production of biodegradable films from mungbean and soy

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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%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


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


Fig. 4 Tensile strength of the protein films with

different plasticizers

Means labeled with different letters are significantlydifferent (P<0.05)

□ Soyprotein


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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


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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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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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100 Wimolrat CHEAPPIMOLCHAI, Yutaka ISHIKAWA, Keo INTABON and Takaaki MAEKAWA

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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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production of biodegradable films from mungbean and soy

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