Jung Han. Innovations in Food Packaging
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Edible films and coatings from starches
335
Kulp, K. and Lorenz, K. (1981). Heat-moisture treatment of starches I: Physicochemical
properties.
Cereal Chem.
58,46-48.
Leloup,
Y
M., Colonna,
P.,
Ring, S. G., Roberts, K. and Wells, B. (1992). Microstructure
of amylose gels.
Carbohydr. Polym.
18,189-1 97.
Liu,
Z.
(2002). Starch: from granules to biomaterials.
In.
Recent Research Developments
in Applied Polymer Science,
Vol.
1,
Part 1 (S. G. Pandalai, ed.), pp. 189-219. Research
Signpost, Trivandrum, India.
LMC International (2002).
Evaluation of the Community Policy for Starch and Starch
Products.
LMC International, Oxford, UK.
Lorenz, K. and Kulp, K. (1982). Cereal- and root starch modification by heat-moisture
treatment. I. Physico-chemical properties.
Starch
34,50-54.
Lourdin, D., Della Valle, G. and Colonna,
P.
(1995). Influence of amylose content on
starch films and foams.
Carbohydr. Polym.
27,261-270.
Lourdin, D., Bizot, H. and Colonna,
P.
(1997a). ccAntiplasticization" in starch-glycerol
films?
J
Appl. Polym. Sci.
63,1047-1053.
Lourdin, D., Coignard, L., Bizot, H. and Colonna,
P.
(1997b). Influence of equilibrium rel-
ative humidity and plasticizer concentration on the water content and glass transition
of starch materials.
Polymer
38,5401-5406.
Lourdin, D., Bizot, H. and Colonna,
P.
(1997~). Correlation between static mechanical
properties of starch-glycerol materials and low-temperature relaxation.
Macromol.
Symp.
114,179-185.
Mali, S., Grossmann, M.
Y
E., Garcia, M. A., Martino, M. N. and
Zaritzky,
N. E. (2002).
Microstructural characterization of yam starch films.
Carbohydx Polym.
50,379-386.
Mani, R. and Bhattacharya, M. (2001). Properties of injection moulded blends of starch
and modified biodegradable polyesters.
Eur. Polym.
J.
37,5
15-526.
Mark, A. M., Roth, W. B., Mehltretter, C. L. and Rist, C.
E.
(1964). Physical properties of films
from dimethyl sulfoxide pretreated-amylomaize starches.
Cereal Chem.
41,197-199.
Mark, A. M., Roth, W. B., Mehltretter, C. L. and Rist, C.
E.
(1966). Oxygen permeability
of amylomaize starch
films.
Food Technol.
20,75-77.
Miles, M. J., Morris,
V
J., Orford, P. D. and Ring, S. G. (1985). The roles of amylose and
amylopectin in the gelation and retrogradation of starch.
Carbohydr. Res.
135,27 1-28 1.
Moates, G. K., Noel, T. R., Parker, R. and Ring, S. G. (2001). Dynamic mechanical and
dielectric characterisation of amylose-glycerol films.
Carbohydx Polym.
44,247-253.
Moore, C.
0.
and Robinson, J. W. (1968). US Patent 3368909.
Muetgeert, J. and Hiemstra, P. (1958). US Patent 2822581.
Muetgeert, J., Bus, W. C. and Hiemstra,
P.
(1962). Influence of formaldehyde on viscosity
stability of concentrated aqueous amylose solutions.
J
Chem. Eng. Data
7,272-276.
Murphy,
P.
(2000).
Handbook of Hydrocolloids
(G. 0. Phillips and
P.
A. Williams, eds),
pp. 41-66. Woodhead Publishing Ltd, Cambridge,
UK.
Myllken,
P.,
BulCon, A., Lahtinen, R. and Forssell,
P.
(2002a). The crystallinity of amy-
lose and amylopectin films.
Carbohydr. Polym.
48,4148.
Myllarinen,
P.,
Partanen, R., Seppala, J. and Forssell,
P.
(2002b). Effect of glycerol on
behaviour of amylose and amylopectin films.
Carbohydr. Polym.
50,355-361.
Nakamura, S. and Tobolsb, A.
Y
(1967). Viscoelastic properties of plasticized amylose
films.
J
Appl. Polym. Sci.
11,1371-1386.
336
Innovations in Food Packaging
-
Narayan, R. (1994). Polymeric materials from agricultural feedstocks. In:
Polymers from
Agricultural Coproducts
(M. L. Fishman, R. B. Friedman and S. J. Huang, eds),
pp. 2-28. American Chemical Society, Washington, DC.
National Starch and Chemical Company (2003).
Food Starch.
http://www.foodstarch.com
Palviainen,
P.,
Heinhiki, J., MyllSirinen,
P.,
Lahtinen, R.,Yliruusi, J. and Forssell,
P.
(2001).
Corn starches as film formers in aqueous-based film coating.
Pharm. Develop. Technol.
6,353-361.
Paris, M., Bizot, H., Emery, J., Buzark, J. Y. and Bulkon, A. (1999). Crystallinity and struc-
turing role of water in native and recrystallized starches by
13c
CP-MAS
NMR
spec-
troscopy.
Carbohydr. Polym.
39,327-339.
Protzman, T. F., Wagoner, J. A. and Young, A. H. (1967). US Patent 3344216.
Rankin, J. C., Wolff,
I.
A., Davis, H. A. and Rist, C. E. (1958). Permeability of amylose
film to moisture vapor, selected organic vapors, and the common gasses.
Ind. Eng.
Chem.
3,120-123.
Rindlav, A., Hulleman, S. H. D. and Gatenholm,
P.
(1997). Formation of starch films with
varying crystallinity.
Carbohydr. Polym.
34,25-30.
Rindlav-Westling, A., Stading, M., Hermansson, A.-M. and Gatenholm,
P.
(1998). Structure,
mechanical and barrier properties of amylose and amylopectin films.
Carbohydr.
Polym.
36,217-224.
Ring, S. G., Colonna,
I?,
IYAnson,
K.
J.
et al.
(1987). The gelation and crystallisation of
amylopectin.
Carbohydr. Res.
162,277-293.
Ritzl, A., Regev,
0.
and Yerushalmi-Rozen, R. (1998). Structure and interfacial inter-
actions of thin films of amylopectin.
Acta Polym.
49,566-573.
Roth, W. B. and Mehltretter, C.
L.
(1970). Films from mixture of viscose and alkali high-
amylose corn starch.
J
Appl. Polym. Sci.
14,1387-1389.
Sair,
L.
(1967). Heat-moisture treatment of starch.
Cereal Chem.
44,8-26.
Sarko, A., Zeitlin,
B.
R.
and Germino, F. J. (1963). US Patent 3086890.
Sears, J.
K.
and Darby, J. R. (1982).
fie Technology of Plasticizers.
John Wiley
&
Sons,
New York,
NY.
Senti, F.
R.
and Dimler, R. J. (1959). High-amylose corn properties and prospects.
Food
Technol.
13,663.
Shannon, J. C. and Garwood, D. L. (1984). Genetics and physiology of starch develop-
ment. In:
Starch: Chemistry and Technology
(R.
L.
Whistler, J. N. BeMiller and
E. F. Paschall, eds), pp. 25-86. Academic Press, New York,
NY.
Strauss, U.
P.,
Porcja, R. J. and Chen, S.
Y.
(1990). Volume effects of amylose-water inter-
action.
Macromolecules
23, 172-1 75.
Stute, R. (1992). Hydrothermal modification of starches: the difference between anneal-
ing and
heatlmoisture-treatment.
Starch
44,205-214.
Thomas, D. J. and Atwell,
W.
A. (1997).
Starches.
Eagan Press, St Paul,
MN.
Unbehend, J. E. and Sarko, A. (1 974). Light scattering and x-ray characterization of amy-
lose films.
J
Polym. Sci. Polym. Phys. Ed.
12,545-554.
van Soest, J. J. G. (1996).
Starch Plastics: Structure-Property Relationships.
Utrecht
University, Utrecht, The Netherlands.
van Soest, J. J. G. and Essers,
F!
(1997). Influence of amylose-amylopectin ratio on properties
of extruded starch plastic sheetsJ
Macromol. Sci.
-
PureAppl. Chem.
A34,1665-1689.
Edible films and coatings fiom starches
337
van Soest, J. J. G. and Knooren, N. (1997). Influence of glycerol and water content on the
structure and properties of extruded starch plastic sheets during aging.
J;
Appl. Polym.
Sci.
64,141 1-1422.
Whistler, R.
L.
(1984). History and future expectation of starch use. In:
Starch: Chemistry
and Technology
(R.
L.
Whistler, J. N. BeMiller and E. F. Paschall, eds), pp. 1-9.
Academic Press, New York,
NY.
Wolff,
1.
A., Davis, H. A., Cluskey, J. E., Gundrum,
L.
J. and Rist, C. E. (1951). Preparation
of films fiom amylose.
Znd. Eng. Chem.
43,9 15-9 19.
Wolff, I. A., Davis,
H.
A., Cluskey, J.
E.
and Gundrum,
L.
J. (1952). US Patent 2608723.
Wu, H.-C. H. and Sarko, A. (1978a). The double-helical molecular structure of crystalline
B-amylose.
Carbohydr. Res.
61,2740.
Wu, H.-C. H. and Sarko, A. (1978b). The double-helical molecular structure of crystalline
B-amylose.
Carbohydr. Res.
61,7-25.
Yoshimoto, Y., Tashiro, J., Takenouchi, T. and Takeda, Y. (2000). Molecular structure and
some physicochemical properties of high-amylose barley starches.
Cereal Chem.
77,
279-285.
Young, A. H. (1967). US Patent 33 12641.
Young, A. H. (1984). Fractionation of starch. In:
Starch: Chemistry and Technology
(R.
L.
Whistler, J. N. BeMiller and
E.
F. Paschall, eds), pp. 249-284. Academic Press,
New York,
NY.
Zobel, H.
F.
(1964). X-ray analysis of starch granules. In:
Methods in Carbohydrate Chem-
istry
(R.
L.
Whistler, ed.), pp. 109-1 12. Academic Press, New York,
NY.
Zobel, H.
F.
(1988). Starch crystal transformations and their industrial importance.
Starch
40, 1-7.
Edible
films and
coat~ngs trom non-
starch polysaccharides
Monique Lacroix and Canh
Le
Tien
Introduction
.......................................................
338
Non-starch polysaccharides used for films and coatings
..........................
341
Applications of edible films and coatings
.....................................
348
Carbohydratechemistry
...................................................
352
Conclusion
............................................................
354
References
............................................................
355
Introduction
The use of polysaccharides as coating materials for food protection has grown exten-
sively in recent years. These natural polymers can prevent the product's deterioration,
extending the shelf life and maintaining the sensory quality and safety of several food
products (Robertson,
1993).
Generally, these systems are designed by taking advan-
tage of their barrier properties against physicallmechanical impacts, chemical reactions,
and microbiological invasion.
In
addition, the use of polysaccharides presents advantages
due to their availability, low cost, and biodegradability. The latter in particular is of great
interest, as it leads to a reduction in the large quantities of non-biodegradable synthetic
packaging materials. Furthermore, polysaccharides can be easily modified in order to
improve their physiochemical properties.
Water-soluble polysaccharides are long-chain polymers that dissolve or disperse in
water to give a thickening or viscosity-building effect (Glicksman,
1982).
These com-
pounds serve numerous functions, such as providing crispness, hardness, adhesiveness
etc. Non-starch polysaccharides are obtained from a variety of sources, such as cellu-
lose derivatives
(carboxymethylcellulose,
methylcellulose, hydroxypropyl cellulose,
hydroxypropyl methyl cellulose, microcrystalline cellulose), seaweed extracts (agar,
alginates, carrageenans, furcellaran), various plant and microbial gums (arabic,
ghatti, karaya, tragacanth, guar, locust bean, xanthan, gellan, pullulan, levan, elsinan),
Innovations in Food Packaging
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Edible films and coatings from non-starch polysaccharides
339
Polysaccharide
type
Food
use
~ellulose and derivatives
8
Carboxymethylcellulose Multipurpose
D
Methylcellulose
B
Hydroxypropyl cellulose
r
Hydroxypropyl methylcellulose
Multipurpose
Emulsifier, film-former, stabilizer, thickener,
suspending agent, protective colloid
Emulsifier, film-former, stabilizer, thickener,
suspending agent, protective colloid
r
Microcrystalline cellulose Multipurpose
Sitosan*
*
D
Gellan gum
Antimicrobial activity, food wraps, controls moistur
transfer, enzymatic browning and respiration rate,
antioxidant, flavoring
Stabilizer
Seaweed extracts
r
Agar
D
Alginates
D
Carrageenans
Furcellaran
Pectins
Microbial firmentution gums
Xanthan
&date gums
Gum arabic
r
Gum ghatti
Drying and flavoring agent, stabilizer, thickener,
surface-finisher, formulation aid, humectant
Stabilizer, thickener, humectant, texturizer,
formulation aid, firming agent, flavor adjuvant,
flavor enhancer, processing aid, surface active agent
Emulsifier, stabilizer, thickener
Emulsifier, stabilizer, thickener
Emulsifier, stabilizer, thickener
Stabilizer, emulsifier, thickener, suspending agent,
bodying agent, foam enhancer
Emulsifier, formulation aid, stabilizer, thickener,
humectant, texturizer, surface-finishing agent,
flavoring agent, adjuvant, emulsifier
Emulsifier
8
Gum karaya Formulation aid, stabilizer, thickener
Gum tragacanth
Emulsifier, thickener, stabilizer, formulation aid
Seed gums
Guargum
Locust bean gum
Emulsifier, formulation aid, stabilizer, thickener,
firming agent
Stabilizer, thickener
*Nisperos-Carriedo (1994); **Rudrapatnam and Farooqahmed
(2003).
and connective tissue extracts of crustaceans (chitosan) (Nisperos-Carriedo, 1994).
The non-starch polysaccharides and their functions are summarized in Table
20.1.
Coatings
are
defmed as
thin
layers of material applied
to
the surface of a food product.
Edible coatings represent a unique category of packaging materials that differ from
other conventional packaging materials in being edible. Edible coatings are applied and
formed directly on the food product either by the addition of a liquid film-forming solu-
tion, or by being applied with a paintbrush, by spraying, dipping or fluidizing (Cuq
et
al.,
1995). Edible coatings form an integral
part
of the food product and hence should not
interfere with the sensorial characteristics of the food (Guilbert
et
al., 1997). The edible
innovation^
Food
Packaging
coating compositions generally contain a polymer as a matrix and a plasticizer or, in cer-
tain cases, a stabilizing agent to improve the rheological properties.
An
edible polymer
should be generally recognized as safe (GRAS), and the materials should be used in
accordance with current good manufacturing practices (food grade, prepared and han-
dled as a food ingredient) and within any limitations specified by the Food and Drug
Administration (Krochta and De Mulder-Johnston, 1997). These considerations are
also valid for additives in edible coating formulations.
The ability of some water-soluble polysaccharides to form thermally induced gelat-
inous coatings can be used for the reduction of oil absorption during frying.
Polysaccharide-based formulations may also retard moisture loss from meat products
during short-term storage. They do this by acting as a sacrificial moisture barrier to the
atmosphere, so that the moisture content of the coated food can be maintained (Kester
and Fennema, 1986). Certain polysaccharide films may provide effective protection
against surface browning, and oxidation of lipids and other food components (Kester
and Fennema, 1986; Nisperos-Carriedo, 1994). In addition to preventing moisture
loss, some types of polysaccharide films are less permeable to oxygen. Decreasing the
oxygen permeability of coatings can help to preserve certain foods. The following is
an overview of several types of polysaccharide coatings and their functions.
On the other hand, edible films are freestanding structures, first formed and then
applied to foods. They are formed by casting and drylng film-forming solutions on a
levelled surface, or by using a
drum
drier or other traditional plastic processing tech-
niques such as extrusion. Edible films can also be formed by applying the coating
solutions directly on a food product. Edible films and coatings may be used to sepa-
rate different components in multicomponent foods, thereby improving the quality of
the product (Krochta and De Mulder-Johnston, 1997).
The film requirements for food products are complex. Unlike inert packaged com-
modities, foods are often dynamic systems with a limited shelf life and very specific
packaging needs. In addition, since foods are consumed to sustain life, the need to
guarantee safety is a critical factor in the packaging requirements. While the issue of
food quality and safety is the priority in the minds of food scientists, a range of other
issues surrounding the development of any food package must be considered before a
particular packaging system becomes a reality.
Secondary packaging is often used for physical protection of the food product. It
may be a box, surrounding a food packaged in a flexible plastic bag. It may be a cor-
rugated box that contains a number of primary packages in order
to
ease handling during
storage and distribution, improve stackability, or protect the primary packages from
mechanical damage. Owing to the barrier properties of edible films and coatings, the
coated foods may not require high-barrier packaging materials. Therefore, the entire
packaging structure can be simplified, by satisfying the barrier requirements. The bar-
rier functions concern oxygen, moisture, and aroma blocks, as well as physical dam-
age prevention.
In addition to the increased barrier properties, edible films and coatings control
adhesion, cohesion, and durability, and improve the appearance of coated foods
(Krochta, 1997). They can incorporate active ingredients such as antioxidants, antirni-
crobial agents, colorants, flavorings, fortified nutrients, andlor spices (Floros
et
al.,
Edible films and coatings from non-starch polysaccharides
341
1997). Edible films and coatings must also meet the criteria that apply to conventional
packaging materials associated with foods. These relate to barrier properties (water,
gases, light, aroma), optical properties (transparency), strength, welding and molding
properties, printing properties, migrationlscalping requirements, chemical and temper-
ature resistance properties, disposal requirements, and issues such as the user-friendly
nature of the materials and whether the materials are price competitive. Edible
fh
materials must also comply with food and packaging legislations, and the interactions
between the food and packaging materials must not compromise food quality or
safety. In addition, the intrinsic characteristics of edible film materials (for example,
whether or not they are biodegradable) can place constraints on their use for foods.
Due to the hydrophilic nature of polysaccharides, polysaccharide-based films
exhibit limited water vapor barrier ability (Gennadios
et
al., 1997). However, films
based on polysaccharides such as like alginate, cellulose ethers, chitosan, carrageenan
or pectins exhibit good gas-barrier properties (Baldwin
et
al., 1995; Ben and Kurth,
1995). The gas-permeability properties of such films result in desirable modified
atmospheres, thereby increasing the product shelf life without creating anaerobic con-
ditions (Baldwin
et
al., 1995). Polysaccharide films are used in Japan for meat prod-
ucts, ham and poultry packaging, before smoking and steaming processes. The film is
dissolved during the process, and the coated meat exhibits improved yield, structure,
and texture, and reduced moisture loss (Labell, 199 1
;
Stollman
et
al., 1994).
Non-starch polpaedharides used for
films and coatings
Cellulosic derivatives
Cellulose is present in all land plants, being the structural material of cell walls
(Nisperos-Carriedo, 1994). Cellulose is the most abundantly occurring natural poly-
mer on earth, and is an almost linear polymer of anhydroglucose. At a molecular level,
cellulose is a relatively simple polymer consisting of P-[1,4] linked D-glucose mole-
cules in a linear chain. Because of its regular structure and array of hydroxyl groups,
it tends to form strong hydrogen-bonded crystalline microfibers, which are insoluble
in several solvents. Cellulose is a cheap raw material, and is highly crystalline and
insoluble. For film production, cellulose is dissolved in an aggressively toxic mixture
of sodium hydroxide and carbon disulfide (xanthation) and then recast into sulfuric
acid to produce cellophane films (Petersen
et
al., 1999). The use of cellulose xanthate
as a matrix for entrapment of cross-linked whey protein can produce insoluble films
with good mechanical properties, good stability, and increased resistance to enzy-
matic attack (Le Tien
et
al., 2000). The application potential of these films as packag-
ing and wrapping materials can be of interest for various materials, and is probably
compatible with several types of foods.
However, the usefulness of cellulose as a starting material for edible coatings can
be extended by chemical modification to cellulosic derivatives. Generally, cellulose
342
Innovations in Food Packaging
derivatives possess excellent film-forming properties, but they are simply too expen-
sive for bulk use. This is a direct consequence of the crystalline structure of cellulose,
making the initial steps of derivatization difficult and costly. Research is required to
develop efficient processing technologies for the production of cellulose derivatives,
if this situation is to change. Cellulose-based films and coatings reduce moisture loss and
reduce the amount of oil absorbed by fried foods (Sanderson, 198 1
;
Dziezak, 199 1).
Edible coatings based on cellulose gums have also been used to delay ripening in
some climatic fruits like mangoes, papayas and bananas. Furthermore, the application
of the same formulation on sliced mushrooms has been shown significantly to reduce
enzymatic browning (Nisperos-Carriedo
et al., 199 1).
Several cellulose derivatives are widely produced commercially, most commonly
carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose
(HPC), and hydroxypropylmethyl cellulose (HPMC). Edible coatings, which include
CMC, MC, HPC, and HPMC, have been applied to a variety of foods to provide mois-
ture, oxygen or oil barriers, and to improve batter adhesion. CMC, MC, HPC or
HPMC can be solubilized in aqueous or aqueous-ethanol solutions, producing films
with good film-forming properties, but are soluble in water (Gennadios
et al., 1997).
These cellulose ether films are generally transparent, flexible, odorless, tasteless,
water-soluble, and resistant to oils and fats (Kester and Fennema, 1986; Hagenmaier and
Shaw, 1990; Hanlon, 1992; Nisperos-Carriedo, 1994). HPC is the least hydrophilic of
the cellulose ethers (Gennadios
et al., 1997); it is also thermoplastic and capable of
injection molding and extrusion. Cellulose can also be chemically modified to give
ethyl cellulose (EC), which is biodegradable but not edible.
Non-ionic cellulose ethers have good film-forming properties. However, MC films
still do not have good moisture barriers, but do provide an excellent barrier against
migration of fats and oils (Nelson and Fennema, 1991). For example, MC and HPMC
can be used to reduce oil absorption in fried products such as potato (Sanderson,
1981), fried poultry (Holownia
et al., 2000) etc. MC and HPMC can reduce moisture
loss during cooking of poultry and seafood (Baker
et al., 1994). Balasubramaniam
et al. (1 997) have demonstrated that meatballs prepared from ground chicken breast and
coated with HPMC absorbed 33.7% less fat and retained up to 16.4% more moisture
than uncoated controls during deep-fat frying in peanut oil. HPC can retard spoilage
and moisture absorption (Ganz, 1969) and retard spoilage and moisture absorption in
coated nuts and candies (Krumel and Lindsay, 1976). CMC is an anionic cellulose
ether and forms a complex in the presence of casein, increasing the coating formula-
tion viscosity (Keller, 1984); it retains the firmness of fruits and vegetables (Mason,
1969), preserves important flavor components of some fresh commodities (Nisperos-
Carriedo and Baldwin, 1990), reduces oxygen uptake without causing carbon dioxide
increase in internal fruits and vegetables (Lowings and Cutts, 1982), and improves the
puncture strength of films based on caseinate (Ressouany
et al., 1998).
Chitosan
Chitosan is a polysaccharide derived from chitin, and is found in abundance in the shells
of crustaceans. Chitosan is mainly composed of
2-amino-2-deoxy-/3-D-glucopyranose
Edible films and coatings from non-starch polysaccharides
343
repeating units, but still retains a small amount of 2-acetamido-2-deoxy-ED-
glucopyranose residues. Chitosan with a high amino content (pKa
=
6.2-7.0) is water-
soluble in aqueous acids @mudo and Dornard, 1989).
In
general, chitosan has numerous
uses; it can be used as a flocculent, clarifier, thickener, gas-selective membrane, pro-
moter of plant disease resistance, wound-healing factor agent, and antimicrobial agent
(Brine et al., 199 1). Chitosan also readily forms films, and in general produces materi-
als with a high gas barrier. Chitosan may also be used as coatings for other bio-based
polymers that lack gas-barrier properties. Moreover, chitosan has been widely used for
the production of edible coatings (Krochta and De Mulder-Johnston, 1997). However,
as with other polysaccharide-based polymers, care must be taken for moist conditions.
The cationic properties of chitosan offer good opportunities to take advantage of elec-
tron interactions with numerous compounds during processing and incorporate spe-
cific properties into the material. The cationic property may fi-u-ther be used for the
incorporation and/or slow release of active components, adding to the possibilities for
the manufacturer in tailoring the properties (Hoagland and Parris, 1996). Further inter-
esting properties of chitosan and chitin in relation to food packaging are their antimi-
crobial properties (Dawson et al., 1998; Coma et al., 2002) and their ability to absorb
heavy metal ions (Chandra and Rustgi, 1998). The former could be valuable in relation
to the microbial shelf life and safety of the food products, and the latter could be used
to diminish oxidation processes in foods catalyzed by free metals.
Chitin and chitosan are natural antimicrobial compounds against different groups of
micro-organisms, such as, bacteria, yeast, and fungi (Yalpani et al., 1992; Ouattara et al.,
2000). Because of the positive charge on the C-2 of the glucosamine monomer at pH 6
and below, chitosan is more soluble and has better antimicrobial activity compared to
chitin (Yalpani et al., 1992). Also, the efficiency of the antimicrobial properties of chi-
tosan depends on the degree of polymerization and of acetylation (Chen et al., 1998).
Sulfonated chitosans (DS
=
0.63) have a minimal inhibitory concentration (MIC) of 100
ppm for Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Ebrio
parahaemolyticus.
A
MIC of 200ppm was observed for Pseudomonas aeruginosa and
Shigella dysenteriae (Chen et al., 1998). Chitosan can also reduce the growth of numer-
ous fungi. Chitosan with an
-NJ&
content of 7.5% markedly reduced the radial growth of
Botrytis cinerea and Rhizopus stolonifr in strawberries (El Ghaouth et al., 199 la).
A
chi-
tosan coating was shown to inhibit sclerotina rot
in
carrots (Cuero et al., 1991). Treatment
with chitosan also induces activity of chitinase enzymes, which are metabolized by the
plant for the purpose of self-protection against pathogens (Mauch et al., 1984).
Coatings and films based on chitosan and its
N,
0-carboxymethyl derivatives were
used to reduce water loss, respiration, and fungal infection in peaches, Japanese pears,
kiwi fruits, strawberries, tomatoes, bell peppers, cucumbers, bananas, and mangoes
(El Ghaouth et al., 1991a, 1991b;
Kittur
et al., 1998). NO-carboxymethyl chitin films
have been approved in several countries to preserve hits over a long period of time
(Rudrapatnam and Farooqahmed, 2003).
Due to their good ability to form semipermeable films, chitosan-based films can be
expected to modify the internal atmosphere as well as decrease the transpiration losses
and delay the ripening in fruits. Chitosan films have good mechanical properties, being
flexible and difficult to tear. Chitosan films also have moderate water vapor permeability
Innovations in Food Packaging
properties, and exhibit good barriers to the permeation of oxygen (Rudrapatnam and
Farooqahmed, 2003). They can also control enzymatic browning in fruits. For exam-
ple, the application of a chitosan film onto lychee fruit delayed changes in the content
of anthocyanins, flavonoids, and total phenolics, delayed an increase in polyphenol
oxidase activity, and partially inhibited the increase in peroxidase activity. Browning
reactions are related to the oxidation of phenolic compounds (Sapers and Douglass,
1987). The preparation of chitosan films and chitosan-laminated films with other
polysaccharides has been reported (Kester and Fennema, 1986; Lobuza and Breene,
1986; Chen
et al., 1996;
Kittur
et al., 1998). Hoagland and Parris (1996) have shown that
the storage and loss moduli of
chitosan-/pectin-laminated films were significantly
greater than the respective moduli of chitosan films alone. However, the water vapor
permeation of laminated chitosanlpectin films was not changed as compared to films
based on chitosan alone. Makino and Hirata (1997) have shown that a biodegradable
laminate consisting of chitosan cellulose and polycaprolactone can be used in modified
atmosphere packaging of fresh produce.
Seaweed
extracts
Alginate
Alginate is a polysaccharide derived from brown seaweed known as Phaeophyceae, con-
sidered to be a (1->4) linked polyuronic, containing three types of block structure:
M block (p-D-mannuronic acid), G block (poly a-L-guluronic acid), and MG block (con-
taining both polyuronic acids) (Whistler and BeMiller, 1973). The relative amounts of
the two uronic acid monomers and their sequential arrangement along the polymer chain
vary widely, depending on the origin of the alginate. Alginates produce uniform, trans-
parent and water-soluble films. Divalent cations are used as gelling agents in alginate
film formation to induce ionic interactions followed by hydrogen bonding (Kester and
Fennema, 1986). Films and coatings can be made from a sodium alginate solution by a
rapid reaction with calcium in the cold, forming intermolecular associations involving
the G-block regions (Nisperos-Carriedo, 1994). The treatment of an alginate film with
multivalent cation (i.e. calcium) solutions converts the film to insoluble (Pavlath
et al.,
1999). Alginates possess good film-forming properties, but tend to be quite brittle when
dry;
however, they may be plasticized with the inclusion of glycerol (Glicksman, 1983).
Alginate-based films are impervious to oils and fats, but are poor moisture barriers
(Cottrell and Kovacs, 1980). However, alginate gel coatings can significantly reduce
moisture loss from foods by acting sacrificially
-
i.e. moisture is lost from the coating
before the food significantly dehydrates. Also, alginate coatings are good oxygen
barriers (Conca and Yang, 1993), can retard lipid oxidation in foods (Kester and
Fennema, 1986), and can improve flavor, texture and batter adhesion. Alginate pro-
vides beneficial properties when applied as an edible coating to precooked pork pat-
ties (Wanstedt
et al., 1981; Amanatidou et al., 2000). Such coatings increase moisture
and reduce flavors due to lipid oxidation. Alginate coatings have been found to reduce
weight loss (Lazarus
et al., 1976) as well as the natural microflora counts in minimally
processed carrots, stored lamb carcasses (Lazarus
et al., 1976; Amanatidou et al., 2000),
fish, shrimps, and sausages (Earle and Snyder, 1966; Earle, 1968; Daniels, 1973), and