Jung Han. Innovations in Food Packaging

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Emulsion and bi-layer edible films

385

lame cr.1 Water vapor permea~~lities of

came

polymer nlms compared to lipids and synthetic polymer nlms

Filma

Test

conditionsb Permeability

;chultz

etal.

(1949)

lankin

etal.

(1 958)

Pectinate

Amylose

iagenmaier and Shaw (1 990) HPMC 27OC, 0/85%RH 9.1

Camper and Fennema (1 984a) HPMC: PEG (9: 1) 2S°C, 85/O%RH 6.5

ianlon (1992)

MC 3S°C, 90/O%RH 4.8

JlcHugh

eta/.

(1 994) WPl:Gly(4:1) 2S°C, 0/77%RH 70

'ark and Chinnan (1 995)

WG:Gly(3.1 :1) 21 OC, 85/O%RH 53

ituchell and Krochta (1994) SPI:Cly(4:1) 2g°C, 0/78%RH 39

ivena-Bustillos and Krochta (1 993)

Sodium caseinate 2S°C, 0/81%RH 37

'ark and Chinnan (1 995) CZ:Gly (4.9: 1) 21 OC, 85/O%RH 9.6

iontard

et al.

(1 992) WC:Gly(5:1) 30°C, 100/O%RH 5.1

.ovegren and Feuge

954) Hydrogenated peanut oil 2SoC, 100/O%RH 3.3

.ovegren and Feuge (1 954) AMG

2S°C, 100/O%RH 1.9-1 3.0

ihellhammer and Krochta (1 997b) Tripalmitin 2g°C, 011 00%RH 0.19

ihellhammer and Krochta (1 997b) CarW 2g°C, 011 00%RH 0.098

ihellhammer and Krochta (1 997a) BW

26OC, 011 00%RH 0.089

.ovegren and Feuge (1 954)

2S°C, 100/0%RH 0.01 9

;hellhammer and Krochta (1 997a) CanW 2S°C, 011 00%RH 0.01 2

ihellhammer and Krochta (1997b) WC

ihellhammer and Krochta (1 997b) PET

ihellhammer and Krochta (1 997b) LDPE

Compositions rounded to nearest whole number.

RHs on top and bottom sides of film (top/bottom).

vIC, methyl cellulose; HPMC, hydroxypropylmethyl cellulose; WPI, whey protein isolate; WC, wheat gluten; SPI, soy protein isolate;

IZ,

corn zein; PEG, polyethylene glycol; Cly, glycerol; AMC, acetylated monoglycerides; CarW, carnauba wax; BW, beeswax;

PW,

)arafin wax; CanW, candelilla wax; WC, polyvinylchloride; PET, polyethylene terephthalate; LDPE, low-density polyethylene.

if they are solids at room temperature, which makes application more difficult

(Krochta, 1997a).

approach to improving film functionality is to combine lipid materials with

polysaccharides or proteins to form composite films. This way, the polysaccharide or

protein provides the film integrity while acting as an entrapping or supporting matrix

for the lipid component, and the lipid provides the moisture barrier (Krochta, 1997a).

This chapter reviews the existing literature on polysaccharide-lipid and protein-lipid

edible composite films. The specific objectives are to summarize the information on edi-

ble composite film formation and properties, as well as factors affecting the perform-

ance of edible composite films.

Composite film formation

composite film can be produced as either a bi-layer or a stable emulsion. In bi-layer

composite films, the lipid forms a second layer over the polysaccharide or protein

layer. In emulsion composite films, the lipid is dispersed and entrapped in the sup-

porting matrix of protein or polysaccharide.

386

Innovations

Food Packaging

61-layer film:

Lipid on hydrophilic film

Coating technique: Two-step technique

Emulsion technique: One-step technique

Emulsion film:

Lipid droplets dispersed within the hydrophilic phase

Figure

22.1

Edible composite

film formation.

Bi-layer film systems can be formed by two different techniques; the "coating tech-

nique" or the "emulsion technique". The coating technique is a two-step technique that

involves casting a lipid layer, either molten or from solvent, onto a previously formed

polysaccharide or protein

film.

The "emulsion technique" is a one-step coating technique

that involves dispersing the lipid into the film-forming solution prior to film casting,

with the bi-layer film resulting from the emulsion when the continuous phase cannot

stabilize the emulsion and phase separation occurs during drying (Figure 22.1).

Emulsion film systems, on the other hand, can only be formed by the emulsion tech-

nique, which involves the dispersion of the lipid into either the polysaccharide or the

protein film-formation solution to make a stable emulsion. In general, the emulsifying

character of proteins makes them appropriate for this technique. However, polysac-

charides are not as effective as emulsifiers, and emulsion film formation generally

requires the addition of an emulsifier to improve emulsion stability (Figure 22.1).

Barrier properties that are commonly studied when determining the ability of edi-

ble films to protect foods from the environment and from adjacent ingredients are film

water vapor permeability

(WVP)

and oxygen permeability (OP) (Pkrez-Gago and

Krochta, 2002). In addition, mechanical properties are evaluated to assess the ability

of edible films to protect foods against mechanical abuse (Krochta, 1997b). Both bar-

rier and mechanical properties of composite films are affected by the film composi-

tion and the distribution (uniform or non-uniform) of the hydrophobic substances in

the composite films (Kamper and Fennema, 1985; Debeaufort

al.,

1993), which in

turn

are affected by the film-forming technique. In addition, for films of similar com-

position and structure, changes in test conditions (specifically temperature and rela-

tive humidity) affect their barrier properties. These effects make comparisons among

films difficult; nonetheless, such comparisons are important and are made wherever

possible in the following sections.

Emulsion and bi-layer edible films

387

Properties

bi-layer

films

Many studies have investigated the properties of bi-layer films prepared either by the

coating technique or the emulsion technique. In general, investigations have shown

that bi-layer films are more effective barriers against water vapor transfer

than

are

emulsion films, due to the existence of a continuous hydrophobic phase in the film.

However, the main disadvantages of the coating technique are that it requires several

steps, and the use of solvents or handling of molten waxes. Below there is an overview

of some of the most relevant works found in the literature with a description of the

film-formation technique and the advantages and disadvantages of the method.

The first work published in the literature relating to edible bi-layer films dates from

1949. Schultz

al.

(1949) prepared glycerol (G1y)-plasticized low methoxyl pecti-

nate films with stearic acid (SA), lauric acid (LA), beeswax

(BW)

or paraffin wax

(PW) by using the coating technique and the emulsion technique.

all the films

formed, WVP decreased as the fatty acid chain length and the degree of saturation of

the waxes increased. The coating technique produced bi-layer films by evaporation of

the ether solvent from the wax coating on the surface of the base pectinate film.

Among the hydrophobic components, the application of the PW layer to form the bi-

layer film reduced the

WVP

of the base pectinate film by 99.8%. The same amount of

PW dispersed in the pectinate solution before drying at room temperature to form

emulsion film produced a moisture barrier that was less effective than the bi-layer film

(Table 22.2). Similarly, better moisture-barrier films were obtained when LA or BW

was added as a surface coating to the preformed pectinate film, compared to suspend-

ing the lipids in the pectinate solution before casting the film. However, the disadvan-

tages of forming the bi-layer film vs the emulsion film are the two-step nature of the

technique, and the use of organic solvent.

Three papers describing the production of bi-layer films composed of a base of

polyethylene glycol (PEG)-plasticized hydroxypropylmethyl cellulose (HPMC) and

an upper layer of lipid were published by Kamper and Fennema (1984a, 1984b, 1985).

Films were prepared by the coating technique and the emulsion technique, both of

which produced bi-layer films. The coating technique involved painting the lipid

material onto HPMC

PEG films which had been previously formed by drymg aqueous-

ethanol solutions at 90°C. The emulsion technique involved adding the lipid directly

to the HPMC :PEG aqueous-ethanol film-forming solution at a temperature higher

than the melting point of the lipid, then casting it hot, and drying at 90°C. As the sol-

vent evaporated, and since the HPMC is not an effective emulsifier, the lipid phase

separated from the mixture, forming two continuous layers with the lipid layer over

the HPMC

PEG layer. In this work, as well as in the Schultz

al.

(1949) work, it was

found that composite films displayed a greater moisture barrier with an increase in the

degree of saturation of the lipid used and of the chain length of fatty acids used

(Kamper and Fennema, 1984a). The moisture barrier was also increased when a blend

of stearic-palmitic acid (SA-PA) was incorporated into the film-forming system prior

to film formation (emulsion technique) rather than being coated onto the surface of

the HPMC :PEG films (coating technique) (Table 22.3). The

WVP

values obtained

388

Innovations in Food Packaging

laole

66.6

vvarer vapur perrneaolllrles or UI-layer ana ernu~s~un pecunare-II~IU eulole rrtrns

Film preparation Test conditionsb Permeability

mm/m2 d

kPa)

Pectinate

Gly (3

)

SAIpectinate: Gly (113

1) Bi-layer film, two-step technique

LAIpectinate: Gly (113: 1)

Bi-layer film, two-step technique

BWIpectinate

Gly (113

1) Bi-layer film, two-step technique

PWIpectinate: Gly (113

1) Bi-layer film, two-step technique

LAIpectinate

Gly (113

Emulsion film

BW/pectinate:Gly (113: 1) Emulsion film

. .

PWIpectinat Emulsion

PW coating

Adapted from Schula

a/.

(1 949).

aCompositions rounded to nearest whole number.

b~~s on top and bottom sides of film (top/bottom).

BW, beeswax; PW, paraffin wax; LA, lauric acid; SA, stearic acid; Gly, glycerol.

- -

Table

22.3

Water vapor permeabilities of bi-layer and emulsion HPMC-lipid edible films

Film' Dqparation techniqup Test conditionsb Permeability

Fennema (1 984a)

iagenmaier and Shaw (1990) HPMC 27OC, 0/85%RH 9.12

<amper and HPMC: PEG (9: 1)

2S°C, 85/O%RH 6.5

SA-PAIHPMC

PEG (3719

BWIHPMC: PEG (3719

Bi-layer film, two-step 2S°C, 85/O%RH

technique

Bi-layer film, two-step 2S°C, 85/O%RH

technique

'W/HPMC: PEG (3719

1) Bi-layer film, two-step 2S°C, 85/O%RH 0.0:

technique

SA-PAIHPMC: PEG (319

)

~i-la~e; film, one-step 2S°C, 85/O%RH 0.052

technique

<ester and SA-PA/MC

HPMC

PEG Bi-layer film, one-step 2S°C, 97/O%RH ".27

:ennema (1 989a) (3.2

2) technique

SA-PA/MC

HPMC

PEG Bi-layer film, one-step 2S°C, 97/65%RH 1.4

(3/2:1 :2) technique

BW/SA-PA: MC: HPMC: PEG Bi-layer film, two-step 2S°C, 97/O%RH 0.057

(211)

technique

BWISA-PA: MC: HPMC: PEG Bi-layer film, two-step 2S°C, 97/65%RH 0.15

(211)

technique

Hagenmaier MAIHPMC (113) Bi-layer film, one-step

3.42

Shaw (1 990 technique

PAIHPMC (113) Bi-layer film, one-step 2.28

technique

SAIHPMC (113) Bi-layer film, one-step 0.095

technique

SAIHPMC (111) Bi-layer film, one-step

^'"

u/aJmnn

u.026

technique

'Compositions rounded to nearest whole number.

'RHs on

to^

and bottom sides of film (to~/bottom).

Emulsion and bi-layer edible films

389

can be compared with WVPs of non-edible synthetic films, such as polyethylene

terephthalate (PET) and low-density polyethylene (LDPE) (Table 22.1). The better

performance of the emulsion technique was attributed to the orientation of the fatty

acid molecules on the surface of the film. In the coating technique the fatty acids are

deposited on the surface of the HPMC

EG film; whereas in the emulsion technique

the fatty acid is allowed to orient at the air-water interface before the lipid solidifies

at the HPMC

PEG surface.

addition, the bi-layer film made using the one-step

technique was found to be very flexible and quite resistant to mechanical damage

compared to the two-step bi-layer film, which was extremely brittle.

With the objective of enhancing the moisture barrier, Kester and Fennema (1989a,

1989b) studied the application of molten beeswax by using the coating technique over

a preformed bi-layer film. This preformed bi-layer film was formed by drying an

aqueous-ethanol solution of SA-PA and methyl cellulose (MC), HPMC, and PEG at

100°C for 15 minutes. Lamination of the SA-PA

HPMC

PEG film with BW

reduced WVP of the films by 79% and 89% when exposed to 974% RH and 97-65%

RH differences, respectively (Table 22.3). In order to explain the permeability results,

scanning electron microscopy was performed. A surprising result was that the degree

of fatty acid surface crystallinity was much less

the SA-PA

HPMC

PEG

film than it was in the SA-PA

HPMC

PEG film developed by Kamper and Fennema

984a, 1984b); however, on the contrary, the WVP was lower

the former. This was

attributed to the greater thermal gelation potential of MC compared to HPMC, which

might cause a greater percentage of the fatty acids to become entrapped in the bulk of

the cellulose matrix during drying. In addition, the SA and PA functioned to increase

the physical bonding of the BW layer to the cellulose matrix, resulting in bi-layer

films with good stability against lipid fracture at low temperature.

Greener and Fennema (1989a, 1989b) studied bi-layer films made by either applying

beeswax in a solvent (BW-S) or molten beeswax (BW-M) to a PEG-MC base film

made from aqueous-ethanol solvent. MC appeared to provide adequate adhesion for

the beeswax layer, probably due to the relatively hydrophobic nature of MC polymer.

WVP of the BW-MIMC

PEG film was lower than that for the BW-SiMC

PEG film

at a 1004%

difference, but similar at a 9745%

difference (Table 22.4).

Scanning electron micrographs of the films showed that the BW-S based films did not

have a uniform surface. This was probably due to the partial solubility of the BW in

the ethanol solution, which might have translated into a greater number of small fis-

sures andlor changes in the composition of the wax components. At the 9745% RH

difference, the moisture barrier of both films was inferior to the moisture barrier of

BW-WSA-PA

HPMC

PEG films produced by Kester and Fennema (1989a,

1989b) (Table 22.3). This was attributed to the thicker BW layer and the fatty acid

content of the base film used for the BW-WSA-PA

HPMC

PEG films.

However, neither the BW-S nor the BW-M based films showed delamination after

testing, whereas delamination of the BW-WSA-PA

HPMC

PEG film was

extensive during testing. Physical abuse tests revealed that the BW-MIMC

PEG film

was more resistant to surface impingement than the BW-SiMC

PEG film, with only

a 2040% increase

WVP after abuse compared to a 6- to 9-fold increase. On the

other hand, a bi-layer film produced by the emulsion method suffered substantial

390

Innovations in

Food

Packaging

hble

22.4

Water vapor permeabilities of bi-layer and emulsion methyl cellulose-lipid edible films

a/.

(1 992a)

ireener and

:ennema (1 989a)

Iebeaufort and

roilley (1 995)

'ark

a/.

(1 994)

Coelsch and

abuza (1 992)

iapru and

abuza (1 992)

Preparation technique Test conditionsb Permeability

rnm/m2

kPa)

BW-S/MC

PEG (4.3

)

BW-S/MC: PEG (413

BW-M/MC: PEG (613

BW-M/MC

PEG (613

)

PW-M/MC

PW (2140

PW-M/MC

PEG (313

)

PW-MC

PEG (515

)

PW:MC:PW(5:5:1)

CZ: SA-PA: Gly

PEGIMC

PEG

SA:MC:PEG(40:10:1)

Bi-layer film, two-step technique

Emulsion film

Bi-layer film, two-step technique

Emulsion film

Bi-layer film, two-step technique

Emulsion film

Compositions rounded to nearest whole number.

RHs on top and bottom sides of film (topfbottom).

vlC, methyl cellulose; CZ, corn zein; PEG, polyethylene glycol; SA, stearic acid; PA, palmitic acid; BW, beeswax; PW, paraffin wax;

.M, molten state; -S, in a solvent.

damage from the impingement test, reflected in a 77-fold increase in

WVP.

Both the

BW-MIMC

PEG film and the BW-SIMC

PEG film showed 3- to Cfold increase in

WVP after weighted deformation, but they maintained their integrity.

Hagenmaier and Shaw (1990) prepared bi-layer edible films made from HPMC and

lauric acid, myristic acid, palrnitic acid, and stearic acid, by using the one-step emulsion

technique, and found that film WVP decreased as fatty acid chain length and concen-

tration increased.

this case, SA/HPMC bi-layer film, made from 95.6% ethanol by

casting a hot solution and then drying at 75OC for

hour, had a low

WVP

quite simi-

lar to that obtained earlier by Kamper and Fennema (1984a) (Table 22.3). However, it

was observed that on day

after preparation the films shrank by 7% in length, and the

HPMC-SA films became covered with stearic acid crystals. On day 6 the surface

powder could be wiped off, resulting in films that were fairly transparent, and a 10-

fold increase in the permeability was observed. This result indicates the need for

fur-

ther research to ensure the integrity of bi-layer films.

Martin-Polo

al.

(1992a) studied the influence of film preparation techniques on

moisture barrier. The films were composed of a hydrophobic substance, either paraffi

wax

(PW)

or oil, with MC as the supporting matrix. Films were prepared by emulsifjmg

the PW with MC

PEG and drying them at room temperature for

hours, or by coat-

ing the MC: PEG films with molten PW. The best results in reducing

WVP

were

Emulsion and bi-layer edible films

391

obtained using the two-step coating technique (Table 22.4), which could be explained by

the deposition of the PW in a continuous layer. Scanning electron microscopy of the

emulsified film showed a non-uniform surface, which allowed moisture transmission

to occur through the non-crystalline areas free of PW. These results indicated that a

bi-layer film was not formed using the emulsion technique, and showed that the ability

of a hydrophobic substance to retard moisture transfer depends on its homogeneity

and distribution in the system.

Results similar to those of Martin-Polo

al. (1992a) were obtained by Debeaufort

al. (1993). MC and PW films were also prepared using both the emulsion technique

and the coating technique. The results showed that a film of laminated PW over the MC

support was 10 times more efficient as a barrier to moisture transfer than an emulsion

film, due to the inability to form a bi-layer film using the emulsion technique (Table

22.4). These results contrast with the ones obtained by Kamper and Fennema (1984a),

and could indicate that bi-layer films using the emulsion technique may only be obtain-

able using fatty acids andlor by drying at elevated temperatures (Krochta, 1997a).

Park

al. (1994) prepared laminated films by casting corn zein-fatty acid solu-

tions onto MC

PEG films. Results showed that

WVP

decreased as chain length and

concentration of fatty acid increased. The best WVP obtained corresponded to films

containing 40% SA-PA blends (Table 22.4). The results were similar to those reported

by Kamper and Fennema (1984a) using the one-step emulsion technique. Such differ-

ences could be due to differences in

gradients and fatty acid concentrations. Since

the corn zein-fatty acid layer is insoluble in water, such films may be useful in high

moisture foods. However, the use of organic solvents is a significant disadvantage.

Debeaufort

al. (2000) prepared two bi-layer films, composed of a MC base layer

coated with a triglyceride or alkane layer, and studied the effect of solid fat content,

thickness, and melting point of the lipid layer on the mechanical and barrier proper-

ties of the films. The MC-PEG film was prepared in a water-ethyl alcohol solution

and dried at

2OC and 7

RH,

and the lipid mixtures were applied in the

molten state. The triglyceride lipid layer consisted of a mixture of hydrogenated palm

oil (HPO) and triolein (Trio), whereas the alkane layer consisted of a mixture of paraf-

fin

oil (PO) and PW. The mechanical properties were mainly attributed to the methyl

cellulose matrix. However, liquid lipids, both triolein and PO, had an antiplasticizing

effect on the hydrocolloid network. The moisture barrier decreased

to 20-fold as a

function of the lipid nature (alkanes or triglycerides) when the solid fat content varied

from 0 to 80%. When emulsion films were prepared with a similar composition,

Quezada-Gallo

al. (2000) observed that the nature of the lipid phase had little influ-

ence on the mechanical properties of emulsified films, but had a great effect on the

water vapor barrier efficiency, with alkanes providing better moisture barriers than

triglycerides. The solid-liquid ratio of the lipid phase had little effect on the moisture

barrier, since water vapor could pass through the hydrophilic MC.

Weller

al. (1998) determined the mechanical properties, WVP, and colorimetric

values of single-layer and bi-layer zein-lipid films. Zein films plasticized with glycerin

and polyethylene glycol were cast from heated (60°C) aqueous-ethanol solutions.

Bi-layer films were prepared by coating dried zein films with either medium chain

length triglyceride oil (MCTO), sorghum

wax

(SW)-MCTO, or carnauba wax

392

Innovations in Food Packaging

Preparation technique Test conditionsb Permeability

mm/m2

d kPa)

NC:Cly (5: 1) 30°C, 100/O%RH 8.3

3W-M/WG

Gly (712

)

Bi-layer film, two-step technique 30°C, IOO/O%RH 0.059

3W-M/WG

DTM

Cly (715

Bi-layer film, two-step technique

30°C, IOO/O%RH 0.036

3W:WG:Cly(2:5:1) Emulsion film 30°C, 100/O%RH 3.0

4dapted from Gontard

a/.

(1 994, 1995).

'Compositions rounded to nearest whole number.

RHs on top and bottom sides of film (top/bottom).

WC, wheat gluten; Gly, glycerol; BW, beeswax; DTM, diacetyl tartaric ester of monoglyceride; -M, molten state.

(Caw>-MCTO. Application of the lipid layer reduced

WVP

up to 98.7% and pro-

duced films with greater elongation. However, tensile strength was not modified by lipid

application. Bi-layer films were less yellow and more opaque

than

single-layer films.

Gontard

al.

(1995) investigated the moisture barrier properties of bi-layer films

consisting of wheat gluten (WG) as the structural layer and a

thin

layer of lipid as a

moisture barrier. Films were prepared by depositing the lipid layer, either in solvent or

molten state, over the surface of dried Gly-plasticizer WG film. Among the lipids

studied, BW was the most effective in reducing WVP, followed by PW and CW. In the

solvent method, an ethanol suspension of BW was cast over the base film at 70°C and

then dried at 30°C. In the molten lipid method, the BW was melted at 100°C and

spread over the previously formed base film, which had also been pre-heated to

100°C. The molten lipid method gave a bi-layer film with lower WVP than the solvent

method. This was attributed to the fact that BW is only partially soluble in hot ethanol,

which led to the formation of a much less continuous BW layer on the film surface.

The problem observed in these films was that the lipid layer became easily detached

from the WG-based film. Lipid adhesion was improved by the incorporation of a

diacetyl tartaric ester of monoglyceride

(DTM)

in the WG

Gly base film, which also

helped to reduce

WVP

(Table 22.5). The quantity of lipid cast over the WG was also

studied in this work, and a sharp decrease in film WVP was found as the lipid quan-

tity increased.

Hutchinson and Krochta (2002) prepared three types of two-step whey protein iso-

late (WP1)-BW composite films, with an aqueous emulsion

(AE),

ethanolic disper-

sion (ED), or hot melt (M-BW) of BW as the second layer. A one-step bi-layer film

was also attempted, using a large lipid particle-size WPI-BW emulsion. The two-step

films were found to be highly variable in quality, making it difficult to draw any con-

clusions about their effectiveness as moisture barriers. The M-BW bi-layer film had

the lowest WVP, reducing the

WVP

by two orders of magnitude over the base film

alone. The one-step bi-layer film was not successfully formed. However, the authors

showed that heating the one-step partial bi-layer film produced a reduction of

WVP

approximately 50%, giving

WVP

equivalent to the

and ED bi-layers, but contain-

ing approximately

50% less BW (Table 22.6).

Emulsion and bi-layer edible films

laole

22.6

Water vapor permeabilities

bi-layer and emulsion WPI-lipid edible films

Filma Preparation technique

Test

conditionsb Permeabiliy

mm/m2

kPa)

Hutchinson and WPI

BW:Gly (6: 3: 1) WPl:Gly (3: 1) 2S°C, 0/77%RH 88.1

Krochta (2002) WPl

BW: Gly (6

1 ) Emuls~on film, drled at 2S°C

2S°C, 0/97%RH 43.9

AE-BW/WPI

BW: Emulslon film, dried at 70°C 2S°C, 0/92%RH 35.0

Gly(4/6:3:1)

Bi-layer film, two-step technique 2S°C, 0/97%RH 21.4

ED-BW/WPI

BW: 81-layer film, two-step technique 2S°C, 0/99%RH 11.0

Gly(4/6:3:1) Bi-layer film, two-step technique 2S°C, O/lOO%RH 0.96

M-BW/WPI

BW:

Gly(4/6:3:1)

Shellhammer and CarW: WPI

Gly (1 1

1) WPI:Gly(15:1) 2S°C, 0/65%RH 45.6

Krochta(l997a) CanW:WPl:Gly(ll:15:1) Emulsion film 2S°C, 0/90%RH 33.6

HAMFF: WPI

Gly (I 1

1) Emulsion film

2S°C, 0/90%RH 31.2

HAMFF: WPI

Cly (24

1) Emulsion film 2S°C, 0/92%RH 21.8

BW:WPl:Gly(4:15:1) Emulsion film 2S°C, 0/99%RH 4.8

BW:WPl:Gly(l1:15:1) Emulsion film

2S°C, 0/92%RH 34.1

BW:WPl:Gly (24: 15:l) Emulsion film 2S°C, 0/94%RH 10.8

Emulsion film 2S°C, 0/98%RH 7.7

"Compositions rounded

nearest whole number.

RHS

on top and bottom sldes of film (top/bottom).

WPI, whey protein isolate; Gly, glycerol; BW, beeswax; CarW, carnauba wax; CanW, candelilla wax; HAMFF, hard anhydrous

milk fat fraction.

AE, aqueous emulr ethal Iten.

Properties of emulsion films

The nature of the interactions between proteins and lipids, or between polysaccharides

and lipids, determines the characteristics of emulsion formulations. In protein-lipid

emulsions, proteins play a major role in stabilizing the system. Due to the amphiphilic

character of proteins, they orient at the protein-lipid interface so that the non-polar

groups align toward the oil and the polar groups align towards the aqueous phase.

Therefore, the stabilization of the emulsions results from a balance between forces of

a different nature, mainly electrostatic and hydrophobic. While protein-lipid emul-

sions are mainly stabilized by electrostatic forces, polysaccharides stabilize emulsions

by stearic effects. To be good stabilizers, polysaccharides should be strongly attached

to the surface of the lipid and also protrude significantly into the continuous phase to

form a polymeric layer or a network of appreciable thickness (Callegarin

al.,

1997).

However, in many cases polysaccharides possess limited amphiphilic character, so the

addition of emulsifiers is required to improve emulsion stability.

Several studies have been conducted in an attempt to produce effective water vapor

barriers by dispersing lipids into either a polysaccharide or a protein film-formation

solution to form an emulsion film (Krochta, 1997a). Issues of lipid type, location, vol-

ume fraction, polymorphic phase, and drying conditions in emulsion composite films

394

Innovations in Food Packaging

have been studied as affecting the barrier properties of protein and polysaccharide-

based emulsion films.

As in bi-layer films, the water vapor resistance of emulsion films depends on the lipid

type. Many works have reported that the barrier properties depend on the polarity and the

degree of saturation of lipids (Martin-Polo

al., 1992a, 1992b; Gontard

al., 1994).

Thus,

high melting-point fatty acids, monoglycerides, hydrogenated fats, and waxes are

useful edible lipid barriers (Shellhammer and Krochta, 1997a; Morillon

al., 2002).

McHugh and Krochta (1994a) showed improved moisture-barrier properties in

whey protein-lipid emulsion films when the hydrocarbon chain length for fatty alco-

hols and monoglycerides increased from 14 to 18 carbon atoms (Table 22.7). In these

protein-lipid emulsion films,

and fatty acids were more effective at reducing

WVP

of WPI-based emulsion films than fatty acid alcohols, which is consistent with

the magnitude of lipid polarity.

WVP

measurements also revealed some emulsion sep-

aration during

drying,

since different

WVP

values were obtained depending on whether

the lipid-enriched side was oriented towards the high or the low

environment.

Koelsch and Labuza (1992) also showed

improvement in moisture-barrier prop-

erties of MC and fatty acids-based edible films as chain length increased from 12 to

18 atoms. However, the behavior changed as chain length increased from 18 to 22 car-

bon atoms. These results were correlated to the physical state and morphological

arrangement of the fatty acid within the film. Fluorescence analysis showed that the

Table

22.7

Effect of lipid chain length and degree of saturation on the water vapor permeability of dispersed lipid (emulsion)

edible films

Test conditionsb Permeability

mm/m2 d kPa)

McHugh and Krochta (1994b) WPl:Sor(4: 1) 23OC, 0/80%RH 51.8

McHugh and Krochta (1994a)

TD:WPI:Sor(2:4:1) 23"C, 0/88%RH 50.9

McHugh and Krochta (1994a) HD:WPl:Sor(2:4:1) 23OC, 0/87%RH 48.5

McHugh and Krochta (1 994a) STAL:WPl:Sor(2:4: 1) 23'C, 0/86%RH 46.3

McHugh and Krochta (1994a)

MA:WPl:Sor(2:4: 1) 23OC, 0/93%RH 23.7

McHugh and Krochta (1 994a) PA:WPI:Sor(2:4:1) 23OC, 0/93%RH 19.2

McHugh and Krochta (1 994b) BW:WPl:Sor(2:4:1)

23OC, 0/98%RH 5.3

Koelsch and Labuza (1 992)

LA:MC:PEG(4:10:1) 23OC, 33156% 2.9

Koelsch and Labuza (1 992) MA:MC:PEG(4:10:1) 23OC, 33156% 0.91

Koelsch and Labuza (1992) PA:MC:PEG(4:10:1) 23OC, 33156% 0.18

Koelsch and Labuza (1 992)

SA:MC:PEG(4:10:1) 23"C, 33156% 0.1 7

Koelsch and Labuza (1 992) AA:MC:PEG(4:10:1) 23OC, 33156% 1

Koelsch and Labuza (1992) BA:MC:PEG(4:10:1)

23OC, 33156% 2.6

Rhim

etal.

(1999)

Rhim

etal.

(1999)

Rhim

etal.

(1 999)

Rhim

etal.

(1 999)

SPI

Gly (2

1) 2S°C, 01100% 5.0

SPI:OA:Gly(2:2:1) 2S°C, 01100% 2.4

SPl:LA:Gly(2:2:1) 2S°C, 0/100% 1.5

SPI:SA:Gly(2:2:1) 2S°C, 01100% 0.5

acornpositions rounded to nearest whole number.

RHs on top and bottom sides of film (top/bottom).

MC, methyl cellulose; WPI, whey protein isolate; SPI, soy protein isolate; BW, beeswax; TD, tetradecanol;

HD, hexadecanol; STAL, stearyl alcohol; LA, lauric acid; MA, myristic acid; PA, palmitic acid; SA, stearic acid;

AA,

arachidic acid; BA, behenic acid; OA, oleic acid; Sor, sorbitol; PEG, polyethylene glycol.