Matrix structure selection in the microparticles of essential oil oregano produced by spray dryer

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ISSN: 0265-2048 (print), 1464-5246 (electronic)
J Microencapsul, Early Online: 1–11
! 2013 Informa UK Ltd. DOI: 10.3109/02652048.2013.778909
Matrix structure selection in the microparticles of essential oil oregano
produced by spray dryer
Joyce Maria Gomes da Costa1, Soraia Vilela Borges1, Ariel Antonio Campos Toledo Hijo1, Eric Keven Silva1,
Gerson Reginaldo Marques1, Marcelo Aˆ
ngelo Cirillo2, and Viviane Machado de Azevedo1
1Department of Food Sciences, Federal University of Lavras (UFLA), Lavras, MG, Brazil and 2Department of Exact Sciences, Federal University of
Lavras (UFLA), Lavras, MG, Brazil
Abstract
The goal of this work was to select the best combination of encapsulants for the
microencapsulation of oregano essential oil by spray dryer with the addition of Arabic gum
(AG), modified starch (MS) and maltodextrin (MA). The simplex-centroid method was used to
obtain an optimal objective function with three variables. Analytical methods for carvacrol
quantification, water activity, moisture content, wettability, solubility, encapsulation efficiency
(ME) and oil retention (RT) were used to evaluate the best combination of encapsulants. The
use of AG as a single wall material increased ME up to 93%. Carvacrol is the major phenolic
compound existent in the oregano essential oil. Carvacrol exhibits a maximum concentration of
57.8% in the microparticle with the use of 62.5% AG and 37.5% MA. A greater RT (77.39%) was
obtained when 74.5% AG; MS 12.7% and 12.7% MA were applied, and ME (93%) was improved
with 100% of gum.
Keywords
Additives, physical properties, simplex
centroid, volatile compounds
History
Received 8 September 2012
Revised 7 February 2013
Accepted 18 February 2013
Published online 25 March 2013
Introduction
Essential oils are extracted from herbs or spices and are sources of
biological active compounds, such as terpenoids and phenolic
acids (Bakkali et al., 2008). Many records report that such
compounds exhibit good antimicrobial activity (Burt, 2004; Burt
et al., 2005; Lo´pez et al., 2007). The oregano essential oil contains
carvacrol and thymol as its major compounds (Al-Bandak and
Oreopoulou, 2007). Carvacrol is a phenolic monoterpene that
shows significant antibacterial activity in vitro (Didry et al.,
1994), as well as antifungal (Burt and Reinders, 2003; Giordani
et al., 2004; Burt et al., 2005), antitoxigenic, insecticide and
antiparasitic activities (Veldhuizen et al., 2006). Thus, putting
oregano essential oil in foods as a natural alternative ensures the
preservation and safety of foods (Souza et al., 2005).
However, the use of essential oils in their conventional form
may have limited applications because of the oils’ high volatility.
The microencapsulation process provides several benefits to
essential oils, such as the protection and stability of released
volatiles and storage that can be applied in textile products,
pesticides, pharmaceuticals, cosmetics and food (Leimann et al.,
2009; Muru´a-Pagola et al., 2009). For example, for microencap-sulation
of compounds found in foods, spray drying is one of the
most commonly used technologies in the food industry (Borges
et al., 2002; Shefer and Shefer, 2003; Fuchs et al., 2006;
Reineccius, 2006; Muru´a-Pagola et al., 2009; Souza et al., 2009,
2011; Ahmed et al., 2010) and has been widely used for essential
oils (Reineccius, 1988; Beristain et al., 2001; Bylaite et al., 2001;
Baranauskiene_ et al., 2006, 2007; Yang et al., 2009), and in recent
years, ultrasound applications have been investigated as devices
on uses of atomisation stage in encapsulation processes in order to
overcome the limitations typical of common equipments such as
the lack of versatility and high consumption of resources
(Dalmoro et al., 2012a).
The main advantage of microencapsulation is the formation of
a barrier between the compound and the environment. This barrier
can protect against oxygen, water and light and can prevent
contact with other ingredients in a prepared meal or, for example,
in a controlled diffusion of the encapsulated compound. The
efficiency of controlled release or protection depends mainly on
the composition and structure of the established wall and on the
process conditions (temperature, pH, pressure and moisture)
during the production and use of such particles. The barrier is
generally formed by components that create a network through the
hydrophilic or hydrophobic properties (Fuchs et al., 2006).
Despite the ease of manufacturing on an industrial scale, the
microspheres may have several disadvantages. The disadvantages
include the low capacity of encapsulation and removal of the core
material during storage that can occur because of the crystalline
structure and polymorphic arrangements characteristic of many
lipid materials during solidification and crystallisation with
reduction in the amorphous regions of the polymer matrix (Sato
and Ueno, 2005; Chambi et al., 2008).
Several auxiliary dryers (carriers or adjuvants), including
starches (corn, cassava and rice), modified starches (MS),
maltodextrins (MAs), gum Arabic (AG), cyclodextrins and corn
syrups, are often added to foods to minimise the loss of bioactive
compounds and act as the encapsulation agents to improve or
modify the physical and chemical composition of a product
(De Souza et al., 2007). The encapsulating agents can be used
alone or in combination, and the ideal composition is set for each
specific situation (Fernandes et al., 2012). The ideal selection of
encapsulants associated with microencapsulation techniques is
Address for correspondence: Joyce Maria Gomes da Costa, Department of
Food Sciences, Federal University of Lavras (UFLA), cx 3037, Lavras
37200-000, MG, Brazil. Tel: +55 35 2142 2016. E-mail: joycecosta
@dca.ufla.br
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2 J. M. G. da Costa et al. J Microencapsul, Early Online: 1–11
valuable in minimising the loss of volatile essential oils, such as
carvacrol, that are extracted from herbs and is notably important
in the efficiency of microencapsulation.
Carbohydrates, such as starches and MAs, have been
demonstrated to be good encapsulating agents, and MA is a
material of major application in the spray-drying process because
of its physical characteristics, such as high solubility and low
viscosity in high solid concentrations (Reineccius, 1991; Goubet
et al., 1998; Cano-Chauca et al., 2005). However, most of these
encapsulants alone have no interfacial properties necessary for
good efficiency of microencapsulation and therefore are often
associated with other encapsulating materials, such as gums and
proteins (Yoshii et al., 2001).
AG is a notably effective encapsulating agent because of its
stabilising-colloid property. AG produces stable emulsions with
most of the oils in a wide pH range, constitutes a visible film on
the oil interface and has good retention of volatile, low viscosity
and high solubility and is compatible with most of the gums,
starches, carbohydrates and proteins (Yang et al., 2009). However,
the cost and limited amount has restricted the use of AG for
encapsulation. An increasingly interesting research field is of the
development of an inexpensive alternative polymer, or combin-ations
of polymers, that is capable of encapsulating flavours with
an efficiency greater than or equal to that of AG.
Hydrophilic polymer blends are widely used in many pharma-ceutical
and food for production of the microparticle (Dalmoro
et al., 2012b). It is well described that a mixture of AG, starch and
MA is suggested as a good wall material alternative for
microencapsulation of essential oil, which could result in powders
with good quality, low water activity (Aw), easier handling and
storage and also protects the active material against undesirable
reactions (Anandaraman and Reineccius, 1987; Reineccius, 1988;
McNamee et al., 2001; You-Jin et al., 2003; Kanakdande et al.,
2007; Carneiro et al., 2013). MAs have been investigated as a
substitute for the AG in emulsions of spray dryer (Anandaraman
and Reineccius, 1986), and a mixture of AG and MA proved to
be effective in the spray-dryer-mediated microencapsulation of
cardamom oil (Sankarikutty et al., 1988). The main deficiency
of MA is the lack of emulsifying capacity and low retention
of volatile compounds (Reineccius, 1988; Buffo and
Reineccius, 2000). The retention of volatile compounds increases
with increasing dextrose equivalent (DE) of MAs (Anandaraman
and Reineccius, 1986), suggesting the importance of DE in
functionality of the wall material. The chemically modified
starches have reproduced the functional properties of AG
(Krishnan et al., 2005).
The aim of this study was to prepare microparticle of oregano
essential oil by spray drying using different materials and to select
the best combination of matrix structure to be used as an
encapsulating agent through analyses of the physical and chemical
properties of the produced microparticle.
Experiment
Materials
MA GLOBE 1905 (DE 20) and MS (Capsul Snow Flake
E6131), both of which were obtained from Corn Products (Mogi
Guaçu, SP, Brazil), and AG (Colloides Natureis SP, Brazil) were
used in order to form matrix structures. The material used was the
essential oil of oregano (Laszlo Aromatherapy Ltd, Belo
Horizonte, MG, Brazil).
Preparation of emulsion
Initially, MA and AG were hydrated in distilled water for 12 h at
10–12 C. Next, these ingredients were dissolved in distilled
water at 60 C using the Ultra Turrax homogeniser at a speed of
20 000 rpm for 30 min. Next, the Capsul was added at 82 C,
maintaining homogeneity until complete dissolution of the wall
materials. Below 10 C, 10% of oregano essential oil (proportional
to the presented encapsulants in the experimental design) was
added, rotating at 20 000 rpm for 5 min, until a completely
homogeneous emulsion was obtained.
Production of the microparticle
The formed emulsion was subjected to drying using a LABMAQ
Brazil 1.0 MSD spray dryer (Ribeiraõ Preto, Saõ Paulo, Brazil),
equipped with a 1.2103 m diameter nozzle. The pressure of
compressed air for the spray flow was adjusted to 5 bars. The inlet
and outlet air temperatures were maintained at 1802 C and
1052 C, respectively, and the feed rate was adjusted to
2.97107m3 s1. The rate of inlet air was maintained at
5.8104 s1m3.
The powders obtained for each treatment were stored under
refrigeration (4–7 C) in glass vials protected from light and gas
permeation to minimise possible changes in the material, such as
agglomeration, caused by water absorption and oxidation.
Experimental design
The interactions among the encapsulants of the variable part were
studied using a simplex centroid experimental design for a
mixture following methods described by Pe´rez-Alonso et al.
(2003) and Abdullah and Chin (2010). The mixture of the
encapsulants was composed of AG (X1), MS (X2) and MA 20 DE
(X3 or MA). The proportions of ingredients were expressed as
fractions of the mixture with the sum of X1, X2 and X3 equal to
one. The three encapsulants and their levels, respective of
the experimental design in terms of pseudo-components with
10 combinations, are shown in Table 1.
In the representation of the adjustment of the response values
(water activity (Aw), moisture (X0), wettability (Wett), solubility
(Sol), encapsulation efficiency (ME) and oil retention (RT)) of the
microparticle, a linear equation, which did not fit the response
variables, was used initially; next, the quadratic equation
(Equation (1)) was used in terms of pseudo-components. The
statistical significance of the equations was determined by
variance analysis at a 10% confidence.
Y ¼ 1X1 þ 2X2 þ 3X3 þ 12X1X2 þ 13X1X3
þ 23X2X3,
ð1Þ
where Y is the response-variable for each treatment (Aw, X0, Wett,
Sol, ME and RT), bn are the regression coefficients determined by
Cornell (2002) and Garcia et al. (2010), and Xn are the
Table 1. Composition of the mixtures in the formulation of
microparticles of oregano essential oil with gum arabic, modified
starch and maltodextrin in a simplex centroid.
Proportions of wall materials
Tests X1 (AG) X2 (MS) X3 (MA)
1 1.00 0.00 0.00
2 0.00 1.00 0.00
3 0.00 0.00 1.00
4 0.50 0.50 0.00
5 0.50 0.00 0.50
6 0.00 0.50 0.50
7 0.33 0.33 0.33
8 0.66 0.16 0.16
9 0.16 0.66 0.16
10 0.16 0.16 0.66
Note: AG, gum Arabic; MS, modified starch; MA, maltodextrin.

DOI: 10.3109/02652048.2013.778909 Matrix structure selection in essential oil oregano 3
proportions of pseudo-components in which X1 is the proportion
of AG, X2 is the proportion of MS and X3 is the proportion of MA.
The response variables of each experiment were analysed
using Statistica (StatSoft, Tulsa, OK, 2007) to analyse the mixture
using a simplex centroid design. The variance analysis was used
to test the fit of the models. The validation and analysis of
regression models were performed by such observations as the
lack of fit of the model, the estimation of the regression model
variance and the degree of fit and significance of the model. To
determine the effect of independent variables on the responses
evaluated, plots with a contour line in the experimental area were
constructed.
The optimisation of the selection of the encapsulants in the
microencapsulation process was aimed at maximising the effi-ciency
of encapsulation and oil retention using Response
Desirability Profiling of the software Statistica (StatSoft, Tulsa,
OK, 2007) according to the methodology described by Derringer
and Suich (1980).
Analysis of the microparticle
Identification and quantification of the major constituent of the
microencapsulated oregano essential oil
To determine the best composition of wall materials used in the
preparation of the microparticle, the identification and quantifi-cation
of the major constituent of the oregano essential oil and of
the obtained microparticle was performed according to the
experimental design. This determination was performed by gas
chromatography, and the quantification was obtained by stand-ardisation
of the areas (%). The analyses were performed using a
gas chromatograph Varian CP 3380 equipped with a flame
ionisation detector (FID). The identification and quantification of
the major constituent of the oregano essential oil was performed
with the standard injection (C10–C17) comparing the retention
time of the standard with the compounds of the samples. The
operating conditions were the following: a high-performance
capillary column (hp), split 1:100, injector temperature of 200 C,
temperature of FID detector of 200 C, programming of the
column with initial temperature of 50 C (3 min), 3 C min1 until
145 C, carrier gas hydrogen (2.0mLmin1) and injection volume
of l mL (1% solution in dichloromethane).
Water activity
The water activity (Aw) was measured by direct lecture in a digital
device AQUALAB, CX-2 model (Decagon Devices Inc., Pullman,
WA) with controlled temperature of 250.5 C.
Moisture
The moisture determination (wet basis) of the microparticle was
performed by the gravimetric method at a temperature of 105 C
until a constant weight was reached (AOAC, 2000).
Wettability
This property was determined by the method proposed by Fuchs
et al. (2006). One gram of powder was spread over 100mL of
distilled water at 25 C without stirring. The time required for the
powder particles to sediment, or sink and disappear from the
surface of the water, was measured and used for a relative
comparison between the samples.
Solubility
Solubility was determined by the method described by Cano-
Chauca et al. (2005), where 25mL of distilled water was
transferred to a beaker and submitted to agitation in a
homogeniser at 2500 rpm. One gram of powder (dry basis) was
gently added to the water, and the agitation was maintained for
5 min. The solution was transferred to a tube and centrifuged for
5 min at 2600 rpm. One aliquot (20 mL) of the supernatant was
transferred to a petri dish and dried for 5 h at 105 C. The percent
solubility (mass of powder/volume of solution) was calculated by
the weight difference.
Encapsulation efficiency
Encapsulation efficiency was determined by the fraction of
encapsulated oil over the total amount of oil (Equation (2)).
ME ¼
ðOiltotalOilsurfaceÞ
Oiltotal
100 ð2Þ
where ME is the encapsulation efficiency, Oiltotal is the total
amount of oil and Oilsurface is the amount of non-encapsulated oil
existent on the surface of the microparticle. The non-encapsulated
oil existent on the particle surface was determined according to the
method described by Bae and Lee (2008). Fifteen millilitres of
hexane was added to 2 g of powder in a sealed glass bottle, which
was shaken for 2 min at room temperature to extract the free oil.
Next, the solvent mixture was passed through a number 1 Whatman
paper filter. The powder collected in the filter was washed three
times with 20mL of hexane. The solvent was evaporated at 60 C
until constant, and the weight of the non-encapsulated oil was
calculated based on the difference in weight between the initial
clean flask and the flask containing the extracted oil residue (Jafari
et al., 2007). Total oil content of the spray-dried encapsulated
products was determined by distilling 10 g of encapsulated powder
for 3 h in a Clevenger-type apparatus (Jafari et al., 2007).
Oil retention
RT was determined by dividing the total oil quantified in the
particles after spray drying by the total oil initially added to the
emulsion preparation (Equation (3)).
RT ¼
Oiltotal
Oilinitial
ð3Þ
where Oilinitial is the concentration of oil before spray drying and
Oiltotal is the concentration of oil after spray drying.
Particle morphology
Particle morphology was evaluated by scanning electron micros-copy
(SEM). Powders were attached to a double-sided adhesive
tape mounted on SEM stubs with 1 cm diameter and 1 cm height,
coated with gold under vacuum and examined with a MEV 1430
VP – LEO scanning electron microscope (Electron Microscopy
Ltd., Cambridge, UK). SEM was operated at 20 kV with
magnifications of 900–1200.
Results and discussion
Identification and quantification of the major constituent
of the microencapsulated oregano essential oil
The results showed that carvacrol is the major phenolic compound
existent in the oregano essential oil, and Table 2 shows the
concentration of carvacrol on the microparticle produced in the
different proportions of wall material and the concentration
carvacrol in the oregano essential oil before the microencapsula-tion
process.
Silva et al. (2010) and Dardioti et al. (2012) obtained levels of
carvacrol in oregano essential oil ranging from 61.66% to 93.42%
and 55.2% to 62.3%, respectively. From these results, it can be

inferred that the microencapsulation process was more efficient
when using combinations of wall materials, such as AG and MA.
Table 3 shows the correlation coefficients of the quadratic
model (Q), R2 and the best fit obtained for the responses
(carvacrol quantification, water activity, moisture, wettability,
solubility, encapsulation efficiency and oil retention) of the
experimental results, as analysed using the simplex centroid
design.
Through the data presented in Table 3, contour curves for the
quantification of carvacrol in the oregano essential oil micro-particle
were constructed as shown in Figure 1, and the
interpretation of the contour lines showed that AG at
concentrations of 60% (as one moves from the AG vertex
towards the peak of the triangle) and MA at a concentration of
43.5% (as one moves from the MA vertex towards the base of the
triangle) caused an increase in the carvacrol concentration.
The results obtained in this work corroborate the reports
indicating that AG and MA can be used as encapsulants for
improving the ME (Anandaraman and Reineccius, 1987;
Reineccius, 1988; McNamee et al., 2001; You-Jin et al., 2003;
Kanakdande et al., 2007).
The concentration of carvacrol near 45% can be explained by
the loss of non-encapsulated volatiles and thus not protected from
evaporation during the process, but these values are still greater
than those obtained in other studies. Baranauskiene´ et al. (2006)
obtained the levels of carvacrol equal to 15.4% and 27.4% for
oregano essential oil microencapsulated with milk powder and
whey protein, respectively; these results are lower than the levels
found in this work.
Water activity and moisture
The water activity and moisture content of the microparticle
are important variables for the shelf life of the dust because
they ensure microbiological stability during storage in the
application of food products. In this work, the microparticle of
oregano essential oil showed average values of water activity
and moisture of 0.13–0.17% and 0.92–3.27%, respectively.
These two variables were significantly influenced by the
independent variables and showed similar responses under the
conditions evaluated. It was observed that higher concentrations
Table 2. Levels of carvacrol microencapsulated with different
proportions of wall materials.
Tests AG (%) MS (%) MA (%) Carvacrol content (%) w/v
1 100 0.0 0.0 46.0
2 25.0 75.0 0.0 46.5
3 25.0 0.0 75.0 45.6
4 62.5 37.5 0.0 54.7
5 62.5 0.0 37.5 57.8
6 25.0 37.5 37.5 48.2
7 49.7 25.1 25.1 51.2
8 74.5 12.7 12.7 56.2
9 36.2 51.0 12.7 50.1
10 36.2 12.7 51.0 49.9
Oregano essential oil 74.5
Table 3. Results of the adjusted models for the chemical and physical properties of encapsulated oregano oil.
Carvacrol (%) Aw (–) X0 (%) Wett (s) Sol (%) ME (%) RT (%)
R2 (%) 87.54 86.45 90.97 76.80 97.61 86.80 84.11
p Value 0.6027 ns 0.0463* 0.1048 ns 0.2305 ns 0.0058* 0.0724* 0.5650ns
b1 46.982.20* 0.160.02* 2.950.35* 21.551.96* 73.712450.23* 92.281.35* 35.720.67*
b2 46.572.20* 0.100.02* 1.130.35* 13.671.96* 76.154320.23* 85.651.35* 61.120.67*
b3 45.512.20* 0.180.02* 3.290.35* 14.081.96* 77.120110.23* 87.101.35* 70.650.67*
b12 28.2210.27* 0.140.08 ns 2.941.64 ns 9.409.14 ns 2.866461.07* 11.836.28 ns 98.862.70*
b13 41.6410.25* 0.120.08 ns 5.441.64* 20.309.12* 0.525891.07ns 15.966.27* 95.782.60*
b23 0.6110.25 ns 0.140.08 ns 3.771.64* 10.419.12 ns 5.604941.07* 2.526.27 ns 56.082.60 ns
Notes: *Significant (p50.1); not significant (p40.1).
Aw, water activity; X0, moisture; Wett, wettability; Sol, solubility; ME, encapsulation efficiency; RT, oil retention.
Figure 1. Contour curves of carvacrol quan-tification
of microcapsules of oregano
essential oil.

of MS had a positive impact on the dependent variables. Figures 2
and 3 show that proportions of the regions near to 25% of AG,
25% of MS and 75% of MA had values of and moisture less than
0.1 and less than 1.2, respectively, which is useful to ensure the
stability of the microparticle. The water removal is important to
ensure the formation of microparticle, but the quantity and the
rate of removal must be controlled. The main constituent in the
spray of emulsion is water, which evaporates during the drying
process (490%); however, the volatile constituents may be
maintained when optimum drying conditions are used
(Reineccius, 1998, 2004). Therefore, it was found that the
microparticle produced with higher concentrations of MS had
lower water adsorption together with the MA 20DE; in contrast,
the samples produced with high concentrations of AG were the
most hygroscopic. These differences in adsorption of water can be
explained by the chemical structure of each agent. AG and MA
20DE have a large number of branches with hydrophilic groups,
and thus can easily adsorb moisture from the ambient air. MS is
less hydrolysed and has fewer hydrophilic groups and thus is less
adsorbent of the water (Tonon et al., 2009). Frascareli et al. (2012)
observed that increasing the content of AG caused an increase in
hygroscopicity of the microparticle of coffee oil, and this increase
was attributed to the hygroscopic nature of AG. The results
obtained in this work confirm that the Aw and humidity of the
microparticle were increased when higher concentrations of AG
were used due to the susceptibility of AG to adsorbing water.
Adhikari et al. (2004) evaluated the effect of the addition of MA
on the drying kinetics and stickiness properties of the sugar using
solutions with different combinations of fructose, glucose,
sucrose, citric acid, MA and water. The authors observed that
the addition of MA significantly reduced the tackiness on the
surface of the sugar solution of low molecular weight, showing its
effective application in the drying process of fruit juices.
Baranauskiene´ et al. (2007) evaluated various MS in the retention
Figure 2. Contour curves of water activity of
microcapsules of oregano essential oil.
Figure 3. Contour curves of moisture content
of the microcapsules of oregano essential oil.

of aroma peppermint essential oil and observed that the water
activity in the microparticle without removal of the oil surface
reached an average of 0.54 and 0.76.
Wettability
It was observed that the microparticle of oregano essential oil
showed better instantisation in water when 36.2% of AG, 12.7% of
MS and 51% of MA (DE 20) were applied than with the
combination of 25% of AG and 75% of MA (Figure 4). The
wettability was decreased due to increased concentration of AG,
and the time taken for the particles of all wet tests ranged from 11
to 22 min. Fuchs et al. (2006) reported 28 min in determining the
wettability of microparticle of vegetable oil mixed with sunflower
oil, rapeseed and grape seed encapsulated by AG and MA (DE
12). In this work, the combination of 25% of AG, 37.5% of MS
and 37.5% of MA resulted in lower capacity of instantisation.
Arbuto et al. (1998) verified that the MS (capsul) showed slow
dissolution in water at 25 C and was optimal when the
temperature was 82 C. A combination that favours capillary
effects and morphological characteristics could explain the low
values found for the time of wetness of all the encapsulant
materials. According to Schubert (1993), among the materials
used in this work, the MAs have larger particle diameters and can
influence the dispersibility, promoting wetting. According to
Shittu and Lawal (2007), the relation between the instantaneous
properties and physicochemical characteristics is not linear and
involves the interaction of both. The solubility of cocoa bever-ages,
for example, was primarily dependent on the chemical
constituents (content of sugar and lipids), while the wetting time
was more affected by the physical properties. Using MAs with
different DEs, Fazaeli et al. (2012) found that the solubility
increased by increasing the DE because of the large number of
ramifications with hydrophilic groups. In spite of the good
wettability of the encapsulants used in this study, the reconsti-tution
of such materials in water can occur distinctly because of
the chemical and structural properties of the wall materials used.
Research by Quek et al. (2007), Pitalua et al. (2010) and
Frascareli et al. (2012) suggest the use of AG as an encapsulant
and additive in the spray-drying process mostly because of AG’s
emulsifying properties and high water solubility. However, MA is
an encapsulant with the best solubilisation properties, and because
this material is more accessible than AG. McNamee et al. (2001)
suggest the partial replacement of AG by the MA. However, the
authors found that MA (DE 18.5) was considered the most
appropriate suitable replacement for AG because it showed rapid
reconstitution of the emulsion in water (Gharsallaoui et al., 2007).
Solubility
High solubility is a desirable property of the powder particles and
is a result of a good encapsulating agent used in the spray drying.
The produced microparticle reached a solubility of 74.2–77.2%
(powder weight/solution volume), which is considered high,
because the encapsulants that were used (amorphous solid) have
high solubility in relation to the crystalline state (Yu, 2001;
Gombas et al., 2003; Cano-Chauca et al., 2005; Lu, 2012). It was
observed that increasing the concentration of MA resulted in an
increased solubility of the microparticle in water, and similar
results were obtained by Moreira et al. (2009) and Fazaeli et al.
(2012), who obtained the solubility of mulberry juice powder and
dry extract of acerola bagasse, respectively, with results near 87%
soluble. These authors also observed that increasing the replace-ment
of AG by MA caused the increased solubility of the powder
in water. This finding can be explained by the high degree of
solubility (490%) of MAs and varies depending on its molecular
weight; the solubility of MAs increases with decreasing degree of
ramification of the a (1–6) (Cano-Chauca et al., 2005). Thus, the
MAs DE 20 show high solubility (Gidley and Bulpin, 1987).
However, it was found that the combination of MA with AG and
MS influences the functional property of microparticle solubil-isation
because of a possible change in the microstructure of the
system. It was observed that the combination of MA with AG and
MS in the evaluated proportions resulted in a decrease in
solubility of microparticle, especially when AG was used in
higher concentrations (Figure 5). It was also observed that the
solubility was lower (73.6%) when high concentrations of the
combination of AG and MS were applied. This result may be
observed because of the low solubility of starch in cold water
(35–40%), which is attributed to the higher organisation of the
particles (crystalline state).
Oil retention and encapsulation efficiency
It was observed that the application of the mixture of the
encapsulants (Figure 6) in the emulsion resulted in a positive
Figure 4. Contour curves of wettability of the

effect on the retention of oil, ranging from 33.10% to 77.39%.
The higher RT was obtained when the proportions of 74.5%
AG, 12.7% MS and 12.7% MA were used with an emphasis in
the combination of AG and MS, which are important for a
stabilising effect. This property can be attributed to the immediate
formation of a semi-permeable membrane that must result from
applying a greater concentration of AG (Re´, 1998; Reineccius,
2004; Fernandes et al., 2008). However, it was found that the use of
a single encapsulation (100% AG) resulted in lower RT in the
microparticle. Although AG was as effective as the wall material in
encapsulating five different monoterpenes (citral, linalool, b-myr-cene,
limonene and b-pinene) in the study by Bertolini et al.
(2001), this encapsulant has a limited barrier ability against
oxidation because it acts as a semi-permeable membrane to oxygen
and is therefore a limiting factor in the shelf life of the active
compound in the core and in the retention of volatile compounds.
Thus, similar results were obtained where AG was
ineffective in the microencapsulation of orange oil compared
to the whey protein and soy protein isolates (Kim and
Morr, 1996).
However, AG combined with other encapsulants may have a
positive effect on RT. Krishnan et al. (2005) tested combinations
of AG, MS and MA, and obtained a high stability and volatile
retention in cardamom oil resin when the concentration of AG
was higher. These combined materials represent an encapsulating
matrix with improved properties in the retention of volatile
compounds, improvement in emulsion stability and protection
against oxidation (Buffo et al., 2002; Krishnan et al., 2005).
The encapsulation of oregano essential oil using gelatin and
sucrose was also studied by Da Costa et al. (2012), and these
authors concluded that the spray drying method provided an
effective retention of essential oil because of the protection
provided by the microcapsules in the spray-drying process,
resulting in less degradation and loss of volatile compounds.
According to the ‘‘selective diffusion’’ theory, when the water
concentration at the droplet surface decreases to 7–23%
Figure 5. Contour curves of solubility of the
Figure 6. Contour curves of retention oil of
the microcapsules of oregano essential oil.

(Aw50.90), this dry surface acts as a semi-permeable membrane
permitting the continued loss (or diffusion) of water but efficiently
retaining flavour molecules (Reineccius, 2001, 2004). Increased
RT during high feed rates can also be related to the rapid formation
of the semi-permeable membrane because of the higher solid
content inside the drying chamber. Further research should focus on
a detailed investigation of the impact of mixture of encapsulant on
RT, and the acoustic levitation technique is an option to analyse the
drying behaviour of single emulsions (Serfet et al., 2013). The
minor retention obtained in other tests was probably because of
different combinations and proportions of the used encapsulant and
the shape in which the core material (volatile) is arranged in the
microparticle. As water is removed by drying the surface of the
droplets, concentration gradients of water are formed. Thus, the RT
depends on the partial pressure of water in the system because the
core of the microparticle is directly accessible to water vapour
(Karel, 1990; Beristain et al., 2001).
The use of different matrix materials may have a significant
influence on emulsion droplet size. Many studies have shown that
the droplet size is related to the viscosity, stability and may result
in great retention of active material (Soottitantawat et al., 2005;
Jafari et al., 2008). However, Carneiro et al. (2013) in the study of
the microencapsulation of flaxseed oil by spray drying with
different wall materials (MA, AG, whey protein concentrate and
MS) reported that the ME could not be related to the emulsion
droplet size or viscosity and the differences between them can be
attributed to the differences between the polymer matrices formed
by each of the materials used, which have different retention
properties and emulsion capacity. Further studies about the
influence of using different matrix material on the oil drop size
distribution will be developed in future work.
ME ranged from 85.3% to 93% and was significantly
influenced by the concentration of AG; in fact, the maximum
efficiency was obtained when 100% AG was applied (Figure 7).
The combination of AG and MS also favourably influenced ME
because of the film-forming properties of these materials (Yang
et al., 2009).
The encapsulation of the curcumin with MS has been studied
by Paramera et al. (2011), and these authors obtained an ME of
56.2%. Through the response surface methodology, Ahn et al.
(2008) obtained 96.6% efficiency in the microencapsulation of
sunflower oil through a structural matrix composed of 19.0% of
milk protein isolate, 2.5% of soy lecithin and 54.8% of dextrin.
Physicochemical properties of the resulting powders and the
microencapsulation performance depend on many process vari-ables,
such as the type of core and wall materials, emulsion
properties, the drying air characteristics and the type of atomiser.
Therefore, for each oil/encapsulant system, it is important to
select the main variables and to optimise the drying process to
obtain good-quality powders. As a result of the data obtained,
mixtures that optimise the response variables are described in
Table 4.
According to the results showed in Table 4, the samples that
contain AG and MA (in higher proportions) were more appro-priate
in the microencapsulation of oregano essential oil, and
these data are in accordance with the discussions presented in this
article, which reported that AG combined with MAs and MS or
alone are encapsulants good applied to improve the ME and
stability of the microparticle.
Powder morphology
Figure 8 shows the SEM microstructure (internal and external) of
powder produced with different matrix materials combination.
Observing the external morphology, most of the microparticles
showed a spherical shape and various sizes with diameter varying
between micrometre and millimetre. This trait depends on the
material and method used to prepare it; it was observed to form
conglomerate, and according to Bhandari et al. (1992) and
Chambi et al. (2008) this happens with the atomisation process
also. Similar structures were obtained by Sansone et al. (2011)
that studied morphology and other proprieties of the MA/pectin
microparticle as carrier for nutraceutical extracts produced by
spray drying. Some microparticles when broken show a porous
wall (Figure 8). According to Fang and Bhandari (2010) and
Teixeira et al. (2004), microparticles produced by spray drying
usually have a spherical shape and in some cases, they can be
hollow (Yao et al., 2008; Sun et al., 2009; Gu et al., 2013). It can
be explained because of a shrinkage process after the solidifica-tion
of the materials followed by the expansion of the bubbles
embedded into the drop. The mechanisms associated with the
formation of this empty space inside the particle are related with
the movement of the material at the last stage of the drying
process. Analysing the internal morphology, all microparticles
were hollow and the active material was adhered to the surface
as small droplets embedded in the wall material matrix.
Figure 7. Contour curves of encapsulation
efficiency of the microcapsules of oregano
essential oil.

Table 4. Summary of results in the optimisation for each response-variable.
AG (%) MS (%) MA (%) Observed mean Predicted mean
Mixtures which provided maximal responses
Carvacrol (%) 50.0 0.0 50.0 57.801 56.663
Aw (–) (%) 0.0 0.0 100.0 0.179 0.178
X0 (%) 0.0 0.0 100.0 3.270 3.290
Wett (s) 100.0 0.0 0.0 22.000 21.550
Sol (%) 0.0 0.0 100.0 77.200 72.120
RT (%) 68.0 16.0 16.0 77.380 65.110
ME (%) 100.0 0.0 0.0 93.00 92.280
Mixtures which provided minimal responses
Carvacrol (%) 0.0 0.0 100.0 45.630 45.510
Aw (–) (%) 16.0 68.0 16.0 0.096 0.092
X0 (%) 16.0 68.0 16.0 0.733 0.852
Wett (s) 16.0 16.0 66.0 11.330 13.890
Sol (%) 100.0 0.0 0.0 73.600 73.710
RT (%) 100.0 0.0 0.0 33.100 35.720
ME (%) 0.0 100.0 0.0 85.330 85.650
Figure 8. Microphotograph of particles of oregano essential oil produced by spray drying.
This emptiness is a result of the quick particles expansion during
the final stages of drying (Jafari et al., 2008). According to Kho
and Hadinoto (2010), to produce the large hollow spherical micro-aggregates,
the spray drying condition (e.g. drying temperature,
feed rate) and the formulation ingredients (i.e. encapsulants type
and its concentration) must be meticulously determined. The
physical mechanism behind the hollow micro-aggregate formation
is described as follows. Liquid evaporation from the droplet
surface exposes the microparticles at the receding liquid–vapour
interface to the vapour phase. As the surface energy of a solid–
vapour interface is greater than that of a liquid–vapour interface,
the microparticles migrate towards the droplet centre to minimise
their surface energy. A fast convective drying rate in which the
liquid evaporation time is shorter than the time needed by the
microparticles to diffuse back towards the droplet centre
is required to produce the hollow morphology. The
microparticles with porous and hollow structure have more
excellent properties such as low density and large encapsulation
capacity. The results also show a preponderance of the
microparticle with rough surface.
Conclusion
In agreement with the proposed objectives, it was concluded that
mixtures model was adequate in the optimisation study and
selection of wall materials used in microstabilisation of oregano
essential oil by spray drying, carvacrol was the major phenolic
compound existing in the oregano essential oil with 57.8%
concentration maximum in microparticle with the use of 62.5%
AG and 37.5% MA. Better RT occurred when using 74.5% AG,
12.7% MS, 12.7% MA and AG as a single wall material
concentration of 100%. These conditions increased the ME up
to values of 93%.
Therefore, according to the results a mixture of AG, MS and
MA could be suggested as a good alternative for stabilisation of
oregano essential oil which result in good microparticle with
physical and chemical properties and better ME.
Declaration of interest
The authors report no conflicts of interest. The authors alone are
responsible for the content and writing of the article.

The authors thank FAPEMIG (Fundaçaõ de Amparo a Pesquisa do
Estado de Minas Gerais, Brazil), and CNPq (Centro Nacional de
Desenvolvimento Cientı´fico e Tecnolo´gico) for providing funding.
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