Characterization of Some Functional Properties of Edible Films

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).
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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


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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.

T.M. Paschoalick et al. / Food Hydrocolloids 17 (2003) 419427 421


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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.



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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.



8/9

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


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




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Characterization of Some Functional Properties of Edible Films

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