J. SASJ, Vol. 33, No. 2
2002. 9, 91-101
Original
Production of Biodegradable Films from
Mungbean and Soy proteins (Part 2)-Modhication of mungbean and soy protein film propenies-*
Wimolrat CHEAPPIMOLCHAI**, Yutaka ISHIKAWA***,
Keo INTABON*** and Takaaki MAEKAWA***
*Presented at the SASJ Annual Meeting in 2001.**Doctoral Program, Institute of Agricultural Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8577, Japan
***Institute of Agricultural and Forest Engineering, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8577, Japan
Abstract
The properties of mungbean protein film plasticized with glycerol have been previously shown to have a low
tensile strength (TS) and high water vapor permeability (WVP) making the film unsuitable for commercial usage as
a packaging material. In this study, improvement of these properties of mungbean protein film and soy protein film
was carried out by two methods: incorporation of starch (tapioca, corn, wheat and potato) and also by using various
other types of plasticizer than glycerol [sorbitol, ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol
(TEG)].TS of the protein films mixed with starch were improved fbr all the starches tested; TS of mungbean protein
film was increased from 0.244 to a rahge of 2.55-3.32 MPa and TS of soy protein film was increased from 0.921 to a
range of 4.91-6.53 MPa. The decrease of WVP value which indicates an improvement of the film's barrier properties,
of the mungbean protein-tapioca starch film was decreased from 22.1 to 5.63×10-11 g/m. s. Pa. WVP of the soy
protein-wheat starch film decreased from 10.7 to 7.01×10-11 g/m. s. Pa. The elongation of film was not improved by
this method. The TS and WVP of films were improved by using sorbitol as a plasticizer. TS of sorbitol-plasticized
film increased from 0.921 to 3.52 MPa for soy protein and increased from 0.264 to 0.95 MPa for mungbean protein
film. WVP of sorbitol-plasdcized film decreased from 8.96×10-11 to 1.16×10-11 g/m. s. Pa for soy protein. WVP of
mungbean protein film plasdcized with sorbitol decreased from 15.05×10-11 to 1.9×10-11 g/m. s. Pa. EG, DEG and
TEG also can improve TS but WVP of film plasticized with these plasdcizers is high.
Keywords: Biodegradable film, mungbean protein, soy protein, starch, plasticizer
Introduction
There has been a continuing interesting in the
development of plastic materials that are biodegrad-
able and can be produced from non-petroleum based
resources. One possibility is by using natural polymers
based on starch, protein and cellulose. Proteinaceous
materials have the ability to form films which have
potential applications in food packaging. Development
of protein films has received considerable attention in
recent years (Gontard et al., 1992; Gennadios et al.,
1994).
Soy protein film has been studied for use in food
and non-food purposes. Selected mechanical and
barrier properties of soy protein film along with
properties of commonly used polymeric packaging
films have been reported by Gennadios et al.(1993a).
Commercialization of soy protein films requires
improvements of its mechanical and barrier properties.
A variety of methods have been used to modify soyReceived on November 26, 2001Correspondence of Author: [email protected]
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92 Wimolrat CHEAPPIMOLCHAI, Yutaka IsHIKAWA, Keo INTABON and Takaaki MAEKAWA
protein film properties including treatment with alkali
(Brandenburg et al., 1993), treatment with propylene
glycol alginate (Shih, 1994), enzymatic treatment with
peroxidase (Stuchell and Krochta, 1994).In Thailand, mungbean vermicelli which is made
from the starch of mungbean (Phaseolus radiatus L.) is
an important agro-industrial product (Prabhavat, 1988).
Mungbean vermicelli is mainly consumed by Thai and
oriental people such as Chinese and Japanese.
Mungbean protein from the vermicelli industry waste
can be readily extracted by precipitation and currently
the extracted protein is mostly used as an animal feed.
In a previous study, Wimolrat et al. (2000) examined
the potential use of this protein source as a basic
ingredient for the production of biodegradable films,
the development and formation of a mungbean protein
film by a casting method, and the effect of film
formation parameters such as the glycerol content.
However, the properties of mungbean protein film
especially the tensile strength (TS) and water vapor
permeability (WYP) of film were weaker compared to
soy protein film.
Proteins bond by intermolecular interactions
(electrostatic, hydrogen and hydrophobic). The protein
structure and conformation influence the intermolecular
interactions necessary for the formation of a gel-type
network, which is then dehydrated to form a film
(Miller and Krochta, 1997). The strength of protein-
protein and protein-water interactions determine the
properties of the materials and these can be controlled
by means of altering the film forming conditions and
the film composition such as by the addition of
additives and plasticizers. Plasticizers decrease the
protein interactions and increase the polymer chainmobility and intermolecular spacing, decreasing also
glass transition (Tg) of the protein. A plasticizer is
required to avoid brittleness and to increase the
flexibility of film. However, the addition of a plasticizer
typically results in a reduction of the barrier properties
(WVP) of the film. Plasticizers must have a low molecular
weight, high boiling point, compatibility with the polymer,
and be soluble in the solvent (Banker, 1966). Hydrophilic
plasticizers, e. g., glycerol, sorbitol or polyethylene
glycol are generally used to improve the tensile
strength and elongation of protein films. A plasticizer's
composition, size and shape influence its ability to
disrupt the protein-chain hydrogen bonding. Thus, the
selection of a suitable plasticizer is one of the important
factors for producing a protein film.
Starch, the most abundant and lowest cost natural
polymer, is utilized in many food and industrial
products. Starch has been used in non-food products
such as paper, textiles, adhesives and as a raw material
in fermented liquors. Another potential application for
starch is as single-use compostable plastics. Most of the
recent research has been focused on the conversion of
starch into thermoplastic materials by the extrusion
process. However, another means of preparing films,
i. e., from a gel solution, has been used as an attractive
alternative (Lourdin et al., 1995).
Compared with other films, such as wheat gluten,
corn zein (Aydt et al., 1991), whey protein isolate
(McHugh and Krochta, 1994) and methylcellulose film
(Park et al., 1994), films made from mungbean and soy
protein are characterized by lower tensile strength and
elongation at break, and rather high water vapor
permeability. For these reasons, the present research
was focused on the possibility of improving the
mechanical properties as well as the barrier properties
of these films. Because starch has the ability to
contribute structure in a biopolymer system, the
improvement of the mechanical properties of the
protein films might occur by adding starch to the protein
film solution. As mentioned above, the mechanical
properties of the protein films can be improved by
using a suitable plasticizer, however, information on
the effects of various types of plasticizer on mungbean
protein film is not available at present. Therefore, in
this study, two methods of modifying the properties of
mungbean protein film were carried out, incorporation
of 4 kinds of starch to the protein solution and the use
of different types of plasticizer. The effect of starch and
plasticizer on the mungbean protein film properties
was investigated and compared with soy protein film.
Materials and Methods
Materials
Dried mungbean (Kaset Brand) was purchased
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Production of Biodegradable Films from Mungbean and Soy proteins (Part 2) 93
from Unibrother Co., Ltd., Bangkok, Thailand. Soy
protein isolate (Fujipro E) was obtained from Fuji
Purina Co., Ltd., Japan. Tapioca starch was obtained
from Nihon Shokuhin Kako Co., Ltd., Japan. Corn, wheat
and potato starch were purchased from Wako Chemicals,
Japan. Glycerol, sorbitol, ethylene glycol, diethylene
glycol and triethylene glycol were purchased from
Wako Chemicals, Japan
Preparation of protein film from mixture of protein
and starch
Either mungbean or soy protein 5.0% (w/v),
glycerol 2.5% (w/v) and potassium sorbate 0.1% (w/v)
was dissolved in distilled water. The potassium sorbate
was added to prevent microbial growth. The film
solution was stirred at 60℃ in a water bath for 10 min.
pH was adjusted to 7.0 using NaOH. When the protein
film solution was obtained, 1 of 4 kinds of starch:
tapioca, wheat, potato or corn starch were added to the
protein solution at 5.0% (w/v) of solution. The mixtureswere heated until 70℃. The film was cast by pouring
20ml of film solution onto a 10×20cm smooth
polypropylene sheet using an auto casting machine
(Automatic Appliactor type A; Toyoseki Co. Ltd., Tokyo,
Japan). Films were peeled off from surface after
drying at 45ーC. Films were conditioned at 25℃, 50±2
%RH for 48 hrs before testing the mechanical
properties and water vapor permeability. The thickness
of film specimen was in the range of 0.08-0.10 mm.
Preparation of film using different types of plasticizer
Either mungbean or soy protein (5.0% w/v) and
potassium sorbate 0.1% was dissolved in distilled water
to prepare the protein solution for the film production.
Different types of plasticizer such as sorbitol (SOR),
ethylene glycol (EG), diethylene glycol (DEG),
triethylene glycol (PEG), polyethylene glycol (PEG),
polypropylene glycol (PPG) and DEGMET (diethylene
glycol monomethyl ether) were used at 2. 0% w/v of
solution. The film solution was stirred at 60℃ in a
water bath for 10 min. pH was adjusted to 7.0 by
NaOH. The film solutions were cast and processed as
detailed above.
Determination of film properties
Tensile strength (TS) and percentage elongation (%E)
TS and %E were evaluated according to the ASTM
standard method D 638-91 (ASTM, 1994) using NRM-
3002D rheometer (Fudou-kougyou Co., Ltd., Japan).
Samples were cut from the central region of film into
dumbell-shaped specimens. Samples were pulled apart
at a crosshead speed of 2 cm/min. TS and %E were
calculated at break according to the following equation.
Tensile strength (TS)=F/A (1)
Elongation at break (%E)=(F-L0)/L0×100 (2)
Where F=loading at break (N)
A=cross-secctional area (m2)
L=stretched length at break (m)
Lo=original length of specimen (m)
Water vapor permeability (WYP)
WVP of films was determined gravimetricall
according to the ASTM standard method E96-95,
known as the "cup method" (ASTM, 1995). Films were
mounted on cups filled with CaCl2 (0%RH). The cups
were placed in an environmental chamber set at 25℃,
50±2% RH. Weight of cups was recorded six times at
1h interval. WVP was calculated from the water vapor
transmission rate (WVTR) as
WVTR=△w/△tA (g/m2. s) (3)
WVP=(WVTR)L/(prPa) (g/m. s. Pa) (4)
Where △w/△t=the amount of moisture gain per unit
time of transfer (g/s)
L=the film thickness (m)
A=the area of film exposed to moisture
transfer (m2)
P1-P2=the difference in partial water pressurebetween two sides of the film specimens.
DSC measurement
The thermal degradation temperature of the films
was measured using a differential scanning calorimeter
(DSC 60, Shimadzu, Japan). Small pieces of sample
(about 5mg) were sealed in the hermetic aluminiumDSC pan. The pan was placed in the DSC cell. The
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94 Wimolrat CHEAPPIMOLCHAI, Yutaka ISHIKAWA. Keo INTABON and Takaaki MAEKAWA
temperature range of the scan was from 25℃ to 300℃
and the heating rate was 5℃/min.
Determination of the amylose content
100mg of starch sample was dissolved in 1ml of
95% of ethanol. 9.0ml of 1 N of NaOH was added into
the starch solution in order to swell the starch. The
swelled starch solution was boiled at 100℃ for 10 min.
After cooling, the total volume of the solution was
adjusted to 100 ml with distilled water to make the stock
solution. 5.0ml of the stock solution was transferred to
a 100 ml volumetric flask. 1.0 ml 1 N acetic acid was
added to netutralize the solution. 2.0ml of KI-I2 solution
was added and the blue color from the reaction with
starch and iodine was developed. The volume of
solution was adjusted to 100 ml with distilled water.
The solution was incubated at 27℃ for 20 min. The
absorbance of solution was measured by spectropho-
tometer at 620 nm and used for calculating the amylose
content.
Results and Discussions
Effect of starch on the film properties
Tensile strength (TS) and percent elongation at
break (%E)
In this study, different types of starch were added
into the protein film solution to make the film stronger.
The results showed that, when starch was added, the
TS of the film remarkably increased for both mungbean
and soy protein films (Fig. 1). TS of the soy protein
films was increased from 0.921 MPa to the range of
4.91-6.53 MPa when starch was added. In the case of
mungbean protein, the TS of the films was increased
from 0.244 MPa to the range of 2.55-3.32 MPa when
starch was added. Among the starches tested in this
study, corn starch gives the film maximum TS (6.53
MPa) for soy protein whereas tapioca gives the
maximum for mungbean protein film (3.32 MPa). TS of
the soy protein film mixed with tapioca, potato and
wheat starch were not significantly different (4.94, 5.57
and 4.91 MPa, respectively). For the mungbean protein
film, the TS of films mixed with corn, potato and wheat
starch were not significantly different (2.55, 2.27 and
2.83 MPa respectively). Comparing the TS of soy protein-
starch and mungbean protein-starch films, TS of soy
protein films was in the range of 1.5-2.6 times higher
than TS of mungbean protein films for all starches
tested. The improvement of TS of the films suggests
the occurrence of cross-linking between protein and
starch as can be observed by the increased thermal
degradation temperature for all types of starch tested.
Table 1 shows the thermal degradation temperature of
protein film and protein-starch film. The thermal
degradation temperature of soy protein film increased
from 152℃ to a range of 239-255℃ when starch was
added. Similarly, for mungbean protein film, the
thermal degradation temperature increased from 160
℃ to the range of 213-239℃.
Incorporation of starch into the protein films did
not improve the film flexibility. As shown in Fig. 2,
flexibility of films mixed with starch decreased
compared to the control as shown by the decreasing of
Fig. 1 Tensile strength (TS) of the protein films withdifferent types of starch
Note: Control is the protein film without adding starch.Means labeled with different letters are significantlydifferent (P<0.05)
□ Soy protein
■ Mungbean protein
Table 1 Thermal degradation temperature of protein-
starch films
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Production of Biodegradable Films from Mungbean and Soy proteins (Part 2) 95
%E. The %E for soy protein mixed with tapioca and for
wheat starch were not significantly different (46.1 and
51.7%, respectively). Films made with soy protein and
potato starch were very brittle which can be observed
from the lowest %E (12.1%). In the case of mungbean
protein film, there was no significant difference of %E
between film mixed with corn and potato starch (40.8
and 38.3%, respectively). Tapioca and wheat starch film
have a similar %E in the case of mungbean protein
(48.1 and 46.1%, respectively). %E of soy protein film
was in the range of 0.3-0.9 times lower than that of
mungbean protein film when potato, corn and tapioca
starch was added. In case of film mixed with wheat
starch, %E of soy protein film was 1 1 times higher than
that of mungbean protein film. In general, the increased
TS of cross-linked protein film is accompanied by a
reduced film E as a tighter and less elastic film
structure is formed. The highly hydrogen bonding
chain between protein and starch chains limits the
elongation properties of the films.
It is known that different starches display different
properties because of differences in their chemical and
physical structures (Swinkels, 1985). The difference inTS of film mixed with various kinds of starch resulted
from the difference in the amylose content in starch.
Amylose which is a linear polysaccharide chain has the
ability to form a gel and has a strong tendency to form
complexes with other components such as proteins or
lipids (Hermansson and Svegmark, 1996). Amylose is
responsible for the film forming capacity of starch. The
linear amylose chains form strong physical crosslinks,
mainly hydrogen bonding and crystallization, resulting
in strong and coherent materials. Lloyd and Kirst
(1963) reported a positive correlation between TS and
the amylose content of starch. However, a clear
correlation between TS and the amylose content was
not observed in this study. For example, potato starch
which has the highest amylose content (53.3%) should
give the highest value of TS but the TS of the soy
protein-potato starch was lower than that of the tapioca-
starch film which contains 37.5% amylose. The amylose
content of starches used in this study is shown in
Table 2. Because starch is a complex material, the
difference in mechanical properties of starch films
might be related to other factors such as granular size,
shape or other physical factors. Lim and Jane (1992)
prepared films with different granular sizes of starch
mixed with polyethylene and found that TS and
elongation of films exhibited an inverse relation to the
average granule size of starch.
Water vapor permeability (WVP)
Water vapor permeability is one of the important
barrier properties of film. Generally, film with good
barrier properties has a low WVP. From Fig. 3, WVP
was remarkably improved by the addition of starch.
WVP of all films was decreased about 50% compared to
the control which implies an improvement of film
barrier properties. WVP of the mungbean protein-
starch films was in the range of 1.1-1.4 times lower
than WVP of the soy protein-starch films. WVP of the
mungbean protein film was reduced from 22.1×10-il to
the range of 5.63-6.94×10-11 g/m. s. Pa. when starch was
added. Whereas, WVP of soy protein film was reduced
Fig. 2 Elongation of the protein films with different
types of starch
Note: Control is the protein film without adding starch.Means labeled with different letters are significantly
different (P<0.05)
□ Soyprotein
■ Mungbean protein
Table 2 Amylose content and granule size of various
kinds of starch
afrom Ra. dley (1968).
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96 Wimoirat CHEAPPIMOLCHAI, YUtaka ISHIKAWA Keo INTABON and Takaaki MAEKAWA
from 10.7×10-11 to the range of 7.01-9.45×10-11
g/m. s. Pa. when starch was added. WVP of the film
prepared in this study was two orders of magnitude
lower compared to the soy protein-dialdehyde starch
film prepared by Rhim et al. (1998)which is 1.57×10-9
g/m. s. Pa. This result indicated the improvement of
barrier properties by the incorporation of starch. The
high WVP of potato starch film resulting from the high
phosphate derivatives content of potato starch. The
phosphate groups covalently linked to amylopectin
increase its hydrophilic nature (Hermansson and
Svegmark, 1996). Moreover, potato starch exhibit high
swelling, indicating a weak internal bonding which in
turn decreases the cohesion in the structure of
polymer resulting in high permeability (Banker, 1966;
Leach, 1965).
Effect of plasticizer on film properties
Preliminary work (Wimolrat et al., 2000) showed
that films formed with glycerol (GLY) as a plasticizer
have weak properties especially the TS value. In this
study, protein films were plasticized with different
types of plasticizer as described in the materials and
methods section. The properties of films were
determined and compared with the films plasticized
with GLY from the previous study (Wimolrat et al., 2000).
After casting protein films with different plasticizers,
the PEG, PPG and DEGMET film samples were brittle
and flaky and thus these films could not be used for
determining the properties. Such observations indicate
the importance of plasticizer selection in film production
from protein. Therefore, film plasticized with SOR, EG,
DEG and TEG were studied for their properties in
comparison with GLY.
Tensile Strength (TS) and percent elongation at
break (%E)
Different types of plasticizer have significant effects
on the TS of film as shown in Fig. 4. TS of film
plasticized with GLY was low and has a value of 0.92
MPa for soy protein film and 0.26 MPa for mungbean
protein film. When the film plasticizer was changed
from GLY to other plasticizers, the TS of film was
significantly increased for both mungbean and soy
protein film. The TS of soy protein film was in the
range of 2.6-3.7 times higher than TS of mungbean
protein film for the 4 plasticizers used in this study.
Using sorbitol (SOR) as a plasticizer, TS of mungbean
protein film was increased to 0.950 MPa. While, TSwas increased to 3.52 MPa for sorbitol plasticized soy
protein film. The influence of the chemical structure of
the plasticizers, especially the length of the molecules,
on the film properties was studied. Using a series of
ethylene glycols (EG, DEG and TEG), it was observed
that the TS of film decreased with the increase of the
Fig. 3 Water vapor permeability (WVP) of the proteinfilms with different types of starch
Note: Control is the protein film without adding starch.Means labeled with different letters are significantlydifferent (P<0.05)
□ Soyprotein
■ Mungbean protein
Fig. 4 Tensile strength of the protein films with
different plasticizers
Means labeled with different letters are significantlydifferent (P<0.05)
□ Soyprotein
■ Mungbean protein
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Production of Biodegradable Films from Mungbean and Soy proteins (Part 2) 97
degree of polymerization over the range 1-3. For soy
protein film, TS of film plasticized with EG, DEG and
TEG was 2.36, 1.87 and 1.85 MPa respectively. TS of
mungbean protein film was 0.901, 0.563 and 0.716 MPa
for film plasticized with EG, DEG and TEG respectively.
Fig. 5 shows that the elongation of soy protein film
plasticized with EG, DEG and TEG was significantly
higher than film plasticized with GLY and sorbitol.
Elongation decreased but not significantly when the
chain length of plasticizer increased. The results were
similar to those reported for pea protein film by
Gueguen et al. (1988). However, in the case of wheat
gliadin film, elongation increased when the chain
length increased (Sanchez et al., 1998). The opposite
phenomenon is due to the difference in nature of
protein. The major fraction in pea, mungbean and soy
protein is globulin which is a soluble protein whereas,
gliadin is an insoluble protein. Mungbean protein film
plasticized with glycerol is the most flexible compared
with films plasticized with other plasticizers based on
the %E. Addition of sorbitol resulted in a more brittle
and tighter film than did glycerol. McHugh and
Krochta (1994) prepared films from whey protein
plasticized with sorbitol and glycerol. At the same
concentration of plasticizer, %E of film plasticized with
sorbitol was about 2 0% while %E of film plasticized
with glycerol was 31%. In the present study, elongation
of soy protein film was higher than mungbean protein
film for all types of plasticizer used. %E of soy protein
film was 1.2 times higher than that of mungbean protein
film when using sorbitol as a plasticizer. However, %E
of soy protein film plasticized with EG, DEG and TEG
was in the range of 2.5-2.6 times higher than %E of
mungbean protein film with the same plasticizer.
From the infrared spectrum of 11 S soy protein
film studied by Gueguen et al. (1998), the film formation
from 11 S protein in the presence of plasticizer was
concluded to be due to intermolecular β-structures
which were maintained by strong hydrogen bonds. An
observation of a shift toward a higher wavelength for
film plasticized with different plasticizers indicated the
weak β-sheet reactions which leading to weaker
mechanical properties of the films. The hydrogen bond
formed between hydroxyl groups and polypeptide
chains are stronger for short aliphatic chains like EG.
If the length of plasticizer increased, this interaction
becomes weaker, resulting in weak TS properties.
Water vapor permeability (WYP)
Plasticizers have significant effects on the WVP of
film as shown in Fig. 6. From the previous study, film
plasticized with glycerol have a high WVP compared to
polymeric film (Smith, 1986). Changing the plasticizer
from glycerol to the series of EG had no effect on the
improvement of the barrier properties of film as seen
from the increase of WVP. WVP of soy protein-EG,
DEG and TEG film was 16.5, 24.9 and 20.8×10-i1
Fig. 5 Elongation of the protein films with different
plasticizers
Means labeled with different letters are significantly
different (P<0.05)
□ Soy protein
■ Mungbean
Fig. 6 Water vapor permeability (WVP) of the proteinfilms with different plasticizers
Means labeled with different letters are significantlydifferent (P<0.05)
□ Soyprotein
■ Mungbean protein
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98 Wimolrat CHEAPPIMOLCHAI, Yutaka ISHIKAWA. Keo INTABON and Takaaki MAEKAWA
(g/m. s. Pa) respectively. The WVP of sorbitol plasticized
soy and mungbean protein films was not significantly
different from each other. Sorbitol-plasticized film gave
the lowest WVP among the other plasticizers which is
1.16 and 1.90×10-11g/m. s. Pa for soy protein and
mungbean protein film respectively. McHugh et al. (1994)
also reported a reduction of WVP of whey protein
isolate film using sorbitol compared to glycerol. WVP of
sorbitol-plasticized whey protein film was 7.16×10-10
g/m. s. Pa, while that of glycerol-plasticized was 1.39×10-9
g/m. s. Pa. This result showed that the barrier property
of film can be improved by using sorbitol as a
plasticizer. WVP of soy protein film was 1.6 and 1.2
times higher than WVP of mungbean protein film
plasticized with DEG and TEG, respectively. Whereas,
WVP of soy protein film was 0.6 and 0.9 times lower
than that of mungbean protein film plasticized with
SOR and EG, respectively. The hygroscopicity of polyols
varies according to the molecular weight. Generally,
the higher the molecular weight, the less hygroscopic
the polyol (Johnson and Peterson, 1974). Sorbitol
molecules are larger (MW=182) than glycerol (MW=
92), thus the ability to bind water of sorbitol was less
than glycerol. This might be the result that film
plasticized with sorbitol has the lowest WVP. The
higher WVP values of film plasticized with EG, DEG
and TEG compared to glycerol plasticized film may be
attributed to the difference in the number of polar
hydroxyl groups contained in these plasticizers. Glycerol
molecules contain three hydroxyl groups while EG
molecules contain two (Table 3). Polar groups in
plasticizers are believed to develop polymer-plasticizerbonds replacing the polymer-polymer secondary bonds.
Therefore, glycerol is expected to provide more
bonding with protein molecular chains, resulting in a
greater barrier ability than with the use of EG.
Implications and potential applications
The improvement of film properties in this study
may lead to the possibility to using mungbean protein
film in renewable packaging applications. In this study,
mixing of tapioca, wheat and corn starch into the
protein film solution gave films with comparative
properties, further study should be considered using
tapioca starch and mungbean protein as ingredients
for biodegradable film production because of their
availability in Thailand and tropical countries. Generally,
protein films have been found to be effective oxygen
barriers (Brandenburg et al., 1993; Gennadios et al.,
1993b). Protein films have also been found to have a
high solubility in water (Kunte et al., 1997; Jangchud
and Chinnan, 1999; Sothornvit and Krochta, 2000).
Therefore, further application of research should be
focused on using mungbean protein film as an edible
packaging, for example, as a small edible ingredient
bag for instant noodles. The bag can be added and
dissolved in hot water with the noodles. The film can
be used to prevent oxidation of ingredients during
marketing because of its high oxygen barrier properties.
Conclusions
1. The properties of mungbean and soy protein
films were improved by incorporation with starch. By
this method, tensile strength (TS) of film increased
and water vapor permeability (WVP) decreased.
However, the elongation (%E) of film was not improved.
2. Another possibility to improve the properties of
mungbean protein film can be done by using of
different types of plasticizer. TS of film was increased
and WVP was decreased when film is plasticized with
sorbitol, but elongation of film was not improved.
Ethylene glycol (EG), diethylene glycol (DEG) and
triethylene glycol (PEG) also can improve TS and %E
Table 3 Formula and molecular weight of the plasticizers used
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Production of Biodegradable Films from Mungbean and Soy proteins (Part 2) 99
of film but WVP of film plasticized with these plasticizers
is high.
3. Comparison of the properties mungbean protein-
starch and soy protein-starch film, film made from soy
protein was in the range of 1.5-2.6 times higher in TS
than mungbean protein film. On the other hand, film
made from mungbean protein showed better proper-
ties in %E and WVP than soy protein. %E of soy protein
film was in the range of 0.3-0.9 times lower than that of
mungbean protein. WVP of soy protein film was in the
range of 1.1-1.4 times higher than WVP of mungbean
protein film.
4. Similar results were observed when different
types of plasticizer were used. TS of film made from
soy protein was in the range of 2.6-3.7 times higher
than mungbean protein film. %E of soy protein-sorbitol
film was 1.2 times higher than that of mungbean
protein-sorbitol film whereas, %E of soy protein film
plasticized with EG, DEG and TEG was 2.5 times
higher than mungbean protein film. The WVP of soy
protein film was 0.6 and 0.9 times lower than that of
mungbean protein film plasticized with SOR and EG,
respectively. Whereas, WVP of soy protein film was 1.6
and 1.2 times higher than WVP of mungbean protein
film plasticized with DEG and TEG, respectively.
5. Improvement of TS and WVP of mungbean and
soy protein film were achieved in this study to some
degree. Due to the effectiveness of protein film as an
oxygen barrier and its high solubility in water, further
application of the film as an edible packaging should be
focused on. However, the high WVP of films in this
study compared to synthetic films limits their use in
commercial application. WVP of films can be improved
by preparing composite film with lipid materials such
as fatty acids. The modification of film properties by
chemical and physical methods is another approach for
the future studies.
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Production of Biodegradable Films from Mungbean and Soy proteins (Part 2) 101
緑豆及び大豆タンパク質による生分解性プラスチックフィルムの試作 (第2報)-緑 豆及び大豆タンパク質フィルム特性 の改善-*
チ イ ー ピ モ ンチ ャ イ ウ イ モ ン ラ ッ ト**・ 石 川 豊***・ 院 多 本 華 夫***・ 前 川 孝 昭***
*平 成13年 度農業施設学会 にて一部発表
**筑 波大学農学研究科, 〒305-8577 つ くば市
***筑 波大学農林工学系, 〒305 -8577 つ くば市
要 旨
グ リセ ロール で可塑化 した緑 豆 フィル ムの特性 は, 引張強度 (TS) が低 く, 透湿度 (WVP) が高 いため に, 包装材
料 としての商業 的な利用 には適 して いない ことを前 に述 べた。 本研究 で は, 緑豆 お よび と大 豆 フィル ムについて, で
んぷん (タピオカ, コー ン, 小麦, じゃがい も) および, 可塑 剤[ソ ル ビ トール, エチ レング リコール (EG), ジエ
チ レング リコール (DEG), トリエチ レング リコール (TEG)] の添加 による これ らの特性 の改善 につ いて検 討 を行 っ
た。 でんぷ んを混合 した場合, 緑 豆 タンパ ク質 フ ィル ムのTSは, 0.244か ら2.55-3.32MPaの 範 囲 まで増 加 し, 大
豆 タンパ ク質 フィル ムで は0.921か ら4.91-6.53MPaの 範 囲 まで増 加 した。WVPは 緑豆 タンパ ク質で はタ ピオ カで
んぷんの添加により, 22.1から5.63×10-11g/m. s. Pa. に低 下 し, 大豆タンパク質では小麦でんぷん添加 によ り10.7か
ら7.01×10-11g/m. s. Pa. に低下 した。一方, フィル ムの伸 度は, この手 法で は改善 され なかった。
可 塑剤の添加 で は, ソル ビ トール によ り最 も特性 が改善 された。 ソル ビ トール を添加 した フ ィル ムのTSは, 大豆
タ ンパ ク質 フ ィル ムでは0.921か ら3.52MPaに 増加 し, 緑 豆 タンパ ク質 フィル ムでは0.264か ら0.95MPaに 増加 した。
WVPは 大 豆 タンパ ク質 フィル ムの場合, 8.96×10-11か ら1.16×10-11g/m. s. Pa. まで低下 し, 緑豆 タ ンパ ク質 フィル ム
の場合, 15.05×10-11か ら1.9×10-11g/m. s. Pa. まで低 下 した。EG, DEG, TEGの 場 合, TSを 改善す る ことはで きた
が, WVPは 高 くなった。
キーワー ド: 生分解 フイル ム, 緑 豆 タンパ ク質, 大豆 タンパ ク質, で んぷん, 可塑剤
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