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Comparing the effectiveness of natural and synthetic emulsifiers on oxidative and physical stability of avocado oil-based nanoemulsions


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Food industries search for replace synthetic surfactant with natural ingredients, but emulsifier type has an impact on lipid oxidation and stability of emulsions. The aim of the study was to evaluate the emulsifier type and concentration effect on avocado oil-based nanoemulsion development, specifically on physical and oxidative stability. O/W nanoemulsions were prepared with 10% avocado oil using natural (lecithin) and synthetic (Tween 80) emulsifiers at different concentrations (2.5–10%). Results showed that nanoemulsions exhibited anionic (Z-potential: − 26 to − 59 mV) lipid droplets with particle size between 103 and 249 nm. Emulsifier type and concentration affected physical stability, being the most stable at 7.5–10% Tween 80 (15 days) and 7.5–10% lecithin (10 days). Meanwhile, emulsifier concentration affected oxidative stability of nanoemulsions, being the most unstable at 2.5% Tween 80 and 10% lecithin. Finally, although Tween 80 was more effective than lecithin, it also could be used to develop natural nanoemulsions with good physical properties.
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Innovative Food Science and Emerging Technologies
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Comparing the eectiveness of natural and synthetic emulsiers on
oxidative and physical stability of avocado oil-based nanoemulsions
Carla Arancibia
, Natalia Riquelme
, Rommy Zúñiga
, Silvia Matiacevich
Food Properties Research Group, Food Science and Technology Department, Facultad Tecnológica, Universidad de Santiago de Chile, Obispo Umaña 050, Estación
Central, Santiago, Chile
Bioprocess Engineering Laboratory, Department of Biotechnology, Universidad Tecnológica Metropolitana, Las Palmeras 3360, Ñuñoa, Santiago, Chile
Tween 80
Physical properties
Lipid oxidation
Food industries search for replace synthetic surfactant with natural ingredients, but emulsier type has an
impact on lipid oxidation and stability of emulsions. The aim of the study was to evaluate the emulsier type and
concentration eect on avocado oil-based nanoemulsion development, specically on physical and oxidative
stability. O/W nanoemulsions were prepared with 10% avocado oil using natural (lecithin) and synthetic (Tween
80) emulsiers at dierent concentrations (2.510%). Results showed that nanoemulsions exhibited anionic (Z-
potential: 26 to 59 mV) lipid droplets with particle size between 103 and 249 nm. Emulsier type and
concentration aected physical stability, being the most stable at 7.510% Tween 80 (15 days) and 7.510%
lecithin (10 days). Meanwhile, emulsier concentration aected oxidative stability of nanoemulsions, being the
most unstable at 2.5% Tween 80 and 10% lecithin. Finally, although Tween 80 was more eective than lecithin,
it also could be used to develop natural nanoemulsions with good physical properties.
1. Introduction
The current demand of consumers on healthy and more natural food
products has led to an increasing interest for food industry by replacing
synthetic ingredients for others more naturals (McClements,
Bai, & Chung, 2017; Walker, Decker, & McClements, 2015). In addition,
driven by the need for edible systems able to encapsulate, protect, and
release functional compounds, the industry and researchers are fo-
cusing their eorts in nanotechnology to address issues relevant to food
and nutrition (Silva, Cerqueira, & Vicente, 2012).
Nanoemulsions are similar systems to conventional emulsions but
their particles and/or dispersed droplets are considerably smaller
(20200 nm of diameter) (Acevedo-Fani, Soliva-Fortuny, & Martín-
Belloso, 2016; Mason, Wilking, Meleson, Chang, & Graves, 2006). In the
last decade, due to nanoemulsions can be fabricated entirely from
generally recognized as safe (GRAS) food ingredients, they are be-
coming increasingly popular because of their several advantages over
conventional emulsions, such as the following: (i) they increase water-
dispersibility of encapsulate oils, obtaining optically transparent or
slightly turbid emulsions and easy manufactured; and (ii) they have
good physical and chemical stability and besides, high bioavailability of
their lipid components (Shin, Kim, & Park, 2015; Walker et al., 2015).
However, from the thermodynamic point of view, nanoemulsions are
unstable colloidal dispersions that are formed from two immiscible
phases, so it is necessary to use an emulsier to achieve stability
(McClements & Li, 2010).
One of the most critical aspects of forming emulsions is the selection
of the emulsier, because they play two key roles: rst, they facilitate
the emulsication, and secondly, they promote physical stability
(Krstonošić, Dokić, Dokić, & Dapčević, 2009) by adsorbing at the oil-
water interface, reducing the interfacial tension and improving the
protection of droplet from aggregation (Bai, Huan, Gu, & McClements,
2016). In addition, emulsier type can have an impact on oxidative
stability, especially when prooxidants compounds (e.g. transition me-
tals) are into the aqueous phase, since metals can be attracted for the
anionic emulsion droplet interface and they can interacted with lipids
in the emulsion droplet core (Fomuso, Corredig, & Akoh, 2002; Uluata,
McClements, & Decker, 2015). There are numerous types of emulsiers
that can be used in food industry, such as: proteins, polysaccharides,
phospholipids, and articial emulsiers (Kralova & Sjöblom, 2009),
where the last ones are the most common used due to the high eec-
tiveness (McClements, 2015; Raikos, Duthie, & Ranawana, 2016).
However, considering the request of changes for more natural food
products with label friendlyingredients (McClements et al., 2017), it
is necessary to increase the studies of natural alternatives in the for-
mulation of new emulsion-based products.
Received 1 February 2017; Received in revised form 20 May 2017; Accepted 15 June 2017
Corresponding author.
E-mail address: (C. Arancibia).
Tween 80 is one of the most used synthetic emulsier in the pre-
paration of nano/conventional emulsions due to good emulsifying
properties (Gutto, Saberi, & McClements, 2015; Raikos et al., 2016;
Salvia-Trujillo, Rojas-Graü, Soliva-Fortuny, & Martín-Belloso, 2015;
Sari et al., 2015). This emulsier has no charge (nonionic) and its hy-
drophilic part is considerably more important than lipophilic (hydro-
philic-lipophilic balance-HLB value is 15.0), which allows eectively
stabilize oil-in-water emulsions. It has very low toxicity as compared to
other synthetic emulsiers, but its consume is limited at an acceptable
daily intake (ADI) of 25 mg/kg (172.840, U.S. FDA) (McClements,
On the other hand, lecithin is the most widely used natural emul-
sifying agent in the food industry (Klang & Valenta, 2011). Food le-
cithin consists in a mixture of phospholipids (phosphatidylcholine,
phosphatidylethanolamine and phosphatidylinositol) with dierent
head and tail groups, as well as other types of lipids, such as trigly-
cerides, glycolipids, and sterols (Guiotto, Cabezas, Diehl, & Tomas,
2013; Ozturk & McClements, 2016). Lecithin is soluble in water and can
be easily dispersed in the aqueous phase forming a colloidal suspension,
favoring oil-in-water emulsion stability due to that contain hydrophilic
and hydrophobic groups, which are easily oriented in the oil-water
interface (Mezdour, Desplanques, & Relkin, 2011), Few studies have
reported useful use of lecithin as an emulsier on food nanoemulsions.
Ozturk, Argin, Ozilgen, and McClements (2014) indicated that lecithin-
coated droplets of vitamin E were stable to droplet aggregation at high
temperature due to the strong electrostatic repulsion between them.
Also, Bai et al. (2016) performed oil-in-water nanoemulsions by mi-
crouidization technique using natural emulsiers (whey protein, gum
arabic, quillaja saponin and soy lecithin), and they found that O/W
nanoemulsions could be produced for all emulsier studied and that
mean particle diameter decreased as increasing emulsier concentra-
In addition, in this study we examined the potential of using O/W
nanoemulsions to encapsulate avocado oil in order to develop healthier
and more natural emulsions, due to the good properties attributed to
this oil type. Avocado oil is rich in monounsaturated fatty acids and low
in saturated fatty acids, and contains no cholesterol
(Dreher & Davenport, 2013). Also, has a high content of phytosterols,
sterols and vitamins A, D and E; it is an oil easily absorbed, induces the
production of collagen which helps to slow the aging of the skin, it has
antioxidant compounds (Dreher & Davenport, 2013) and its fatty acid
composition, lowering LDL cholesterol (badcholesterol) and in-
creasing HDL cholesterol (goodcholesterol) in the blood, reducing
the incidence of cardiovascular disease (Rader & Hovingh, 2014 ).
However, the current use of this oil is for direct consumption, since
there are not healthy products based on avocado oil in the market.
Therefore, due to its good characteristic could be used to develop a
natural and healthy stable nanoemulsion.
In this context, the aim of the study was to evaluate the eect of
type and concentration of emulsiers in the development of stable
nanoemulsions based on avocado oil, comparing a natural (lecithin)
and a synthetic (Tween 80) emulsier and also, to establish the inu-
ence of physical properties on their physical and oxidative stability.
2. Materials and methods
2.1. Materials
Nanoemulsions were elaborated with avocado oil (Casta de Peteroa)
purchased from Terramater S.A. (Santiago-Chile) and two types of
emulsiers: natural: soy lecithin (Emultop, Cargill, Decatur-USA) do-
nated by Blumos S.A. (Santiago-Chile) and synthetic: Tween 80 ob-
tained from Sigma-Aldrich S.A. (St. Louis-USA). Puried water (con-
ductivity: 28.07 μs/cm) from an inverse osmosis system (Vigaow S.A.,
Santiago-Chile) was used as dispersant.
For oxidative stability measurements, the reagents used were:
thiobarbituric acid obtained from Merck Co. (Steinheim-Germany),
trichloroacetic acid and 1,1,3,3-tetraethoxypropane from Sigma-
Aldrich S.A. (St. Louis-USA) and chloride acid from J.T. Baker
2.2. Preparation of nanoemulsions
Oil in water (O/W) nanoemulsions were prepared with avocado oil
at 10% w/w, and emulsiers (lecithin and Tween 80) at four con-
centrations (2.5, 5, 7.5 and 10% w/w). The aqueous phase for the
formation of nanoemulsions was prepared dispersing each emulsier in
the puried water using a magnetic stirrer (Arex, VelpScientica,
Usmate Velate MB-Italy) at 200 rpm for 10 min at room temperature.
Then, avocado oil was slowly added to the aqueous phase, whilst pre-
homogenizing to 16,800 rpm using a high-speed homogenizer (Hauser
D130, Wiggen, Berlin-Germany). After adding all oil phase, pre-emul-
sion was continued pre-homogenizing for 15 min more in a water bath
at 5 ± 1 °C, to prevent overheating of the samples. Subsequently, in
order to decrease the particle size, pre-emulsions were homogenized
using a homogenizer by ultrasound (VCX500, Sonics, Newtown-USA)
with a 13 mm (diameter) stainless steel ultrasound probe. The process
of ultrasonic homogenization was performed for 20 min at 90% am-
plitude, in a pulsed mode of 15 s and 5 s of rest and at frequency of
20 kHz. Finally, before measurements, the nanoemulsions were stored
at 5 ± 1 °C for 24 h. Notably, under these conditions of storage, no
phenomena of destabilization of the nanoemulsions were observed.
2.3. Interfacial tension
The interfacial tension between the continuous and dispersed
phases was determined using an optical tensiometer (Ramé-Hart Inc.,
model 250-F4, Roxbury-USA) at room temperature. The method used to
determine the interfacial tension was the pendant drop(drop of
emulsier dispersion in oil), which consists in capturing an image of the
dispersion drop by a digital high-speed camera and analyzing their
dimensions. An axisymmetric drop (38μL) of emulsier dispersion
was delivered and allowed to stand at the tip of the needle inside a
quartz container with 30 mL of avocado oil for 12 min to achieve
emulsier adsorption at the oil-water interface. The interfacial tension
(mN/m) was calculated by DropImage software (DropImage Advanced,
Roxbury-USA) by tting the Laplace equation to the drop shape and
each sample was measured in triplicate. Data reported is the average of
triplicate with their corresponding standard deviation.
2.4. Particle characterization
2.4.1. Particle size and polydispersity index
The particle size and polydispersity index of dierent nanoemul-
sions were determined by Dynamic Light Scattering (DLS) using a
Zetasizer (NanoS90, Malvern Instruments, Malvern-UK). In order to
perform measurements, each nanoemulsion was deposited into a cuv-
ette and diluted with milli-Q water to obtain a clear solution (ap-
proximately 8% v/v concentration), in order to obtain a concentration
detectable by the equipment and to avoid interferences in the mea-
surement. Refractive indices of 1.47 for the dispersed phase (avocado
oil) and 1.33 for the continuous phase (water) were used, which were
determined by a refractometer (RA-130, Kyoto Electronics, Tokyo-
Japan). The particle size of samples was described by the zeta-average
particle size (PS) and the size distribution was described by the poly-
dispersity index (PdI). The values reported are an average of 10 de-
terminations and each sample was measured in triplicate.
2.4.2. Zeta potential
Zeta potential (mV) of dierent nanoemulsions was determined by
Electrophoretic Light Scattering using a Zetasizer (Nano-ZS, Malvern
Instruments, Malvern-UK). Nanoemulsions were diluted (20 μL of
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nanoemulsion in 1 mL of milli-Q water) and deposited in capillary cells
equipped with two electrodes. Particle charge data was collected over
30 continuous readings and all measurements were made in triplicate.
2.5. Stability of nanoemulsions
2.5.1. Physical stability
The stability of nanoemulsions was analyzed using a vertical scan
analyzer (Turbiscan MA2000, Formulation, L'Union-France). The
reading head is composed of a pulsed near-IR light source
(λ= 850 nm) and two synchronous detectors: transmission (T) and
backscattering (BS), which can detect the change of the particle size of
the nanoemulsions due to coalescence and/or occulation phenomena,
and the gravitational separation of the phases by sedimentation or
creaming processes, as a function of the sample height into the cy-
lindrical glass tube. For the measurements, a volume of 8 mL of dif-
ferent samples were added to a glass tube of 14 cm high and 1.5 cm in
diameter and were storage at 20 °C during 25 days. Measurements were
made at days: 0, 5, 10, 15, 20 and 25.
Stability was evaluated as Turbiscan stability index (TSI), which is a
statistical parameter used to estimate the suspension stability
(Wiśniewska, 2010), where a low TSI value indicate high stability of the
system (Wiśniewska, Urban, Nosal-Wiercińska, Zarko, & Gunko, 2014;
Xu, Zhang, Cao, Wang, & Xiao, 2016 ). The TSI value was calculated
using Eq. (1) reported for Xu et al. (2016):
scan h scan h
SI |() ()|
where: scan i(h) is the average backscattering for each time (i) of
measurement, scan i 1(h) is the average backscattering for the i1
time of measurement and His the number of scan for each sample.
Instability of nanoemulsions during storage, was characterized by
the level of creaming, which is measured by the creaming index (H);
where at high creaming index value is representative of high instability
of nanoemulsion. Creaming index was calculated according Eq. (2)
described by Petrovic, Sovilj, Katona, and Milanovic (2010):
reaming Index (%) HS
HE 100
where, HE is the total height of the nanoemulsion (mm) and HS is the
height of cream layer (mm), which was visually measured as a function
of time. All measurements were performed in triplicate for each
2.5.2. Oxidative stability
Lipid oxidation was measured during storage time; where 30 mL of
each nanoemulsion were placed in plastic centrifuge tubes and stored
for 20 days at 50 °C (to accelerate oxidation). Oxidative stability was
evaluated by determination of thiobarbituric acid reactive substances
(TBARs). TBARs were measured according to the methodology of
McDonald and Hultin (1987). First, TBA (thiobarbituric acid) solution
was prepared by mixing 15% w/v trichloroacetic acid, 0.375% w/v
TBA in 0.25 M HCl. Then, 250 μL of each nanoemulsion, 2 mL of TBA
solution and 1 mL of distilled H
O were added to a test tube and
homogenized in a vortex mixer (ZX3, VelpScientica, Usmate Velate
MB-Italy). After that, the mixture was heated in a water bath (WB 14,
Memmert, Schwabach-Germany) at 90 °C for 15 min, cooled at room
temperature, and centrifuged (Mini Spin Plus, Eppendorf, Hamburg-
Germany) at 14,000 rpm for 15 min. Finally, the supernatant was
measured at 580 and 520 nm in a microplate-reader (Multiskan Go,
Thermo Fisher, Waltham-USA). The absorbance was calculated as
532 nm
580 nm
, according to Mei, McClements, and Decker (1999),
where absorbance at 580 nm was used to correct for any potential light
scattering, since 580 nm represents the closest non-TBARS absorbing
Fig. 1. Interfacial tension (AB) and time-dependent surface pressure (CD) of lecithin and Tween80 at dierent concentrations. Error bars indicate standard deviation of mean of
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wavelength to 532 nm. Concentrations of TBARs were determinated
from a standard curve prepared using solution of 1,1,3,3-tetra-
ethoxypropane (12.5 μM) with an increasing concentration from 0 to
1μM/2 mL of TBA solution.
2.6. Statistical analysis
An analysis of variance (ANOVA) of two factors (type and con-
centration of emulsier) was carried out for physical parameter values:
particle size and polydispersity index, zeta potential, creaming index
and oxidative stability. Tukey's test (α= 0.05) was used to calculate
the minimum signicant dierence among samples. All calculations
were carried out with XLSTAT Pro software 2015 (Addinsoft, Paris-
3. Results and discussions
3.1. Interfacial tension
Interfacial properties of emulsiers play an important role in their
ability to form and stabilize nanoemulsions. Interfacial tension proles
of lecithin and Tween 80 measured at the oil-water interface are shown
in Fig. 1A and B. It was observed that lecithin showed higher interfacial
tension values than Tween 80, due probably to dierences in orienta-
tion and conguration of the emulsiers at the interface. This result is
in agreement with a study realized by Nash and Kendra (2017) where it
was found that Tween 20 was adsorbed in the interface more rapidly
than lecithin; however, the O/W interface containing lecithin displayed
much higher viscoelasticity than interface with Tween 20, which it was
correlated well with kinetic stabilization properties. The emulsier
concentration also had an eect on interfacial tension proles, since the
interfacial tension values decreased as the emulsier concentration
increased (Fig. 1A and B). The decrease of interfacial tension as in-
creasing emulsier concentration can be related to a faster emulsier
adsorption to the oil-droplets surface. However, it was observed that
the interfacial tension reached relatively constant values at the highest
Tween 80 (7.5 and 10%) and lecithin (10%) concentrations, which
could indicate the saturation of the oil-water interface by emulsier
molecules (Bai et al., 2016).
The rate at which an emulsier adsorbs to an interface is one of the
important factors to consider during emulsion formation (McClements,
2015; Ozturk & McClements, 2016). If the diusion of surfactant at the
interface controls the adsorption process, a plot of surface pressure
against time
can be used to calculate diusion rate (k
), which
corresponds at the slope of the plot (Martinez, Carrera,
Rodríguez, & Pilosof, 2009; McClements, 2015; McClements & Gumus,
2016; Mezdour et al., 2011). The plots of surface pressure versus time
and the values of diusion rate (k
) for samples containing lecithin
and Tween 80 at dierent concentrations are shown in the Fig. 1CD
and Table 1, respectively. In the case of surface pressure plot, it was
observed that at early stages of adsorption, the diusion of Tween 80
from the bulk onto the interface was faster than lecithin ones, and at the
later stages, the diusion of Tween 80 remained almost constant, in-
dicating that the interface becomes saturated with emulsier molecules
because there were less sites available to adsorb into the interface
(McClements, 2015). As at the early stages surface pressure was linearly
related to the square root of time, diusion rate (k
) was calculated in
this period (211 s
). The coecient of determination (R
) showed
the good of t (R
> 0.97) of these data to the adsorption kinetic
model for all samples. ANOVA results showed that emulsier con-
centration aected diusion rate values (Table 1), but this eect de-
pended on emulsier type. Tween 80 exhibited a higher diusion rate
than lecithin, but an increasing of concentration varied slightly diu-
sion rate (from 0.21 to 0.17), whilst k
of lecithin samples decreased
signicantly (p < 0.05) (from 0.27 to 0.10) as increasing its con-
centration. The diminish of diusion rate by increasing lecithin con-
centration was attributed to a higher viscosity of continuous phase as
increasing lecithin concentration (data not shown). This increase of
viscosity could be attributed to the formation of phospholipid vesicles
in the aqueous phase (McClements & Gumus, 2016; Pan,
Tomas, & Anon, 2004). Finally, results showed that the emulsier ef-
fectiveness to reduce interfacial tension depended on both emulsier
type, being more eective Tween 80, and concentration, which aect
the diusion rate. However, although the same diusion rate is possible
to obtain with lecithin, the interfacial tension decrease could not be
enough to reduce the particle size during emulsion formation, and
therefore have an impact on physical stability of nanoemulsions.
3.2. Particle characterization
Table 2 shows the values of particle size (PS), polydispersity index
(PdI) and zeta potential (ZPot) of nanoemulsions with dierent type
and concentration of emulsier. In the case of particle size, it was ob-
served that both factors studied (type and concentration of emulsier)
and its interaction had a signicant eect (p < 0.05) on PS values
(data not shown). At the same level of emulsier, nanoemulsions with
Tween 80 presented signicantly (p < 0.05) lower PS values than ones
with lecithin. This result was attributed to the rapid adsorption of the
Tween 80 on the surface of the oil droplets during homogenization
process, observed as higher k
(Table 1), causing a lower interfacial
tension, which also was observed in Fig. 1ab, that therefore, facilitate
rupture of the oil droplets (McClements & Gumus, 2016). As expected,
by increasing emulsier concentration PS values decreased signicantly
(p < 0.05), except in the nanoemulsions with the highest Tween 80
concentrations (7.5 and 10%). The dependence between emulsier
concentration and the droplet size is known (Bai et al., 2016;
McClements et al., 2017; Surh, Decker, & Mcclements, 2017;), since the
minimum droplet size that can be produced is mainly determined by the
Table 1
Eect of emulsier type and concentration on diusion rate (K
) obtained by adsorption
kinetic model.
Emulsier type Emulsier concentration (% w/w) K
Lecithin 2.5 0.27 ± 0.01
5.0 0.22 ± 0.02
7.5 0.17 ± 0.01
10 0.10 ± 0.004
Tween 80 2.5 0.21 ± 0.01
5.0 0.21 ± 0.01
7.5 0.19 ± 0.001
10 0.17 ± 0.01
Means values within a column with dierent superscripts dier signicantly
(p < 0.05).
Table 2
Mean values and signicant dierences of particle size (PS), polydispersity index (PdI)
and zeta potential (ZPot) for nanoemulsions with dierent type and concentration of
Emulsier type Emulsier
(% w/w)
PS (nm) PdI () ZPot (mV)
Lecithin 2.5 249 ± 7
0.17 ± 0.02
57.7 ± 2.1
5.0 209 ± 12
0.17 ± 0.01
59.7 ± 1.0
7.5 180 ± 10
0.17 ± 0.02
57.9 ± 0.4
10 152 ± 3
0.18 ± 0.01
59.4 ± 1.4
Tween 80 2.5 208 ± 17
0.17 ± 0.03
35.7 ± 1.4
5.0 167 ± 1
0.19 ± 0.04
32.0 ± 2.2
7.5 115 ± 4
0.26 ± 0.04
29.4 ± 2.0
10 103 ± 3
0.29 ± 0.01
26.6 ± 0.8
Means values within a column with dierent superscripts dier signicantly
(p < 0.05).
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initial emulsier concentration added, thus an increase of emulsier
concentration increases the molecules of emulsier available to coat the
surface of oil droplets and decreases the interfacial tension during
homogenization, which it ease droplet disruption
(McClements & Gumus, 2016). However, the droplet size of nanoe-
mulsion also depend on homogenization process, since in this case an
increase of Tween 80 concentration from 7.5% to 10% almost did not
vary PS values, probably because the limit for droplets disruption by the
sonication process used was already reached.
Regarding to PdI, results showed that the eect of emulsier con-
centration on PdI values was dierent depending on emulsier type.
Lecithin-based nanoemulsions did not dier signicantly (p > 0.05)
on PdI values ranging between 0.17 and 0.18, whilst the nanoemulsions
with the highest concentrations of Tween 80 (7.5 and 10%) showed a
higher polydispersity of particle size with values between 0.26 and
0.29. In general, it is considered that PdI values below 0.2 indicate
uniformity among droplet sizes or monomodal distributions and
therefore good physical stability (Guerra-Rosas, Morales-Castro, Ochoa-
Martinez, Salvia-Trujillo, & Martín-Belloso, 2016). In this case, most of
samples showed PdI values below 0.2 which could suggested a good
stability during storage, although this eect not only depended on
particle size distribution, but also on continuous phase viscosity, elec-
trostatic and steric repulsive interactions, density of each phase, etc.
(McClements, 2015).
Results of ZPot for both emulsiers (lecithin and Tween 80) at the
dierent concentrations studied are also shown in Table 2. In general, it
was observed that all nanoemulsions exhibited a negative electrical
charge, being samples with lecithin signicantly (p < 0.05) more
electronegative than ones with Tween 80. This dierence between
emulsiers can be due to electrical charge dierences between both
emulsiers, Tween 80 is a non-ionic emulsier, whilst lecithin is an
amphiphilic phospholipid that at neutral pH of the samples (pH be-
tween 6.5 and 7) presents negatively charged the phospholipid head
groups (Ozturk & McClements, 2016; Uluata et al., 2015). On the other
hand, all Tween 80-based nanoemulsions showed negative charge,
which it was not an expected result. These negative values of ZPot may
be due to the ability of oil-water interfaces to preferentially adsorb
hydroxyl ions from water or due to the presence of anionic impurities in
the oil or surfactant (McClements, 2015; Troncoso,
Aguilera, & McClements, 2012). The emulsier concentration eect was
also dependent on emulsier type. Lecithin-based nanoemulsions did
not dier signicantly (p > 0.05) among them on ZPot values,
showing values approximately of 58 mV (Table 2), whilst Tween 80-
based samples showed an increase signicantly (p < 0.05) of ZPot
absolute values from 26 to 36 mV as Tween 80 concentration in-
creased. Considering that large absolute surface charge values higher
than ± 30 mV can lead to oil droplet repulsion and thus a better sta-
bility against coalescence (Guerra-Rosas et al., 2016; Klang & Valenta,
2011); in this study, most of samples showed ZPot absolute values over
30 mV, so these nanoemulsions could be considered stable; however,
these results cannot guarantee nanoemulsion stability, since there are
other factors that aect the emulsion stability, as droplet size and dis-
tribution, interfacial tension reduction, environmental conditions, etc.
(Ozturk & McClements, 2016).
3.3. Physical stability
In Fig. 2 can be observed the backscattering (BS) proles during
storage at 20 °C for 25 days of storage for nanoemulsions with lecithin
and Tween 80 at the lowest (2.5%) and the highest (10%) concentra-
tions studied. First, in all samples at zero time, a linear BS is observed,
indicating that initial emulsions were homogenous. In general, nanoe-
mulsions with 2.5% showed a BS over 70%, whilst nanoemulsions with
10% emulsier presented lower %BS that varied between 30 and 50%
(Fig. 2), obtaining the lowest BS on Tween 80 samples. The dierences
on the %BS were attributed to the particle size dierences among these
samples (Table 2), since larger particles scatter the light more intensely
than smaller ones (Salvia-Trujillo et al., 2015). On the other hand,
comparing BS prole during storage time at the lowest concentration
(2.5%) for both emulsiers, it was observed that %BS decreased in the
bottom of the glass tube (between 5 and 15 mm) and increased in the
top (55 and 65 mm) as increasing storage time (Fig. 2a and c). This
prole is indicative of destabilization mechanism of clarication and
formation of a cream layer, mainly due to the migration of oil droplets
by action of gravity force, which it can be attributed to poor coverage of
droplets by surfactants. The amount of emulsier required to stabilize
an emulsions depends on the surface load, which is determined by the
mass of surfactant per unit surface area at saturation
(Ozturk & McClements, 2016). In this case, there was more surface load
than surfactant available to cover the droplets, therefore a higher
droplet aggregation and creaming were observed. This creaming de-
stabilization mechanism was observed in all samples independently of
emulsier type and its concentration. However, it is also observed that
at highest concentration (10%) for both emulsiers, a slight sedi-
mentation destabilization mechanism is observed in the bottom of the
tube (approx. at 10 mm) after 20 days of storage, possible attributed to
sedimentation of oil droplets.
In order to compare between samples, the Turbiscan stability index
(TSI) of dierent nanoemulsions was calculated using Eq. (1) as a global
destabilization parameter. In general, TSI values vary in a range be-
tween 0 and 100, where the high TSI value corresponds to the more
unstable system (Wiśniewska et al., 2014). In this case, it was observed
that TSI values only increased until ~ 2.4 during the rst 5 days and
then decreased slightly to remain constant (TSI = 1.0 ± 0.2) during
the following 20 days of storage (Fig. 3). Besides, the increase of
emulsier concentration had not signicant (p > 0.05) eect on TSI
values, except at day 5 in Tween 80-based nanoemulsions where the
samples with the highest concentration (10% Tween 80) showed the
lowest TSI values (0.95 ± 0.1). The TSI values near to zero as observed
in this samples (lower than 2) can indicate a great stability of dierent
nanoemulsions; however, nanoemulsions showed higher creaming
index values during storage time at 20 °C (Fig. 4). Therefore, this global
destabilization parameter was not useful to describe stability of this
kind of emulsions, for this reason, creaming index was calculated.
Regarding to creaming index (CI), it depended of type and con-
centration of emulsier. It was observed that nanoemulsions with
Tween 80 were more stable than lecithin-based ones, exhibiting at
higher concentrations creaming formation from day 15 (Fig. 4), whilst
lecithin-based nanoemulsions showed cream formation from day 10. It
is know that emulsions containing Tween 80 as emulsier present a
good physical stability during storage (Arancibia, Navarro-Lisboa,
Zúñiga, & Matiacevich, 2016; Raikos et al., 2016; Züge, Haminiuk,
Maciel, Silveira, & de Paula Scheer, 2013), because this surfactant can
rapidly adsorb to oil droplet surfaces during homogenization and
quickly reduce the interfacial tension, producing small droplets during
emulsion formation and giving a better stability to gravitational se-
paration. This result is in agreement with the interfacial tension and
particle size results observed in this study (Fig. 1 and Table 2), since
Tween 80 samples showed the lowest values of these parameters. Be-
sides, although the lowest Z-potential and PdI values of lecithin samples
(Table 2) could indicate higher stability of samples, the physical sta-
bility was more attributed to the nal particle size than those para-
meters. On the other hand, it was observed that emulsier concentra-
tion had a signicant eect (p < 0.05) on CI values and, as expected,
an increase of emulsier concentration decreased CI values signicantly
(p < 0.05). The highest stability of nanoemulsions with Tween 80 can
be related to its smaller particle size. The creaming rate is proportional
to the square of droplet radius according to Stokes' law, and so a re-
duction in droplet size decreases the rate of gravitational separation
(Bai et al., 2016; McClements, 2009) and therefore increases the sta-
bility. Finally, the most stable nanoemulsions were those that contained
high emulsier concentration (7.5 and 10% w/w) for both emulsiers,
C. Arancibia et al. ,QQRYDWLYH)RRG6FLHQFHDQG(PHUJLQJ7HFKQRORJLHV[[[[[[[[[[²[[[
010 20 30 40 50 60 70
100 A: 2. 5 % w / w Le c i th i n
Tube length (mm)
%Back Scattering
010 20 30 40 50 60 70
Time (days)
B: 10% w/w Lecithin
Tube length (mm)
%Back Scattering
010 20 30 40 50 60 70
100 C: 2 .5% w /w Twee n 80
Tube length (mm)
010 20 30 40 50 60 70
100 0
Time (days)
D: 10 % w/w Twe en 80
Tube length (mm)
Fig. 2. Backscattering proles as a function of the tube length after 20 days in quiescent conditions for nanoemulsions stored at 20 °C with: 2.5% w/w (A) and 10% w/w (B) of soy
lecithin, and 2.5% w/w (C) and 10% w/w (D) of Tween 80.
0 5 10 15 20 25
2.5% Lecit hin
5% Lecit hin
7.5% Lecit hin
10% Lecit hin
Time (days)
0 5 10 15 20 25
2.5% Twe en 80
5% Twe en 80
7.5% Twe en 80
10% Twe en 80
Time (days)
Fig. 3. Turbiscan stability index (TSI) of nanoemulsions with dierent emulsiers: A) soy lecithin and B) Tween 80, stored during 20 days at 20 °C. Error bars indicate standard deviation
of mean of triplicates.
0 5 10 15 20
30 2.5% Lecith in
5% Lecith in
7.5% Lecith in
10% Lecith in
Storage time (days)
Creaming index (%)
0 5 10 15 20
30 2.5% Twe en 8 0
5% Twe en 80
7.5% Twe en 8 0
10% Twe en 80
Storage time (days)
Creaming index (%)
Fig. 4. Creaming index of nanoemulsions with dierent emulsiers: A) soy lecithin and B) Tween 80, during 20 days of storage at 20 °C. Error bars indicate standard deviation of mean of
C. Arancibia et al. ,QQRYDWLYH)RRG6FLHQFHDQG(PHUJLQJ7HFKQRORJLHV[[[[[[[[[[²[[[
being not statistically dierent (p > 0.05) between them; showing CI
values of 7.0 ± 0.4% (lecithin-based samples) and 5.6 ± 0.3%
(Tween 80-based samples) after 20 days of storage.
3.4. Oxidative stability
The formation of thiobarbituric acid reactive substances (TBARs) of
dierent nanoemulsions stored at 50 °C for 20 days is shown in the
Fig. 5. In general, it was observed that lecithin-based nanoemulsions
were less stable to lipid oxidation than Tween 80-based ones. This
dierence can be due to emulsier nature, since phospholipids (soy
lecithin) themselves are susceptible to lipid oxidation (Cui & Decker,
2015), autoxidation and photosensitized lipid oxidation in oil-in-water
emulsions (Uluata et al., 2015).
In relation to emulsier concentration, signicant dierences
(p < 0.05) were found among nanoemulsions with lecithin, being the
samples with 10% of emulsier the least stable to lipid oxidation. The
existence of a greater amount of phospholipids in this nanoemulsion
can increase the extent of oxidation; however, that is not completely
clear because some studies have found that soy lecithin as emulsier
delays lipid oxidation of emulsions (García-Moreno, Frisenfeldt-
Horn, & Jacobsen, 2014), but there are also other studies where it was
observed an antagonistic behavior of lecithin on oxidative stability of
emulsions (Yang & Xiong, 2015). Besides, it is important to consider
that the promotion or inhibition of the lipid oxidation by natural
emulsiers could also depend on other factors, such as molecular
properties, location and environmental conditions
(McClements & Gumus, 2016). In the case of Tween 80-based nanoe-
mulsions, it was obtained a contrary behavior (Fig. 5), since at the
highest concentrations of emulsier (7.5 and 10% w/w) there was a
greater oxidative stability, which can be due to the fact that Tween 80
has a low critical micelle concentration (CMC: < 0.1 mM) (Walker
et al., 2015); therefore, at higher concentrations, there may be an ex-
cess of emulsier, forming micelles that have been shown to decrease
lipid oxidation (Richards, Chaiyasit, McClements, & Decker, 2002).
4. Conclusions
This study compared the eectiveness of two (natural and synthetic)
food-grade emulsiers on develop of healthy nanoemulsions and on
their physical and oxidative stability. Results showed that emulsier
type and concentration aected physical characteristics of nanoemul-
sions. Tween 80 was more eective in decrease interfacial tension than
soy lecithin, which it eased the droplet disruption and the decrease of
particle size of theses nanoemulsions. In addition, an increase of sur-
factant concentrations gave rise higher amount of available surfactant
to cover oil droplet surface, which boosted their physical stability.
Nanoemulsions with 7.5 and 10% of emulsier were the most stable to
gravitational separation for both emulsiers, but showing instability by
creaming after storage at 20 °C for 10 days for samples containing le-
cithin and 15 days using Tween 80. Besides, nanoemulsions containing
Tween 80 were more stable against to lipid oxidation, and as increasing
emulsier concentration oxidative stability increased. Finally, these
results have demonstrated that although physical properties such as PS,
PdI and ZPot could infer a better physical stability of emulsions con-
taining lecithin, this one was less eective than the synthetic emulsier,
at the same concentration, to prevent lipid oxidation and gravitational
separation of nanoemulsions. However, natural surfactant could be
used to develop edible nanoemulsions with considerable physical
properties due to Tween 80 concentrations used in this study are over
the acceptable daily intake (ADI) (25 mg/kg of body weight), whilst soy
lecithin concentration depend on Good Manufacturing Practice.
The authors acknowledge nancial support from CONICYT for
and Technological Faculty) for Project Basal MECESUP-USA1555LD
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... Nevertheless, the Wilhelmy plate method allows measuring even if the solution is opaque. The interfacial tension of soy lecithin at the avocado oil-water interface was evaluated, where 5 mN/m at a concentration of 2.5% was achieved [39]. In another study, the interfacial tension was between 1.2 and 15 mN/m at vegetable oil-water interface in the presence of 1% of lecithin [31]. ...
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High purity insoluble dietary fiber (HPIDF) was extracted from Okara by compound enzyme method, and solid emulsifiers with different particle sizes were prepared by wet grinding. Its composition, structure and physicochemical properties were studied, and the influence mechanism of solid emulsifiers with different particle sizes on emulsifying properties and interface stability of Pickering emulsion was systematically studied. The results showed that the particle size of HPIDF decreased significantly, the ζ-potential, contact Angle and swelling capacity of HPIDF ncrease significantly ( p < 0.05). HPIDF forms an adsorption layer at the oil-water interface, and some of them are connected to form a bridge network structure, which plays a role of steric hindrance. And the emulsion has excellent stability under different environmental factors. HPIDF are suitable raw materials as natural food-grade solid emulsifiers. It is cost-effective and eco-friendly to realize the high-value utilization of Okara resources, reduce resource waste, and extend the industrial chain.
Microemulsions, as isotropic, transparent, nano size (<100 nm), and thermodynamically stable dispersions, are potentially capable of being used in food formulations, functional foods, pharmaceuticals, and in many other fields for various purposes, particularly for nano-encapsulation, extraction of bioactive compounds and oils, and as nano-reactors. However, their functionalities, and more importantly their oil extraction capability, strongly depend on, and are determined by, their formulation, molecular structures and the type, ratio and functionality of surfactants and co-surfactants. This review extensively describes microemulsions (definition, fabrication, thermodynamic aspects, and applications), and their various mechanisms of oil extraction (roll-up, snap-off, and solubilization including those by Winsor Types I, II, III, and IV systems). Applications of various food grade (natural or synthetic) and extended surfactants for edible oil extraction are then covered based on these concepts.
Nanotechnology is being utilized in various industries to increase the quality, safety, shelf-life, and functional performance of commercial products. Nanoemulsions are thermodynamically unstable colloidal dispersions that consist of at least two immiscible liquids (typically oil and water), as well as various stabilizers (including emulsifiers, texture modifiers, ripening inhibitors, and weighting agents). They have unique properties that make them particularly suitable for some applications, including their small droplet size, high surface area, good physical stability, rapid digestibility, and high bioavailability. This article reviews recent developments in the formulation, fabrication, functional performance, and gastrointestinal fate of nanoemulsions suitable for use in the pharmaceutical, cosmetic, nutraceutical, and food industries, as well as providing an overview of regulatory and health concerns. Nanoemulsion-based delivery systems can enhance the water-dispersibility, stability, and bioavailability of hydrophobic bioactive compounds. Nevertheless, they must be carefully formulated to obtain the required functional attributes. In particular, the concentration, size, charge, and physical properties of the nano-droplets must be taken into consideration for each specific application. Before launching a nanoscale product onto the market, determination of physicochemical characteristics of nanoparticles and their potential health and environmental risks should be evaluated. In addition, legal, consumer, and economic factors must also be considered when creating these systems.
An ideal hair-care product can restore the hydrophobicity and neutralize the static electricity of hair. As an effective ingredient in hair-care products, silicone oil is difficult to form emulsions due to its hydrophobic and oleophobic properties. To overcome these issues, a new system with natural polysaccharide-based particles and cationic conditioning agent as efficient emulsifier for hair-care product has been designed. In this study, a facile emulsifier formed with cellulose nanocrystals (CNCs) and hexadecyltrimethylammonium chloride (CTAC) was prepared. Compared with commercial emulsifiers, the CNCs/CTAC complex showed significant synergetic effect in preparing and stabilizing silicone oil emulsion. The properties of the gained silicone oil emulsion, deposition of silicone oil onto hair and combing work of hair could be controlled depending on CTAC concentration. Considering the functional properties of CTAC, which can absorb onto the hair to neutralize negative charges, silicone oil emulsion stabilized by CNCs/CTAC complex would be applied to hair-care product.
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Clove oil-based Nanoemulsions (NE) were prepared ultrasonically using Tween 80 and soy lecithin as synthetic and natural surfactants, respectively. The developed NEs were characterized for various parameters (particle size, polydispersity index, zeta potential, morphology, viscosity, colour, turbidity, and pH) and the comparative effect of both the surfactants at variable levels (oil: tween 80-1:1, 1:2, 1:3, and 1:4 and oil: soy lecithin- 1:1, 1:1.5 and 1:2) was assessed. It was found that the type of surfactant and oil to surfactant ratio significantly affected particle size and stability of NEs. The NE prepared using tween 80 @1:3 had the smallest average droplet diameter (40.9 nm). The formulated NEs were stored at 25 ºC and 4 ºC and analyzed for turbidity, pH, and phase separation up to 90 days. Results revealed that the type and concentration of the surfactant significantly influenced the particle size and stability of NEs. NEs prepared using tween 80 were found to be more viscous than those prepared with soy lecithin. The prepared clove oil NEs have important implications to be used as a natural delivery system to increase the shelf life of food products.
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Carboxymethyl cellulose (CMC) is a hydrocolloid with surface activity that could act as emulsifiers in oil-in-water emulsions; however the principal role is that it acts as structuring, thickening, or gelling agent in the aqueous phase. This study aims to evaluate the application of CMC as thickener into nanoemulsions based on olive oil and their influence on particle characteristics, flow behavior, and color. Four nanoemulsions with different oil (5% and 15% w/w olive oil) and CMC (0.5% and 0.75% w/w) concentration and two control samples without CMC added were prepared using Tween 80 as emulsifier. All physical properties studied on nanoemulsions were depending on both oil and CMC concentration. In general, z -average particle size varied among 107–121 nm and those samples with 5% oil and CMC were the most polydisperse. The addition of CMC increased anionic charge of nanoemulsions obtaining zeta potential values among −41 and −55 mV. The oil concentration increased both consistency and pseudoplasticity of samples, although samples were more stable to gravitational separation at the highest CMC concentration. Color of nanoemulsions was affected principally by the oil concentration. Finally, the results showed that CMC could be applied in nanoemulsions as thickener increasing their physical stability although modifying their physical properties.
Food Emulsions: Principles, Practice, and Techniques, Second Edition introduces the fundamentals of emulsion science and demonstrates how this knowledge can be applied to better understand and control the appearance, stability, and texture of many common and important emulsion-based foods. Revised and expanded to reflect recent developments, this second edition provides the most comprehensive and contemporary discussion of the field of food emulsions currently available. It contains practical information about the formulation, preparation, and characterization of food emulsions, as well as the fundamental knowledge needed to control and improve food emulsion properties. New features include updates of all chapters, a critical assessment of the major functional ingredients used in food emulsions, and reviews of recent advances in characterizing emulsion properties.
Factors influencing the formation and properties of lutein-loaded nanoemulsions fabricated using spontaneous emulsification (SE) were investigated. Nanoemulsion formation depended on oil type: small droplets (diameter ≈ 200 nm) with a narrow monomodal particle size distribution (polydispersity index ≈ 0.23) could be formed using medium-chain triglycerides (MCT), but not long-chain triglycerides. Nanoemulsion formation also depended on surfactant type and concentration, with Tween 80 being the most effective surfactant. Optimisation of lutein-loaded nanoemulsions formed by SE led to systems with a final composition of 10 wt% oil phase (0.12 wt% lutein + 9.88 wt% MCT), 10 wt% Tween 80, and 80 wt% aqueous phase. The nanoemulsions were stable to droplet aggregation when stored at ambient temperature for up to 1 month; however, some colour fading occurred due to lutein degradation. This study indicated the potential of nanoemulsion-based delivery system fabricated using a low-energy method for encapsulation and protection of lutein.
Consumer concern about human and environmental health is encouraging food manufacturers to use more natural and sustainable food ingredients. In particular, there is interest in replacing synthetic ingredients with natural ones, and in replacing animal-based ingredients with plant-based ones. This article provides a review of the various types of natural emulsifiers with potential application in the food industry, including phospholipids, biosurfactants, proteins, polysaccharides, and natural colloidal particles. Increased utilization of natural emulsifiers in food products may lead to a healthier and more sustainable food supply. However, more research is needed to identify, isolate, and characterize new sources of commercially viable natural emulsifiers suitable for food use. Expected final online publication date for the Annual Review of Food Science and Technology Volume 8 is February 28, 2017. Please see for revised estimates.
The rheology of oil-in-water (O/W) droplet interfaces stabilized by food-grade emulsifiers (soy lecithin or Tween 20) under controlled aqueous conditions was investigated to elucidate its contribution in the kinetic stabilization of nanoemulsion-based delivery systems containing carvacrol, a naturally-derived antimicrobial compound. Dilational rheology of surfactant-laden O/W interfaces was measured using axisymmetric drop shape analysis. The kinetic stability of corresponding nanoemulsions (containing mixtures of carvacrol and medium-chain triglyceride (MCT) oil dispersed in water (pH 7)) was characterized using dynamic light scattering. Zwitterionic lecithin molecules adsorbed to the O/W interface for 24 h formed a notably viscoelastic layer, compared to nonionic Tween 20 molecules. The kinetic stability within the first 24 h for each nanoemulsion was strongly dependent upon encapsulated carvacrol concentration, with higher carvacrol concentrations leading to lower kinetic stability. Lecithin-stabilized nanoemulsions (pH 7) were highly stable, yielding monodispersed droplet size distributions and high resistance to increases in droplet size over 30 days. Contrarily, corresponding Tween 20-stabilized nanoemulsions showed large increases in the droplet size and developed a bimodal droplet size distribution over time. The initial size of oil droplets stabilized by lecithin was slightly dependent on pH, yielding smaller droplets at pH 7 and larger droplets at pH 3; however, the extended kinetic stability was not greatly impacted by pH modulation. Determining a positive association between interfacial viscoelasticity and nanoemulsion stability may potentially be very useful for food manufacturers seeking to optimize the encapsulation and delivery of lipophilic antimicrobial molecules using food-grade emulsifiers.
Background: Nowadays, consumers are increasingly demanding high-quality, safe and healthy food products. Nanostructured emulsions and nanolaminates may have the potential to protect and transport lipophilic and hydrophilic active compounds commonly incorporated to food products, such as natural antimicrobials and nutraceuticals, while protecting or even enhancing their functional properties. Scope and approach: This review deals with the most important aspects concerning to the use of nanostructured emulsions and nanolaminates as delivery systems of active ingredients, including the advantages and challenges of incorporating plant-derived antimicrobials and nutraceuticals in foods, relevant factors affecting the formation of these nanostructures, fabrication methods, their advantages as delivery systems, and the current trends in food applications. In addition, concerns regarding the potential toxicity of nanomaterials are also discussed. Key findings and conclusions: The successful production of nanostructured emulsions and nanolaminates depends on several physicochemical factors that should be controlled in order to reach stable systems. Research evidences that nanostructured emulsions and nanolaminates are able to improve the delivery and biological activity of encapsulated active compounds. Antimicrobial and bioactive nanostructured emulsions and nanolaminates exhibit some promising advantages in food preservation and may represent a new strategy to produce functional foods. However, the knowledge in this area is still limited. The potential toxicological effects of nanostructured delivery systems are a current concern. Therefore, future investigations should be directed towards more comprehensive studies to shed light on the formation, physicochemical stability, functional performance, interactions with food matrices and toxicity of nanostructured delivery systems before their commercialization.
The aim of this study was to compare the efficiency of three different food-grade emulsifiers to form and stabilise an orange oil-in-water emulsion. The emulsifier type and concentration had a profound effect on the initial particle size of the oil droplets with Tween 80 being the most effective in reducing the particle size (1% w/w, 1.88 ± 0.01 μm) followed by sodium caseinate (10% w/w, 2.14 ± 0.03 μm) and gum arabic (10% w/w, 4.10 ± 0.24 μm). The long-term stability of the concentrated beverages was monitored using Turbiscan analysis. The Turbiscan stability indices after 4 weeks of storage followed the order: Tween 80 (1.70 ± 0.08) < gum arabic (4.83 ± 0.53) < sodium caseinate (6.20 ± 1.56). The protein emulsifier was more capable to control the oxidation process, and this was attributed to the excess amount of emulsifier present in the aqueous phase. This study provides useful insights into the formulation of flavour emulsions by the beverage industry.
Nanoemulsions are utilized within the food, pharmaceutical, and personal care industries because of their unique physicochemical properties and functional attributes: high optical clarity; prolonged stability; and, enhanced bioavailability. For many applications, it is desirable to utilize natural ingredients to formulate nanoemulsions so as to create “label-friendly” products. In this study, we compared the effectiveness of a number of natural emulsifiers at fabricating corn oil-in-water nanoemulsions using dual-channel microfluidization. These emulsifiers were either amphiphilic biopolymers (whey protein and gum arabic) or biosurfactants (quillaja saponin and soy lecithin). Differences in the surface activities of these emulsifiers were characterized using interfacial tension measurements. The influence of emulsifier type, concentration, and homogenization pressure on the efficiency of nanoemulsion formation was examined. The long-term stability of the fabricated nanoemulsions was also monitored during storage at ambient temperature. For all of the natural emulsifiers, nanoemulsions could be produced by dual-channel microfluidization, with the mean particle diameter decreasing with increasing emulsifier concentration and homogenization pressure. Whey protein isolate and quillaja saponin were more effective at forming nanoemulsions containing fine droplets than gum arabic and soy lecithin, with a lower amount of emulsifier required and smaller droplets being produced. This effect was attributed to faster emulsifier adsorption and a greater reduction in interfacial tension leading to more efficient droplet disruption within the homogenizer for saponins and whey proteins. This study highlights the potential of dual-channel microfluidization for efficiently producing label-friendly nanoemulsions from natural emulsifiers.
There is increasing consumer pressure for commercial products that are more natural, sustainable, and environmentally friendly, including foods, cosmetics, detergents, and personal care products. Industry has responded by trying to identify natural alternatives to synthetic functional ingredients within these products. The focus of this review article is on the replacement of synthetic surfactants with natural emulsifiers, such as amphiphilic proteins, polysaccharides, biosurfactants, phospholipids, and bioparticles. In particular, the physicochemical basis of emulsion formation and stabilization by natural emulsifiers is discussed, and the benefits and limitations of different natural emulsifiers are compared. Surface-active polysaccharides typically have to be used at relatively high levels to produce small droplets, but the droplets formed are highly resistant to environmental changes. Conversely, surface-active proteins are typically utilized at low levels, but the droplets formed are highly sensitive to changes in pH, ionic strength, and temperature. Certain phospholipids are capable of producing small oil droplets during homogenization, but again the droplets formed are highly sensitive to changes in environmental conditions. Biosurfactants (saponins) can be utilized at low levels to form fine oil droplets that remain stable over a range of environmental conditions. Some nature-derived nanoparticles (e.g., cellulose, chitosan, and starch) are effective at stabilizing emulsions containing relatively large oil droplets. Future research is encouraged to identify, isolate, purify, and characterize new types of natural emulsifier, and to test their efficacy in food, cosmetic, detergent, personal care, and other products.