J, Pack. Sci. Technol. Vol. 3 No. 2 (1994)

Apparent Diffusion Coefficient of Oxygen through
Dehydrated Protein or Saccharide Films
Shuji ADACHI*, Koji MURAYA*, Tatsuji ISHIGURO*and Ryuichi MATSUNO*

Thin dehydrated films ofpullulan, maltodextrin, sodium caseinate, and gelatin were prepared without addition of any plasticizer. The apparent diffusion coefficient Dapp of oxygen throughthem were measured under various conditions. Film formation at higher temperatures seemed
to be unfavorable to reduce the Dapp value. The Dapp value for sodium casemate film largely depended on the film thickness. There was no effect of relative humidity of air on the Dapp values
for all the films. The temperature dependence of Dapp for sodium caseinate film obeyed the Arrhenius equation, but not for other films. Mixing of sodium caseinate with pullulan or maltodextrin
resulted in an increase of Dapp value. Pullulan films incorporated with emulsified methyl oleate
were also prepared. The Dapp values through them increased as the content of methyl oleate inc r e a s e d .
Keywords: Diffusion coefficient, Oxygen, Edible film, Permeability

INTRODUCTION

through the matrixes are required. Measurement of the diffusion coefficient of oxygen in

Encapsulation of liquid lipids, many ofwhich originally possess physiological functions,
into powdery matrixes of proteins and saccharides may provide some advantages or
add new functions to the lipids1). One of themis a retardation of lipid oxidation2). To estimate
whether the retardation is due to only diffusional resistance of the dehydrated matrixes
to oxygen or not, knowledges on both the oxidation kinetics and the diffusivity of oxygen

small spherical matrixes of protein or saccharide, which is referred to as an entapping
agent, may be difficult. Therefore, we preparedthin films of entrapping agents and measured the apparent diffusion coefficient of oxygen through the films.
Liquid lipids encapsulated disperse in thedehydrated droplets ofproteins or saccharides.
To estimate the mass transfer characteristics
in the droplets, pullulan films including* Department of Food Science and Technology, Faculty of Agriculture, Kyoto University, Sakyo-ku, Oiwakecho, Kitashirakawa, Kyoto, 606-01 Japan- 9 3 -

O x y g e n d i f f u s i v i t y t h r o u g h e d i b l e f i l ms

Table 1 Suitableness of polyethylene terephtalate
films in preparation of entrapping agent films.

emulsified lipids were prepared and th e apparent diffusion coefficient of oxygen throughthem were also measured. The effect of the content of lipid on the apparent diffusion coefficient
was discussed.

MATERIALS AND METHODS
1.

Materialsa) PET: polyethylene terephtalate.
b) P: PET film of normal type.
c) S: PET film coated by silicone resin.
d> C: PET film treated by corona discharge.
The symbols ○ and × indicate that the PET film
is adequate or preparation of entrapping agent
film and not, respectively.

Maltodextrin (DE 2-5, Matsutani Chemical
Industry), pullulan (PI-20, Hayashibara),
sodium caseinate (Nacalai Tesque), and gelatin(CP-379, Osaka Kagaku-Gokin) were useda s en t ra pp in g ag en t s . Pu ll ul an , g e la ti n, a nd

1 shows which type of PET film is usable for film

three kind of polyethylene terephthalate

preparation. The thickness of film was mea-

(PET) films (normal film, film coated by silicone

sured at some random positions (at least 5

resin, and film treated by corona discharge)

points) by a dial thickness guage (Teclock Corp.,
SM-1201) and averaged.

were kindly supplied from Osaka KagakuGokin. Salts of analytical grades were pu rc h a s e d f r o m W a k o P u r e C h e mi c a l s .

3. Preparation of pullulan film
containing methyl oleate droplet

2. Preparation of protein or saccha ridefilm

A mixture of methyl oleate (2 g) and l%(w/v)
Tween 20 solution (7.5 ml) was homogenized in

A dense solution of entrapping agent, the con-a test tube for 1 min at power control 7 by Poly-

centration of which is shown in Table 1, was de-tron PCU-2 (Kinematica Gmb) consisting of sta-gassed by aspiration to remove air bubbles. An

tor rotor with blade. The emulsions wereadequate volume of the solution was poured on

used directly or after further emulsification,a PET film placed on a dick and flat glass, andwhich was done as follows: the emulsions werethen cast by an applicator (Yoshimitsu Seiki,

diluted 5 times by 1% (w/v) Tween 20, and thenYBA type). The clearance of the applicator could

p a s s e d r e p e a t e d l y t h r o u g h h yd r o p h i l i c c e ll u -be adjusted to a given distance in a range of0lose acetate membrane with a pore size ofto 250 μm. The cast solution was dehydrated

0 . 8 μ m( A d v a n t e c T o y o , D I S M I C - 2 5 c s ) . H y -by putting it in a temperature-controlled

drophobic membranes were unadequate forchamber to form its film. The film formed wase mu l s i f i c a t i o n . I n b o t h c a s e s , t h e e mu l s i o n speeled off and then used for measurement of diffusion coefficient of oxygen through it. Table

were centrifuged for 30 min at 1000 rpm to forma cream layer. An adequate volume of the cream- 9 4 -

J. Pack. Sci. Technol. Vol. 3 No. 2 (1994)

layer was mixed with 25% (w/v) pullulan andmoto Iron Works. The diffusion cell consisted

degassed. Then, the pullulan film containingof two chambers isolated by a film, which wasemulsified methyl oleate was prepared as
me n t i o n e d a b o v e .

fasten ed after k eep ing it u nder atmo sp here
equilibrated with a given saturated salt solution
for 2 days or longer. Air in both the chambers

4. Apparatus for measurement of

was first replaced by nitrogen gas. After thethe apparent diffusion coefficient ofcomplete replacement, the valves of the upper

oxygenchamber were closed and then air was begun
to supply continuously to the lower chamber.

Fig. 1 (a) illustrates the apparatus used for

The change of the partial pressure of oxygen inmeasurement of the apparent diffusion coef-

the upper chamber was continuously monitored

ficient of oxygen. Nitrogen gas or air was sup-by an oxygen electrode of Galvanic cell typeplied through a saturated salt solution to the
diffusion cell, the details of -which is shown in
Fig. 1(b) and which was kindly made by Kuri-(Oriental Denki, RA type) and recorded. It had
been confirmed in preliminary experiments thatthe electrode made response proportional to thepartial pressure of oxygen. The volume of theupper chamber V was 17.0 cm3 and the area offilm available diffusion A was 19.6 cm 2 .

5. Evaluation of the apparent diffusion
coefficient of oxygen
In our expriments, the partial pressure ofoxygen in the upper chamber began to increase
after a short lag-time for each film. The lag-time
was too short to evaluate precisely the solubility
coefficient of oxygen to the film S. Therefore,
we assumed a pseudosteady state and expressed
the mass balance of oxygen in the upper
chamber by Eq. (1) using the difference in concentration of oxygen between the lower and upper chambers as a driving force.

VdC/dt=kapp A(C0 -C)
Fig. 1 Schematic diagram of the apparatus used
for measurement of the apparent diffusion
coefficient of oxygen through a film (a), andthe details of the diffusion cell (b).
1 ; air compressor, 2; nitrogen gas cylinder,
3; three-way valve, 4; saturated salt solution, 5; flow meter, 6; stop valve, 7;diffusion cell, 8;film, 9; oxygen electrode,
10; oxygen meter, ll; recorder, and 12;
thermostated water bath.

(1)

where C 0 and C are the concentrations ofoxygen in the lower and upper chambers, respectively, and t is the time. The concentrations- 9 5 -

Oxygen diffusivity through edible films

can be easily related to the partial pressure ofoxygen by the equation of state for ideal gas.

mersed in methyl oleate and kept under reducedpressure. After wiping away excess oil on the

kapp is the apparent mass transfer coefficient offilm, the film was fastened in the diffusion cell.

oxygen through a film, and is related to the apparent diffusion coefficient of oxygen Dapp by

The diffusion coefficient was obtained bymultiplying the k value, determined by thea b o v e me t h o d , b y t h e t h i c k n e s s o f f i l m L a n dkapp =Dapp /L( 2 )then by dividing by the opening.

Equation (1) can be solved under an initial
Condition of C=0 at t =0, and gives
C/C0=1－exp(－kappAt)

6. Differential scanning colorimetry of

(3)

films

By plotting In [l - (C/C0 )against t ,the k app value
was determined and converted to the Dappvalue by multiplying the film thickness L. The

andpowders

Differential scanning calo rimetric (DSC) mea-

measurement of D a p p was made in duplicate orsurements of entrapping agents (powders)
and their films were made at the temperature-

triplicate for a film, and the least value wasraising rate of 5 or 7 K/min using a differential

adopted because the film preparation in thatscanning calorimeter (Seiko Denshi Kogyo,case might be the best.

DSC-100). The films were cut to small pieces

The D app value can be also determined by us-

and 21 mg of them was used in DSC mea-

ing the analytical solution of the diffusion equation 3 ) 4 ) . Since both the methods gave a similarsurement. The same weight of Al 2 O 3 , was put ina reference pan.

value of D app , the method mentioned above was

RESULTS AND DISCUSSION

used because of its simplicity.
Although the permeability P is generally used
to characterize the mass transfer properties of

1. Effect of drying temperature on Dappfilms, the D a p p was evaluated in this study for

Fig. 2 shows the effect of drying temperature,

purpose in use. The D app value can be converted
to the P value by P= Dapp/RT, where R and T are

a t w h i c h f i l ms w e r e p r e p a r e d , o n t h e D a p p v a l -the gas constant and the absolute temperature.

dehydration at higher temperatures causes

The intrinsic diffusion coefficient within a film
D is related to the permeability P by P = SD.

higher diffusivities. This might be due to

The measurement of the diffusion coefficient

is liab le to result in film d efects. 5 ) All the fol-of oxygen in methyl oleate was also made us-

lowing experiments were made by using thefilms prepared at 50°C.

ing the diffusion cell shown in Fig. 1. Polyfuron
film (Advantec Toyo, PF050) with opening of
70% and with the thickness of 400 μm was im-- 9 6 -

ues at 25°C. There seems to be a tendency thatthat rapid dehydration at higher temperatures

2. Effectof film thickness on Dapp
Films with various thickness were prepared and the D a p p values, which were the small -J. Pack. Sci. Technol. Vol. 3 No. 2 (1994)

est at 5 μm intervals, were plotted against film
thickness in Fig. 3 for each entrapping agent.
The D app value through sodium caseinate film
remarkably depended on the thickness. Similar dependency has been reported in terms of

i<r"|-

water vapor permeability through sodium
caseinate film6). If the film consisted of dense
and rough layers and the thickness of the dense10"

layer was constant, such a tendency could be
qualitatively explained. We observed the section of the film by a scanning electron micro-

10

scope. However, such two-layer structure
50

100

could not be clearly observed. For other films,

Drying temperature [°C]

the Dapp values seemed to depend slightly on the
thickness. The DSC measurements were also
made for sodium caseinate and pullulan films
with different thickness to evaluate theirenthalpy changes ΔH. However, we could
Fig. 2 Effect of the drying temperature in preparation of films on the apparent diffusion
coefficient Dapp of oxygen through films at
25℃.

not get conclusive results due to a problem inregistration of ΔH by the DSC apparatus
u s e d .

3. Effect of relative humidity on D app
The humidity of air introduced to the diffusion cell was controlled by passing it throughsaturated salt solu tion (potasium acetate(0.23), magnesium chloride (0.33), potasium carbonate (0.44), magnesium nitrate (0.55),
sodium nitrate (0.65), sodium chloride (0.75),
and lithium sulfate (0.85), where the figures in
the parentheses indicate the water activity ofsaturated aqueous solution). The films were
equilibrated at the same humidity for 2 daysor more before use. We had not confirmed
whether the period was enough for equilibration
or not. In Fig. 4, the D app values are plotted

20
40
Film thickness [μm]Fig. 3 Effect of the film thickness on the apparent
Diffusion coefficient Dapp of oxygen throughfilms at 25°C.
The key are the same as in Fig. 2.

- 9 7 -

Oxygen diffusivity through edible films

Fig. 4 Dependence of the apparent diffusion coefficient Dapp of oxygen through films at 25°C
on the relative humidity of air.
The keys are the same as in Fig. 2.
Fig. 5 The Arrhenius plots of the apparent diffusion coefficient D of oxygen throughfilms
The keys are the same as in Fig. 2.

against the relative humidity of air introduced
to the diffusion cell. In our experiments, the relative humidity did not affect the diffusivity ofoxygen through the films, although it was reported that the permeability of oxygen throughs h o w e d a n o ma l o u s d e p e n d e n c e s o n t h e t e m perature. As a reason for this, the phasepullulan films depended on the relative hu-transition of the films might be consider-midity7). The reason for this discrepancy remains
unclear.

able. The DSC measurements of the films andthe powders of the film-forming materials weremade (Fig. 6). Although it was showed that all
the films changed their structures within a

4. Effect of temp erature on D a p p

range of temperature where the D a p p values wereserved at the relative humidity ca. 0.75 of air

measured, it was difficult to find the correlation between the D a p p values and the DSC measurements. As another reason for the anomalous

introduced. The Dapp value for gelatin film wasdependence of the D a p p on the temperature, ex-almost independent of the temperature. Thatistence of pinholes in the films used for the D app

for sodium caseinate film could be expressedmeasurement may be considered 9 ) . However, wehave not examined in this point.

Fig. 5 shows the Arrhenius plot of D app ob-

by the Arrhenius equation, the apparent activation energy being 45 kJ/mol. The activationenergies for oxygen permeation process throughcorn zein, wheat gluten, and wheat gluten/soy
protein isolate films have been reported to be

5. Dapp through film prepared by mixing
protein and saccharide

ca. 46 kJ/mol8), which is close to that mentioned
above. The D app for pullulan and gelatin films

Proteins were mixed with saccharides at var -- 9 8 -

J. Pack. Sci Technol. Vol. 3 No. 2 (1994)

Fig. 7 Effect of mixing of protein and saccharide
on the apparent diffusion coefficient Dapp ofoxygen through films at 25℃.
Symbols: ○, pullulan + sodium casemate;△, pullulan + gelatin; □, maltodextrin +sodium caseinate; ▽, maltodextrin +gelatin.

6. D a p p through pullulan films with
Fig. 6 Differential scanning calorimetric measurements of dehydrated films and their constituent powders.
The solid and broken curves indicate thefilms and powders, respectively. The temperature-raising rate was 7°C/min except
for puilulan (5°C/min).

emulsified methyl oleate
The Dapp values are plotted against thevolumetric content of methyl oleate in Fig. 8.
The D a p p values did not depend on the method
for emulsification, mechanical and mechani-

ious ratios and the films of the mixturesc a l + me m b r a n e e mu l s i f i c a t i o n s . T h e s i z ewere prepared. The D app values through them

distributions of emulsions, which were mea-

were observed at 25°C (Fig.7). Mixing ofsured by a centrifugal particle size analyzer

sodium caseinate with saccharides resulted in( S h i ma d z u , S A - C P 3 L ) a f t e r d i s s o l v i n g t h e

an increase of Dapp,while the mixing of gelatinpullulan films by 0.1% (w/v) sodium dodecyl-

showed no significant effect on D a p p . Thissulfate, is shown in Fig. 9. The solid curves I and

may be due to the molecular shape of protein
mixed.

II in Fig. 8 were the D a p p values calculated by
the series and parallel models, respectively.
They are expressed by- 9 9 -

Oxygen diffusivity through edible films

Fig.9

Fig.8

Dependence of the apparent diffusion coefficient Dapp of oxygen through pullulan films
containing emulsified methyl oleate at 25°C
on the volumetric content of methyl oleate.
The curves Ⅰ and II are those calculated by
the series and parallel models, respectively. The symbols ○ and △ indicate thatthe emulsions were prepared by mechanical and mechanical + membrane methods.

Size distribution of methyl oleate droplets
entrapped in pullulan film.
The solid and broken lines are for emulsions prepared by mechanical and mechanical + membrane methods,
respectively.

to that there were large droplets in the films,
which were in the same order as the film thickn e s s .

ACKNOWLEDGEMENT(4)

We thank Kurimoto Iron Works, Ltd. for production of the diffusion cell, and Osaka Kagaku(5)Gokin, Ltd. for supply of PET films andgelatin and for advice on the method forp rep aring entrapping agen t films. Dr. N.

where DXO and DXL are the diffusion coefficients

Kitabatake, Research Institute for Food Sci-of oxygen in dehydrated entrapping agent film

ence, Kyoto University, is acknowledged for
DSC measurements.

and methyl oleate, respectively. H is the solubility coefficient of oxygen to methyl oleate.
Because we could not find the H value for

REFERENCES

methyl oleate, the H value for soybean oil ,10)indicates the volumetric content of1) R. Matsuno and S. Adachi, Trends in Food
Sci. &Technol., 4(8), 256 (1993)

methyl oleate in the films. The observed Dapp val-

2) J. Imagi, K. Muraya, D.Yamashita, S.

ues are between the curves I and II, and if anything, are close to the curve II. This may be due

Adachi and R. Matsuno, Biosci. Biotech.
Biochem., 56(8), 1236 (1992)

which is rich in oleate, was used in the calculation.

- 1 0 0 -

J. Pack. Sci. Technol. Vol. 3 No. 2 (1994)

8) G. Gennadios, C. L. Weller and R. F.
Testin, J. Food Sci., 58(1), 212 (1993)
9) A. Tanioka, Abstracts of 2nd Annual
Meeting of The Society of Packaging Scienceand Technology, Japan (1993), p.58
10) N. Tomoto and K. Kusano, Yukagaku,
16(3), 108 (1967)(Received 27 October 1993)(Accepted 7 February 1994)

3) C. R. Paul andA.T. Dibenedetto,J. Polym.
Sci., 1O (PartC), 17 (1965)
4) J. D. FlorosandM. S. Chinnan,J. FoodEng.
9,129,(1989)/

5 ) J. J. Ke st e r a n d O. R. Fe n n e m a , F o o dTechnol., 40(12), 47 (1986)
6) T. H. McHugh, R. Avena-Bustillos andJ.
M. Krochta, J. Food Sci., 58(4), 899 (1993)
7) S. Nakamura, Yukagaku, 34(10), 86(1985)

タンパク質および糖の乾燥薄膜における酸素の見掛けの拡散係数
安達修二* 村谷浩二* 石黒達治* 松野隆一*
プルラン、マルトデキストリン、カゼインナトリウムおよびゼラチンの乾燥薄膜を調整し、種々の条件下で酸素の見掛けの拡散係数Dappを測定した。製膜時の乾燥温度を高くすると、Dappが大きくなる傾向にあり好ましくなかった。カゼインナトリウム膜でのDappは膜厚に大きく依存した。いずれの膜についても、相対湿度は測定範囲内(0.23～0.85)でDappに影響を及ぼさなかった。カゼインナトリウム膜ではDappの温度依存性はアレニウスの式で整理できたが、他の膜では適用できなかった。カゼイン
ナトリウムをプルランやマルトデキストリンに混合して調整した膜ではDappが大きくなり好ましくなかった。エマルション化したおれいん酸メチルを含むプルラン膜では、脂質含有率の増加に伴いDappが大きくなった。

キーワード：拡散係数、酸素、可食性フィルム、透過性-101-