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Research Article
Enhancement of antioxidant and skin
moisturizing effects of olive oil by
incorporation into microemulsions
Wantida Chaiyana, Pimporn Leelapornpisid,
Rungsinee Phongpradist, and Kanokwan Kiattisin
Abstract
The aims of the present study were to develop olive oil microemulsions and characterize their antioxidant and skin
moisturizing properties. The acid, iodine, and saponification values of olive oil were 0.38 +0.01 mg potassium hydroxide/g,
88.2 +5.9 mg iodine/g, and 192.2 +1.4 mg potassium hydroxide/g, respectively. Pseudoternary phase diagrams, con-
structed using the water titration method, produced suitable microemulsions: microemulsion 1 (10% olive oil, 64% Tween
85, 16% propylene glycol, and 10% water) and microemulsion 2 (10% olive oil, 64% Tween 85, 16% ethanol, and 10% water).
Microemulsions 1 and 2 exhibited Newtonian flow behavior with internal droplet sizes of 443.60 +27.66 nm and 139.37 +
12.15 nm, respectively. Their in vitro antioxidant and skin moisturizing properties were investigated in comparison with
native olive oil. Microemulsion 2 possessed the highest significant antioxidant effect (p< 0.05) giving half maximal inhibitory
concentration values in radical-scavenging activity against 1,1-diphenyl-2-picrylhydrazyl and 2,20-azino-bis(3-
ethylbenzothiazoline-6-sulphonic acid) of 4.78 +1.25 mg/mL and 14.85 +11.18 mg/mL, respectively. The lipid peroxidation
inhibition of microemulsion 2 was comparable to native olive oil, whereas the skin moisturizing effect of microemulsion 1
was comparable to the well-known skin moisturizer, hyaluronic acid. In conclusion, microemulsions enhanced both anti-
oxidant and skin moisturizing effects and were attractive formulations for using as a cosmetic or drug delivery system.
Keywords
Antioxidant, moisturizing, microemulsion, olive oil, Olea europaea, cosmetics, drug delivery system
Date received: 20 April 2016; accepted: 22 August 2016
Topic: Synthesis of Nanostructured and Nanoscale Materials
Topic Editor: Di Gao
Topic: Nanoparticles
Topic Editor: Raphael Schneider
Introduction
Microemulsions (MEs) represent a promising delivery
system for pharmaceuticals and cosmeceuticals due to its
numerous advantages over the existing conventional formu-
lations.
1,2
There is a growing recognition of their potential
benefits in the field of cosmetic sciences in addition to the
drug delivery abilities. MEs are widely investigated for pre-
paring personal care products with superior features such as
high efficiency, good stability, and improved aesthetic
appearance.
3
The key difference between MEs and conven-
tional emulsions is that MEs exhibit excellent thermodynamic
stablility, therefore, phase separation is not likely to occur,
4
whereas conventional emulsions exhibit fundamentally ther-
modynamic unstablility and phase separation could eventu-
ally take place. The internal droplet size of MEs is below the
Department of Pharmaceutical Science, Chiang Mai University, Chiang
Mai, Thailand
Corresponding Author:
Wantida Chaiyana, Department of Pharmaceutical Science, Faculty of
Pharmacy, Chiang Mai University, Chiang Mai 50200, Thailand.
Email: wantida.chaiyana@gmail.com
Nanomaterials and Nanotechnology
Volume 6: 1–8
ªThe Author(s) 2016
DOI: 10.1177/1847980416669488
nax.sagepub.com
Creative Commons CC-BY: This article is distributed under the terms of the Creative Commons Attribution 3.0 License
(http://www.creativecommons.org/licenses/by/3.0/) which permits any use, reproduction and distribution of the work without
further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/
open-access-at-sage).
wavelength of visible light, leading to an optically transparent
appearance.
5,6
The smaller size of MEs results in a deeper
skin penetration compared to conventional emulsions.
7
Moreover, MEs can increase the dermal delivery of active
compounds by enhancing their solubility, leading to a
greater degree of encapsulation compared to other conven-
tional topical formulations such as ointments, creams, gels,
and lotions.
1,2
Normally, MEs are quaternary systems com-
posed of oil, water, and surfactant/cosurfactant mixtures.
They are spontaneously formed isotropic colloidal system-
s.
8
Therefore, the methods of preparation are distinctly dif-
ferent, since emulsions require a large input of energy,
whereas MEs do not require any input energy, leading to
reductions of the relative cost of commercial production.
9
Olive oil is the oil extracted from the fruit of olive tree
(Olea europaea). There are several methods to produce olive
oil, however, a mechanical process without the use of exces-
sive heat gives the highest quality olive oil which is classified
as virgin olive oil.
10
Oliveoilhasbeenwidelyusedinseveral
cosmetic products, such as skin and hair care formulations.
There are several studies reporting the potent antioxidant
activity of olive oil.
11,12
The active compounds responsible
for the antioxidant activity, belong to three different classes,
including simple phenols, secoiridoids, and lignans.
11
More-
over, olive oil may be used to protect the skin from ultravio-
let B in the sunlight based on a study reporting that mice
receiving olive oil after UVB exposure showed a signifi-
cantly lower number of developing tumors per mouse than
those in the control group receiving nothing.
13
Therefore, the
aims of the present study were to develop MEs from olive oil
and characterize their antioxidant activity and skin moistur-
izing properties for further applications in cosmetics.
Materials and methods
Materials
Extra virgin olive (Olea europaea) oil was purchased
from the local market in Chiang Mai, Thailand. Hyarulo-
nic acid, quercetin, gallic acid, trolox (6-hydroxy-2,5,7,8-
tetramethylchroman-2-carboxylic acid), 2,20-Azino-bis
(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 1,1-
diphenyl-2-picrylhydrazyl radical (DPPH), linoleic acid,
phenolphthalein test solution (TS), triethanolamine, and
carbopol 940 were purchased from Sigma-Aldrich
(St Louis, Missouri, USA). Disodium hydrogen phosphate,
dipotassium hydrogen phosphate, sodium hydroxide, potas-
sium hydroxide (KOH), potassium iodide (KI), iodobromide,
and sodiumthiosulfate, ammonium thiocyanate, and ferrous
chloride were purchased from Fisher Chemicals (Loughbor-
ough, UK). Hydrochloric acid was analytical reagent (AR)
grade and purchased from Merck (Darmstadt, Germany).
Ethanol, propan-2-ol, dimethyl sulfoxide, hexane, ethyl acet-
ate, and ether (all AR grade) were purchased from Labscan
(Dublin, Ireland). Propylene glycol (PG), polyethylene gly-
col (PEG) sorbitan monolaurate (Tween 20), PEG sorbitan
monopalmitate (Tween 40), PEG sorbitan monostearate
(Tween 60), PEG sorbitan monooleate (Tween 80), PEG
sorbitan trioleate (Tween 85), and sorbitan monooleate
(Span 80) purchased from Acros Organics (Morris Plains,
New Jersey, USA). PEG 400, us pharmacopeia (USP), and
mineral oil were purchased from Wilhelmshaven, Germany.
Characterization of olive oil
Acid value determination. Acid value of olive oil was deter-
mined by the indirect titration method with slight modifi-
cations
14
Briefly, 10 g of olive oil was mixed with 50 mL of
an ethanol/ether mixture (1:1). The mixture was then sha-
ken until homogeneous. Phenolphthalein TS was added as
an indicator in the titration with 0.1 N sodium hydroxide
(NaOH). The end point of the titration was indicated at the
first permanent pink color which was persisted for at least
10 s. The acid value, which was expressed as the amount of
NaOH (in milligrams) necessary to neutralize free fatty
acidscontainedin1gofoil,wasthencalculated.The
measurements were done in triplicate.
Iodine value determination. Determination of the iodine value
was conducted according to the American Oil Chemists’
Society (AOCS) official method with slight modification.
15
Briefly, 0.2 g of olive oil was dissolved in 10 mL of chloro-
form and the mixture was shaken until homogenous. Then
25 mL of iodobromide was added, and the reaction was
carried out in the dark for 30 min. KI solution (30 ml of
KI in 100 mL of water) was then added to stop the reaction.
The remaining iodine was titrated using 0.1 N sodium thio-
sulfate solution. The iodine value which is expressed as
grams of halogen (calculated as iodine) absorbed by 100 g
of olive oil. The measurements were done in triplicate.
Saponification value determination. The saponification value
of olive oil was determined according to the AOCS official
method with slight modification.
15
Briefly, 2 g of olive oil
was dissolved in 25 mL of alcoholic KOH. After 30 min of
reflux with heating from a water bath, the sample was
titrated with 0.5 N hydrochloric acid (HCl) using 1 mL of
phenolphthalein as an indicator. The end point was indicated
at the appearance of an amber yellow color. The saponifica-
tion value was expressed as milligrams of KOH necessary to
neutralize the free acids and saponify the esters present in 1 g
of substance. The experiments were done in triplicate.
ME development
Pseudoternary phase diagram construction. Pseudoternary
phase diagrams of olive oil were constructed using a
slightly modified water titration method.
16
Various nonio-
nic surfactants (Tween 20, Tween 40, Tween 60, Tween 80,
Tween 85, or Span 80) were mixed with a cosurfactant
(ethanol, propan-2-ol, PG, or PEG-400) at a weight ratio
of 1:2, 1:1, 2:1, or 4:1 to obtain surfactant mixture (Smix).
The oil and Smix were then mixed at various weight ratios
2Nanomaterials and Nanotechnology
(0:1, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, and 1:0) and
the resulting mixtures were subsequently titrated with
water under moderate agitation at room temperature. The
samples were classified as MEs when they appeared
visually as clear liquids. The different formulations were
made in triplicate. The pseudoternary phase diagrams were
drawn using OriginPro 8 software. The areas of the ME
regions were measured by ImageJ 1.47v software.
Characterization of ME
Photon correlation spectroscopy. Particle size analysis was
carried out using photon correlation spectroscopy (Zetasizer
®
version 5.00, Malvern Instruments Ltd, Malvern, UK). The
sizing measurements were carriedout at a fixed angle of 173.
The reported results are the mean and standard deviation (SD)
of at least 10 measurements on each sample.
Rheology study. Viscosity of the MEs was measured using
a Brookfield DVIII rheometer (Brookfield Engineering
Laboratories, Stoughton, Massachusetts, USA) fitted
with a bob spindle. Brookfield Rheocalc operating
software [version 2.8] was used to control the measure-
ment. A sample volume of 70 mL was used. The measure-
ments were performed in triplicate at 25C.
Antioxidant activity of olive oil and ME
ABTS assay. Olive oil and MEs were tested for ABTS radical
cation scavenging activity using the method reported by
Fellegrin et al.
17
with slight modification. Briefly, ABTS
solution (7 mM) was reacted with potassium persulfate
(140 mM) solution and kept in the dark overnight (16 h) to yield
a dark colored solution containing radical cation (ABTS
þ
).
Prior to use, ABTS
þ
was diluted with ethanol for an initial
absorbance of about 0.500 at 734 nm. After the addition of
1.0 mL of diluted ABTS
þ
to 10 mL of sample, the absorbance
was measured after 6 min of initial mixing. The percentage
inhibition was calculated using the following equation:
% Scavenging effect ¼1S
C
100;
where Sis the absorbance of ABTS
þ
with sample and Cis the
absorbance of ABTS
þ
without sample. The experiment was
done in triplicate. Half maximal inhibitory concentration (IC
50
)
was calculated using GraphPad Prism version 2.01 software.
DPPH assay. Olive oil and MEs were tested for radical
scavenging activity against stable DPPH using the method
reported by Blois
18
with slight modification. Briefly, 20 mL
of test sample was mixed with 180 mL of 167 mM DPPH
solution. The reaction was carried out in the dark for 30 min
at room temperature. Then the absorbance was measured at
520 nm using a DTX-880 multimode detector. %Inhibition
was calculated using the following equation:
% Inhibition ¼ f½ð PC NCÞðSBÞ =ðPC NCÞg
100;
where PC is the absorbance of 20 mL of acetone and 180 mL
of 167 mM DPPH mixture, NC is the absorbance of 200 mL
of acetone, Sis the absorbance of 20 mL of test sample and
180 mL of 167 mM DPPH mixture, and Bis the absorbance
of 20 mL of test sample and 180 mL of acetone mixture. The
experiment was done in triplicate. IC
50
was calculated
using GraphPad Prism version 2.01 software.
Inhibition of lipid peroxidation by ferric thiocyanate. Olive oil
and MEs were tested for lipid peroxidation inhibition by the
ferric thiocyanate using the method reported by Niehius
and Samuelson
19
with slight modification. Briefly, 100
mL of test sample was mixed with 1 mL of 25 mM linoeic
acid in acetone and 1 mL of 0.1 M phosphate buffer pH 7.0
in the test tube with a cork lid stock. The reaction was
allowed to carry out in the dark for 6 h at 60C. Then a
50 mL aliquot of the mixture was mixed with 3 mL of 75%
ethanol, 20 mLof35%ammonium thiocyanate, and 20 mL
of 20 mM ferrous chloride in 3.5%HCl. After vortexing the
mixture for 1 min, the absorbance was measured at 500 nm
using an ultraviolet–visible spectrophotometer (Shimadzu,
japan). %Inhibition was calculated using the following
equation:
% Inhibition ¼BS
B
100;
where Bis the absorbance of the combined mixture of
100 mL of acetone, 1 mL of 25 mM linoleic acid in acetone,
and 1 mL of 0.1 M phosphate buffer pH 7.0 and Sis the
absorbance of the combined mixture of 1 mL of 25 mM
linoleic acid in acetone, and 1 mL of 0.1 M phosphate
buffer pH 7.0 and 100 mL of test sample. The experiment
was done in triplicate.
In vitro skin moisturizing test of olive oil and ME
Skin preparation. Full-thickness skin from the flank area of
stillborn piglets was used for skin moisturizing studies.
Stillborn piglets were obtained fresh from a local farm. The
hair was trimmed off with electrical clippers and the skin
pieces from the flank area were carefully dissected with a
surgical blade. After washing in phosphate buffer solution
(PBS; pH 7.4), the skin was wrapped in tin foil and stored at
20C for up to 1 month.
20
Prior to use in studies, skin was
defrosted and hydrated in PBS overnight at room tempera-
ture. Before experimentation, the subcutaneous fat layer
was carefully trimmed off and the skin was cut into a square
shape (2 2cm
2
) using surgical scissors.
In vitro skin moisturizing test. The skin hydration was mea-
sured using a Corneometer#CM 825 (Courage-Khazaka
Electronic, Cologne, Germany). A baseline measurement
was performed before applying 100 mL of olive oil or MEs
followed by three additional measurements at 30, 60, and
120 min after application. Three pieces of skin were used
for each measurement. DI water was used as a negative
Chaiyana et al. 3
control and 1%hyaluronic acid solution was used as a
positive control. Skin moisturizing efficacy (%) was calcu-
lated using the formula:
Relative skin hydration ð%Þ¼ ðAtA0Þ
A0
100;
where A
t
is skin capacitance at a specified time and A
0
is
skin capacitance at the baseline. This method was modified
from O’Goshi et al.
21
Statistical analysis
All data were presented as the mean +SD. Individual
differences were evaluated by one-way analysis of var-
iance: post hoc test. In all cases, p< 0.05 indicated
significance.
Results and discussion
Olive oil characteristics
The characteristic of olive oil as the function of acid
value, iodine value, and saponification value are shown
in Table 1.
The acid value can be used to indicate the oil quality and
a low acid value indicates the oxidative stability of the oil.
However, the acid value also depends on the type of oil and
the storage conditions as the acid value will increase over
longer times of storage.
23
Since the acid value is twice that
of the free fatty acid, it could be used to determine trigly-
ceride hydrolysis, which is often related to the quality of oil
against oxidative reaction.
23
Therefore, olive oil with a low
acid value and a low free fatty acid value would be stable
against oxidation and not easily become rancid.
24
The iodine value represents the number of reactive
double bonds in the oil. The iodine value of oleic acid,
an unsaturated free fatty acid containing one double bond,
is 90 while that of linoleic, an unsaturated free fatty acid
containing two double bonds, is 282. The low iodine value
of olive oil places it in the nondrying oil group which is oil
that does not solidify when exposed as a thin film to air.
25
Normally, nondrying oils contain only small amount of
either linoleic acid that possess three double bonds in one
molecule or linoleic acid that possess two double bonds.
26
Therefore, the oxidative cleavage of unsaturated bond
decrease and the oxidation slows down. The results
related well with the previous study reported that olive
oil contained 64.4–81.0%unsaturated free fatty acid con-
taining one double bond, 12.6–19.7%unsaturated free
fatty acid containing two double bonds, and 6.0–15.9%
unsaturated free fatty acid containing several double
bonds.
27
Oleic acid was the major component (62.0–
80.0%) found in the oil.
28
High saponification value represents high ester con-
tent or a high number of carboxylic functional groups
per unit mass of olive oil. The results suggested that
olive was suitable for self-emulsification process and
ME formation.
28
ME development
The effect of surfactant type was studied using various
surfactants, including Tween 20, Tween 40, Tween 60,
Tween 80, Tween 85, and Span 80. When the cosurfactant
was PG and the Smix ratio was 2:1, only Tween 85 could
produce an ME region in the pseudoternary phase diagram
(Figure 1(a)). These results were in a good agreement with
a previous study reporting that Tween 85 showed an excel-
lent ability to produce ME among several surfactants.
29
However, the type of oil phase affected the ability of
Tween 85 to produce the ME. A previous study reported
that Tween 85 could produce a small ME region in the
psuedoternary phase diagram of ME containing an essential
oil.
16
The likely explanation was that there was no univer-
sal good surfactant that is suitable for all types of oil in ME
development. For olive oil, Tween 85 was a suitable sur-
factant since it could produce the largest ME region in the
pseudoternary phase diagram. The effect of cosurfactant
type was also studied. Ethanol produced the highest ME
region followed by PG and isopropanol, whereas PEG-400
could not produce any ME (Figure 1). PG and ethanol gave
a good promising ME region. Therefore, the effect of Smix
ratio was studied in the system containing these two cosur-
factants. When the Smix ratio increased from 1:2 to 4:1, the
ME region was significantly increased (Figures 2 and 3).
The results related well with the previous study of Gao
et al.
22
who reported that the polyoxyethylated castor oil
ME region respectively increased when the ratio of poly-
ethylene glycol (35) castor oil to transcutol increased
from 0.5:1 to 4:1. Similarly, Chaiyana et al.
16
reported that
the ME region increased when the ratio of Tween 20 to
PEG-400 increased from 1:2 to 4:1. Additionally, Kale and
Allen
30
reported that an increase in the Smix ratio could
increase ME formation of mineral oil using a surfactant of
Brij 96 and a cosurfactant ofglycerin, ethylene glycol, or PG.
Two MEs from the systems in Figures 2(d) and 3(d)
were formulated and named as ME1 and ME2, respec-
tively. ME1 contained 10%olive oil, 64%Tween 85,
16%PG, and 10%water, whereas ME2 contained 10%
olive oil, 64%Tween 85, 16%ethanol, and 10%water.
Both MEs were transparent isotropic yellow liquids. The
internal droplet size of ME1 was larger than that of ME2
and both of them showed moderate polydisperse index as
Table 1. Characteristics of olive oil (mean +SD, n¼3).
Characteristic Results Standard
22
Acid value 0.38 +0.01 mg KOH/g <0.5 mg KOH/g
I
2
value 88.2 +5.9 mg I
2
/g 75–94 mg I
2
/g
Saponification
value
192.2 +1.4 mg KOH/g 190–195 mg KOH/g
KOH: potassium hydroxide; I
2
: iodine.
4Nanomaterials and Nanotechnology
shown in Table 2. Furthermore, ME1 and ME2 both
showed Newtonian flow behavior with low viscosity
(Table 1) confirming the formation of MEs.
31,32
The likely
explanation of the elevated viscosity of ME1 was from the
larger internal droplet size.
Antioxidant activity
The antioxidant activity of olive oil, ME1, and ME2 was
analyzed by means of the DPPH, ABTS, and lipid perox-
idation assays. Several methods were used since it is rec-
ommended to base the conclusions of antioxidant activity
on at least two different test methods and the antioxidant
activity is dependent on the method used.
33
DPPH and
ABTS assay are test systems using a stable free radical to
give information on the radical scavenging or antiradical
activity,
34
whereas the lipid peroxidation assay is the most
studied biologically relevant free radical chain reaction that
gives information on antioxidant activity.
35
The IC
50
cal-
culated from the concentration curve versus free radical
scavenging activity against DPPH and ABTS radicals of
Figure 1. Pseudoternary phase diagram of olive oil/Tween 85 and cosurfactant (2:1)/water, when the cosurfactant was (a) PG, (b)
ethanol, (c) isopropanol, and (d) PEG-400. The dark area represents the ME region. PG: propylene glycol; PEG: polyethylene glycol; ME:
microemulsion.
Figure 2. Pseudoternary phase diagram of olive oil/Tween 85/PG/water when the Smix ratios were (a) 1:2, (b) 1:1, (c) 2:1, and (d) 4:1.
The dark area represents the ME region. PG: propylene glycol; ME: microemulsion.
Figure 3. Pseudoternary phase diagram of olive oil/Tween 85/ethanol/water when the Smix ratios were (a) 1:2, (b) 1:1, (c) 2:1, and
(d) 4:1. The dark area represents the ME region. ME: microemulsion.
Table 2. Characterization of MEs (mean +SD, n¼3).
Formulation
Internal
droplet size (nm)
Polydisperse
index
Viscosity
(MPa)
ME1 443.60 +27.66 0.30 +0.10 1.95 +0.03
ME2 139.37 +12.15 0.33 +0.02 0.11 +0.00
ME: microemulsion.
Chaiyana et al. 5
olive oil, ME1, and ME2 is presented in Table 3. Both ME1
and ME2 increase the antioxidant activities of the native oil
because of the higher solubilizing power and the larger
surface area of the ME droplets. It is noted that ME2 exhib-
ited the highest radical scavenging activity as it showed the
significantly lowest IC
50
value against DPPH and ABTS
radicals (p< 0.05). However, the lipid peroxidation inhibi-
tion of ME2 was not different from the native olive oil. The
likely explanation of the distinctly superior antioxidant
activities of ME2 was its lower viscosity and smaller inter-
nal droplet size led to an increase in surface area and sub-
sequently an increase in intimate contact between ME
droplet and the target site. These factors promoted better
efficacy in antioxidant activity.
Skin moisturizing property
The relative skin hydration at 30, 60, and 120 min after
applying 1%hyaluronic acid solution, olive oil, ME1, and
ME2 is shown in Figure 4. ME1 possessed a significantly
higher skin moisturizing effect comparing to a native
olive oil (p< 0.05), whereas ME2 showed almost the
same results as the olive oil. Interestingly, the skin moist-
urizing effect of ME1 was comparable to the hyaluronic
acid. The likely explanation was that the ME1 contain PG
which acts as a humectant. However, the ME of olive oil
was less expensive than the hyaluronic acid solutions,
therefore, it could be used as an alternative choice in
cosmetic preparation.
Tween 85, a major component of the formulation, is not
thought to produce adverse health effects or skin irritation.
Bicontinuous MEs containing Tween 85 were reported as a
safe vehicle for topical drug delivery.
36
However, it may
cause skin irritation after prolonged or repeated exposure.
Therefore, the skin irritation tests in human subjects are
necessary and need further study.
Conclusion
Olive oil used in the present study met the standard criteria
of acid, iodine, and saponification values which were 0.38
+0.01 mg KOH/g, 88.2 +5.9 mg iodine/g, and 192.2 +
1.4 mg KOH/g, respectively. Two MEs including ME1
(10%olive oil, 64%Tween 85, 16%PG, and 10%water)
and ME2 (10%olive oil, 64%Tween 85, 16%ethanol, and
10%water) were developed and characterized. The larger
internal droplet size of ME1 was correlated well with its
higher viscosity. The internal droplet size of ME1 and ME2
was 443.60 +27.66 and 139.37 +12.15 nm, respectively.
Besides, the viscosity of ME1 and ME2 was 1.95 +0.03
and 0.11 +0.00 mPas, respectively. Comparing to the
native olive oil, ME2 possessed the significant highest anti-
oxidant activity (p< 0.05) with IC
50
of radical scavenging
activity against DPPH and ABTS radicals of 4.78 +
1.25 mg/mL and 14.85 +11.18 mg/mL, respectively.
Therefore, the olive oil ME significantly possessed higher
antioxidant and skin moisturizing effect than the native
olive oil. However, an effect on their biological activities
depended on the composition of MEs. The lipid peroxida-
tion inhibition of ME2 was comparable to that of native
olive oil. On the other hand, ME1 possessed high skin
moisturizing effect which was comparable to the hyaluro-
nic acid. Therefore, it could be concluded that olive oil ME
is an attractive formulation in the cosmetic development
studies and could be used as a delivery system for cos-
metics ingredients or biological active compouds. The skin
irritation and moisturizing test in human subjects are sug-
gested for further study. Moreover, permeability evaluation
of the olive oil MEs which is a major consideration in drug
delivery system is also recommended for further work.
Acknowledgement
We thank Dr Karl Bailey, Scientific Officer, Department of
Human Nutrition, University of Otago for improving the use of
English in the manuscript.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Table 3. Antioxidant activity of olive oil and MEs (mean +SD,
n¼3).
Sample
IC
50
(mg/mL)
DPPH assay ABTS assay
Lipid
peroxidation assay
Olive oil 11.67 +1.44 112.30 +31.05 16.27 +5.51
a
ME1 12.70 +3.62 25.22 +3.95* 10.03 +0.43
a,
*
ME2 4.78 +1.25* 14.85 +11.18* 15.61 +1.08
a
IC
50
: half maximal inhibitory concentration; DPPH: 1,1-diphenyl-2-
picrylhydrazyl radical; ABTS: 2,20-azino-bis(3-ethylbenzothiazoline-6-
sulfonic acid); ME: microemulsion.
a
% Inhibition at the concentration of 5 mg/mL.
*p< 0.05: compared to olive oil.
0
20
40
60
80
100
120
0 30 60 90 120
Relative skin hydration (%)
Time (min)
*
*
*
**
*
Figure 4. Relative skin hydration after applying with 1% hya-
luronic acid solution (~), olive oil (), ME1 (♦), and ME2 (&)for
30, 60, and 120 min. *p< 0.05: compared to 1% hyaluronic acid
solution.
6Nanomaterials and Nanotechnology
Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: The
financial support was received from Chiang Mai University grant
for new researchers.
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