Food and Nutrition Sciences, 2013, 4, 289-298
http://dx.doi.org/10.4236/fns.2013.43039 Published Online March 2013 (http://www.scirp.org/journal/fns)
Physicochemical and Functional Properties of Dehydrated
Japanese Quail (Coturnix japonica) Egg White
Maira Segura-Campos1, Roberto Pérez-Hernández2, Luis Chel-Guerrero1, Arturo Castellanos-Ruelas1,
Santiago Gallegos-Tintoré1, David Betancur-Ancona1*
1Faculty of Chemical Engineering, Campus of Exact Sciences and Engineering, Autonomous University of Yucatán, Merida, Mexico;
2Inalim Food Industry, Oaxaca, Mexico.
Received February 7th, 2013; revised March 6th, 2013; accepted March 12th, 2013
ABSTRACT
Physicochemical, functional and digestibility analyses were done of dehydrated quail egg white to determine its possi-
ble practical applications. Quail egg white was dehydrated by air convection using one of two temperatures and times:
M1 (65˚C, 3.5 h), M2 (65˚C, 5.0 h), M3 (70˚C, 3.5 h) and M4 (70˚C, 5.0 h). Lyophilized quail egg white was used as a
standard. All four air-dried treatments had good protein levels (92.56% to 93.96%), with electrophoresis showing the
predominant proteins to be lysozyme, ovalbumin and ovotransferin. Denaturation temperatures ranged from 81.16˚C to
83.85˚C and denaturation enthalpy values from 5.51 to 9.08 J/g. Treatments M1-4 had lower water-holding (0.90 - 2.95
g/g) and oil-holding (0.92 - 1.01 g/g) capacities than the lyophilized treatment (4.5 g/g, 1.95 g/g, respectively). Foaming
capacity was pH-dependent in all five treatments, with the lowest values at alkaline pH and the highest (153% to 222%)
at acid pH (pH 2). Foam stability was lowest at acid pH and highest at alkaline pH. Emulsifying activity in the air-dried
treatments was highest at pH 8 (41% - 46%). Emulsion stability was pH-dependent and highest in M3 between pH 2
and 4 (96.16% to 95.74%, respectively). In the air-dried treatments, in vitro protein digestibility was as high as 83.02%
(M3).
Keywords: Coturnix japonica; Dehydrated Egg White; Physicochemical Properties; Functional Properties
1. Introduction
Japanese quail Coturnixjaponica belongs to the order Gal-
liformes, family Phasidae, and is a separate species from
the common quail Coturnixcoturnix Wild Japanese quail
were first documented in the 8th Century [1] and had
been domesticated as a pet song bird by around the 11th
Century. The species has gained value as a food animal
due to the unique flavor of its eggs and meat. Quail egg
production is important in Japan and Southeast Asia,
while quail meat is an element in many European cui-
sines. Its small body size (80 - 300 g) and consequent
low maintenance cost, in addition to its short generation
interval, disease resistance and high egg production make
this species an excellent laboratory animal. Japanese
quail is also the smallest avian species produced for meat
and eggs, and has been extensively studied [2].
Although not yet accepted as a food source worldwide,
quail is becoming increasingly important in various coun-
tries. In the Philippines, the rich taste of quail eggs has
caused demand to surpass supply [3]. Quail products are
popular as conventional food in countries such as France,
Italy, Greece, Japan and China, and interest is growing in
them as a dietetic food rich in vitamins and minerals,
particularly for children and the elderly [4]. In Mexico,
quail egg demand is concentrated in Toluca, Valle de
Bravo, Temascaltepec and Tejupilco where it is mainly
consumed in restaurants [5].
The high protein content of quail egg white makes it
an excellent potential protein source for food industry
applications. As with any protein source, its actual use-
fulness will depend on its functional properties, which
affect food sensory characteristics and play an important
role in the physical behavior of food and/or its ingredi-
ents during preparation, processing and storage. Many
functional properties depend on exposure of hydrophobic
groups on the molecular surface and the interactions of
these groups with oil (emulsion), air (foam) or other pro-
tein molecules such as gels and coagula. Considering that
hydrophobic amino acid residues are generally located
inside globular protein molecules, unfolding of the native
structure during processing steps such as homogenization,
liquefaction or heating may be necessary to allow these
*Corresponding author.

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 290
hydrophobic groups to participate in intermolecular in-
teractions. A protein’s molecular flexibility can be con-
strained by the strength of hydrophobic and internal elec-
trostatic interactions, which maintain the native structure,
as well as by the presence of covalent disulphide in-
tramolecular bonds [6].
Emulsification, foam formation and gelation, among
other functional properties, are essential in food products
such as desserts, puddings, reformulated meat products,
tofu and surimi. The success of many cooked foods de-
pends on protein coagulation, especially coagulation of
egg proteins since when they coagulate they act as a
structural bond with other ingredients. Foam contributes
to the texture of bread, cakes, cookies, meringues, ice
creams, and several bakery products, all of which require
the incorporation of air to maintain texture and structure
during and after processing. Air encapsulation and reten-
tion by proteins improves desirable textural attributes;
this capacity to form and stabilize foam is related to pro-
teins’ amphiphilic behavior (polar/nonpolar) [6]. Chicken
egg white has been used extensively in processed food
because of its gelation and foam formation properties,
and chicken egg ovalbumin proteins are common ingre-
dientsin processed food. Quail egg white may also have
potential applications as a food ingredient, depending on
the required function in the final product. The present
study objective was to characterize the physicochemical
and functional properties of dehydrated Japanese quail
(Coturnix japonica) egg white.
2. Materials and Methods
2.1. Materials
Japanese quail eggs were obtained from a commercial
producer (Mexicapam Poultry Farm, San Martín Mexi-
capam, Oaxaca, Mexico). Reagents were analytical grade
and purchased from J.T. Baker (Phillipsburg, NJ, USA),
Sigma (Sigma Chemical Co., St. Louis, MO, USA), Merck
(Darmstadt, Germany) and Bio-Rad (Bio-Rad Laborato-
ries, Inc. Hercules, CA, USA).
2.2. Dehydrated Egg White
Egg white was isolated mechanically by foaming with a
Moulinex blender and drying the foam in an air convec-
tion oven under four sets of conditions: M1 (65˚C, 3.5 h);
M2 (65˚C, 5.0 h); M3 (70˚C, 3.5 h); and M4 (70˚C, 5.0
h). As a control (ML), egg white was also freeze-dried
(lyophilized) at −47˚C and 13 × 10−3 mbar for 48 h.
2.3. Physicochemical Characterization
2.3.1. Proximate Composition
Official AOAC procedures were used to determine ni-
trogen (method 954.01), fat (method 920.39), ash (method
923.03) and moisture (method 925.09) contents in the
dehydrated quail egg white [7]. Nitrogen was determined
with a Kjeltec System (Tecator, Sweden), protein calcu-
lated as nitrogen × 6.25, and fat determined with a 4-h
hexane extraction. Ash was calculated from sample weight
after heating to 550˚C for 2 h. Moisture was measured
based on sample weight loss after oven drying at 110˚C
for 4 h.
2.3.2. Electrophoresis
Sodium dodecyl sulfate polyacrylamide gel electropho-
resis (SDS-PAGE) was done as described by Schagger
and von Jagow [8]. Briefly, 13% acrylamide gels were
prepared by mixing 2.6 mL 49.5% acrylamide-bisacryla-
mide (48% acrylamide and 1.5% bisacrylamide), 3.3 mL
gel regulator (3 M Tris adjusted to pH 8.45 and 0.3% l
ammonium persulphate and 0.3% SDS), 1.03 mL glyc-
erol, 2.8 mL distilled water, 50 μl ammonium persul-
phate and 20 μl TEMED. Running buffer composition
was 0.1 M Tris, 0.1 MTricine (Sigma T-5816) and 0.1%
SDS for the cathode buffer, and 0.2 MTris (Sigma T-
1503) at pH 8.9 for the anode buffer. Samples were
heated to 95˚C for 2 min in 0.6 mL 0.1 M Tris-HCl at pH
6.8, 5 mL 50% glycerol (w/v), 2 mL 10% SDS, 1 mL 1%
bromophenol blue (Sigma B-5525) (w/v) and 1.4 mL
distilled water. Molecular weight standard (Bio-Rad) pro-
tein composition ranged from 20 to 111 kDa. Electro-
phoresis was run at a constant 20 mA/gel voltage for 2 h
before staining (0.10% Coomassie blue G-250 in water:
methanol: acetic acid 4:1:5 v/v/v for 1 h). Destaining was
done with a 10% (v/v) acetic acid and 40% methanol
solution for 12 h.
2.3.3. Temperature and Denaturalization Enthalpy
Temperature and denaturalization enthalpy were deter-
mined with a DSC-7 (Perkin-Elmer Corp., Norwalk, CT)
according to Martínez & Añon [9]. Three milligrams (dry
base—d.b.) of sample were placed in an aluminum pan,
moisture level adjusted to 70% by adding de-ionized
water, the pan hermetically sealed and left to equilibrate
for 1 h at room temperature. It was then placed in the
calorimeter and heated from 30˚C to 130˚C at a rate of
10˚C/min, using an empty pan as reference.
2.4. Functional Properties
2.4.1. Water-Holding (WHC) and Oil-Holding
Capacity (OHC)
These properties were determined by first weighing out 1
g sample and stirring it into 10 mL distilled water or corn
oil (Mazola, CPI International) for one minute. These
protein suspensions were then centrifuged at 2200 xg for
30 min, and supernatant volume measured. Water-hold-
ing capacity was expressed as g water held per g sample.

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 291
Oil-holding capacity was expressed as g oil held per g
protein sample [10].
2.4.2. Foaming Capacity and Foam Stability
Foam properties were evaluated over a pH range of 2 to
10. A 100 mL sample of 1.5% protein (w/v) suspension
was blended at low speed in a Waring blender (Osterizer
10S-E) for 5 min, and foam volume recorded after 30 s.
Foaming capacity was expressed as the percentage in-
crease in foam volume measured at 30 s. Foam stability
was quantified by measuring residual foam volume 5, 30
and 120 min after blending. Both properties were deter-
mined as a function of pH [10].
2.4.3. Emulsifying Activity (EA) and Emulsion
Stability (ES)
Emulsion properties were analyzed using 10 mL samples
of a 2% (w/v) suspension adjusted to pH values ranging
from 2 to 10. These were homogenized using a Caframo
RZ-1 homogenizer at 2000 rpm for 2 min, 10 mL corn
oil (Mazola, CPI International) added to each sample and
the mixture homogenized for 1 min. The emulsions were
centrifuged in 15 mL graduated centrifuge tubes at 1200
xg for 5 min and emulsion volume measured. Emulsify-
ing activity was expressed as the percentage represented
by the emulsified layer volume of the entire layer in the
centrifuge tube. To determine emulsion stability, the emul-
sions were heated to 80˚C for 30 min, cooled to room
temperature and centrifuged at 1200 xg for 5 min. Emul-
sion stability was expressed as the percentage repre-
sented by the remaining emulsified layer volume of the
original emulsion volume [10].
2.5. In Vitro Protein Digestibility
Following Hsu et al. [11], a multienzyme system con-
sisting of porcine pancreatic trypsin type IX, bovine pan-
creatic chymotrypsin type II, and porcine intestinal pep-
tidase grade III (Sigma Chemical Co, St. Louis, MO,
USA) was selected. A total volume of 50 mL of an
aqueous protein suspension (6.25 mg/mL) was prepared
by mixing the sample with distilled water, adjusting pH
to 8.0, and stirring in a water bath at 37˚C. The multien-
zyme solution was maintained in an ice bath and adjusted
to pH 8.0. While stirring, a 5 mL aliquot of multienzyme
solution was added to the protein suspension at 37˚C. A
rapid decline in pH occurred which was recorded over a
10 min period using a pH meter. In vitro protein digesti-
bility was calculated with the equation PD = 210.46 −
18.10 (pH after 10 min).
2.6. Statistical Analysis
All results were analyzed using descriptive statistics with
a central tendency and dispersion measures. Data were
analyzed using a one-way analysis of variance (ANOVA)
and a Duncan’s multiple range test; all calculations were
done in triplicate. All analyses were done according to
Montgomery [12] and processed using the Statgraphics
Plus version 5.1 software.
3. Results and Discussion
3.1. Proximate Composition
Proximate analyses showed moisture content of the de-
hydrated quail egg white to range from 6.16 (M2) to 7.42
(M3) (Table 1). Initial moisture content in quail albumen
is reported to be 87.82% (Dudusola, 2010), meaning a
substantial loss of moisture occurred. Ash content ranged
from 5.96% (M2) to 7.08% (M4), which are higher than
reported for quail (1.00%) and guinea fowl (0.79%) al-
bumen [13]. This relatively high ash content suggests
that dehydrated quail egg white is a good source of min-
erals. Protein content ranged from 92.56% (M4) to
93.96% (M1). These values are higher than the 80.72%
[14] and 90% [15] reported for aspersion-dried chicken
egg, the 80% reported for dehydrated chicken egg white
[16], and the 83.9% reported for quail albumen [13]. The
protein content observed here in dehydrated quail egg
white was also higher than protein content in young
(18.99 %) and spent (17.48%) quail meat [17]. Fat con-
tent ranged from 0.42 (M2) to 0.58 (M1), which is higher
than reported for dehydrated chicken egg white (0.04%),
and quail (0.09%) and guinea fowl (0.13%) albumen
[14].
3.2. Electrophoresis
Electrophoresis showed the lyophilized quail egg white
Table 1. Moisture, ash, protein and fat contents in quail egg white dried by air convection at two temperatures and two times.
Components M1
65˚C, 3.5 h
M2
65˚C, 5.0 h
M3
70˚C, 3.5 h
M4
70˚C, 5.0 h
Moisture (6.36  0.08)b (6.16  0.02)b (7.42  0.03)a (6.24  0.05)b
Ash 6.06  0.15b 5.96  0.22c 6.63  0.28b 7.08  0.09a
Protein 93.96  0.50a 93.71  0.07a 93.16  0.24a 92.56  0.06c
Fat 0.58  0.01a 0.42  0.01b 0.49  0.01b 0.56  0.06a

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 292
(ML) to exhibit eight bands between 17 and 170 kDa
(Figure 1). The four air-dried treatments (M1, M2, M3
and M4) had similar profiles, with the exception of the
bands at 55 and 65, which probably correspond to avidine
and G2 or G3 globulins, respectively [18]. The bands at
17 (lysozime), 47 (ovoalbumin) and 74 (ovotransferin)
kDa were similar to those reported for chicken egg white
[19].
Overall, the dehydrated quail egg white exhibited a
number of similarities to chicken egg white. Ovalbumin
(approx. 45 kDa) is the predominant protein in egg white
and represents 54% of total egg white protein. It is a
monomer, globular phosphoglycoprotein with 385 amino
acid residues, half of which are hydrophobic. Chicken
egg protein is easily denatured by heat, but has a rela-
tively high denaturation temperature of about 84˚C (Ah-
med et al., 2007). In the present study, quail egg white
protein did not denature in any of the treatments, sug-
gesting it may also have a high denaturing temperature.
The band at 17 kDa is analogous to that reported for ly-
sozyme (approx. 15 kDa) in chicken egg white [6]. Ly-
sozyme is a glycoprotein representing 3.5% of chicken
egg white, and consists of a single polypeptide chain
with 129 amino acids linked by four disulphide bonds.
Given their molecular weights in chicken egg white, it is
probable that avidin (53 kDa) and conalbumin (80 kDa)
are also present in quail egg white. Conalbumin is a gly-
coprotein accounting for 13% of chicken egg white. It
can bind to metal ions and form a protein-metal complex
resistant to denaturation by heat, pressure, proteolithic
enzymes and denaturing agents. After drying chicken egg
white at 60˚C for 180 min, Matsuda et al. [19] reported
an 80 kDa band corresponding to ovotransferin (conal-
bumin) while CarraroAlleoni [6] reported that conalbu-
min’s denaturation temperature is 61˚C. Given the above,
the 65˚C dehydration temperature and 3.5 and 5 h times
used in the present study were probably insufficient to
denature this protein fraction in quail egg white. In con-
trast, ovomucin was absent in the studied quail egg white.
Ovomucoid is a glycoprotein (approx. 28 kDa) with tryp-
sin inhibitory activity, and has an important effect on
albumin consistency. Low-intensity signals were observed
for ovoinhibitor (approx. 49 kDa), a trypsin and chy-
motrypsin inhibitor. These were lower in the M1-4 treat-
ments than in ML, perhaps due to partial denaturation.
3.3. Denaturation Temperature and Enthalpy
Absorption peaks in the thermograms for M1-4 ranged
from 81.16˚C to 83.85˚C (Table 2). Denaturation tem-
peratures for the M1, M2 and M3 treatments were similar
(a) Lyophilized treatment (b) Air convection-dried treatments
Figure 1. Electrophoresis (SDS-PAGE) profiles for dehydrated quail egg white: (a) Standard = 1, 2; ML = 3, 4; (b) Standard
= 1, 2; M1 = 3, 4; M2 = 4, 5; M3 =6, 7; M4 = 8, 9.

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 293
Table 2. Denaturation temperatures (Td) and enthalpies
(ΔH) of quail egg white dried by air convection (M1, 65˚C
and 3.5 h; M2, 65˚C and 5 h; M3, 70˚C and 3.5 h; M4, 70˚C
and 5 h), and lyophilization (ML).
Treatment Td (˚C) ΔH (J/g)
M1 83.43 ± 0.0a 7.79 ± 0.02b
M2 83.85 ± 0.32a 7.39 ± 0.24b
M3 83.61 ± 0.24a 5.51 ± 0.17c
M4 82.86 ± 0.18b 5.59 ± 0.05c
ML 81.16 ± 0.01b 9.08 ± 0.03a
to the 84.5˚C reported by Raeker and Johnson [20] for
chicken egg ovalbumin suggesting that the denaturation
temperatures observed here corresponded to ovalbumin.
During storage, ovalbumin is altered to s-ovalbumin, a
much more thermo-stable form (denaturation at 92.5˚C)
than ovalbumin (denaturation at 84˚C) [6]. S-ovalbumin
has a slightly lighter molecular weight than ovalbumin
and its relative proportion in the egg white can increase
from 5% in fresh egg to 81% after six months of refrig-
erated storage. The present results suggest that ovalbu-
min had not converted to s-ovalbumin in the studied
treatments. Denaturation temperature was slightly lower
in the ML treatment than in the M1-4 treatments, possi-
bly due to conformational changes caused by drying
method [21].
Protein denaturation involves alteration of a protein’s
native form through significant changes in its three-di-
mensional (3D) conformation produced by movements of
different protein domains, a phenomenon which increases
molecular entropy. These changes cause a loss in secon-
dary, tertiary and quaternary structure, generating greater
interaction between hydrophobic residues and resulting
in aggregation of deployed proteins. Heat is one of the
most frequently used denaturing methods, and affects
stability in the non-covalent interactions of a protein’s
3D structure because it lowers molecule enthalpy and
breaks the bonds which maintain balance within the
structure. In the present study, denaturation enthalpy
ranged from 5.51 J/g in M3 to 9.08 J/g in ML, meaning
the former requires less energy to denature than the latter.
Air drying at the studied temperatures may therefore
have partially denatured the protein in the quail egg
white, whereas drying by lyophilization probably did not
[22]. Air-dried quail egg white is therefore a promising
ingredient in baked products such as breads and cakes
because its denaturation temperature is similar to that of
starch gelatinization (85˚C - 90˚C). Incorporation of this
ingredient into baked products would allow an increase
in shake viscosity and attainment of maximum volume
and texture before and during the baking.
3.4. Functional Characterization
3.4.1. Water-Holding (WHC) and Oil-Holding
Capacity (OHC)
Water-holding capacity was higher in ML (4.5 g/g) than
in M1-4 (0.90 to 2.95 g/g). Similar values have been re-
ported for chicken egg white: untreated white (1.30 g/g)
[22], lyophilized white (2.58 g/g) [23]. Differences in
WHC between the ML and M1-4 treatments can proba-
bly be attributed to heat-induced changes in conforma-
tion or partial denaturation. Denaturation led to increased
dispersion velocity as the protein molecule unfolded and
consequently expanded molecule dimensions. The air-
dried treatments may have had primarily attractive forces
which would force water out of the network matrix and
lower WHC. External factors (e.g., stirring velocity, pH,
and protein concentration) which can be manipulated
during recovery or measurement may also have influ-
enced this property. Food processing and development of
new food products require ingredients such as gelling
agents which can build up a structural matrix and provide
a desirable texture. The dehydrated quail egg white stud-
ied here is a promising alternative ingredient in products
such as desserts, puddings and reformulated meat prod-
ucts.
Oil-holding capacity was also higher in the ML (1.95
g/g) than in the M1-4 treatments (0.92 to 1.01 g/g). The
higher OHC in the ML treatment was probably due to a
higher nonpolar residue content, which would have pro-
vided more contact surface and therefore increased OHC.
The OHC values from the M1-4 treatments were lower
than reported for lyophilized chicken egg white (4.22 g/g)
[23]. Based on its OHC values, the ML treatment would
be useful in improving structural interactions in food
such as flavor retention and improvement of palatability,
while the M1-4 treatments would be useful as ingredients
in fried products since they would provide a non-greasy
sensation.
3.4.2. Foaming Capacity and Foam Stability
The ability of the quail egg white proteins to form and
stabilize foams was related to their amphiphilic behavior
(polar/nonpolar). Foams consist of an aqueous continu-
ous phase and a gaseous disperse phase [24]. Textural
properties in foams depend on dispersion of numerous air
bubbles and formation of a thin film (lamella) in the liq-
uid-gas interphase. The proteins in the dehydrated quail
egg white effectively formed a gaseous disperse phase
with each droplet enveloped by a thin, continuous film of
protein molecules and each bubble separated by a dense
lamella. Foaming capacity in the dehydrated quail egg
white was pH-dependent (Figure 2): alkaline pH resulted
in low values, and acid pH (pH 2) produced high values.
The higher foaming capacity observed at acid pH was

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 294
Figure 2. Effect of pH on the foaming capacity (%) in de-
hydrated quail egg white: Air convection-dried treatments
M1 (65˚C, 3.5 h), M2 (65˚C, 5 h), M3 (70˚C, 3.5 h) and M4
(70˚C, 5 h); Lyophilized treatment, ML.
probably due to an increase in proteinnet charge. This
weakens hydrophobic interactions and increases protein
flexibility, allowing them to more rapidly spread the
air-water interface, encapsulate air particles and increase
foam formation. At acid pH (2), the M1 treatment exhib-
ited a higher (p < 0.05) foaming capacity (222%) than
M2-4 (153% - 198%) and ML (168%). In M1, this be-
havior could be explained by a loss of secondary and
tertiary structure due to the air-drying treatment (65˚C,
3.5 h), which would increase molecule surfactant power.
This suggests that a certain sequence of reactions oc-
curred during foam formation with the quail egg white
proteins. Energy input would have triggered the process,
causing soluble proteins to reach the air-water interface
by diffusion, adsorption, concentration and critical sur-
face tension. Polypeptide rearrangement in the interface
was oriented by polar mobility, with polar segments
drawn to water and non-polar segments drawn to air par-
ticles. During interfacial movement, the partially-opened
proteins would have formed new intermolecular associa-
tions with neighboring molecules, generating the cohe-
sive and continuous films essential to foam formation.
The main attractive forces in this process may have been
hydrogen bonds, hydrophobic interactions, and electro-
static and van der Waals forces. At alkaline pH values,
foaming capacity in the dehydrated quail egg white treat-
ments was similar to the 60% reported for dehydrated
chicken egg white at pH 10 and a 2% concentration [16].
Superficial activity in the quail egg white proteins de-
pended on both the hydrophobic/hydrophilic relationship
and protein conformation. The high foaming capacity in
the M1 treatment was therefore a product of the polypep-
tide chain stability/flexibility relationship, its adaptability
to environmental changes and the distribution patterns of
hydrophilic and hydrophobic groups on the protein sur-
face.
Foam stability was lowest in the M1-4 treatments at
pH 2, with losses of 137 (M1), 116 (M2), 103 (M3) and
91% (M4) from 30 seconds to 120 min (Figure 3). These
values reflect the rapid loss of the proteins’ capacity to
stabilize foam against gravitational and mechanical stress.
The foams steadily lost volume after rapid adsorption of
the proteins into the interphase, which depended on dis-
tribution of hydrophobic and hydrophilic zones on the
surface. This loss of volume may have occurred because
the protein film formed around each gas bubble was not
sufficiently viscous, elastic and resistant to produce gas
permeability and inhibit foam coalescence. Therefore, at
pH 2 the dehydrated quail egg white in all the treatments
was unable to support the weight of the very high foam
volume produced. During the same time period (30 sec to
120 min), foam stability was highest in M1 (17%) at pH
10, in M2 (11%) at pH 8, in M3 (12%) at pH 4 and in M4
(10%) at pH 6. The structural components and attractive
electrostatic interactions (forces) present under these
Figure 3. Effect of pH on foam stability (%) in air convec-
tion-dried quail egg white: M1 (65˚C, 3.5 h); M2 (65˚C, 5 h);
M3 (70˚C, 3.5 h); M4 (70˚C, 5 h).

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 295
conditions enabled the formation of intermolecular asso-
ciations and improved foaming properties. Non-polar
residues intensively contribute to interactive forces at the
hydrophobic interface, increasing the surface activity
within which hydrophilic residues associated to decrease
surface activity, thus improving film quality and foam
stability. Foam stability depended on the ability of pro-
tein surface activity to improve film elasticity, and was
reflected in the balance between forces inside the film
and the forces among adjacent bubbles. The high foam
stability at alkaline pH values may also be an artifact of
the lower foam volume at these pH values, which led to
lower bubble coalescence.
The proteins which stabilize foams are more stable at
their isoelectric point than at other pH levels. For in-
stance, chicken egg white has good foaming properties at
pH 8 - 9, but at or near its isoelectric pH (4 - 5) the re-
duced presence of repulsion interactions promotes pro-
tein-protein interactions and the formation of a viscous
film in the interphase which favors foaming capacity and
foam stability. In a study of dehydrated chicken egg
white, Vani and Zayas [16] reported foam stability values
of 52 (30 min), 46.6 (60 min), 42 (90 min) and 37.6%
(120 min) at pH 10 and a 2% concentration. Foam stabil-
ity at 30 min increased at protein concentrations of 8%
due to a lower liquid flow inside the lamella. Effectively
forming a protein capsule that holds air bubbles also re-
quires non-covalent interactions, such as electrostatic and
hydrophobic forces, hydrogen bounds, and disulphide
linkages. A balance between non-covalent interactions
may help to form a cohesive, viscous film, which is re-
quired for foam stability. The lower foam stability values
observed in the present study were possibly due to elec-
trostatic repulsions. Disulphide linkages reduce protein
flexibility, and the change of a thiol group to a disulphide
has significant repercussions on functional properties.
For example, molecular alterations induced by reduction
of disulphide linkages between protein molecules im-
prove film formation in foam and contribute to its stabi-
lization [25]. In another study, Doi et al. [26] found that
the essential factor in the formation of stable foam with
ovalbumin was not disulphide linkage formation, but
network formation by other non-covalent interactions.
Disulphide bindingis critical to stabilizing protein struc-
ture, constraining molecular unfolding and preventing
total exposition of hydrophobic regions, meaning forma-
tion of disulphide linkages at the air-water interface may
improve foam stability [27]. The proteins in dehydrated
egg white encapsulate and retain air, making them useful
in improving desirable textural attributes in products such
as bread, cookies, meringues, ice creams, and other bak-
ery products during and after processing. However, foam-
ing properties also depend on protein concentration, film
thickness, ionic strength, pH, temperature, the presence
of other components in food systems, and protein phys-
icochemical properties.
3.4.3. Emulsifying Activity (EA) and Emulsion
Stability (ES)
Proteins are excellent surfactants in the formulation of
food emulsions (oil-water) because their surface is active
and favors resistance to coalescence. In the air-dried
quail egg white treatments, EA was highest overall at pH
8 (41% - 46%), values only slightly lower than that of
chicken egg white (53%) [28]. Overall EA ranges dif-
fered (p < 0.05) between treatments across the studied
pH levels (2 - 10): M1 = 3% to 40%; M2 = 4% to 42%;
M3 = 3% to 43%; M4 = 2% to 45%; and ML = 5% to
15% (Figure 4). At pH levels from 2 to 6, M1-4 exhib-
ited EA values between 8 and 23%. At pH 8 they reached
peak EA and then decreased drastically to the lowest
levels at pH 10. The ML treatment exhibited EA values
(5% - 18%) lower than those of the air-dried treatments
at all pH levels. Conformational stability was a deter-
mining factor in the EA behavior of the dehydrated quail
egg white as shown by their ΔH values. Greater instabil-
ity and emulsifying activity are associated with low ΔH
values, and the relatively lower values for the M1-4
treatments compared to the ML treatment indicate that
the conditions in the air-dried treatments allowed the
protein to unfold within the oil-water interface, thus re-
ducing interfacial tension and aiding in emulsion forma-
tion. According to Chau et al. [29], the viscosity gener-
ated by variation in pH allows formation of a rigid and
elastic protein film appropriate for reducing interfacial
tension and producing high EA values at pH 8.
Emulsion stability was pH-dependent in the dehy-
drated quail egg white (Figure 5). Maximum values were
observed at pH 2 and 4 in M1 (91.81% and 88.98%, re-
spectively), M3 (97.50% and 92.16%, respectively) and
M4 (96.16% and 95.74%, respectively). The amphiphilic
Figure 4. Effect of pH on emulsifying activity (%) in dehy-
drated quail egg white: Air convection-dried treatments M1
(65˚C, 3.5 h), M2 (65˚C, 5 h), M3 (70˚C, 3.5 h) and M4
(70˚C, 5 h); Lyophilized treatment, ML.

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 296
Figure 5. Effect of pH on emulsion stability (%) in dehy-
drated quail egg white: Air convection-dried treatments M1
(65˚C, 3.5 h), M2 (65˚C, 5 h), M3 (70˚C, 3.5 h) and M4
(70˚C, 5 h); Lyophilized treatment, ML.
nature of the proteins in these treatments at these pH lev-
els probably allowed the oil-water interphase to stabilize
because the proteins’ free energy was lower in the inter-
phase than in the aqueous phase. These proteins formed a
highly viscous film in the interphase which concentrated
there and conferred resistance to emulsion particle coa-
lescence. A dramatic decrease in ES occurred at pH 8
(34% to 37%) in the air-dried treatments (M1-4). Emul-
sifying activity was highest at pH 8, the higher EA sug-
gesting that the protein film could not resist the interfa-
cial tension at the oil-water interphase. Formation of a
stable emulsion due to spontaneous and rapid adsorption
of the quail egg white proteins into the interphase de-
pended on the distribution of hydrophobic and hydro-
philic zones on the surface. When hydrophobic zones are
numerous and distributed with enough energy to interact,
the probability of adsorption toward the interphase is
much greater. The number of peptidic segments in the
interphase depends on molecule flexibility. In stable
emulsions, the hydrophobic domains are guided toward
the oleaginous phase. In general, emulsions stabilized by
proteins are affected by the molecular characteristics of
these proteins, as well as by intrinsic factors such as pH,
ionic force, temperature, low-molecular-weight surfac-
tants, oleaginous phase volume, protein type, oil fusion
point, oil incorporation rate and stirrer level. Increased
protein flexibility due to denaturation during the drying
process allowed the quail egg white proteins to make
contact with the oil and water phases, modifying their
conformation and allowing them to locate in the inter-
phase. Partial protein denaturation through drying im-
proves emulsifying properties because it increases mo-
lecular flexibility and superficial hydrophobicity, thus
favoring formation of viscoelastic films in the oil-water
interphase.
The present results indicate that convection air-dried
quail egg white is probably an effective emulsifier, pro-
viding it potential applications in food systems such as
sausage, mayonnaise, and seasonings, and any other prod-
uct in which molecule emulsiondue to increasing tem-
perature occurs before coalescence [10].
3.5. In Vitro Protein Digestibility
In vitro protein digestibility for the air-driedtreatments
ranged from 81.30% in M2 to 83.02% in M3 (Table 3).
These are similar to the 82.4% reported for pasteurized
chicken egg albumen [30], but higher than the 74.51%
for the lyophilized quail egg white (ML). This higher
digestibility in the air-dried treatments may be explained
by elimination of anti-nutritional factors and protein de-
naturation during drying, which would have made the
proteins more vulnerable to enzyme action. Lower ∆H
values (5.51 - 7.79 J/g) in the M1-4 treatments suggest
that conformational changes had occurred in the protein
molecules, making them more susceptible to enzymatic
attachment and therefore producing higher digestibility
values. Lack of anti-nutritional factors in the M1-4 treat-
ments is supported by the absence of bands correspond-
ing to anti-nutritional factors such as ovomucoid (trypsin
inhibitor) and ovoinhibitor (trypsin and chymotrypsin
inhibitor) in the electrophoretic profile. In contrast, a 49
kDa band corresponding to ovoinhibitor was observed in
the ML profile, and is probably the reason for its rela-
tively lower in vitro digestibility.
4. Conclusion
Based on the present results, dehydrated quail egg white
has potential uses in the food industry. Its protein content
is adequate, and convection air drying partially denatured
the protein, preserving fractions such as ovalbumin and
conalbumin while eliminating anti-nutritional factors such
as ovoinhibitor. Denaturation temperature in the dehy-
drated quail egg white corresponded to ovalbumin, the
main protein in egg white. Use of air convection in dry-
ing the egg white required less energy to denaturize the
protein than lyophilization, making it a promising ingre-
dient in baked products. Heat-induced conformational
changes resulted in water-holding capacity values that
Table 3. In vitro digestibility of quailegg white dried by air
convection (M1, 65˚C and 3.5 h; M2, 65˚C and 5 h; M3,
70˚C and 3.5 h; M4, 70˚C and 5 h), and lyophilization (ML).
Treatment Digestibility (%)
M1 82.11 ± 0.00b
M2 81.30 ± 0.09c
M3 83.02 ± 0.18a
M4 82.39 ± 0.27b
ML 74.51 ± 0.18d

Physicochemical and Functional Properties of Dehydrated Japanese Quail (Coturnix japonica) Egg White 297
could make dehydrated quail egg white useful in the
manufacture of desserts and puddings, while the oil-
holding capacity values indicate it would provide a non-
greasy sensation in fried products. Both pH and the am-
phiphilic behavior (polar/nonpolar) of the dehydrated
quail egg white proteins affected its foaming behavior,
with the highest foaming capacity at acid pH and the
highest foaming stability at alkaline pH. The dehydrated
quail egg white effectively formed oil-water emulsions,
particularly at pH 8, but its emulsion stability was high-
est at pH 2, making it useful in food systems such as
sausage. Air convection drying increased in vitro digesti-
bility of the quail egg white by eliminating antinutritional
factors and exposing its proteins to enzymatic action.
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