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Olive oil and lemon salad dressing microencapsulated by freeze-drying
Kelly A. Silva
a
,
*
, Maria Alice Z. Coelho
b
, Verônica M.A. Calado
b
, Maria H.M. Rocha-Leão
b
a
Programa Ciência de Alimentos, Instituto de Química, Universidade Federal do Rio de Janeiro, Centro deTecnologia, Bloco A, 21949-900 Rio de Janeiro, RJ, Brazil
b
Programa Ciência de Alimentos, Departamento de Engenharia Bioquímica, Escola de Química, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco E, 21945-970 Rio
de Janeiro, RJ, Brazil
article info
Article history:
Received 11 April 2012
Received in revised form
31 July 2012
Accepted 7 August 2012
Keywords:
Food emulsion
Maltodextrin
Arabic gum
Lemon juice
Olive oil
abstract
An instantaneous food emulsion was formulated containing olive oil and lemon juice using combinations
of polymers, such as Alginate (ALG), Arabic gum (AG), Maltodextrin (MD) and Carboxymethyl cellulose
(CMC) and freeze-dried, aiming at the development of a new microencapsulated product. The charac-
terization of particle size, the surface analysis by scanning electron microscopy, the X-ray diffraction and
the differential scanning calorimetry were performed with the emulsions that showed a good oil
encapsulation. Mixtures of maltodextrin and arabic gum showed the lowest average values of particle
size. Moreover, these samples presented rounded shapes and some depressions shown by scanning
electron microscopy and proved to be an amorphous material by X-Ray Diffraction. The glass transition
temperatures of samples C (12.5 g/100 g MD and 7.5 g/100 g AG), 146.60
C, and D (10 g/100 g MD and
8.5 g/100 g AG), 147.54
C, were similar, because the type of polymers was similar. This study shows that
it is possible to microencapsulate emulsion oil in water (1:1) by freeze-drying to use an instant sauce
salad.
Ó2012 Elsevier Ltd. All rights reserved.
1. Introduction
The molecular gastronomy is the study of chemical and physical
processes that occur during food preparation. Considering this, new
methods and techniques can be created or improved. The micro-
encapsulation is a process in which tiny particles or droplets are
surrounded by a coating, or embedded in a homogeneous or
heterogeneous matrix, to form small capsules (Gharsellaoui,
Roudaut, & Chambin, 2007). Most edible oils are chemically
unstable and susceptible to oxidative deterioration, especially
when exposed to oxygen, light, moisture, and high temperature.
That oxidative degradation results in a loss of nutritional quality
and a development of undesired flavors, affecting shelf stabilityand
sensory properties of the oil (Velasco, Dobarganes, & Márques-Ruiz,
2003). Therefore, the encapsulation by freeze drying of salad
dressing, which is composed of olive oil and lemon juice, aims to
increase the stability of this food by decreased activity of water,
contributing to the reduction of weight and density of the product
and reducing costs in transportation and storage. Lyophilization is
carried out using a simple principle of physics called sublimation.
Sublimation is the transition of a substance from the solid to the
vapor state, without first passing through an intermediate liquid
phase. The process of lyophilization consists of freezing the food so
that the water in the food becomes ice, under a vacuum, subli-
mating the ice directly into water vapor and draw off the water
vapor. Once the ice is sublimated, the foods are freeze-dried and
can be removed from the machine. Emulsions as salad dressings
can quickly lose stability, differently from dry presentation that
allows an increase in shelf life, retaining the functional and nutri-
tional compounds for longer time; besides, it is easier to
commercialize (Fonseca, 2008;Profiqua, 2002). Food emulsions are
compositionally complex; their droplets are stabilized within
different extents by proteins, small-molecule surfactants (emulsi-
fiers), and polysaccharides (Dickinson, 2010). The alginates are
natural polymers that are widely regarded as biocompatible and
non-toxic (Thevenet, 1988). Carboxymethyl cellulose (CMC) as
a typical hydrocolloid, has no direct influence on the taste and
flavor of foodstuffs, but at the same time has a significant effect on
gel formation, water retention, emulsifying and aroma retention. In
the food industry CMC is used as a stabilizer, binder, thickener,
suspending and water-retaining agent, in ice-cream and other
frozen desserts, sauces and creams (Hegedu
si, Herceg, & Rimac,
2000). Maltodextrins are widely used in food emulsions as stabi-
lizers (Chronakis & Kasapis, 1995) and their addition is mainly
performed in materials that are hard drying (Sablani, Shestha and
Bhandari, 2008). Arabic gum is a complex heteropolysaccharide
with a highly ramified structure, with the main chain formed by
D
-
galactopyranose units (Bemiller & Whistler, 1996). It has been used
*Corresponding author.
E-mail address: kalenkar@yahoo.com.br (K.A. Silva).
Contents lists available at SciVerse ScienceDirect
LWT - Food Science and Technology
journal homepage: www.elsevier.com/locate/lwt
0023-6438/$ esee front matter Ó2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.lwt.2012.08.005
LWT - Food Science and Technology 50 (2013) 569e574
as an encapsulating agent in microencapsulation by spray drying
because of its good emulsification capacity and low viscosity in
aqueous solution (Gabas, Telis, Sobral, & Telis-Romero, 2007). The
microencapsulation process transforms oils into easily-handled
solids and protects them from oxidation through a solid wall that
acts as a physical barrier limiting the diffusion of oxygen
(Gharsellaoui, Roundaut, Chambin, Volley, & Saruel, 2007). To
evaluate the procedure encapsulation, techniques with laser
diffraction were chosen in this work in order to measure the size of
particles formed, along with the scanning electron microscopy to
visualize the surface of the tablet, the X-ray diffraction to evaluate
the amorphous material and differential scanning calorimeter to
determine the glass transition temperature (Tg) values. Thus, this
work aimed to characterize a microencapsulated food emulsion
based on olive oil and lemon juice, obtained by freeze-drying to use
an instant sauce salad.
2. Materials and methods
2.1. Materials
Arabic gum, carboxymethyl cellulose and alginate were
purchased from VETEC
Ò
LTDA, (Rio de Janeiro, Brazil) and malto-
dextrin, with dextrose equivalent of ca 20, was obtained as a gift
sample from PluryQuimica
Ò
, (São Paulo, Brazil). The olive oil Por-
tucale (Vienes
Ò
Fátima, Portugal) and lemon were purchased in
a local supermarket (Cofrutagem Araquara LTDA, São Paulo, Brazil).
2.2. Oil-in-water emulsions preparation
The polysaccharides were slowly dispersed in a lemon juice
(10 ml), followed by the addition of olive oil (10 ml) and homoge-
nized for 40 s at 9600 rpm by using an Ultra-Turrax T25 homoge-
nizer (IKA Instruments, Germany) equipped with a dispersing tool.
Different concentrations of hydro-soluble polymers used to prepare
the samples are summarized in Table 1. These samples were stored
in round plastic pots with 3.6 cm diameter and 2.0 cm in height,
frozen at 50
C for 24 h and then freeze-dried in equipment of
Enterprise
Ò
for approximately 18 h. The samples remained with the
same form of the container. Only the samples with all oil encap-
sulated in container were characterized.
2.3. Particle size
A little amount of a tablet was dissolved in 10 ml of propan-2-ol,
for 30 s in an ultrasonic, model Ultra Clean 800A Unic
Ò
. After, the
particle size was measured by laser diffraction (SALD-2201,
SHIMADZU
Ò
) obtaining particles with a refraction index of 1.70e
0.20. Analyzes were performed in duplicate and the mean, the
mode and the cumulative distribution d [25], d [50] and d [75] was
obtained. The cumulative distribution d [25], d [50] and d [75] are
size values corresponding to the cumulative distribution at 25%,
50% and 75%, respectively. Thus, the d [25] represents a size value
below which 25% of the cumulative distribution is present.
2.4. Surface analysis by scanning electron microscopy (SEM)
Images of samples and polymers (in a powder presentation and
coated by a gold blade) were recorded using a Scanning Electron
Microscope (model JSM5800LV-JEOL
Ò
, Japan), operated at 20 kV
electron bean acceleration voltage. These images were magnified
5.000 and 10.000 times.
2.5. X-ray diffraction (XRD)
X-ray diffraction measurements were performed in a diffrac-
tometer X’Pert PRO (PANalytical), and data were collected over an
angular range of 10e100
, at a count rate of 1 s per step of 0.05
.
2.6. Differential scanning calorimetry (DSC) and moisture
A differential scanning calorimeter (Diamond DSC, Perkin
Elmer) was used to determine the glass transition temperature (Tg)
values. Samples, with approximately 5.0 mg, were enclosed in
hermetically sealed aluminum pans just before analysis and then
loaded into the equipment at room temperature. The DSC curves
were obtained in the temperature range of 20 to 200
C and the
samples were heated at 20
C/min under the inert N
2
atmosphere.
The Tg was measured by the peak half height of samples.
2.7. Centesimal composition
The Centesimal Composition was the determination of
humidity, ashes, protein by Kjeldahl and lipid byBligh Dyer method
(Instituto Adolfo Lutz, 1985). Carbohydrate content was calculated
by subtracting humidity rate, ashes, protein and lipid from a 100 g
sample. Total Energetic Value was calculated based on Atawer
conversion factors, which considers 4 kcal/g of protein, 4 kcal/g of
carbohydrate and 9 kcal/g of lipid (Lima, Silma, Trindade, Torres, &
Manchini-Filho, 2007).
3. Results and discussion
In order to trap the amount of oil contained in this type of
emulsion, the proportions of polymers reported in this study were
taken from a preliminary study. First, the polymers used by Silva,
Rocha-Leão, and Coelho (2010) were tested in order to trap the
emulsion, but despite the author have been able to maintain stable
emulsion, the proportions used were not sufficient to microen-
capsulate the oil. Other combinations of polymers such as modified
starch, arabic gum, maltodextrin, dextrin, vicilina, alginate, car-
boxymethyl cellulose and beta-cyclodextrin, were tested and many
defects were seen in the samples after being freeze-dried. The most
recurrent defects seen were: 1) the unencapsulated oil, because of
insufficient amount of polymer, 2) samples with intense yellow
color, in which occurred fast oxidation and exposure to oil, 3)
freeze-dried sample showing spongy layer, probably owing to
emulsion separation of phase during the freezing, and 4) the
presence of holes in the middle of sample. After making a screen to
discover the lowest ratio of polymers to encapsulate the emulsion
shown in Table 1, the studies of characterization continued for
discovering the best type of polymer to be used. The polymer
proportions shown in Table 1 are those that kept the state solid
product without suffering collapse after freeze-drying. The tablet
had the format of the container in which it was dried; this was
round with a diameter of 3.5 cm. The process of freeze drying
involves removing water from food without using high tempera-
ture, the food is quickly frozen producing smaller ice crystals; then
the sublimation process occurs, ensuring food sensorial character-
istics, without degradation of substances (Pegg & Shahidi, 2007).
Table 1
Emulsion compositions, considering olive oilelemon juice (1:1) microencapsulated.
Emulsions
Polymers (g/100 g) A B C D
Alginate (ALG) 2.5
Gum arabic (GA) 7.5 8.5
Maltodextrin
DE10
(MD) 10 12 12.5 10
Carboxymethyl cellulose (CMC) 1.0
K.A. Silva et al. / LWT - Food Science and Technology 50 (2013) 569e574570
This process can be a good option to dry food emulsion because
according to Frascareli, Silva, Tonon, and Hubinger (2012), the
increase of the drying air temperature in spray dryer results in
a decrease of encapsulation efficiency and oil retention. In addition,
the high temperature during drying in a spray dryer can accelerate
the oil oxidation.
3.1. Particle size
Particle size of core materials in emulsions is a significant factor
for their retention. Small particle size of the dispersed phase during
emulsification results in better retention levels of encapsulated
compound (Soottitantawat, Yoshii, Furuta, Ohkawara, & Linko,
2003). The mean diameter, the mode and the cumulative distri-
bution d 25, d 50 and d75 of each polymer used in the preparation
of freeze-dried samples are presented inTable 2. The microparticles
presented mono-modal distributions for all samples including the
powder polymers. The arabic gum showed the highest mean, mode
and cumulative distribution (d25, d50, d75) compared to other
polymers that showed similar particle size and mode. The particle
size of samples revealed that mixtures of maltodextrin and arabic
gum(C and D) showed lower averages(41.3 and 41.8
m
m) than other
emulsions without arabic gum (A e81.4
m
m and B e161.0
m
m). In
addition, the arabic gum powder used to prepare the emulsions had
higher value (58.2
m
m) than other polymers used in this study. But,
the distribution of cumulative growing fraction of emulsions C and
D was high, as seen in Table 2. The particle size distribution per-
formed by laser diffraction shows the distribution values of poly-
mer particles and micelles of oil of emulsion. Silva, Rocha-Leão, and
Coelho (2010) evaluated the aging mechanisms of olive oilelemon
juice emulsion prepared with xanthan gum in which different
concentrations of modified starch and maltodextrin reported that
all samples presented phase separation after 203 days of storage.
Large droplet mean diameter was obtained large droplet mean
diameter in samples containing maltodextrin and only xanthan
gum. The option of microencapsulating this type of sample
(emulsion food) allows obtaining a much higher stability. The
amount of polymers used by Silva, Rocha-Leão and Coelho (2010)
was tested in this study to dry the samples, but despite of main-
taining the stable of emulsion, it was not able to encapsulate the oil.
3.2. Surface analysis by scanning electron microscopy (SEM)
The visualization of sample surface was performed by scanning
electron microscope with magnification of 500 and 5000 times
to complement analysis of particle size, and verify if large and
heterogeneous particles influence on sample surface. The samples
showed an irregular arrangement: elevations and dents can be
viewed in the photographs. Nevertheless, with 5000 of magnifi-
cation, it was possible to observe that the polymers used in each
sample formed a homogeneous layer protecting the oil. This
occurred in all samples regardless of size measured by the particle
analyzer. Sample A, containing carboxymethyl cellulose and mal-
todextrin, was more fragile than the others. In the SEM images
of 500 magnification, greater clustering can be visualized, prob-
ably because of moisture uptake. Besides the clustering, it was
possible to observe elevated edges and rounded shape, but in large
magnification it was found that the formed polymer layer was
homogeneous. Sample B, containing alginate and maltodextrin, and
samples C and D, containing maltodextrin and arabic gum in
different proportions, presented rounded shapes and some
depressions. In most cases, the scanning electron microscopies of
lyophilized products show a flat surface, although but the samples
in this study presented rounded forms, probably because of two
reasons: a) the presence of oil in polymeric matrix, and b) the
presence of droplets caused by homogenization in ultra turrax.
Beside this, the oil presence that remains surrounded by polymers
can contribute to this format. The holes viewed, probably, are
related to the way that water comes out during lyophilization. Loss
of stability of the products is not expected while the polymer layer
remains homogeneous. The maltodextrin concentration also has an
effect on porosity of tablets. In some studies, the porosity of tablet
decreased with increasing maltodextrin D38 concentration. Higher
maltodextrin concentrations in the solution to be freeze-dried
result in smaller ice crystals and smaller pore sizes (Corveleyn &
Remon, 1997;1998). No significant effect of maltodextrin type,
value of DE nor residual moisture concentration in the tablet was
observed. Fig. 1 presents the polymers used for preparing encap-
sulation and Figs. 2 and 3illustrate samples A, B, C and D with
magnification 5000 and 500 times. Other studies have also
shown similar surface topologies with surface depression or
collapse from spray dried particles containing maltodextrin as part
of wall materials (Bae & Lee, 2008;Tewa-Tagne, Briancon, & Fessi,
2007). According to the physical observation from four samples
and from the results of particle size distribution analysis and
scanning electron microscopy, it was decided to continue the
characterization of two samples: those containing only mixtures of
arabic gum and maltodextrin (C and D). Because they had smaller
particle size, homogeneous surface and also they resisted physically
for two months in the refrigerator without compromising their
reconstitution in water. For these samples, differential scanning
calorimetry and X-ray diffraction were carried out in order to know
a little more about the structure that holds the oil in the tablet.
3.3. X-ray diffraction (XRD)
To know if the products are amorphous or crystalline is of great
importance for the stability of dried products the determination of
X-ray diffraction analysis.The presence of diffuse and large peaks in
X-ray diffraction containing amorphous material is due to the fact
that in the amorphous state, the molecules are disorderly
producing disperse bands, whereas crystalline materials yield
sharp and defined peaks, because they are presented in a highly
ordered state. The powders of maltodextrin and arabic gum have
amorphous characteristics (Landim, 2008). This analysis was per-
formed to characterize the structure of polymer in this sample type
with freeze-drying and also to see if the product would behave as
an amorphous form. This analysis was performed after two months
of storage. The spectra presented in Fig. 4 show absence of crys-
tallinity of the amorphous glassy matrix, demonstrated by absence
of defining peaks, showing that during this period the sample did
not suffered change such as collapse neither clumping, which
would result in decreased stability of the microencapsulated
material. This characteristic demonstrates the interaction of the
system emulsified with the encapsulants. Studies of X-ray
Table 2
Particle size of polymer and emulsions in powder presentation.
Polymers Mean
(
m
m) SD
Mode
(
m
m)
Percentage distribution
d[25]
(
m
m)
d[50]
(
m
m)
d[75]
(
m
m)
Alginate 43.9 0.4 44.6 22.4 44.0 86.3
Gum arabic 58.2 0.3 56.2 35.8 58.2 94.3
Maltodextrin 44.0 0.3 44.6 23.8 44.0 81.1
CMC 48.9 0.3 44.6 27.7 48.8 86.3
Emulsions
A 81.4 0.4 89.1 40.6 81.4 163.3
B 161.0 0.4 177.8 82.9 161.1 312.0
C 41.3 0.6 44.6 15.7 41.3 108.6
D 41.8 0.5 44.6 17.4 41.8 99.6
K.A. Silva et al. / LWT - Food Science and Technology 50 (2013) 569e574 571
diffraction suggest that the oil presence changes peak intensity of
crystalline polymers used; this is an indication that the oil is
dispersed in the matrix in microspheres form (Senhorini, 2010).
According to the scanning electron microscopy results of the
sample, homogeneous and amorphous surfaces were detected.
3.4. Glass transition temperature (Tg)
Phase transitions in foods are often a result of changes in
composition or temperature during processing or storage. The
knowledge of transition temperatures and thermodynamic
Fig. 2. Scanning electron microscopyimage of samples A (10% maltodextrin and 1.0% carboxymethyl cellulose), B (2.5% alginate and 12% maltodextrin), C (7.5% gum arabic and 12.5%
maltodextrin) and D (8.5% gum arabic and 10% maltodextrin) with 5000.
Fig. 1. Scanning electron microscopy image of powder polymers used in emulsions of 500 0 (1 -alginate, 2-gum arabic, 3-maltodextrin and 4-carboxymethyl cellulose).
K.A. Silva et al. / LWT - Food Science and Technology 50 (2013) 569e574572
quantities is important in order to understand the processes such
as: dehydration, evaporation, freezing and conservation. These
processes are governed by the transition of water into the gaseous
or crystalline state; the water is the most important non-nutrient
component, solvent and plasticizer of food solids. Changes that
are observed at transition temperatures can be used for analyzing
the effects on physical properties (Ross, 1995). The glass transition
temperature (Tg) varies, as it depends on many factors, like sample
preparation and size, heating/cooling rate, sample holding time,
moisture content, among other things (Ahmed & Ramaswamy,
2006). The Tg of sample C (12.5 g/100 g MD and 7.5 g/100 g AG)
occurred at 146.60
C, while for sample D (10 g/100 g MD and 8.5 g/
100 g AG) was at 147.54
C. These samples had similar glass tran-
sition temperatures because the amount of polymers was similar,
and the type of sample is same. Ross and Karel (1991) showed that
maltodextrin with DE5 had a glass transition temperature of 188
C.
When the temperature of the dehydrated product is above the glass
transition temperature (Tg), collapse or shrinkage occurs. The
stickiness, compaction and crystallization are phenomena related
to the collapse that occurs when a matrix can no longer support its
own weight, leading to structural changes demonstrated by
a decreasing of the physical structure. As the samples were freeze-
dried, their water activity was minimal. Over time, it was observed
that these products did not support storage at room temperature
because of variation in temperature. However, when stored at 4
C,
the samples did not undergo apparent physical changes. Studies on
drying temperatures and glass transition behavior showed that
spraying at temperatures above glass transition could obtain
amorphous particles very stick during the drying process (Ross &
Karel, 1991). The moisture of sample D was 1.89 0.007 g/100 g
and the material remained yellow in appearance; no oil came out of
the matrix. According to Quispe-Condori, Saldana, and Temelli
(2011), the moisture of samples microencapsulated by freeze
drying containing zein (6 g/100 g) and flax oil (1.5 g/100 g) and
other proportion with flax oil (0.5 g/100 g) were respectively
5.33 0.33 g/100 g and 4.94 0.05 g/100 g. Although the samples
and their elaboration are different, the moisture from salad
dressing microencapsulated with maltodextrin and arabic gum was
lower.
3.5. Centesimal composition
The sample D containing (10 g/100 g MD and 8.5 g/100 g AG)
was able to encapsulate the olive oil, its centesimal composition
presented about 34.84 kcal in 5 g of lyofilizated product, remem-
bering that 5 g of lyophilized must be reconstituted for 10 g
emulsion adding about 5 ml of water. In comparison with others
labels sauces salads, only emulsified, this is more caloric, but the
ingredients are proven nutritional quality and health benefices,
such as olive oil and lemon juice. To 100 g of salad dressing
Fig. 3. Scanning electron microscopy image of samples A0(10% Maltodextrin and 1.0% Carboxymethyl cellulose), B0(2.5% Alginate and 12% Maltodextrin), C0(7.5% Gum arabic and
12.5% Maltodextrin) and D0(8.5% Gum arabic and 10% Maltodextrin) with 500.
Fig. 4. X-ray diffraction pattern of samples C (7.5% gum arabic and 12.5% maltodex-
trin), D (8.5% gum arabic and 10% maltodextrin) and polymers arabic gum and
maltodextrin.
K.A. Silva et al. / LWT - Food Science and Technology 50 (2013) 569e574 573
microencapsulated the moisture was 1.89 g, ashes 0.59 g, lipid
61.29, protein 0.54 g and carbohydrate of difference was 35.69 g.
4. Conclusion
The characterization of samples indicated the suitability of
arabic gum in combination with maltodextrin as a better mixture
for microencapsulating emulsion with 50% v/v of olive oilelemon
juice, by freeze-drying. The particle size was smaller and its
surface was homogeneous. Moreover, the X-ray diffraction showed
that these samples were amorphous. The glass transition temper-
ature curves were similar for samples C (12.5 g/100 g MD and 7.5 g/
100 g AG),146.60
C, and D (10 g/100 g MD and 8.5 g/100 g AG), and
147.54
C, because they had the same type of polymer and
proportions similar. Although most studies use the microencap-
sulation of oil for spray drying, this study had good results for
microencapsulated emulsion by freeze-drying using mixtures of
maltodextrin and arabic gum. Furthermore, the sample D showed
the lowest value of moisture which helps achieve longer shelf life
for dry products.
Acknowledgments
This work was partly supported by CAPES and CNPq.
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