Emulsion technology is a suitable way of encapsulating, protecting and releasing hydrophobic bioactive compounds for application in food industries, but they are thermodynamically unstable systems. Good results have been achieved for emulsions stabilized by protein-polysaccharide complexes subjected to high-pressure homogenization. Improved stabilization of oil-in-water emulsions results from electrostatic complexes formed between proteins and polysaccharides at pH lower than the protein isoelectric point, which adsorb at the oil-water interface. In addition, polysaccharides contribute to emulsion stability by increasing viscosity of the continuous phase. The aim of this work is to investigate the production of carotenoid-rich buriti oil emulsions using soy protein isolate and high-methoxyl pectin as stabilizers.
Using a rotatable central composite experimental design, we assessed the effects of oil content, soy protein isolate/high-methoxyl pectin ratio and homogenization pressure on the stability, droplet size, electrical conductivity, electrical charge, microstructure and rheological behaviour of the emulsions.
An optimized emulsion was produced with 28% buriti oil, 55% soy protein isolate, and homogenization pressure of 380·105 Pa. This emulsion was stable for at least seven days, presenting reduced average droplet size, low electrical conductivity and high modulus of negative charges. The mechanical spectra showed that the emulsion behaved as a viscoelastic gel under oscillatory, non-destructive shearing, whereas shear-thinning behaviour took place under steady shear conditions.
The optimized buriti oil emulsions stabilized by soy protein isolate and high-methoxyl pectin could be suitable for fat substitution, energy reduction and carotenoid enrichment in food products, such as dairy and bakery products, ice cream, salad sauces and vegetable-based cream.
Emulsion technology is suitable for encapsulation, protection and modulation of the release of hydrophobic bioactive compounds for use in food and pharmaceutical industries. However, emulsions are thermodynamically unstable systems and require addition of emulsifiers and/or stabilizers, as well as the use of energy (homogenization process) to attain kinetic stability (
Soy protein isolate (SPI) and high-methoxyl pectin (HMP) are examples of a protein and anionic polysaccharide that may form electrostatic complexes when pH is lower than the protein isoelectric point (
At pH lower than 4.6, which corresponds to the isoelectric point of SPI, the negatively charged HMP interacts with the protein positive charges to form a biopolymer double layer, preventing droplet coalescence and stabilizing the emulsion (
In addition to using surface-active agents, like emulsifiers, to reduce surface tension of dispersed systems, achievement of kinetic stability of oil-in-water (O/W) emulsions requires the use of energy to reduce droplet sizes and thus prevent creaming, which is a consequence of the difference in density between disperse and continuous phases. The homogenization step is also of crucial importance to modulate physicochemical and organoleptic properties, such as texture, taste, appearance and stability of emulsified systems (
Knowledge of the rheological properties of emulsions is important for several reasons, which include the design of processing equipment (
Oil-in-water emulsions have been recognized as appropriate systems to encapsulate and vehiculate hydrophobic nutrients and functional compounds, such as carotenoid-rich vegetable oil. Palm trees belonging to the
Considering this context, the aim of this work is to investigate the production of buriti oil emulsions by high pressure homogenization using soy protein isolate and high-methoxyl pectin as stabilizers, as well as characterizing the resulting systems by evaluating their stability, droplet size, electrical conductivity, electrical charge, rheological behaviour and morphology. Emulsions containing the carotenoid-rich buriti oil stabilized by SPI/HMP could be valuable structured systems applied in foods such as dairy and bakery products, ice cream, salad sauces and vegetable-based cream for fat substitution, energy reduction and carotenoid enrichment.
The raw materials used were buriti oil (Amazon Oil IndustryTM, Ananindeua, Pará, Brazil), soy protein isolate (SPI) (Tovani Benzaquen IngredientesTM, São Paulo, São Paulo, Brazil) and high-methoxyl pectin (HMP) (CP KelcoTM, Matão, São Paulo Brazil). Preparation of samples required deionized water, 1 M solutions of sodium azide, hydrochloric acid or sodium hydroxide (all DinâmicaTM, Indaiatuba, São Paulo, Brazil) and McIlvaine buffer (pH=3.5) prepared using disodium phosphate and citric acid (DinâmicaTM).
Oil-in-water emulsions were prepared with different mass fractions of oil (10-30%) and SPI in the continuous phase (50-80%), and different applied homogenization pressures (200·105-400·105 Pa). These were the three independent variables. The HMP content was not included as an independent variable in the experimental design since it was added in the amount necessary to attain a fixed total mass fractions of biopolymers (SPI+HMP) in the continuous phase of the emulsion.
All the emulsions were prepared using McIlvaine buffer at pH=3.5, which is below the isoelectric point of SPI and allows the biopolymers in the solution to acquire opposite charges in a sufficient amount to form electrostatic complexes that remain dispersed in the aqueous phase (
Emulsions were produced by following the method described by Kaltsa
The assays were carried out according to a 23 rotatable central composite design (RCCD) to analyze the effects of three independent variables (
Assay | RCCD | Emulsion composition | |||||||
---|---|---|---|---|---|---|---|---|---|
Oil | SPI | HMP | water | ||||||
O14S56P240 | -1 (14) | -1 (56) | -1 (240) | 14.00 | 1.20 | 0.93 | 83.87 | ||
O14S56P360 | -1 (14) | -1 (56) | +1 (360) | 14.00 | 1.20 | 0.93 | 83.87 | ||
O14S74P240 | -1 (14) | +1 (74) | -1 (240) | 14.00 | 1.70 | 0.60 | 83.70 | ||
O14S74P360 | -1 (14) | +1 (74) | +1 (360) | 14.00 | 1.70 | 0.60 | 83.70 | ||
O26S56P240 | +1 (26) | -1 (56) | -1 (240) | 26.00 | 1.02 | 0.80 | 72.18 | ||
O26S56P360 | +1 (26) | -1 (56) | +1 (360) | 26.00 | 1.02 | 0.80 | 72.18 | ||
O26S74P240 | +1 (26) | +1 (74) | -1 (240) | 26.00 | 1.45 | 0.50 | 72.05 | ||
O26S74P360 | +1 (26) | +1 (74) | +1 (360) | 26.00 | 1.45 | 0.50 | 72.05 | ||
O10S65P300 | -1.68 (10) | 0 (65) | 0 (300) | 10.00 | 1.49 | 0.81 | 87.70 | ||
O30S65P300 | +1.68 (30) | 0 (65) | 0 (300) | 30.00 | 1.16 | 0.63 | 68.21 | ||
O20S50P300 | 0 (20) | -1.68 (50) | 0 (300) | 20.00 | 0.96 | 0.96 | 78.08 | ||
O20S80P300 | 0 (20) | +1.68 (80) | 0 (300) | 20.00 | 1.74 | 0.44 | 77.82 | ||
O20S65P200 | 0 (20) | 0 (65) | -1.68 (200) | 20.00 | 1.30 | 0.70 | 78.00 | ||
O20S65P400 | 0 (20) | 0 (65) | +1.68 (400) | 20.00 | 1.30 | 0.70 | 78.00 | ||
O20S65P300 | 0 (20) | 0 (65) | 0 (300) | 20.00 | 1.30 | 0.70 | 78.00 | ||
O20S65P300 | 0 (20) | 0 (65) | 0 (300) | 20.00 | 1.30 | 0.70 | 78.00 | ||
O20S65P300 | 0 (20) | 0 (65) | 0 (300) | 20.00 | 1.30 | 0.70 | 78.00 | ||
O20S65P300 | 0 (20) | 0 (65) | 0 (300) | 20.00 | 1.30 | 0.70 | 78.00 | ||
O20S65P300 | 0 (20) | 0 (65) | 0 (300) | 20.00 | 1.30 | 0.70 | 78.00 |
where y is the response variable, x1 is the oil mass fraction (
The results were subjected to analysis of variance (ANOVA) and the fitted model was tested regarding the lack of fit and coefficient of regression using the software STATISTICA v. 7.0 (
The emulsions were stored at 25 °C for a 7-day period after production. Then they were analyzed in triplicate regarding stability, droplet size, electrical conductivity, electrical charge and morphology using optical microscopy and scanning electron microscopy (SEM) and rheological behaviour. Confocal laser scanning microscopy (CLSM) was performed on the same day of emulsion preparation with fluorescent dyes to avoid fluorescence losses. For samples that show phase separation after 7 days, the analyses were performed using the samples from the creamed phase. The responses for the experimental RCCD were stability, droplet size, electrical conductivity and electrical charge. The analytical procedures are described as follows.
Transparent tubes containing the emulsions were closed and stored at 25 °C. When phase separation took place, a lower density upper phase (cream) was formed. The creaming index (CI), indicative of emulsion stability, was determined as the ratio of the lower phase height (
The average droplet size was evaluated using an optical microscope (OM model CX31; Olympus, Tokyo, Japan) with a 40× magnification objective coupled with a digital camera (SC30; Olympus) and software Image-Pro Plus 6.0 (
In addition to optical microscopy, droplet size distribution was evaluated by laser diffraction (LD; Mastersizer 2000 with Hydro 2000S dispersion unit; Malvern, Malvern, Worcestershire, UK). The samples were dispersed in deionized water at 10% obscuration and kept under stirring during analysis. The refractive indices used for droplets and dispersant phase were 1.46 (buriti oil) and 1.33 (deionized water), respectively. Considering that some samples showed bimodal particle size distribution, the mode of the cumulative frequency distribution was adopted as the most representative particle size (
The emulsion electrical conductivity was measured using a conductivity meter (Seven Compact S230-USP/EP; Mettler Toledo, Columbus, OH, USA) at room temperature (
Electrical charges were analyzed by zeta potential measurements (Zetasizer NanoZ; Malvern). The emulsion or cream phase samples (0.05%) were dispersed in ultrapure water followed by pH=3.5 adjustment using HCl solution to maintain the dispersing medium as close as possible to the emulsion continuous phase, according to the proposed method (
Rheological analyses were performed on an AR-2000EX (TA Instruments, New Castle, DE, USA) rheometer with geometry of serrated parallel plates of 40 mm diameter and gap of 300 μm at 25 °C. To avoid droplet crushing, the distance between parallel plates (gap) was defined as being at least 10 times larger than the maximum droplet size (
Steady shear tests were performed following downward (100 to 0.1 s-1) and upward (0.1 to 100 s-1) shear rate ramps to obtain apparent viscosity
Where
The Sisko model is interesting because it presents, in addition to the consistency index (
The viscoelastic properties were evaluated along frequency sweeps between 0.03 and 30 rad/s at maximum deformation of 0.001, which was in the linear viscoelastic region. A power law model was applied to describe the frequency (
and
where
The fitting quality of Sisko (Eq. 3) and power law models (Eqs. 4 and 5) were evaluated by the coefficient of determination, R2, and the root mean squared errors, RMSE.
Analyses by confocal laser scanning microscopy (CLSM) were carried out according to Lamprecht
Scanning electron microscopy (SEM) images were obtained in a TM 3000 (Hitachi, Tokyo, Japan) microscope with a 600× magnification. The samples were inserted into the chamber and immobilized by vacuum application during image capture.
Experimental validation of the models resulting from the RCCD (Eq. 1) was carried out based on the results of stability, droplet size, electrical conductivity and electrical charge. Selected values for buriti oil and SPI mass fractions, and homogenization pressure were applied to produce an emulsion and the corresponding experimental results were compared with those predicted by the fitted models. In addition, this emulsion was characterized by rheological and morphological analyses (as described above).
The emulsions prepared with different buriti oil and SPI contents and subjected to various homogenization pressures, according to the RCCD in
The obtained results (
Assay | CI/% | Span (droplet OM) | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
O14S56P240 | 28.0±0.6 | 3.4 | 1.2 | 26.0±0.3 | 2.97±0.01 | -20.3±1.3 | |||||||||||
O14S56P360 | 11.7±0.6 | 2.9 | 1.1 | 38.9±0.6 | 3.08±0.01 | -20.0±0.8 | |||||||||||
O14S74P240 | 20.3±1.2 | 3.4 | 1.2 | 51.5±1.2 | 2.47±0.01 | -16.3±1.2 | |||||||||||
O14S74P360 | 22.3±1.6 | 2.4 | 1.3 | 51.7±1.9 | 2.81±0.01 | -18.3±2.0 | |||||||||||
O26S56P240 | 3.7±6.4 | 4.4 | 1.3 | 39.5±2.7 | 2.29±0.01 | -20.5±1.0 | |||||||||||
O26S56P360 | 0.0±0.0 | 4.5 | 1.9 | 42.4±0.6 | 2.18±0.01 | -22.2±0.6 | |||||||||||
O26S74P240 | 11.6±0.6 | 5.7 | 1.9 | 40.2±0.2 | 2.00±0.01 | -15.2±1.3 | |||||||||||
O26S74P360 | 14.7±1.6 | 4.7 | 1.3 | 35.0±0.5 | 2.38±0.01 | -15.6±0.6 | |||||||||||
O10S65P300 | 35.6±1.9 | 2.9 | 1.1 | 46.5±0.3 | 2.82±0.01 | -20.4±0.8 | |||||||||||
O30S65P300 | 0.0±0.0 | 6.8 | 2.4 | 40.6±0.8 | 2.16±0.01 | -21.9±0.8 | |||||||||||
O20S50P300 | 14.0±5.9 | 3.9 | 1.4 | 43.1±0.8 | 2.53±0.01 | -22.3±0.7 | |||||||||||
O20S80P300 | 16.4±1.4 | 4.3 | 1.7 | 66.3±0.8 | 2.02±0.01 | -15.3±0.6 | |||||||||||
O20S65P200 | 17.3±0.5 | 3.6 | 1.4 | 37.4±0.3 | 2.27±0.01 | -19.6±1.2 | |||||||||||
O20S65P400 | 10.1±1.5 | 2.9 | 0.9 | 53.1±1.2 | 2.47±0.01 | -14.6±1.7 | |||||||||||
O20S65P300 | 16.6±0.6 | 3.8 | 1.1 | 51.5±0.8 | 2.31±0.01 | -20.7±1.8 | |||||||||||
O20S65P300 | 14.5±1.5 | 3.9 | 1.4 | 50.3±1.5 | 2.70±0.01 | -18.7±1.4 | |||||||||||
O20S65P300 | 18.2±4.8 | 3.9 | 1.3 | 49.0±0.7 | 2.21±0.01 | -17.8±1.4 | |||||||||||
O20S65P300 | 14.0±0.9 | 3.4 | 1.3 | 48.0±0.4 | 2.38±0.01 | -17.7±0.7 | |||||||||||
O20S65P300 | 13.4±2.0 | 3.3 | 1.1 | 43.2±0.5 | 2.44±0.01 | -20.6±0.4 | |||||||||||
Regression analysis coefficient | CI/% | ||||||||||||||||
16.27 | 3.77 | 49.34 | 2.44 | -19.45 | |||||||||||||
-13.10 | 0.99 | n.s. | -0.26 | n.s. | |||||||||||||
7.66 | n.s. | 5.16 | -0.12 | 2.16 | |||||||||||||
-0.60 | -0.25 | 2.73 | 0.09 | n.s. | |||||||||||||
n.s. | 0.37 | -3.35 | n.s. | n.s. | |||||||||||||
n.s. | n.s. | n.s. | n.s. | n.s. | |||||||||||||
n.s. | -0.19 | -2.75 | n.s. | 0.87 | |||||||||||||
9.28 | 0.26 | -5.63 | n.s. | n.s. | |||||||||||||
n.s. | n.s. | n.s. | n.s. | n.s. | |||||||||||||
10.66 | -0.20 | n.s. | n.s. | n.s. | |||||||||||||
R2 | 0.88 | 0.94 | 0.71 | 0.74 | 0.66 |
The values are mean with standard deviations; n.s.=non-significant (p>0.10)
The creaming index was significantly affected (p≤0.10) by the mass fractions of oil (β1) and SPI (β2), and homogenization pressure (β3). In addition, there were significant interactions between the oil and SPI mass fractions (β12), as well as between SPI mass fraction and homogenization pressure (β23) (
The increase of emulsion stability with increasing concentration of the dispersed phase is probably related to the higher viscosity associated with the increased concentration of emulsion droplets (
With respect to droplet size measured by OM, the variables with significant effects (p≤ 0.10) were the oil mass fraction (linear, β1, and quadratic, β11), homogenization pressure (β3 and β33), the interactions between the oil and SPI mass fractions (β12) and between the SPI mass fraction and homogenization pressure (β23). The oil mass fraction and the interaction between mass fractions of oil and SPI had positive effects on droplet size, while the homogenization pressure and the interaction between the SPI mass fractions and homogenization pressure had negative effects. This suggests that high HMP levels helped to stabilize the emulsions, although the smaller amount of SPI was not sufficient to produce emulsions with small droplets, since a larger amount of proteins would be needed to cover the larger interfacial area.
The droplet sizes determined by LD were represented by the distribution model and were significantly affected (p≤0.10) by the mass fractions of oil (β11) and SPI (β2), homogenization pressure (β3 and β33) and by the interaction between the oil and SPI mass fractions (β12). The SPI content and homogenization pressure had positive effects, whereas the oil content, homogenization pressure, and the interaction between the oil and SPI mass fractions had negative effects. It is interesting to note the large difference between the results for droplet size determined by OM and LD. Differences could also be observed in the variables that exerted significant effects on these results. The laser diffraction technique applied requires sample dilution, which does not happen in the optical microscopy technique. This fact led to the hypothesis that the dilution was not enough to completely disperse the oil droplets, which remained arranged in clusters. This hypothesis was confirmed by observing the emulsions at the same dilution in the optical microscope. Despite the observed differences, the results from LD are relevant, since this is the standard technique used for droplet size analysis in emulsions (
The electrical conductivity was significantly affected (p≤0.10) by the mass fractions of oil (β1) and SPI (β2) and homogenization pressure (β3). The oil and SPI mass fractions had negative effects and the homogenization pressure had positive effect on the electrical conductivity of emulsions or on cream phases. These results can be explained considering that the systems with higher SPI mass fractions had lower HMP mass fraction and, that pectin helps to maintain oil droplets apart from each other. Therefore, in these systems there was a great possibility that oil droplets were flocculated, or even merged (coalescence) in the creamed phase, leading to lower electrical conductivity values. On the other hand, in emulsions subjected to higher homogenization pressures, smaller oil droplets and greater homogeneity are expected, thus, resulting in higher electrical conductivity values.
According to Bruttel (
The zeta potential, or electrokinetic potential, is related to the electrophoretic mobility, gives a measure of the net charge on the surface of a macromolecule, and is used to describe the surface charge of polyelectrolytes of dispersed droplets. Like the electrical conductivity, zeta potential is related to emulsion stability. The more charged the droplets, the greater is the repulsion among them, which contributes to a more stable suspension. In order to prevent irreversible oil droplet flocculation, an emulsion should have a zeta potential greater than 25 mV (in modulus), characterizing a metastable system (
Stable emulsions (O26S56P240, O26S56P360 and O30S65P300) showed high chargemodulus (
The curves obtained for: a) apparent viscosity for downward (closed symbols) and upward (open symbols) shear rate ramps, b) storage
The emulsions showed similar shear-thinning behaviour, with their apparent viscosity decreasing with increasing shear rate. Comparing the emulsions O26S56P360 (circles) and O26S74P360 (stars) produced with the same oil mass fraction and homogenization pressure, slightly higher viscosity values were observed in the emulsion with the lower SPI mass fraction and, consequently, higher HMP mass fraction. On the other hand, comparing the emulsions O26S74P240 (triangles) and O26S74P360 (stars) that are of the same composition but homogenized at different pressures, it was noted that the higher homogenization pressure slightly reduced the apparent viscosity, probably because of the smaller oil droplets produced, which is in accordance with the discussion on the creaming index (see
The Sisko model (Eq. 3) presented satisfactory fit to the apparent viscosity curves (
Assay | Sisko viscosity model | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Downward shear rate ramp | Upward shear rate ramp | |||||||||||||||||||
R2 | RMSE | R2 | RMSE | |||||||||||||||||
O14S74P360 | 4.54 | 0.01 | 0.17 | 0.99 | 0.04 | 5.25 | 0.03 | 0.10 | 0.99 | 0.14 | ||||||||||
O26S56P360 | 2.82 | 0.23 | 0.11 | 0.99 | 0.02 | 3.04 | 0.25 | 0.09 | 0.99 | 0.01 | ||||||||||
O26S74P240 | 3.69 | 0.15 | 0.20 | 0.99 | 0.05 | 4.36 | 0.21 | 0.11 | 0.99 | 0.03 | ||||||||||
O26S74P360 | 1.28 | 0.11 | 0.14 | 0.99 | 0.05 | 1.72 | 0.19 | 0.07 | 0.99 | 0.03 | ||||||||||
Assay | Power law model fitted to frequency sweeps | |||||||||||||||||||
R2 | RMSE | R2 | RMSE | |||||||||||||||||
O14S74P360 | 12.10 | 0.09 | 0.99 | 0.20 | 1.83 | 0.18 | 0.93 | 0.20 | 0.13 | |||||||||||
O26S56P360 | 16.76 | 0.09 | 0.99 | 0.13 | 2.61 | 0.19 | 0.87 | 0.41 | 0.14 | |||||||||||
O26S74P240 | 16.75 | 0.11 | 0.99 | 0.30 | 2.84 | 0.19 | 0.89 | 0.42 | 0.15 | |||||||||||
O26S74P360 | 7.41 | 0.11 | 0.98 | 0.27 | 1.49 | 0.23 | 0.89 | 0.27 | 0.17 |
The apparent viscosity curves corresponding to the downward and upward shear rate ramps practically overlap, suggesting that the rheological behaviour of the emulsions was independent of the shearing time, which could be an interesting characteristic for industrial processing such as pumping and pipe flow.
The storage (
The samples differed in storage and loss modulus magnitude, and the O26S74P360 emulsion (stars) had the lowest modulus. The O14S74P360 (squares) emulsion was the most unstable one, and despite this, its creamed phase showed similar viscoelastic results to O26S56P360 (circles) assay, which was a stable emulsion.
An appropriate way to analyze the mechanical spectra of biopolymer systems is based on fitting a power law model (Eqs. 4 and 5) to
and
The parameter
Optical microscopy was used to observe the emulsion or creamed phase morphology and it was also possible to analyze and compare oil droplet arrangement among different assays.
Images of emulsions: a) O14S74P360 (
Emulsions O14S74P360 (
The images corresponding to emulsions O14S74P360, O26S56P360, O26S74P240 and O26S74P360 (
Images of emulsions: a-c) O14S74P360 (
It is observable that the SPI covered the oil droplets, which are seen as green spheres when observed individually (
Emulsion O26S56P360 (
The microstructure of emulsions or creamed phases was also analyzed by scanning electron microscopy.
Images of emulsions: a) O14S74P360 (
It is possible to observe a dense continuous phase, probably due to the excess of high-methoxyl pectin and buriti oil droplets embedded into this biopolymer matrix. Comparing the images, once more a difference in morphology is observable comparing different formulations. The droplets of O14S74P360 emulsion (
In order to produce a stable emulsion with high carotenoid and tocopherol contents, which corresponds to a higher buriti oil content, with reduced size droplets, low electrical conductivity, and high electrical charge, the optimal values for the independent variables were fixed at 28% buriti oil, 55% SPI, and homogenization pressure of 380·105 Pa.
The observed results, as well as those predicted by the regression models (
Analysis | Experimental result | Predicted result | Fitting error | Relative error/% |
---|---|---|---|---|
CI/% | 0.0±0.0 | - | - | - |
4.6±1.1 | 5.01 | 0.43 | 8.58 | |
38.2±0.3 | 44.47 | 6.29 | 14.14 | |
2.23±0.03 | 2.34 | 0.11 | 4.70 | |
-17.7±0.7 | -20.11 | -2.46 | 12.23 |
-=The model predicts that there would be no creaming index (CI). OM=optical microscopy, LD=lase diffraction
The images obtained by optical microscopy, SEM and CLSM allowed to observe that the optimized buriti oil emulsion morphology is small and less flocculated.
The pseudoplastic behaviour of this system was confirmed by the good fitting of the Sisko viscosity model. The mechanical spectra revealed that the sample was located in the viscoelastic plateau region and its microstructure revealed weak gel characteristics.
The results obtained in the present work may be compared to similar investigations reported in literature. Goyal
The rotatable central composite design (RCCD) was suitable for investigating the formation of buriti oil emulsions stabilized by soy protein isolate (SPI) and high-methoxyl pectin (HMP) electrostatic interactions. Thus we obtained an optimized emulsion produced with 28% buriti oil, 55% SPI in the continuous phase, and homogenized at 380·105 Pa, which was stable for at least 7 days, having reduced droplet size (4.58 µm), low electrical conductivity (2.23 mS/cm), and high modulus of negative charges (-17.65). This emulsion behaved typically for a weak gel and an excess of pectin in the continuous phase was observed to contribute to the emulsion stability. Emulsions containing the carotenoid-rich buriti oil stabilized by SPI/HMP could be valuable structured systems applied for fat substitution, energy reduction, and carotenoid enrichment in foods such as dairy and bakery products, ice cream, salad sauces, and vegetable-based cream.
This study was financed in part by the Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES), Brasília, Brasil, Finance Code 001, and in part by the Sao Paulo Research Foundation, FAPESP (grant numbers 2014/08520-6 and 2014/02910-7).
In this study, there is no conflict of interest.