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Physical and structural properties of extra-virgin olive oil based mayonnaise
LWT - Food Science and Technology xxx (2014) 1e7
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Physical and structural properties of extra-virgin olive oil based mayonnaise Carla Di Mattia a, *, Federica Balestra b, Giampiero Sacchetti a, Lilia Neri a, Dino Mastrocola a, Paola Pittia a a Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, Via C.R. Lerici 1, 64023, Mosciano S. Angelo, Teramo, Italy b CIRI Interdepartmental Centre for Agri-Food Industrial Research, Alma Mater Studiorum, University of Bologna, Campus of Food Science, Piazza Goidanich 60, 47521, Cesena, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 February 2014 Received in revised form 12 September 2014 Accepted 30 September 2014 Available online xxx
The purpose of this work was to study the physical and structural properties of mayonnaises made with extra virgin olive oils (EVOO). To this aim, different EVOOs were selected according to their phenolic content along with other vegetable oils, peanut and sunflower, taken as reference. Mayonnaises were characterized by droplet size distribution, microstructure, textural, rheological and sensory properties. The droplet size distribution and microstructural properties of the mayonnaises resulted significantly affected by the type of oil used. Samples produced with EVOO showed lower dispersion level, a more coarse and irregular structure and the lowest consistency and firmness when compared to sunflower or peanut oils. The elastic and viscous modulus G0 and G00 , evaluated by rheological measurements, resulted inversely related to the content of polyphenolic compounds. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Olive oil Mayonnaise Microstructure Texture Rheological properties
1. Introduction Mayonnaise is a semi-solid, formulated sauce prepared by mixing vegetable oil, egg yolk, vinegar and salt (Depree & Savage, 2001). Its structure, creaminess, appearance and rheological behaviour are of outstanding importance for the sensory properties and perceived texture as well as for the physical stability, parameters which represent key factors for determining consumers' choice and satisfaction. From the colloidal point of view, mayonnaise is a low-pH O/W emulsion characterized by a very high oil content, ranging from 65 up to 85% depending on the formulation. The distribution of the fat phase, the size of the droplets as well as their interaction affect the texture and stability of the product. The stabilization of the oilewater interface in mayonnaise is mainly due to the granular micro-particles formed from the phosphoprotein and coalesced low-density lipoprotein constituents of egg yolk; in this high-lipid product, the granules keep the oil droplets well separated and prevent coalescence (Kiosseoglou & Sherman,
* Corresponding author. Tel.: þ39 0861 266912; fax: þ39 0861 266915. E-mail address: [email protected] (C. Di Mattia).
€r, Sørensen, & Hermansson, 1983; Langton, Jordansson, Altska 1999). As far as mayonnaise formulation is concerned, low cost and worldwide distributed vegetable oils (e.g. soybean, sunflower, corn and rapeseed oils) are mainly used. Extra virgin olive oil (EVOO) represents one of the most important dietary lipid obtained from olive trees crops in Italy as well as in other south Europe countries (e.g. Greece, Spain) (Zampounis, 2006). This vegetable oil has nutritional and sensory characteristics (Bendini et al., 2007, Boskou, Blekas, & Tsimidou, 2006), that make it unique and a basic component of the Mediterranean diet being used as seasoning for the preparation of traditional formulated sauces and dishes. Despite its high nutritional and health value, quite limited is the use of EVOO oils as ingredient in complex formulated foods, especially in the most industrialised ones, partly because of its peculiar sensory properties and partly for its relatively high cost in respect to other vegetable oils. Nevertheless, the use of olive oil in complex formulated systems could arise some issues related to the dispersion degree and the physical stability of the emulsified system that originates during food manufacturing which, in turn, may affect the quality of the final product and its stability during storage.
http://dx.doi.org/10.1016/j.lwt.2014.09.065 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Di Mattia, C., et al., Physical and structural properties of extra-virgin olive oil based mayonnaise, LWT - Food Science and Technology (2014), http://dx.doi.org/10.1016/j.lwt.2014.09.065
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The colloidal properties of an emulsion and its thermodynamic and kinetic instability are indeed highly dependent on the intrinsic chracteristics of the system and in particular on the presence of components that may either positively or negatively affect the chemical and physico-chemical properties of the dispersed and dispersing phases and of the interfaces as well. Olive oil, especially the extra virgin one, is a lipid source naturally rich in bioactive molecules of various nature and chemical properties including phenolic compounds which are known to exert a powerful antioxidant activity (Bendini et al., 2007; Del Carlo et al., 2004). However, recent studies have been carried out to exploit also the technological properties of EVOO in emulsified model systems and the role of its complex composition (e.g. free fatty acids, phospholipids and polyphenols) on the physical properties of the systems and their stability (Di Mattia, Sacchetti, Mastrocola, & Pittia, 2009; Di Mattia, Sacchetti, Mastrocola, Sarker, & Pittia, 2010; Di Mattia, Sacchetti, & Pittia, 2011). Results of these investigations have shown that some surface active endogenous amphiphylic molecules may affect the formation of oil/ water interfaces and the physical and chemical stability of dispersed emulsified systems. To the authors' knowledge, however, no studies have been carried out to study the effect of polyphenols on the structure of real emulsified matrices (e.g. mayonnaise, sauces, etc.), likely due to the complexity of their formulation that could hinder the understanding of the role of relatively low concentrations of surface active bioactive compounds. The aim of this work was, thus, to study the physical and structural properties of mayonnaise made with extra virgin olive oils (EVOO). To this purpose, different EVOOs were selected according to their polyphenolic content and, to compare the technological performances, peanut and sunflower oils were also considered. Mayonnaise samples were produced by using a single recipe and a standardized homogenization procedure and then characterized by droplets size distribution, colour, microstructure, mechanical, rheological and sensory properties. The mayonnaise sample prepared with sunflower oil was used as reference.
content of polyphenolic compounds, as measured by the FolinCiocalteau assay, was 0.52 ± 0.03 g GAE/g extract.
2. Material and methods
2.4. Measurement of rheological properties
2.1. Materials
Mayonnaise rheological measurements were performed by a controlled stress-strain rheometer (MCR 300, Physica/Anton Paar, Ostfildern GermanyeEurope) connected to a circulating water bath for the temperature control. The viscoelastic behaviour of the samples was evaluated at 25 C by using a parallel plate (diameter: 50 mm) and a gap distance of 2 mm. Excess sample protruding from the edge of the sensor was trimmed off carefully with a thin blade. Firstly, the extent of the linear viscoelastic region was determined by performing a strain sweep (0.1e100%) at a fixed frequency of 1 Hz. Subsequently, a dynamic frequency sweep was conducted by applying a constant strain of 0.5% within the linear viscoelastic region, over a frequency range between 0.1 and 100 Hz (Mancini, Montanari, Peressini, & Fantozzi, 2002). Before starting the measurements, all samples were allowed to rest for 5 min after loading to allow temperature equilibration and induced stress to relax. The rheological parameters used for this study were the storage (G0 ), the loss (G00 ) and the complex (G*) moduli. The experimental data of all frequency sweep tests were correlated according to the following power law (Gabriele, de Cindio, & D'Antona, 2001):
The following vegetable oils were used: sunflower (SO), peanut (PO), refined olive oil (RO), olive oil (OO) and four extra virgin olive oils according to the EU regulation (EVOO1-EVOO4). The EVOOs were chosen and ranked according to their polyphenolic contents which were as following: 233.26 ± 5.88 for EVOO1, 321.00 ± 7.64 for EVOO2, 389.05 ± 5.36 for EVOO3 and 764.24 ± 7.33 mg/L Gallic Acid Equivalents (GAE) for EVOO4. For SO, PO and RO oils it was not possible to quantify the total content of polyphenols since it was below the limit of detection of the method used. For the determination of the total polyphenols contents, the oils were extracted according to the procedure described by Pirisi, Cabras, Falqui Cao, Migliorini, and Muggelli (2000). The total polyphenol content of the methanol extracts was evaluated colourimetrically using the Folin-Ciocalteau reagent, with a method adapted from Singleton and Rossi (1965). Sunflower and peanut oils were purchased from a local supermarket; the refined olive oil was gently provided by Adriaoli (Mosciano S. Angelo, Italy) and used without any further purification. The EVOO oils were supplied by a local olive oil mill (Frantoio Montecchia, Morro d'Oro, Italy). A commercial food-grade olive fruit extract (OE) rich in phenolic compounds was kindly provided by Indena (Milan, Italy). The olive dry purified polyphenolic extract was 90% (w/w); other components were represented by dehydrated corn syrup (10%). The total
2.2. Mayonnaise preparation A reference recipe was used throughout the study based on the following formulation: oil (500 g), 2 eggs (120 g), vinegar (30 g), salt (1 g). Mayonnaise samples were prepared using a lab-scale mixer (Bimby TM31, Vorwerk, Wuppertal, Germany) in a two-steps standardized process: eggs, vinegar and salt were preliminary mixed (100 rpm, 3 min) and then oil was slowly added under vigorous mixing rate (from 3200 rpm up to 6000 rpm in 5 min). Mayonnaise samples made with refined olive oil (RO) and enriched with the polyphenol-rich olive fruit extract (OE) were also prepared; different amounts were added and solubilised during the first step of the homogenization procedure. The amounts of OE added were calculated as percentages on the basis of the oil content; RO1, RO3 and RO6 mayonnaise samples were thus obtained and the phenolic contents, calculated on the amount added, were of 120, 350 and 700 mg/L respectively. Mayonnaise was prepared in 500 g of oil each time and for each formulation three batches were considered. 2.3. Particle size distribution Particle size distribution was measured as described by Santipanichwong and Suphantharika (2007) with some modification. Mayonnaise samples (1 g) were diluted with 200 mL 0.2 g/ 100 mL sodium dodecyl sulphate (SDS) solution and gently stirred with a spatula until completely dispersed. Samples were analysed by a particle size analyser (Mastersizer 3000, Malvern Instruments Ltd, Worcestshire, UK). The sample solution was dispersed in distilled water at 2000 rpm until an obscuration rate of 12% was reached. Optical properties were defined as following: refractive index 1.46 and absorption 0.00. Droplet size measurements are reported as the volume-weighted mean diameter D4,3.
G* ðuÞ ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 00 G0 ðuÞ2 þ G ðuÞ2 ¼ Au1=z
(1)
where G* is the complex modulus in Pa, u is the frequency in Hz, z (dimensionless) is the coordination number and A (G* in Pa at 1 Hz) is the proportional coefficient.
Please cite this article in press as: Di Mattia, C., et al., Physical and structural properties of extra-virgin olive oil based mayonnaise, LWT - Food Science and Technology (2014), http://dx.doi.org/10.1016/j.lwt.2014.09.065
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2.5. Back extrusion test Measurements were carried out according to Liu, Xu, and Guo (2007) with some modification, by using a Dynamometer Instron Mod. 5542 (Instron Universal Testing Machine, Royal Street Canton Ma, USA). A back extrusion cell with 35 mm diameter compression disc was used. Samples were carefully scooped into glass cylindrical containers (i.d.: 50 mm, h: 75 mm) to a depth of 40 mm. One cycle was applied at a constant crosshead rate of 1 mm/s to a sample deformation of 50% of the initial height. From the resulting forceetime curve, the maximum force and the area of the curve up to this point were obtained as indices of firmness and consistency, respectively. 2.6. Optical microscope observation The glassy flat was coated with mayonnaise sample and placed on the stage of a light microscope (Olympus Microscope BX53, Tokyo, Japan); pictures of mayonnaise microstructure were obtained at a 40 magnification by a digital camera (Qimaging Fast 1394, Surrey, BC, Canada) connected to the microscope. 2.7. Sensory analysis Sensory evaluation was carried out by quantitative descriptive analysis by a trained panel consisting of 8 assessors (3 males, 5 femals; age range: 25e55). Panelists were preliminarily trained in sessions to develop a common language for descriptors and range of scores. The attributes taken into consideration were sour and freshly-cut grass for smell; sweetness, bitterness, spicy and astringent for flavour and taste; spreadability, creaminess and thickness for texture and mouthfeel. The ranking was as following: 1 ¼ the least, the lowest; 10 ¼ the most, the highest. Samples (10 g) were served at 20 C in red plastic cups with lids. Judges were asked to first take a deep sniff and evaluate smell and then appearance; after recovering smell sensitivity, they were asked to take a teaspoon mayonnaise (z5 mL) into the mouth and evaluate flavour, taste and texture attributes. Water and neutral wafer were used for cleaning the palate between samples. 2.8. Statistical analyses Three batches of mayonnaise were prepared from a unique lot of oil. All measurements were made in triplicate on samples from each batch (n ¼ 9) and results are expressed as mean and standard deviation. A one-way analysis of variance (ANOVA) and Tukey's test were used to establish the significance of differences among the mean value at the 0.05 significance level. Non-linear regression analysis was performed with Equation (1) as the model function, using the algorithm “Rosenbrock pattern search” supplied by the STATISTICA (StatSoft^TM Tulsa, Oklahoma) package. 3. Results & discussion 3.1. Droplet size distribution The properties and stability of mayonnaise are generally linked, as for other emulsified foods, to the droplet size and to the uniformity of the oil droplets. Fig. 1a shows the mean droplet size of the mayonnaise samples as expressed by the D4,3 value (mm). The RO- and PO-mayonnaise samples did not show any significant droplet size difference if compared to the control sample SO. The smallest droplet size was exhibited by the mayonnaise made with olive oil (OO) which thus showed higher emulsifying properties in
Fig. 1. Particle size (a) and distribution profiles (b) of the different samples of mayonnaise. In Fig. 1b: sunflower oil SO (A), peanut oil PO ( ), Refined oil ( ), Olive oil OO (B), Extra-virgin olive oils EVOO1 (-), EVOO2 (✕), EVOO3 (þ), EVOO4 (C).
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comparison with the other vegetable oils; on the contrary, the biggest droplets size was observed when EVOO was used. Moreover, the droplet size of the EVOO based mayonnaises increased from EVOO1 up to EVOO4, which corrisponded to an increasing phenolic contents of the oils. Besides droplet size, interesting information on the colloidal state of the different systems could be achieved by considering the profiles of the droplet size distribution (Fig. 1b). The particle size range of the mayonnaises under investigation (1e300 mm) resulted close to that reported by Liu et al. (2007) but markedly higher than those obtained by Worrasinchai, enz, Paredes, Suphantharika, Pinjai, and Jamnong (2006); Laca, Sa and Diaz (2010) and Nikzade, Mazaheri Tehrani, and SaadatmandTarzjan (2012). However, while the SO-mayonnaise was characterized by a monomodal distribution centred at around 20 mm, the use of PO, RO and OO led to the samples with a bimodal distribution of the oil globules particularly evident in the OO-based mayonnaise where the presence of larger droplets characterized by a mean volume-surface diameter of around 80 mm was detected. Moreover, the use of EVOO determined the formation of broader distribution within a size range of 1e300 mm in contrast to the 1e150 mm range of the non-EVOO samples; the droplet size distribution of the latter systems was also characterized by the appearance of a third population of bigger particles whose amount increased with the increasing of the polyphenolic content of the EVOO oils. 3.2. Optical microscope observation Microstructural properties of the mayonnaise samples were investigated by optical microscopy and the microphotographs
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show the market effect of the use of different oils with the formation of a wide variety of microstructures (Fig. 2). SO-mayonnaise showed a fine and well dispersed oil-inwater structure in which fat globules resulted spherical and highly packed together; similar packing structure could be observed for PO-, RO-, and OO-based mayonnaise samples even though with same differences related to the polydispersity of the droplets.
On the other hand, the use of EVOOs determined a more coarse distribution of the oil particles in the macromolecular network (Fig. 2, eeh). The presence of polyphenols as well as of other amphyphylic compounds present in the EVOOs seems to affect the development of the emulsified system and/or the threedimensional egg protein network. From EVOO1 to EVOO4, thus at increasing content in phenolic compounds, a more open and coarse structure could be observed suggesting that these compounds may
Fig. 2. Optical micrographs of the mayonnaises produced with different oils: sunflower SO (a), peanut PO (b), refined RO (c), olive OO (d), EVOO1 (e), EVOO2 (f), EVOO3 (g) and EVOO4 (h).
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also affect, under the experimental condition used in this study, the formation of the gelled pH-induced structure of the egg protein network.
3.3. Textural properties The values of Fmax and Etot parameters, corresponding to the first peak extrusion force and the total work obtained by the back extrusion test, are shown in Table 1. Fmax was taken as an index of firmness whilst Etot as a measure of consistency (Liu et al., 2007; Nikzade et al., 2012; Santipanichwong & Suphantharika, 2007; Worrasinchai et al., 2006). The highest firmness was found in the reference sample, the SO-mayonnaise, in agreement with results previously observed for mayonnaise having similar fat content (Liu et al., 2007; Nikzade et al., 2012). The substitution of sunflower oil with other oils caused a general reduction of the Fmax which was significantly (p < 0.05) higher when EVOO was used with a negative relationship between the firmness of the samples and the polyphenolic content. For these products the decrease in firmness ranges from 42% up to 70%. A similar trend was observed also for the consistency with higher Etot values obtained in the case of the mayonnaises made with SO, PA, RO and OO. The use of EVOOs generally caused, again, a lower Etot of the correspondent emulsified products with a similar negative correlation between the total polyphenolic content and the consistency. These results could be attributed to some microstructural properties and, in particular, to the bigger size of the fat globules in the EVOOs made-maionnaises, which led to a lower surface area contact between droplets and, consequently, a lower degree of interaction, as well as to the droplet size distribution, both related, in turn, to the amount of phenolic compounds of the oils. Since the olive oils used to formulate the systems may be characterized by very different phenolic pattern, the influence of the sole phenolic content on the mechanical properties was further studied by the investigation of RO-mayonnaise samples added with increasing amounts of a commercial olive fruit extract (OE) with a standardised phenolic pattern (RO1, RO3 and RO6) whose results are reported in Table 1. This approach permitted to modify the phenolic content without any influence on the phenolic composition of the systems. Both the textural parameters Fmax and Etot showed a similar trend: small addition of phenolic compounds had little effect on Fmax and Etot whilst a significant decrease of the firmness and consistency occurred when the OE was added at the highest concentration (1360 mg L1). This result further supports the hypothesis that olive oil phenolic compounds could impair the textural attributes of
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mayonnaise. However, contrary to the results obtained from the artificially enriched maionnayses, the decrease of firmness and consistency occurred also in the products obtained with EVOOs containing lower phenolic concentrations (Table 1), and this may suggest that factors other than total polyphenols content are worthwile to be further investigated: the phenolic pattern of the oils and the content of other minor compounds, which may interfere with the formation of the emulsified and partly gelled structure. 3.4. Rheological properties Dynamic oscillatory shear tests were carried out to characterize the viscoelastic properties of the mayonnaises samples made by using different oils. Data of the elastic modulus (G0 ) and loss modulus (G00 ) are shown Fig. 3 (a, b). At small strains mayonnaise samples showed a linear visco-elastic response. The magnitude of storage modulus G0 (Fig. 3a) was greater than loss modulus G00 (Fig. 3b) for all samples. This behaviour is typical of concentrated emulsion as previously reported for commercial or model mayonnaise (Laca et al., 2010; Liu et al., 2007; Mun et al., 2009; Worrasinchai et al., 2006). The experimental linearity of the moduli suggests that mayonnaise may be considered as gel-like network in the frequency range of 0.1e100 Hz (Mancini et al., 2002). In general, G0 values showed a slight increase at increasing frequency and this could be related to the strong interactions among the droplets that contributes to the elastic modulus and need a longer time to relax. This further supports the gel-like
Table 1 Textural parameters of the mayonnaise samples as measured by the Fmax (N) and Etot (mJ). Data were averaged from n ¼ 9 measurements made on three different batches (three repeats for each batch). Samples
Fmax (N)
SO PO RO OO EVOO1 EVOO2 EVOO3 EVOO4 RO1 RO3 RO6
2.09 1.79 1.59 1.27 1.06 1.04 0.91 0.60 1.58 1.52 0.70
± ± ± ± ± ± ± ± ± ± ±
0.14 0.41 0.18 0.11 0.16 0.11 0.09 0.10 0.20 0.15 0.09
Etot (mJ) 32.6 26.8 26.5 20.5 17.8 18.4 16.3 11.3 28.7 28.5 11.1
± ± ± ± ± ± ± ± ± ± ±
2.0 2.7 2.1 2.8 2.0 2.1 2.1 1.6 3.2 5.3 2.5
Fig. 3. Dynamic oscillatory response G0 (a) and G00 (b) of the mayonnaise samples (sunflower oil SO (A), peanut oil PO ( ), Refined oil ( ), Olive oil OO (B), Extra-virgin olive oils EVOO1 (-), EVOO2 (✕), EVOO3 (þ), EVOO4 (C)).
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Please cite this article in press as: Di Mattia, C., et al., Physical and structural properties of extra-virgin olive oil based mayonnaise, LWT - Food Science and Technology (2014), http://dx.doi.org/10.1016/j.lwt.2014.09.065
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structure predominant in this kind of emulsified systems (Hayati, Man, Tan, & Aini, 2007). The EVOOs samples showed in general lower elastic moduli (G0 ), if compared to the mayonnaises made with SO, PO, RO and OO. This result could be due to the lower dispersion levels of the EVOO samples, as already observed in literature and, therefore, to a lower degree of interactions among the droplets (Langton et al., 1999). In general low storage modulus implies that low stresses are necessary for the emulsion to flow, reflecting a less compact structure and a more liquid-like behaviour, confirming thus the results obtained from the mechanical measurements and the microscopy observations. According to the weak gel model proposed by Gabriele et al. (2001), as a general predictive model applicable to many food systems, the rheological structure of mayonnaise can be considered as a three-dimensional network in which droplet particles and similar units are linked by weak and strong interactions. The weak gel is made by strong topological points connected by weak strands constituted by a sort of necklace of flow units with a coordination degree of z (Gabriele et al., 2001). The coordination number z is the number of rheological units correlated with one another in the three-dimensional structure, while the parameter A (Equation (1)) is the strength of the interaction between those units. A rheological characterization based on the coordination number z and the coefficient A was useful for distinguishing rather well the structural properties of mayonnaise made with different formulations (Laca et al., 2010; Peressini, Sensidoni, & de Cindio, 1998). The values of z and A for all the samples analysed, including the RO1- RO3 and RO6-mayonnaises added with OE, are reported in Table 2. The z parameter ranged from 8.62 ± 0.22 to 10.96 ± 0.32, values close to those found in literature (Laca et al., 2010; Mancini et al., 2002; Peressini et al., 1998). The SO-mayonnaise (reference), presented the highest coordination number and gel strength, corresponding to the most complex structure and high physical stability (Mancini et al., 2002). Slight differences were observed in the z values of the mayonnaises made with different EVOO which were lower if compared to the reference but without a significant correlation due to the phenolic content of the initial oils. On the other hand, a significantly lower A value and in the range of 440 ± 5 to 687 ± 6 kPa was shown by the EVOOs-mayonnaises compared to the reference sample (1337 ± 29 kPa) to indicate a reduced gel strength. However, also in this case, no clear relationships were observed between the polyphenolic content and the gel strength of EVOOs mayonnaise. Thus, on the basis of the coordination number and the gel strength, it could be concluded that the gel network of the mayonnaise samples prepared with EVOO oils resulted to be characterised by a smaller number of units linked by weaker interactions.
The Gabrieli model was applied also to the rheological results of the RO-mayonnaise samples added with OE (Table 2) (RO1-RO6). At increasing phenolic extract addition a decrease of both coordination number z and gel strength A occurred, showing a zero and first order relationship with OE concentration respectively (R2 ¼ 0.9928; 0.9865). On the basis of these results, the RO6 sample, characterised by the lowest values of z and A, is supposed to be the most exposed to physical instability due to coalescence phenomena when the system undergoes mechanical stress, as observed in other works (Peressini et al., 1998). Even though this is a main issue in the study of the stability of emulsified systems, stability issues over time were not considered in this work. Phenolic compounds were thus proven to interfere with the stabilization of the emulsified systems and to impair the structure properties and stability. This behaviour is rather clear in the OE added mayonnaises whilst a more complicated mechanism should be hypothesised when considering the EVOOs samples, due to the complex composition of the oils. A correlation matrix was finally tested in order to find significant correlations among the parameters taken into consideration: the gel strength A resulted significantly related to both the textural indices Fmax and Etot (p < 0.05); this represents an important result since textural measurements could provide important informations on the strength of a gel network.
3.5. Sensory evaluation Results of the sensory analyses are presented in the form of a spider web plot which show the profiles of the mayonnaise samples prepared with the different oils (Fig. 4). The standard error of the mean values of the various sensory attributes varied between 0.10 and 0.44, in accordance to other studies in the literature for similar matrices (Wendin, Risberg Ellekjaer, & Solheim, 1999). The results obtained allow the classification of the samples into two groups: in the first one are included mayonnaises prepared with EVO oils and in the second those made with the other ones. The SO reference sample, along with the samples prepared with peanut, refined and olive oils, showed very similar sensory profiles, as described by a rather sweet taste, low spicy and astringent properties and high scores of the attributes related to texture. In the EVOOs samples are in general characterised by a freshlycut grass smell due to the peculiar aroma of the oils. However, main difference was found in the mean values given to odour and taste
Table 2 Power-law parameters describing frequency sweeps for the mayonnaise samples prepared with the different oils and the samples added with OE [z: coordination coefficient A: proportionality coefficient (G* at 1 Hz)]. Samples
A (kPa)
SO PO RO OO EVOO1 EVOO2 EVOO3 EVOO4 RO1 RO3 RO6
1337 1136 1050 1024 580 687 440 514 876 587 404
± ± ± ± ± ± ± ± ± ± ±
R2
z () 29 73 29 20 28 6 5 15 37 34 24
10.92 10.96 10.59 10.54 10.35 10.31 9.67 10.60 10.29 9.73 8.62
± ± ± ± ± ± ± ± ± ± ±
0.68 0.32 0.24 0.52 0.86 0.17 0.76 0.70 0.46 0.06 0.22
0.999 0.999 0.995 0.999 0.997 0.996 0.993 0.995 0.998 0.954 0.962
Fig. 4. The sensory profiles of mean values for the mayonnaise samples produced with different vegetables oils (sunflower oil SO (A), peanut oil PO ( ), Refined oil ( ), Olive oil OO (B), Extra-virgin olive oils EVOO1 (-), EVOO2 (✕), EVOO3 (þ), EVOO4 (C)).
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attributes. In particular, the EVOO-mayonnaise was also perceived as bitter, spicy and astringent, with the EVOO4-product the ones judged as the most bitter while the EVOO3 the most spicy and astringent. Such properties might be related to the content and qualitative profile of the phenolic compounds present in the oil which is known can deeply affect the sensory response (Bendini et al., 2007). From a textural viewpoint, the assessors were not able to discriminate the EVOOs based mayonnaise for their creaminess and thickness whilst differences were observed in their spreadability resulting higher in the EVOO1-mayonnaise. Moreover, the EVOO4mayonnaise, characterised by the highest total phenolic content, showed the lowest scores for all the textural properties. No significant correlations were found among textural attributes as perceived by the sensory test and rheological and textural measurements, as observed in other studies (Liu et al., 2007; Laca et al., 2010; Worrasinchai et al., 2006). 4. Conclusions The use of polyphenols-rich EVOOs for the preparation of mayonnaise generally resulted in complex dispersed systems characterized by a lower dispersion degree, lower firmness and consistency, and a lower elastic behaviour, when compared to the control. Based also on the results obtained from the samples made with olive oils artificially added with phenolic oil extracts, the changes of the physical and structural properties seem to be related to the presence and content of polyphenolic compounds, which are then confirmed to play a crucial role both in the formation and in the stabilization of emulsified and gel-like products. Further investigations are needed to understand the specific technological functionality of olive polyphenols as well as of the other amphyphylic EVOO compounds in complex emulsified structures. References Bendini, A., Cerretani, L., Carrasco-Pancorbo, A., Gomez-Caravaca, A. M., SeguraCarretero, A., Fernandez-Gutierrez, A., et al. (2007). Phenolic molecules in virgin olive oils: a survey of their sensory properties, health effects, antioxidant activity and analytical methods. An overview of the last decade. Molecules, 12, 1679e1719. Boskou, D., Blekas, G., & Tsimidou, M. (2006). Olive oil composition. In D. Boskou (Ed.), Olive oil: Chemistry and technology (2nd ed.). (pp. 41e72). Champaign, Illinois: AOCS Press. Del Carlo, M., Sacchetti, G., Di Mattia, C., Compagnone, D., Mastrocola, D., Liberatore, L., et al. (2004). Contribution of the phenolic fraction to the antioxidant activity and oxidative stability of olive oil. Journal of Agricultural and Food Chemistry, 52, 4072e4079.
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Depree, J. A., & Savage, G. P. (2001). Physical and flavor stability of mayonnaise. Trends in Food Science and Technology, 12, 157e163. Di Mattia, C. D., Sacchetti, G., Mastrocola, D., & Pittia, P. (2009). Effect of phenolic antioxidants on the dispersion state and chemical stability of olive oil O/W emulsions. Food Research International, 42, 1163e1170. Di Mattia, C. D., Sacchetti, G., Mastrocola, D., Sarker, D. K., & Pittia, P. (2010). Surface properties of phenolic compounds and their influence on the dispersion degree and oxidative stability of olive oil O/W emulsions. Food Hydrocolloids, 24, 652e658. Di Mattia, C. D., Sacchetti, G., & Pittia, P. (2011). Interfacial behavior and antioxidant efficiency of olive phenolic compounds in o/w olive oil emulsions as affected by surface active agent type. Food Biophysics, 6(2), 295e302. Gabriele, D., de Cindio, B., & D'Antona, P. (2001). A weak gel model for foods. Rheologica Acta, 40, 120e127. Hayati, I. N., Man, Y. B. C., Tan, C. P., & Aini, I. N. (2007). Stability and rheology of concentrated O/W emulsions based on soybean oil/palm kernel olein blends. Food Research International, 40, 1051e1061. Kiosseoglou, V. D., & Sherman, P. (1983). Influence of egg yolk lipoproteins on the rheology and stability of oil/water emulsions and mayonnaise 1. Viscoelasticity of groundnut oil-in-water emulsions and mayonnaise. Journal of Texture Studies, 14, 397e417. Laca, A., S aenz, M. C., Paredes, B., & Diaz, M. (2010). Rheological properties, stability and sensory evaluation of low cholesterol mayonnaises prepared using egg yolk granules as amulsifying agent. Journal of Food Engineering, 97, 243e252. €r, A., Sørensen, C., & Hermansson, A. (1999). Langton, M., Jordansson, E., Altska Microstructure and image analysis of mayonnaises. Food Hydrocolloids, 13, 113e125. Liu, H., Xu, X. M., & Guo, S. D. (2007). Rheological, texture and sensory properties of low-fat mayonnaise with different fat mimetics. LWT Food Science and Technology, 40, 946e954. Mancini, F., Montanari, L., Peressini, D., & Fantozzi, P. (2002). Influence of alginate concentration and molecular weight on functional properties of mayonnaise. LWT Food Science and Technology, 35, 517e525. Mun, S., Kim, Y. L., Kang, C. G., Park, K. H., Shim, J. Y., & Kim, Y. R. (2009). Development of reduced-fat mayonnaise using 4aGTase-modified rice starch and xanthan gum. International Journal of Biological Macromolecules, 44, 400e407. Nikzade, V., Mazaheri Tehrani, M., & Saadatmand-Tarzjan, M. (2012). Optimization of low-cholesterol-fat mayonnaise formulation: effect of soy milk and some stabilizer by a mixture design approach. Food Hydrocolloids, 28, 344e352. Peressini, D., Sensidoni, A., & de Cindio, B. (1998). Rheological characterization of traditional and light mayonnaises. Journal of Food Engineering, 35, 409e417. Pirisi, F. M., Cabras, P., Falqui Cao, C., Migliorini, M., & Muggelli, M. (2000). Phenolic compounds in virgin olive oil. 2. Reappraisal of the extraction, HPLC separation, and quantification procedures. Journal of Agricultural and Food Chemistry, 48, 1191e1196. Santipanichwong, R., & Suphantharika, M. (2007). Carotenoids as colorants in reduced-fat mayonnaise containing spent brewer's yeast b-glucan as a fat replacer. Food Hydrocolloids, 21, 565e574. Singleton, V. L., & Rossi, J. (1965). A colorimetry of total phenolics with phosphomolibdic-phosphotungstic acid reagents. American Journal of Enology and Viticulture, 16, 144e158. Wendin, K., Risberg Ellekjaer, M., & Solheim, R. (1999). Fat content and homogenization effects on flavour and texture of mayonnaise with added aroma. LWT Food Science and Technology, 32, 377e383. Worrasinchai, S., Suphantharika, M., Pinjai, S., & Jamnong, P. (2006). b-Glucan prepared from spent brewer's yeast as a fat replacer in mayonnaise. Food Hydrocolloids, 20, 60e78. Zampounis, V. (2006). Olive oil in the world market. In D. Boskou (Ed.), Olive oil: Chemistry and technology (2nd ed.). (pp. 21e39). Champaign, Illinois: AOCS Press.
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Physical and structural properties of extra-virgin olive oil based mayonnaise Carla Di Mattia a, *, Federica Balestra b, Giampiero Sacchetti a, Lilia Neri a, Dino Mastrocola a, Paola Pittia a a Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, Via C.R. Lerici 1, 64023, Mosciano S. Angelo, Teramo, Italy b CIRI Interdepartmental Centre for Agri-Food Industrial Research, Alma Mater Studiorum, University of Bologna, Campus of Food Science, Piazza Goidanich 60, 47521, Cesena, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 February 2014 Received in revised form 12 September 2014 Accepted 30 September 2014 Available online xxx
The purpose of this work was to study the physical and structural properties of mayonnaises made with extra virgin olive oils (EVOO). To this aim, different EVOOs were selected according to their phenolic content along with other vegetable oils, peanut and sunflower, taken as reference. Mayonnaises were characterized by droplet size distribution, microstructure, textural, rheological and sensory properties. The droplet size distribution and microstructural properties of the mayonnaises resulted significantly affected by the type of oil used. Samples produced with EVOO showed lower dispersion level, a more coarse and irregular structure and the lowest consistency and firmness when compared to sunflower or peanut oils. The elastic and viscous modulus G0 and G00 , evaluated by rheological measurements, resulted inversely related to the content of polyphenolic compounds. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Olive oil Mayonnaise Microstructure Texture Rheological properties
1. Introduction Mayonnaise is a semi-solid, formulated sauce prepared by mixing vegetable oil, egg yolk, vinegar and salt (Depree & Savage, 2001). Its structure, creaminess, appearance and rheological behaviour are of outstanding importance for the sensory properties and perceived texture as well as for the physical stability, parameters which represent key factors for determining consumers' choice and satisfaction. From the colloidal point of view, mayonnaise is a low-pH O/W emulsion characterized by a very high oil content, ranging from 65 up to 85% depending on the formulation. The distribution of the fat phase, the size of the droplets as well as their interaction affect the texture and stability of the product. The stabilization of the oilewater interface in mayonnaise is mainly due to the granular micro-particles formed from the phosphoprotein and coalesced low-density lipoprotein constituents of egg yolk; in this high-lipid product, the granules keep the oil droplets well separated and prevent coalescence (Kiosseoglou & Sherman,
* Corresponding author. Tel.: þ39 0861 266912; fax: þ39 0861 266915. E-mail address: [email protected] (C. Di Mattia).
€r, Sørensen, & Hermansson, 1983; Langton, Jordansson, Altska 1999). As far as mayonnaise formulation is concerned, low cost and worldwide distributed vegetable oils (e.g. soybean, sunflower, corn and rapeseed oils) are mainly used. Extra virgin olive oil (EVOO) represents one of the most important dietary lipid obtained from olive trees crops in Italy as well as in other south Europe countries (e.g. Greece, Spain) (Zampounis, 2006). This vegetable oil has nutritional and sensory characteristics (Bendini et al., 2007, Boskou, Blekas, & Tsimidou, 2006), that make it unique and a basic component of the Mediterranean diet being used as seasoning for the preparation of traditional formulated sauces and dishes. Despite its high nutritional and health value, quite limited is the use of EVOO oils as ingredient in complex formulated foods, especially in the most industrialised ones, partly because of its peculiar sensory properties and partly for its relatively high cost in respect to other vegetable oils. Nevertheless, the use of olive oil in complex formulated systems could arise some issues related to the dispersion degree and the physical stability of the emulsified system that originates during food manufacturing which, in turn, may affect the quality of the final product and its stability during storage.
http://dx.doi.org/10.1016/j.lwt.2014.09.065 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
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The colloidal properties of an emulsion and its thermodynamic and kinetic instability are indeed highly dependent on the intrinsic chracteristics of the system and in particular on the presence of components that may either positively or negatively affect the chemical and physico-chemical properties of the dispersed and dispersing phases and of the interfaces as well. Olive oil, especially the extra virgin one, is a lipid source naturally rich in bioactive molecules of various nature and chemical properties including phenolic compounds which are known to exert a powerful antioxidant activity (Bendini et al., 2007; Del Carlo et al., 2004). However, recent studies have been carried out to exploit also the technological properties of EVOO in emulsified model systems and the role of its complex composition (e.g. free fatty acids, phospholipids and polyphenols) on the physical properties of the systems and their stability (Di Mattia, Sacchetti, Mastrocola, & Pittia, 2009; Di Mattia, Sacchetti, Mastrocola, Sarker, & Pittia, 2010; Di Mattia, Sacchetti, & Pittia, 2011). Results of these investigations have shown that some surface active endogenous amphiphylic molecules may affect the formation of oil/ water interfaces and the physical and chemical stability of dispersed emulsified systems. To the authors' knowledge, however, no studies have been carried out to study the effect of polyphenols on the structure of real emulsified matrices (e.g. mayonnaise, sauces, etc.), likely due to the complexity of their formulation that could hinder the understanding of the role of relatively low concentrations of surface active bioactive compounds. The aim of this work was, thus, to study the physical and structural properties of mayonnaise made with extra virgin olive oils (EVOO). To this purpose, different EVOOs were selected according to their polyphenolic content and, to compare the technological performances, peanut and sunflower oils were also considered. Mayonnaise samples were produced by using a single recipe and a standardized homogenization procedure and then characterized by droplets size distribution, colour, microstructure, mechanical, rheological and sensory properties. The mayonnaise sample prepared with sunflower oil was used as reference.
content of polyphenolic compounds, as measured by the FolinCiocalteau assay, was 0.52 ± 0.03 g GAE/g extract.
2. Material and methods
2.4. Measurement of rheological properties
2.1. Materials
Mayonnaise rheological measurements were performed by a controlled stress-strain rheometer (MCR 300, Physica/Anton Paar, Ostfildern GermanyeEurope) connected to a circulating water bath for the temperature control. The viscoelastic behaviour of the samples was evaluated at 25 C by using a parallel plate (diameter: 50 mm) and a gap distance of 2 mm. Excess sample protruding from the edge of the sensor was trimmed off carefully with a thin blade. Firstly, the extent of the linear viscoelastic region was determined by performing a strain sweep (0.1e100%) at a fixed frequency of 1 Hz. Subsequently, a dynamic frequency sweep was conducted by applying a constant strain of 0.5% within the linear viscoelastic region, over a frequency range between 0.1 and 100 Hz (Mancini, Montanari, Peressini, & Fantozzi, 2002). Before starting the measurements, all samples were allowed to rest for 5 min after loading to allow temperature equilibration and induced stress to relax. The rheological parameters used for this study were the storage (G0 ), the loss (G00 ) and the complex (G*) moduli. The experimental data of all frequency sweep tests were correlated according to the following power law (Gabriele, de Cindio, & D'Antona, 2001):
The following vegetable oils were used: sunflower (SO), peanut (PO), refined olive oil (RO), olive oil (OO) and four extra virgin olive oils according to the EU regulation (EVOO1-EVOO4). The EVOOs were chosen and ranked according to their polyphenolic contents which were as following: 233.26 ± 5.88 for EVOO1, 321.00 ± 7.64 for EVOO2, 389.05 ± 5.36 for EVOO3 and 764.24 ± 7.33 mg/L Gallic Acid Equivalents (GAE) for EVOO4. For SO, PO and RO oils it was not possible to quantify the total content of polyphenols since it was below the limit of detection of the method used. For the determination of the total polyphenols contents, the oils were extracted according to the procedure described by Pirisi, Cabras, Falqui Cao, Migliorini, and Muggelli (2000). The total polyphenol content of the methanol extracts was evaluated colourimetrically using the Folin-Ciocalteau reagent, with a method adapted from Singleton and Rossi (1965). Sunflower and peanut oils were purchased from a local supermarket; the refined olive oil was gently provided by Adriaoli (Mosciano S. Angelo, Italy) and used without any further purification. The EVOO oils were supplied by a local olive oil mill (Frantoio Montecchia, Morro d'Oro, Italy). A commercial food-grade olive fruit extract (OE) rich in phenolic compounds was kindly provided by Indena (Milan, Italy). The olive dry purified polyphenolic extract was 90% (w/w); other components were represented by dehydrated corn syrup (10%). The total
2.2. Mayonnaise preparation A reference recipe was used throughout the study based on the following formulation: oil (500 g), 2 eggs (120 g), vinegar (30 g), salt (1 g). Mayonnaise samples were prepared using a lab-scale mixer (Bimby TM31, Vorwerk, Wuppertal, Germany) in a two-steps standardized process: eggs, vinegar and salt were preliminary mixed (100 rpm, 3 min) and then oil was slowly added under vigorous mixing rate (from 3200 rpm up to 6000 rpm in 5 min). Mayonnaise samples made with refined olive oil (RO) and enriched with the polyphenol-rich olive fruit extract (OE) were also prepared; different amounts were added and solubilised during the first step of the homogenization procedure. The amounts of OE added were calculated as percentages on the basis of the oil content; RO1, RO3 and RO6 mayonnaise samples were thus obtained and the phenolic contents, calculated on the amount added, were of 120, 350 and 700 mg/L respectively. Mayonnaise was prepared in 500 g of oil each time and for each formulation three batches were considered. 2.3. Particle size distribution Particle size distribution was measured as described by Santipanichwong and Suphantharika (2007) with some modification. Mayonnaise samples (1 g) were diluted with 200 mL 0.2 g/ 100 mL sodium dodecyl sulphate (SDS) solution and gently stirred with a spatula until completely dispersed. Samples were analysed by a particle size analyser (Mastersizer 3000, Malvern Instruments Ltd, Worcestshire, UK). The sample solution was dispersed in distilled water at 2000 rpm until an obscuration rate of 12% was reached. Optical properties were defined as following: refractive index 1.46 and absorption 0.00. Droplet size measurements are reported as the volume-weighted mean diameter D4,3.
G* ðuÞ ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 00 G0 ðuÞ2 þ G ðuÞ2 ¼ Au1=z
(1)
where G* is the complex modulus in Pa, u is the frequency in Hz, z (dimensionless) is the coordination number and A (G* in Pa at 1 Hz) is the proportional coefficient.
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2.5. Back extrusion test Measurements were carried out according to Liu, Xu, and Guo (2007) with some modification, by using a Dynamometer Instron Mod. 5542 (Instron Universal Testing Machine, Royal Street Canton Ma, USA). A back extrusion cell with 35 mm diameter compression disc was used. Samples were carefully scooped into glass cylindrical containers (i.d.: 50 mm, h: 75 mm) to a depth of 40 mm. One cycle was applied at a constant crosshead rate of 1 mm/s to a sample deformation of 50% of the initial height. From the resulting forceetime curve, the maximum force and the area of the curve up to this point were obtained as indices of firmness and consistency, respectively. 2.6. Optical microscope observation The glassy flat was coated with mayonnaise sample and placed on the stage of a light microscope (Olympus Microscope BX53, Tokyo, Japan); pictures of mayonnaise microstructure were obtained at a 40 magnification by a digital camera (Qimaging Fast 1394, Surrey, BC, Canada) connected to the microscope. 2.7. Sensory analysis Sensory evaluation was carried out by quantitative descriptive analysis by a trained panel consisting of 8 assessors (3 males, 5 femals; age range: 25e55). Panelists were preliminarily trained in sessions to develop a common language for descriptors and range of scores. The attributes taken into consideration were sour and freshly-cut grass for smell; sweetness, bitterness, spicy and astringent for flavour and taste; spreadability, creaminess and thickness for texture and mouthfeel. The ranking was as following: 1 ¼ the least, the lowest; 10 ¼ the most, the highest. Samples (10 g) were served at 20 C in red plastic cups with lids. Judges were asked to first take a deep sniff and evaluate smell and then appearance; after recovering smell sensitivity, they were asked to take a teaspoon mayonnaise (z5 mL) into the mouth and evaluate flavour, taste and texture attributes. Water and neutral wafer were used for cleaning the palate between samples. 2.8. Statistical analyses Three batches of mayonnaise were prepared from a unique lot of oil. All measurements were made in triplicate on samples from each batch (n ¼ 9) and results are expressed as mean and standard deviation. A one-way analysis of variance (ANOVA) and Tukey's test were used to establish the significance of differences among the mean value at the 0.05 significance level. Non-linear regression analysis was performed with Equation (1) as the model function, using the algorithm “Rosenbrock pattern search” supplied by the STATISTICA (StatSoft^TM Tulsa, Oklahoma) package. 3. Results & discussion 3.1. Droplet size distribution The properties and stability of mayonnaise are generally linked, as for other emulsified foods, to the droplet size and to the uniformity of the oil droplets. Fig. 1a shows the mean droplet size of the mayonnaise samples as expressed by the D4,3 value (mm). The RO- and PO-mayonnaise samples did not show any significant droplet size difference if compared to the control sample SO. The smallest droplet size was exhibited by the mayonnaise made with olive oil (OO) which thus showed higher emulsifying properties in
Fig. 1. Particle size (a) and distribution profiles (b) of the different samples of mayonnaise. In Fig. 1b: sunflower oil SO (A), peanut oil PO ( ), Refined oil ( ), Olive oil OO (B), Extra-virgin olive oils EVOO1 (-), EVOO2 (✕), EVOO3 (þ), EVOO4 (C).
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comparison with the other vegetable oils; on the contrary, the biggest droplets size was observed when EVOO was used. Moreover, the droplet size of the EVOO based mayonnaises increased from EVOO1 up to EVOO4, which corrisponded to an increasing phenolic contents of the oils. Besides droplet size, interesting information on the colloidal state of the different systems could be achieved by considering the profiles of the droplet size distribution (Fig. 1b). The particle size range of the mayonnaises under investigation (1e300 mm) resulted close to that reported by Liu et al. (2007) but markedly higher than those obtained by Worrasinchai, enz, Paredes, Suphantharika, Pinjai, and Jamnong (2006); Laca, Sa and Diaz (2010) and Nikzade, Mazaheri Tehrani, and SaadatmandTarzjan (2012). However, while the SO-mayonnaise was characterized by a monomodal distribution centred at around 20 mm, the use of PO, RO and OO led to the samples with a bimodal distribution of the oil globules particularly evident in the OO-based mayonnaise where the presence of larger droplets characterized by a mean volume-surface diameter of around 80 mm was detected. Moreover, the use of EVOO determined the formation of broader distribution within a size range of 1e300 mm in contrast to the 1e150 mm range of the non-EVOO samples; the droplet size distribution of the latter systems was also characterized by the appearance of a third population of bigger particles whose amount increased with the increasing of the polyphenolic content of the EVOO oils. 3.2. Optical microscope observation Microstructural properties of the mayonnaise samples were investigated by optical microscopy and the microphotographs
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show the market effect of the use of different oils with the formation of a wide variety of microstructures (Fig. 2). SO-mayonnaise showed a fine and well dispersed oil-inwater structure in which fat globules resulted spherical and highly packed together; similar packing structure could be observed for PO-, RO-, and OO-based mayonnaise samples even though with same differences related to the polydispersity of the droplets.
On the other hand, the use of EVOOs determined a more coarse distribution of the oil particles in the macromolecular network (Fig. 2, eeh). The presence of polyphenols as well as of other amphyphylic compounds present in the EVOOs seems to affect the development of the emulsified system and/or the threedimensional egg protein network. From EVOO1 to EVOO4, thus at increasing content in phenolic compounds, a more open and coarse structure could be observed suggesting that these compounds may
Fig. 2. Optical micrographs of the mayonnaises produced with different oils: sunflower SO (a), peanut PO (b), refined RO (c), olive OO (d), EVOO1 (e), EVOO2 (f), EVOO3 (g) and EVOO4 (h).
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also affect, under the experimental condition used in this study, the formation of the gelled pH-induced structure of the egg protein network.
3.3. Textural properties The values of Fmax and Etot parameters, corresponding to the first peak extrusion force and the total work obtained by the back extrusion test, are shown in Table 1. Fmax was taken as an index of firmness whilst Etot as a measure of consistency (Liu et al., 2007; Nikzade et al., 2012; Santipanichwong & Suphantharika, 2007; Worrasinchai et al., 2006). The highest firmness was found in the reference sample, the SO-mayonnaise, in agreement with results previously observed for mayonnaise having similar fat content (Liu et al., 2007; Nikzade et al., 2012). The substitution of sunflower oil with other oils caused a general reduction of the Fmax which was significantly (p < 0.05) higher when EVOO was used with a negative relationship between the firmness of the samples and the polyphenolic content. For these products the decrease in firmness ranges from 42% up to 70%. A similar trend was observed also for the consistency with higher Etot values obtained in the case of the mayonnaises made with SO, PA, RO and OO. The use of EVOOs generally caused, again, a lower Etot of the correspondent emulsified products with a similar negative correlation between the total polyphenolic content and the consistency. These results could be attributed to some microstructural properties and, in particular, to the bigger size of the fat globules in the EVOOs made-maionnaises, which led to a lower surface area contact between droplets and, consequently, a lower degree of interaction, as well as to the droplet size distribution, both related, in turn, to the amount of phenolic compounds of the oils. Since the olive oils used to formulate the systems may be characterized by very different phenolic pattern, the influence of the sole phenolic content on the mechanical properties was further studied by the investigation of RO-mayonnaise samples added with increasing amounts of a commercial olive fruit extract (OE) with a standardised phenolic pattern (RO1, RO3 and RO6) whose results are reported in Table 1. This approach permitted to modify the phenolic content without any influence on the phenolic composition of the systems. Both the textural parameters Fmax and Etot showed a similar trend: small addition of phenolic compounds had little effect on Fmax and Etot whilst a significant decrease of the firmness and consistency occurred when the OE was added at the highest concentration (1360 mg L1). This result further supports the hypothesis that olive oil phenolic compounds could impair the textural attributes of
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mayonnaise. However, contrary to the results obtained from the artificially enriched maionnayses, the decrease of firmness and consistency occurred also in the products obtained with EVOOs containing lower phenolic concentrations (Table 1), and this may suggest that factors other than total polyphenols content are worthwile to be further investigated: the phenolic pattern of the oils and the content of other minor compounds, which may interfere with the formation of the emulsified and partly gelled structure. 3.4. Rheological properties Dynamic oscillatory shear tests were carried out to characterize the viscoelastic properties of the mayonnaises samples made by using different oils. Data of the elastic modulus (G0 ) and loss modulus (G00 ) are shown Fig. 3 (a, b). At small strains mayonnaise samples showed a linear visco-elastic response. The magnitude of storage modulus G0 (Fig. 3a) was greater than loss modulus G00 (Fig. 3b) for all samples. This behaviour is typical of concentrated emulsion as previously reported for commercial or model mayonnaise (Laca et al., 2010; Liu et al., 2007; Mun et al., 2009; Worrasinchai et al., 2006). The experimental linearity of the moduli suggests that mayonnaise may be considered as gel-like network in the frequency range of 0.1e100 Hz (Mancini et al., 2002). In general, G0 values showed a slight increase at increasing frequency and this could be related to the strong interactions among the droplets that contributes to the elastic modulus and need a longer time to relax. This further supports the gel-like
Table 1 Textural parameters of the mayonnaise samples as measured by the Fmax (N) and Etot (mJ). Data were averaged from n ¼ 9 measurements made on three different batches (three repeats for each batch). Samples
Fmax (N)
SO PO RO OO EVOO1 EVOO2 EVOO3 EVOO4 RO1 RO3 RO6
2.09 1.79 1.59 1.27 1.06 1.04 0.91 0.60 1.58 1.52 0.70
± ± ± ± ± ± ± ± ± ± ±
0.14 0.41 0.18 0.11 0.16 0.11 0.09 0.10 0.20 0.15 0.09
Etot (mJ) 32.6 26.8 26.5 20.5 17.8 18.4 16.3 11.3 28.7 28.5 11.1
± ± ± ± ± ± ± ± ± ± ±
2.0 2.7 2.1 2.8 2.0 2.1 2.1 1.6 3.2 5.3 2.5
Fig. 3. Dynamic oscillatory response G0 (a) and G00 (b) of the mayonnaise samples (sunflower oil SO (A), peanut oil PO ( ), Refined oil ( ), Olive oil OO (B), Extra-virgin olive oils EVOO1 (-), EVOO2 (✕), EVOO3 (þ), EVOO4 (C)).
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structure predominant in this kind of emulsified systems (Hayati, Man, Tan, & Aini, 2007). The EVOOs samples showed in general lower elastic moduli (G0 ), if compared to the mayonnaises made with SO, PO, RO and OO. This result could be due to the lower dispersion levels of the EVOO samples, as already observed in literature and, therefore, to a lower degree of interactions among the droplets (Langton et al., 1999). In general low storage modulus implies that low stresses are necessary for the emulsion to flow, reflecting a less compact structure and a more liquid-like behaviour, confirming thus the results obtained from the mechanical measurements and the microscopy observations. According to the weak gel model proposed by Gabriele et al. (2001), as a general predictive model applicable to many food systems, the rheological structure of mayonnaise can be considered as a three-dimensional network in which droplet particles and similar units are linked by weak and strong interactions. The weak gel is made by strong topological points connected by weak strands constituted by a sort of necklace of flow units with a coordination degree of z (Gabriele et al., 2001). The coordination number z is the number of rheological units correlated with one another in the three-dimensional structure, while the parameter A (Equation (1)) is the strength of the interaction between those units. A rheological characterization based on the coordination number z and the coefficient A was useful for distinguishing rather well the structural properties of mayonnaise made with different formulations (Laca et al., 2010; Peressini, Sensidoni, & de Cindio, 1998). The values of z and A for all the samples analysed, including the RO1- RO3 and RO6-mayonnaises added with OE, are reported in Table 2. The z parameter ranged from 8.62 ± 0.22 to 10.96 ± 0.32, values close to those found in literature (Laca et al., 2010; Mancini et al., 2002; Peressini et al., 1998). The SO-mayonnaise (reference), presented the highest coordination number and gel strength, corresponding to the most complex structure and high physical stability (Mancini et al., 2002). Slight differences were observed in the z values of the mayonnaises made with different EVOO which were lower if compared to the reference but without a significant correlation due to the phenolic content of the initial oils. On the other hand, a significantly lower A value and in the range of 440 ± 5 to 687 ± 6 kPa was shown by the EVOOs-mayonnaises compared to the reference sample (1337 ± 29 kPa) to indicate a reduced gel strength. However, also in this case, no clear relationships were observed between the polyphenolic content and the gel strength of EVOOs mayonnaise. Thus, on the basis of the coordination number and the gel strength, it could be concluded that the gel network of the mayonnaise samples prepared with EVOO oils resulted to be characterised by a smaller number of units linked by weaker interactions.
The Gabrieli model was applied also to the rheological results of the RO-mayonnaise samples added with OE (Table 2) (RO1-RO6). At increasing phenolic extract addition a decrease of both coordination number z and gel strength A occurred, showing a zero and first order relationship with OE concentration respectively (R2 ¼ 0.9928; 0.9865). On the basis of these results, the RO6 sample, characterised by the lowest values of z and A, is supposed to be the most exposed to physical instability due to coalescence phenomena when the system undergoes mechanical stress, as observed in other works (Peressini et al., 1998). Even though this is a main issue in the study of the stability of emulsified systems, stability issues over time were not considered in this work. Phenolic compounds were thus proven to interfere with the stabilization of the emulsified systems and to impair the structure properties and stability. This behaviour is rather clear in the OE added mayonnaises whilst a more complicated mechanism should be hypothesised when considering the EVOOs samples, due to the complex composition of the oils. A correlation matrix was finally tested in order to find significant correlations among the parameters taken into consideration: the gel strength A resulted significantly related to both the textural indices Fmax and Etot (p < 0.05); this represents an important result since textural measurements could provide important informations on the strength of a gel network.
3.5. Sensory evaluation Results of the sensory analyses are presented in the form of a spider web plot which show the profiles of the mayonnaise samples prepared with the different oils (Fig. 4). The standard error of the mean values of the various sensory attributes varied between 0.10 and 0.44, in accordance to other studies in the literature for similar matrices (Wendin, Risberg Ellekjaer, & Solheim, 1999). The results obtained allow the classification of the samples into two groups: in the first one are included mayonnaises prepared with EVO oils and in the second those made with the other ones. The SO reference sample, along with the samples prepared with peanut, refined and olive oils, showed very similar sensory profiles, as described by a rather sweet taste, low spicy and astringent properties and high scores of the attributes related to texture. In the EVOOs samples are in general characterised by a freshlycut grass smell due to the peculiar aroma of the oils. However, main difference was found in the mean values given to odour and taste
Table 2 Power-law parameters describing frequency sweeps for the mayonnaise samples prepared with the different oils and the samples added with OE [z: coordination coefficient A: proportionality coefficient (G* at 1 Hz)]. Samples
A (kPa)
SO PO RO OO EVOO1 EVOO2 EVOO3 EVOO4 RO1 RO3 RO6
1337 1136 1050 1024 580 687 440 514 876 587 404
± ± ± ± ± ± ± ± ± ± ±
R2
z () 29 73 29 20 28 6 5 15 37 34 24
10.92 10.96 10.59 10.54 10.35 10.31 9.67 10.60 10.29 9.73 8.62
± ± ± ± ± ± ± ± ± ± ±
0.68 0.32 0.24 0.52 0.86 0.17 0.76 0.70 0.46 0.06 0.22
0.999 0.999 0.995 0.999 0.997 0.996 0.993 0.995 0.998 0.954 0.962
Fig. 4. The sensory profiles of mean values for the mayonnaise samples produced with different vegetables oils (sunflower oil SO (A), peanut oil PO ( ), Refined oil ( ), Olive oil OO (B), Extra-virgin olive oils EVOO1 (-), EVOO2 (✕), EVOO3 (þ), EVOO4 (C)).
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Please cite this article in press as: Di Mattia, C., et al., Physical and structural properties of extra-virgin olive oil based mayonnaise, LWT - Food Science and Technology (2014), http://dx.doi.org/10.1016/j.lwt.2014.09.065
C. Di Mattia et al. / LWT - Food Science and Technology xxx (2014) 1e7
attributes. In particular, the EVOO-mayonnaise was also perceived as bitter, spicy and astringent, with the EVOO4-product the ones judged as the most bitter while the EVOO3 the most spicy and astringent. Such properties might be related to the content and qualitative profile of the phenolic compounds present in the oil which is known can deeply affect the sensory response (Bendini et al., 2007). From a textural viewpoint, the assessors were not able to discriminate the EVOOs based mayonnaise for their creaminess and thickness whilst differences were observed in their spreadability resulting higher in the EVOO1-mayonnaise. Moreover, the EVOO4mayonnaise, characterised by the highest total phenolic content, showed the lowest scores for all the textural properties. No significant correlations were found among textural attributes as perceived by the sensory test and rheological and textural measurements, as observed in other studies (Liu et al., 2007; Laca et al., 2010; Worrasinchai et al., 2006). 4. Conclusions The use of polyphenols-rich EVOOs for the preparation of mayonnaise generally resulted in complex dispersed systems characterized by a lower dispersion degree, lower firmness and consistency, and a lower elastic behaviour, when compared to the control. Based also on the results obtained from the samples made with olive oils artificially added with phenolic oil extracts, the changes of the physical and structural properties seem to be related to the presence and content of polyphenolic compounds, which are then confirmed to play a crucial role both in the formation and in the stabilization of emulsified and gel-like products. Further investigations are needed to understand the specific technological functionality of olive polyphenols as well as of the other amphyphylic EVOO compounds in complex emulsified structures. References Bendini, A., Cerretani, L., Carrasco-Pancorbo, A., Gomez-Caravaca, A. M., SeguraCarretero, A., Fernandez-Gutierrez, A., et al. (2007). Phenolic molecules in virgin olive oils: a survey of their sensory properties, health effects, antioxidant activity and analytical methods. An overview of the last decade. Molecules, 12, 1679e1719. Boskou, D., Blekas, G., & Tsimidou, M. (2006). Olive oil composition. In D. Boskou (Ed.), Olive oil: Chemistry and technology (2nd ed.). (pp. 41e72). Champaign, Illinois: AOCS Press. Del Carlo, M., Sacchetti, G., Di Mattia, C., Compagnone, D., Mastrocola, D., Liberatore, L., et al. (2004). Contribution of the phenolic fraction to the antioxidant activity and oxidative stability of olive oil. Journal of Agricultural and Food Chemistry, 52, 4072e4079.
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Please cite this article in press as: Di Mattia, C., et al., Physical and structural properties of extra-virgin olive oil based mayonnaise, LWT - Food Science and Technology (2014), http://dx.doi.org/10.1016/j.lwt.2014.09.065