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8/11/2019 Characterization of Some Functional Properties of Edible Films
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Characterization of some functional properties of edible filmsbased on muscle proteins of Nile Tilapia
T.M. Paschoalick, F.T. Garcia, P.J.A. Sobral*, A.M.Q.B. Habitante
Universite de sao Paulo, FZEA-ZAZ-CP, P.O. Box 23, Pirassununga, SP 13630-900, Brazil
Received 19 July 2002; revised 18 November 2002; accepted 11 December 2002
Abstract
Recently, it was observed that the myofibrillar as well as the sarcoplasmatic proteins obtained from fish are capable to form films. The
objectives of this work was to elaborate and to characterize the water vapor permeability (WVP), the color and opacity, the mechanical
properties, and the viscoelastic properties of films made with muscle proteins of Nile Tilapia (Oreochromis niloticus). The proteins were
obtained by finely grinding the fish muscle, followed by separation of the connective tissue and freeze-drying after liquid nitrogen freezing.
The films were prepared from filmogenic solutions (FS) by the casting technique, as follows: 1 g of protein/100 g of FS, 1565 g of
glycerin/100 g of protein, pH 2.7 (acetic acid) and FS thermal treatment of 40, 65 and 90 8C/30 min. The WVP was determined by a
gravimetric method, and the color and opacity of the films were determined with a colorimeter (model MiniScan XE, HunterLab). The
mechanical properties, force and elongation at puncture, were determined with the help of a texturometer (model TA.XT2i, TA Instruments),
at 25 8C. The viscoelastic properties were determined by dynamic mechanical analysis, with a DMA2980 apparatus (TA Instruments)
operating in the frequency scanning mode, at 30 8C, with the viscoelastic properties being calculated at 1 Hz. It was observed that the WVP
increased with the concentration of glycerin Cg as expected and that an increase in temperature of FS thermal treatment also caused an
increase in the WVP of the films. The color and the opacity of the films decreased with Cg;and were proportional to the thermal treatment
temperature of the FS. In general, it was observed that increasing the Cgprovoked linear reduction of puncture force and an increase on the
elongation at break, due to its plasticizer effect. It was also observed that increasing theCg caused depression on both the storage and loss
moduli values but increased the tand:The presence of sarcoplasmatic proteins did not affect the quality of functional properties of films based
on muscle proteins of Nile Tilapia.
q 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Edible films; Myofibrillar protein; Water vapor permeability; Color; Mechanical properties; Viscoelastic properties; Tilapia
1. Introduction
In the middle of the nineties, Cuq, Aymard, Cuq, and
Guilbert (1995) working with Atlantic sardines, demon-
strated that the myofibrillar proteins had the capacity to
form transparent and resistant films. Since then, other works
were done with myofibrillar proteins from fish (Cuq et al.,
1995; Cuq, Gontard, Cuq, & Guilbert, 1996a,b; Cuq,
Gontard, Cuq, & Guilbert, 1997a; Cuq, Gontard, &
Guilbert, 1997b; Monterrey-Quintero & Sobral, 1999,
2000; Sobral, 2000) and beef (Ocuno & Sobral, 2000;
Sobral, Ocuno, & Savastano, 1998; Souza, Sobral, &
Menegalli, 1997; Souza, Sobral, & Menegalli, 1998).
To be used in the film elaboration process, the
myofibrillar proteins have to be prepared adequately.After slaughter and evisceration, the muscles are grounded
and washed conveniently to eliminate the sarcoplasmatic
proteins. After that, the material is minced and passed
through a screen, to separate the connective tissue (insoluble
proteins) (Cuq et al., 1995; Monterrey-Quintero & Sobral,
2000).
For making films based on myofibrillar proteins or on
other macromolecules, the utilization of plasticizers is
necessary to reduce brittleness, i.e. to improve the work-
ability of the material. The plasticizers, which are generally
polyols, reduce the intermolecular interactions between
adjacent chains of the biopolymer, resulting in an increase
of mobility of these chains and consequently, in flexiblefilms (Gennadios, McHugh, Weller, & Krochta, 1994;
0268-005X/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0268-005X(03)00031-6
Food Hydrocolloids 17 (2003) 419427www.elsevier.com/locate/foodhyd
* Corresponding author. Fax: 55-19-35654114.
E-mail address:[email protected] (P.J.A. Sobral).
http://www.elsevier.com/locate/foodhydhttp://www.elsevier.com/locate/foodhyd8/11/2019 Characterization of Some Functional Properties of Edible Films
2/9
Torres, 1994). As a consequence, at a macroscopic level, a
reduction in the mechanical resistance and an increase in the
elasticity and water vapor permeability (WVP) of the films
may occur.
Considering that this increase in the WVP is undesirable
for the guaranty of quality of some packaged foods,
Sothornvit & Krochta (2000a,b) recommended another
approach for the reduction of intermolecular forces in the
case of whey protein isolate based films: reduction of the
molecular mass of whey proteins by the utilization of
proteins with certain degree of hydrolysis. According to
these authors, this would make the reduction of the
utilization of plasticizers possible.
In addition to these studies on molecular mass reduction
of whey proteins, Japanese researchers were able to
elaborate films with the sarcoplasmatic proteins (whichhave a low molecular weight) from fish muscles (Iwata,
Ishizaki, Handa, & Tanaka, 2000; Tanaka, Iwata, &
Sanguandeekul, 2001). Iwata et al. (2000) worked with a
unique content of plasticizer, which could be considered as
elevated (50 g of glycerol/100 g of proteins), and studied the
effect of protein concentration, pH and thermal treatment of
the filmogenic solution (FS) upon certain properties of the
films. On the other side, Tanaka et al. (2001) studied the
effect of the type and concentration of the plasticizer on
some functional properties of these films.
Considering that the sarcoplasmatic proteins also have
the capacity to form a continuous matrix, it may be
supposed that edible films can be produced by the mixtureof these proteins with myofibrillar proteins, avoiding the
washing process of the muscles. So, the objectives of this
work was the elaboration of edible films based on muscle
proteins of Nile Tilapia (without the proteins of stroma),
and the characterization of the WVP, color, opacity,
mechanical and viscoelastic properties of these films as a
function of the concentration of plasticizer and the thermal
treatment of the FS.
2. Material and methods
2.1. Proteins preparation
The proteins were prepared initially by grounding the
deboned muscle (filets) of Nile Tilapia (Oreochromis
niloticus), ante rigor mortis. A paste was obtained using a
food processor for 10 min, adding ice to avoid the heating of
the material. The proteins of stroma were eliminated using a
screen (ABNT 100). The fine paste obtained was freeze-
dried after quench freezing in liquid nitrogen, in a
laboratory scale freeze-drier (Heto, model FD3). The
freeze-dried muscle proteins were grounded and tamized
in a sieve with an opening of 0.18 mm (ABNT 80),
obtaining a homogeneous powder.
This powder, that constituted the muscle protein of NileTilapia (MPNT), was analyzed to determine the humidity,
lipids and proteins content, using classical methods (AOAC,
1995). The amino acid composition of MPNT was
determined after acid hydrolysis, by ionic exchange
chromatography with derivatization post-column with
ninhidrin (Monterrey-Quintero & Sobral, 2000). These
analyses were realized in duplicate.
2.2. Films elaboration
The MPNT films were prepared by drying the FS,
conveniently applied on a support. FS were prepared under
the following conditions: protein, 1 g of MPNT/100 g of SF;
plasticizer, 15 65 g glycerin/100 g protein; pH maintained
at 2.7 using acetic acid, and thermal treatment of 40, 65 or
90 8C/30 min.
Initially, the adequate amounts of glycerin and water
were added in a beaker, followed by adding MPNT, under
moderate agitation obtained with a magnetic mixer (Hanna,
HI 190 M). After that, the acetic acid was added to reduce
the pH of FS. The pH was measured every time with the
help of a digital pH meter (Tecnal, TEC-2). The FS was
thermally treated in a water bath with digital control
(^0.5 8C) of temperature (Tecnal, TE184), kept at 40, 65 or
90 8C during 30 min. Finally, the FS was conveniently
applied on Plexiglas plates (12 12 cm2) previously
prepared and dehydrated in an oven with air renewal and
circulation (Marconi, MA037), with PI control (^0.5 8C) of
temperature, at 30 8C and room relative humidity (5565%), for 24 h (Monterrey-Quintero & Sobral, 2000).
Weighting (^0.0001 g) of all films components was
accomplished using an analytical scale (Scientech, SA210).
For functional properties characterization, the films were
conditioned at 2225 8C and 58% of relative humidity, in
desiccators with saturated solution of NaBr, for 7 days.
Then, the thickness of the films was measured averaging
nine different positions, with a digital micrometer
(^0.001 mm) with a 6.4 mm diameter probe. All the
characterizations were accomplished in climatized room
conditions (T 2225 8C and relative humidity between
55 and 65%). Only one sample per film was taken for test,
i.e. each film originated only one replicate. All tests weremade in quadruplicate.
2.3. Water vapor permeability
The WVP was determined according to a method
proposed by Gontard, Guilbert, and Cuq (1993). The
edible films were firmly fixed onto the opening of cells
containing silica gel. These cells were placed in
desiccators with distilled water maintained in an oven
(Marconi, model MA415/S) with electronic control of
temperature (^0.2 8C), at 25 8C. The cells were weighted
(^0.01 g) daily, in a semi-analytic balance (Marte,AS2000), for 8 days. The WVP was calculated with
T.M. Paschoalick et al. / Food Hydrocolloids 17 (2003) 419427420
8/11/2019 Characterization of Some Functional Properties of Edible Films
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Eq. (1) (Gontard et al., 1993)
WVPw
tA
x
DP 1
where x is the average thickness of the MPNT films, A is
the permeation area (12.29 cm2), DP is the difference of
partial vapor pressure of the atmosphere with silica gel
and pure water (2642 Pa, at 22 8C), and the term w=t was
calculated by linear regression from the points of weight
gain and time, in the constant rate period.
2.4. Color
The color of the MPNT films was determined with a
colorimeter (HunterLab, model Miniscan XE), working
with D65(day light) and a measure cell with an opening of30 mm, being used the CIELab color parameters: Lp; from
black (0) to white (100);ap;from green (2) to red (); and
bp; from blue (2) to yellow ( ) (Gennadios, Weller,
Hanna, & Froning, 1996; Kunte, Gennadios, Cuppett,
Hanna, & Weller, 1997). The MPNT films were applied in
the surface of a white standard plate, the color parameters
were measured, and transferred and calculated (Eq. (2)) in
real time for a microcomputer. The films color was
expressed as difference of color DEp
DEp
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiDLp2 Dap2 Dbp2
q 2
where DLp
; Dap
and Dbp
are the differentials between thecolor parameter of the samples and the color parameter ofwhite standard (Table 1).
The color of the freeze-dried MPNT was also determined
using the same colorimeter (Table 1), but in this case, the
powder was put in a quartz sample cup.
2.5. Opacity
The opacity of the MPNT films was determined
according to a Hunterlab method (Sobral, 2000), with the
same equipment for color measures, also operating in the
reflectance mode. The opacity Y of the samples was
calculated as the relationship among the opacity of eachsample on the black standard Yb and the opacity of each
sample on the white standard Yw: This calculation Y
Yb=Yw was made automatically by the Universal Software
3.2 (Hunterlab Associates Laboratory).
2.6. Mechanical properties
The force and the deformation at breaking point of the
film were determined in puncture tests (Gontard et al.,
1993). The films were fixed in a 52.6 mm diameter cell and
perforated by a 3 mm diameter probe, moving at 1 mm/s.
These tests were accomplished with an instrument of
physical measures TA.XT2i (SMS, Surrey, UK). The
puncture force F and the displacement of the probe D
at break were determined with the software Texture Expert
V.1.15 (SMS) directly from the force X displacement
curves. The puncture deformationDl0=l0can be calculated
with D considering that stress was perfectly distributed
along the film at breaking point (Sobral, Menegalli,
Hubinger, & Roques, 2001).
2.7. Viscoelastic properties
The viscoelastic properties of the MPNT films were
characterized by dynamic mechanical analysis, using an
equipment DMA TA2980 controlled by a TA5000 module
(TA Instruments, New Castle, DE, USA), and with the film
grips clamps that allowed possible uniaxial traction tests.
The analysis were carried out in the frequency scanning
(0.01 200 Hz) mode, with constant temperature (30 8C),
the amplitude of deformation (0.2%) and the flow of N2in
the measure cell (1180 ml/min).
Rectangular samples of about 19 mm 5 mm, were
submitted to oscillatory traction (senoidal stress applied)analysis, obtaining the storage modulus E0; the loss
modulus E00 and the phase angle tand E00=E0 in
function of the frequency. For the study of the plasticizing
effect of glycerin on viscoelastic properties,E0;E00 and tan d
were calculated from DMA results at 1 Hz frequency
(Lazaridou & Biliaderis, 2002), with the software Universal
Analysis V1.7F (TA Instruments).
2.8. Statistical analysis
The linear regressions necessary to the calculation of
WVP R2 . 0:98; were accomplished with Excel 2000
software (Microsoft, Seattle, WA). All linear and non-linearregressions for the functional properties were done with the
Microcal Origin V.4.0 software (Microcal Software, North-
ampton, USA).
3. Results and discussions
The chemical analysis made in samples of freeze-dried
muscle proteins of Nile Tilapia indicated the following
average composition: 80% protein, 7% humidity and 8%
lipids. The protein content obtained was lower than that
determined by Monterrey-Quintero and Sobral (2000), but
of the same order of that obtained by Sobral (2000), whodetermined concentration of proteins as 93.2 and 85%,
Table 1
Color parameters of white standard plate and of freeze-dried MPNT
Lp ap bp
White standard 94.89 20.78 1.43
Freeze-dried MPNT1 90.02 20.92 11.34
D2 23.72 0.02 98.21
1 Muscle protein of Nile Tilapia.
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respectively, working with myofibrillar proteins of the same
species of Tilapias used in this work. However, the results of
this study were closer to the minimum amounts encountered
by Candido (1998): 84.1 97.7% proteins, also obtained
with samples of freeze-dried myofibrillar protein of Nile
Tilapia. The content of fat obtained was also closer to that
obtained by Sobral (2000) and to the maximum amounts
obtained by Candido (1998), which were 6.7 5.1%,
respectively; while Monterrey-Quintero and Sobral (2000)
obtained 2.4%.
The amino acid composition of the MPNT is
presented in Table 2. It can be observed that the polar
ionic amino acids are in high concentration (aspartic
acid, glutamic acid, arginine and lysine), such as in the
myofibrillar proteins obtained by Monterrey-Quintero and
Sobral (2000). The difference between the composition ofthe MPNT and that of myofibrillar proteins may be
explained by the presence of sarcoplasmatic proteins
(Candido, 1998).
The freeze-dried proteins obtained showed an inter-
esting fluidity, i.e. without a characteristic of agglomera-
tion. However, they were not as bright as the myofibrillar
proteins of Nile Tilapia, obtained by Monterrey-Quintero
and Sobral (2000), which were almost white.
In general, the films prepared with these proteins were
well flexible and easily handled, with a good visual aspect.
The average thickness (^standard deviation) of all the films
utilized in the characterization of optical and viscoelasticpropert ies and WVP was 0.076 ^ 0.002 mm at
40 8C/30 min, 0.077^ 0.003 mm at 65 8C/30 min, and
0.091^ 0.005 mm at 90 8C/30 min. In the case of charac-
terization of the mechanical properties, the average thickness
(^standard deviation) of the films was the following:
0.081^ 0.004 mm at 40 8C/30 min; 0.083 ^ 0.002 mm at
65 8C/30 min; and 0.084 ^ 0.008 mm at 90 8C/30 min.
3.1. Water vapor permeability
The results of the WVP tests of the films elaborated with
1 g of MPNT by 100 g of SF and treated at 40, 65 and 90 8C,
are shown in Fig. 1. As expected, in general the WVP
increased with the increment of Cg: This behavior is
common in hygroscopic edible films and it is well-explained
in terms of molecular mobility in the specialized literature
(Cuq et al., 1997a; Gennadios et al., 1994; McHugh, Aujard,
& Krochta, 1994; Ocuno & Sobral, 2000; Sobral et al.,
2001; Sothornvit & Krochta, 2000a; Tanaka et al., 2001;
Torres, 1994).In general, the variation of the experimental data of WVP
of the films as a function of the Cg; followed a parabolic
behavior being well-represented by a second order poly-
nomial equation, with satisfactory adjustments (Table 3).
On the contrary,McHugh et al. (1994)determined that the
WVP of gluten films, plasticized by glycerin, determined at
25 8C, increased linearly R2 0:966 with the concen-
tration of plasticizer. This same behavior has been seen by
Gontard et al. (1993)also with gluten films plasticized with
glycerin.
The study of the WVP as a function of the effect of
thermal treatment was prejudiced by the dispersion of the
experimental data. However, it could be suggested that the
more intense SF thermal treatment (90 8C/30 min) pro-
portioned more permeable films.
The films produced in this work showed to be more
permeable to water vapor than those of myofibrillar proteins
of Atlantic sardines elaborated by Cuq et al. (1997a),
who determined the WVP in the order of 2:7 1024 g mm
h21 m22 Pa21 in films with 40% of glycerin, T 20 8C,
pH 3.0 and 2.6 mg of proteins/cm2, and those of
Table 2
Amino acid composition (g amino acids/100 g of protein) for Tilapia
proteins
Muscle proteins1 Myofibrilar proteins2
Alanine 5.50 (0.12) 5.00
Arginine 6.15 (0.00) 2.71
Aspartic acid 9.20 (0.03) 12.08
Glutamic acid 14.69 (0.03) 12.20
Phenylalanine 3.55 (0.08) 4.07
Cystine 0.78 (0.06) 0.67
Glycine 3.97 (0.03) 4.35
Histidine 2.05 (0.03) 2.57
Isoleucine 4.19 (0.14) 5.86
Leucine 7.35 (0.04) 8.36
Lysine 8.65 (0.07) 10.30
Methionine 2.30 (0.00) 3.15
Proline 3.03 (0.06) 8.95
Serine 3.48 (0.02) 4.41
Tyrosine 2.84 (0.06) 3.43
Threonine 4.18 (0.01) 4.63
Valine 4.29 (0.10) 6.22
1 Average (standard deviation).2 FromMonterrey-Quintero and Sobral (2000).
Fig. 1. Water vapor permeability of films based on the muscle protein of
Nile Tilapia: (W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
T.M. Paschoalick et al. / Food Hydrocolloids 17 (2003) 419427422
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myofibrillar proteins of Nile Tilapia plasticized by 45% of
glycerin, pH 2.7 and treated at 40 8C/30 min, in which the
WVPcould be calculated as 4.8 1024 g mm h21 m22 Pa21
(x 0:077 mm) and 5.4 1024 g mm h21 m22 Pa21
(x 0:087 mm) (Sobral, 2000). In the present work, the
films with glycerin concentration around 40% presented
Pva . 6 1024 g mm h21 m22 Pa21. These films were
more permeable to water vapor, possibly due to the
plasticizing effect of the proteins with low molecular weight
present in the freeze-driedproduct, contraryto the filmsbased
only on myofibrillar proteins with fat content of the same
order (Cuq et al., 1997a; Sobral, 2000).
3.2. Color
The results of the determination of film color, expressed
as the difference of color DEp in relation to the white
standard plate, are shown inFig. 2. It can be observed that
the films produced in this study, and which SF was treated at
30 and 65 8C/30 min, showed a DEp which decreased
linearly (Table 4) with the increment ofCg;while in the case
of SF treated at 90 8C/30 min, this behavior is the opposite.
The reduction of films color with the increase ofCg
should
probably be an effect of the dilution of the proteins because
glycerin is an uncolored compound. This means that as the
glycerin concentration increases, the film should present
less and less color in such a manner that the difference of
color will tend to zero. On the other hand, the increase of
DEp; with the concentration ofCg;at 90 8C/30 min, can be
explained by some alteration of the macromolecular
structure which may have occurred, however, more analyses
are necessary to confirm this explanation. In general, it
could be suggested that the increase of temperature caused a
slight increase of films color, possibly due to the occurrence
of reaction among the glycerin molecules and the reactive
group of lysine.Comparing the behaviors and the values of DEp
presented in Fig. 2 with the results (not shown) of the
differences of chromeDLp;Dap;Dbp;it could be suggested
that the behavior of color difference was mainly due to the
variation of chromebp:On another side, the initial values of
DEp were well related with the color DEp 11:04 of
freeze-dried MPNT. The important difference noted in the
parameter bp (Table 1) indicated that the films color was
tending to yellow.
Using equations determined bySobral (2000), for films
elaborated with 1 g of myofibrillar proteins/100 g of SF,
45% of glycerin, pH 2.7 and SF thermal treatment of
40 8C/30 min, it can be calculatedDEp values around 7 and8 for films with 0.077 and 0.087 mm of thickness,
respectively. These values were comparable to those
determined in films of this work elaborated with 45% of
glycerin and treated at 40 8C/30 min (Fig. 2). The increase
Table 3
Parameters of the second order polynomial equation Y A BX CX2
calculated by non-linear regression
Properties Thermal
treatment
(8C/30 min)
A B C R2
WVP 40 3.719 0.097 23.647 1024 0.969
65 1.132 0.192 21.460 1023 0.722
90 20.227 0.371 23.700 1023 0.885
E0 40 935.98 224.130 0.187 0.963
65 974.62 227.103 0.216 0.984
90 1128.92 236.636 0.321 0.961
E00 40 100.23 21.672 0.009 0.947
65 118.02 22.731 0.020 0.991
90 150.67 24.333 0.036 0.960
Fig. 2. Color difference of films based on the muscle protein of Nile Tilapia:
(W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
Table 4
Parameters of the linear equation Y A BX calculated by linear
regression
Properties Thermal treatment
(8C/30 min)
A B R2
DEp
40 10.403 20.055 0.83465 14.425 20.110 0.929
90 9.201 0.082 0.571
Opacity 40 6.046 20.036 0.754
65 8.721 20.043 0.335
90 7.575 20.096 0.921
Puncture force 40 7.45 20.078 0.978
65 9.54 20.115 0.951
90 5.81 20.059 0.972
Puncture deformation 40 2.99 0.054 0.674
65 1.98 0.098 0.908
90 2.16 0.068 0.738
tand 40 0.110 1.47 1023 0.961
65 0.112 1.40 1023
0.99190 0.117 1.85 1023 0.966
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of protein concentration in SF or treatment temperature
provoked an increase of film color in relation to those
elaborated with myofibrillar proteins of Nile Tilapia
(Sobral, 2000). In addition, the film color elaborated
in this work was higher than that based on egg albumins
DEp 1:72:3;x 0:099 mm (Gennadios et al., 1996)
and pigskin gelatin DEp , 3;x , 0:090 mm (Sobral,
1999). However, it was comparable to the color of soybean
protein films DEp 8:511:6;x 0:0540:065mm
(Kunte et al., 1997).
3.3. Opacity
With relation to the opacity, it could be observed that it
also decreased with the increase ofCg(Fig. 3), possibly due
to the diluting effect of glycerin, which is a transparentcompound (low opacity). The opacity behavior in function
of the Cg could be represented by the linear equation with
satisfactory regression coefficients (Table 4), except in the
films treated at 65 8C/30 min due to data dispersion,
problem reported in some works about this property (Sobral,
1999, 2000).
The opacity of films produced in this work was greater
than the opacity of pigskin gelatin films Y, 0:5;x , 0:1
mm; which were extremely transparent, but were compar-
able to the opacity of films based on myofibrillar proteins of
Nile Tilapia Y, 3:5;x , 0:090 mm; especially in the
case of films elaborated with more than 40% of glycerin.
3.4. Mechanical properties
The mechanical properties determined by perforation
tests, also were influenced by Cg; as expected. InFig. 4, it
could be observed that the increase ofCgprovoked a linear
reduction (Table 4) of the puncture force, in the domain of
Cg studied. This behavior was according to Cuq et al.
(1997a) and Monterrey-Quintero and Sobral (1999), who
also observed a linear reduction of puncture force of similar
films, between 0 and 40 g of glycerol/100 g of myofibrillar
protein of Atlantic Sardine, and 30 and 70 g of glycerol/
100 g of myofibrillar proteins of Nile Tilapia, respectively.
On the other hand,Sobral et al. (1998)observed that the
puncture force in perforation tests with films based on
myofibrillar protein from beef and acidified by acetic or
lactic acid, was reduced exponentially with the Cg between
25 and 100% of glycerin. This same exponential behavior
was observed byGhorpade, Gennadios, Hanna, and Weller
(1995) in soybean protein films and by Sothornvit and
Krochta (2001) in films ofb-lactoglobulin, both working
with traction tests.
It can be observed in the work ofMonterrey-Quintero
and Sobral (1999), that the films of 1.25% of myofibrillar
protein of Nile Tilapia in SF and with 30 and 50% glycerin,presented a puncture force of about 6.7 and 4.3 N,
respectively. This was equivalent to that of the films
produced in this project under similar conditions. However,
all these films were less resistant than the films of
myofibrillar protein of beef, with 30% of glycerin and
acidified by acetic acid, which presented a puncture force
around 8.7 N. Possibly, these disagreements may be
explained by differences in the amino acids compositions
between these two myofibrillar proteins that caused
different macromolecular interactions.
It can be observed inFig. 5that the puncture deformation
of the films increased linearly (Table 3) with Cg: This
behavior agrees with the results observed by Sobral et al.
(1998), working with films of myofibrillar protein of bovine
meat and acidified by acetic acid. However, Gontard et al.
(1993) observed an increase of 6 20% in the puncture
deformation of films based on gluten, caused by the increase
of 1633 g of glycerin/100 g of dry material, following a
segment of parabola, whileCuq et al. (1997a), working with
films of myofibrillar protein of Atlantic Sardine, observed a
sigmoid behavior, for values of Cg lower than 40%.
Fig. 3. Opacity of films based on the muscle protein of Nile Tilapia: (W)
40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
Fig. 4. Puncture force of films based on the muscle protein of Nile Tilapia:
(W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
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The films of MPNT produced in this work presented values
of puncture deformation slightly lower to that of the
respective films of myofibrillar proteins of Nile Tilapia
(Monterrey-Quintero and Sobral, 1999). However, they were
equivalent to films of myofibrillar protein of Atlantic Sardine
at similar conditions of formulation (Cuq et al., 1997a).
3.5. Viscoelastic properties
The viscoelastic properties of the films of MPNT varied
subtly as a function of the oscillation frequency of the strain
applied by the dynamic-mechanical analyzer (except
between 100 and 200 Hz due to resonance problem).
Examples of responses obtained during analyses at 30 8C
of the films elaborated with 15% of glycerin and thermal
treatment of 40 8C/30 min, and 65% of glycerin and thermal
treatment of 90 8C/30 min could be observed in Fig. 6: E0
was always greater thanE00 in the entire frequency domain,
which is a characteristic of physical gels; and tan d
decreased smoothly with the increase of frequency, while
E0 increased after 0.1 Hz, a typically post glass transition
material behavior (Ferry, 1980). Effectively, based on the
glass transition of the films of myofibrillar protein of Nile
Tilapia (Sobral, Monterrey-Quintero, & Habitante, 2002), it
could be supposed that under the conditions of these
analyses, the films of this work were in the rubbery state. A
similar behavior of E0; between 0.1 and 100 Hz, could be
observed in the work ofLazaridou and Biliaderis (2002).
The values ofE0 andE00 calculated at 1 Hz, are presented
in Figs. 7 and 8, respectively, as a function of Cg: These
properties decreased with the increase of Cg due to the
plasticizing effect of glycerin. In general, the values ofE0
andE00 dropped around 80 and 70%, respectively, following
a parabolic segment in both the cases. Thus, these behaviorscould be represented by a second order polynomial equation
with very good regression coefficients (.0.94) observed in
Table 3.
It can be observed inFigs. 7 and 8, that the increasing of
temperature of thermal treatment caused more important
reduction in E0 and E00 as a function of Cg: In molecular
terms, this would occur due to possible reduction of
molecular weight of proteins, which was not probable.
Normally, heating of SF could provoke the formation of
aggregates by disulphide bonds involving residues of amino
acids with sulfur (Perez-Gago & Krochta, 2001; Vachon
et al., 2000), which might implicate on an increment of
apparent molecular weight of the protein in such a way that,
for a same concentration of glycerin, this film would be less
plasticized. This way, the observed behavior, contrarily to
the one described, was difficult to explain.
The results of the last viscoelastic property, the phase
angle, well called tand and calculated as the relation
betweenE00 andE0;are shown inFig. 9. It could be observed
that, contrarily toE0 andE00; tan dincreased with the Cg in
Fig. 5. Puncture deformation of films based on the muscle protein of NileTilapia: (W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
Fig. 6. Examples of results of dynamic mechanical analysis of films based on the muscle protein of Nile Tilapia: () Cg 15%; 40 8C/30 min; (- - -)
Cg 65%;90 8C/30 min.
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all the thermal treatments. This could be explained,
according toFerry (1980), by the fact that both the solvent
(glycerin) and the solute (proteins) contributed toE00;while
only the solute contributed to E0: This way, the greater
influence (reduction) of glycerin onE0;caused the increment
in tan d:
Moreover, considering that the reductions ofE0 and E00
followed the same behavior, evidently with different
intensities, the consequent increase in tan d was linear. It
could be observed in Table 4, that the adjustments of the
linear equation to the experimental points, in general, werevery good with only one value ofR2 lower than 0.96.
The values of the viscoelastic properties (E0; E00 and
tand) determined in this work, were of the same order of
magnitude of the values observed in the papers ofCuq et al.
(1997b), who worked with films of myofibrillar protein of
Atlantic Sardine, and Cherian, Gennadios, Weller, and
Chinachoti (1995) and Gontard and Ring (1996), who
worked with gluten films containing various plasticizers. In
general, it is very difficult to compare these types of results,
because most of the authors worked with temperature
scanning, and above all, because they verified the plasticizer
effect of the sample humidity, and not necessarily of the
added plasticizer agent, as in the present work.
4. Conclusion
The utilization of muscle proteins of Nile Tilapia that is,
including the sarcoplasmatic proteins and excluding theproteins from stroma, for the elaboration of the edible films
with glycerin is an alternative for the utilization only of the
myofibrillar proteins, once that reduces the washing stage of
the ground muscle. By this way, the industrial process can
be considered starting from fish collecting, slaughter,
cleaning, evisceration and filleting, where the fillet will be
directly taken to the elaboration line of films, starting by
grinding.
The presence of sarcoplasmatic proteins caused little
alteration of the functional properties of films, in relation to
the films elaborated only with myofibrillar proteins. But, the
WVP, the color, the opacity, and the mechanical and
viscoelastic properties of the films elaborated in this workwere of the same order of magnitude of those based on the
myofibrillar protein of Nile Tilapia. Moreover, it should be
emphasized that the differences of the functional properties
would not constitute necessarily a disadvantage, because
there could be a demand for packages with these
characteristics.
Acknowledgements
To FAPESP, for the financial support (00/14091-8,
02/03203-5) and IC fellowship of TMP (00/14466-1); to
CAPES for the MS fellowship of FTG and to CNPq for theresearch fellowship of PJAS (522953/95-6).
Fig. 7. Storage modulus, at 1 Hz, of films based on the muscle protein of
Nile Tilapia: (W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
Fig. 8. Loss modulus, at 1 Hz, of films based on the muscle protein of Nile
Tilapia: (W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
Fig. 9. Phase angletand;at 1 Hz, of films based on the muscle protein of
Nile Tilapia: (W) 40 8C/30 min; (A) 65 8C/30 min; (K) 90 8C/30 min.
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