however, in theterms highest of both viscosity, the dispersion which in degree turn was of reflectedthe oil droplets by the lowestand lubricantspreadability, properties led toof athe di ffemulsions;erent sensory however, perception the highest with respect viscosity, to both which the in control turn was and reflected Mayo + OLEby thesamples. lowest spreadability, The addition of led OLE, to a either different as pure sensory extract perception or encapsulated with respect in alginate to both/pectin the microparticles,control and Mayoslightly + OLE affected samples. the chromaticThe addition parameters of OLE, witheither respect as pure to extract the control or encapsulated sample. The in sensory alginate/pectin evaluation microparticles,depicted a lower slightly overall affected acceptability the chromatic for both parameters of the enriched with respect samples, to likelythe control due to sam theple. increased The sensorysalty and evaluation bitter perception. depicted a The lower encapsulation overall acceptability technique for adopted both of was the thusenriched not able samples to mask, likely or control due to thethe bitternessincreased perception,salty and bitter leading perception. to the conclusion The encapsulation that further technique investigations adopted are was needed thus innot terms able of to encapsulationmask or control methods, the bitterness bead compositions perception, leading and structures, to the conclusion and mayonnaise that further formulations investigations to overcome are neededsuch issues.in terms The of proposed encapsulation research methods, could representbead composition a valid contributions and structure in thes, and wide mayonnaise panorama of formulationfunctionals foodsto overcome and opens such new issues. opportunities The proposed for formulatingresearch could healthier represent foodstu a validffs contribution while valorizing in theolive wide by-products. panorama of functional foods and opens new opportunities for formulating healthier foodstuffs while valorizing olive by-products.

Foods 2020, 9, 997 11 of 12

Author Contributions: Conceptualization, F.F. and C.D.D.M.; formal analysis, F.F., G.S., and C.D.D.M.; investigation, F.F.; resources, C.D.D.M. and L.N.; data curation, F.F., L.N., G.S., and C.D.D.M.; writing—original draft preparation, F.F.; writing—review and editing, C.D.D.M., P.P., and D.M.; visualization, C.D.D.M.; supervision, C.D.D.M., D.M., and P.P.; funding acquisition, C.D.D.M.; project administration, C.D.D.M. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by AGER 2 Project–“S.O.S—Sustainability of the Olive-Oil System”—grant no. 2016-0105. Acknowledgments: The authors are grateful to Domenico Cifà from Oleafit srl (Isola del Gran Sasso, Teramo, Italy) for providing the olive leaf extract and Chiara Di Giacinto for her contribution to this work. Conflicts of Interest: The authors declare no conflicts of interest.

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