Jung Han. Innovations in Food Packaging
Подождите немного. Документ загружается.
Edible films
and coatings: a
review
255
The determination of most physical and mechanical characteristics of film structures
is related to physical chemistry parameters, which include mechanical strength, elas-
ticity, moisture and gas permeation, cohesion of polymers, film adhesion onto food
surfaces, surface energy, surface roughness/smoothness, light transmittance, color
(opaque/gloss), viscosity, thermoplastic characteristics and others. More research is
needed to identify the relationship of these physical properties with the polymer struc-
ture chemistry (Sothornvit and Krochta, 2000).
Cohesion of film-forming materials is a very important parameter that influences
the mechanical strength of films, especially homogeneously continuous film struc-
tures (Guilbert
et
al., 1996). Cohesion is the attractive force between molecules of the
same substance (Anonymous, 1992). If the film-forming materials contain heteroge-
neous ingredients that are not compatible with the main biopolymers, the cohesion of
the film-forming materials decreases and the film strength weakens. When the use of
new biopolymers or additives is investigated, the compatibility of all film-forming
ingredients should be maintained to obtain strong cohesion. Plasticizers are the agents
reducing the cohesion of film-forming polymers (Guilbert
et
al., 1996).
Adhesion of film-forming materials is an important parameter, practically, for film
casting and coating processes (Peyron, 1991; Guilbert
et
al., 1996). Adhesion is the
attractive force between the surface molecules of different substances, such as
between coating materials and food surfaces (Anonymous, 1992). A low adhesion
force results
in
incomplete coatings on the surface, or easy peel-off of the coating lay-
ers from the surface. The surface energy of film-forming materials (surface tension of
the film-forming solution), the solid surface energy of uncoated product, and that of the
dried film should be determined to achieve strong adhesion.
A
larger difference of
the surface energy of a coating material from the uncoated product surface lowers the
work of adhesion and results in a poor coating performance (Peyron, 199 1). Surface-
active agents, such as emulsifiers and other amphiphilic chemicals in the film-forming
solution, reduce the surface tension of the coating solution, thus decreasing the dif-
ference between the solid surface energy and the surface tension of the coating solu-
tion and ultimately increasing the work of adhesion. From the following Young-Duprk
equation (Good, 1993), the work of adhesion (Wad) can be increased by decreasing y,,
(interfacial energy between the solid surface and liquid), which means reducing the
difference of energy between the solid food surface
(ys)
and liquid coating solution
(y,) and lowering the contact angle 8 (i.e., increasing cos 8).
Practical parameters for commercialization
Film-production processes
There are two categories of film-production processes; dry and wet (Guilbert
et
al.,
1997). The
dry process of edible film production does not use liquid solvents, such as
Innovations in Food Packaging
water or alcohol. Molten casting, extrusion, and heat pressing are good examples of
dry
processes. For the dry process, heat is applied to the film-forming materials to
increase the temperature to above the melting point of the film-forming materials, to
cause them to flow. Therefore, the thermoplastic properties of the film-forming mate-
rials should be identified in order to design film-manufacturing processes. It is neces-
sary to determine the effects of plasticizers and any other additives on the
thermoplasticity of the film-forming materials. Plasticizers decrease the glass transi-
tion temperature (Guilbert
et
al.,
1997; Krochta, 2002).
The wet process uses solvents for the dispersion of film-forming materials, fol-
lowed by drying to remove the solvent and form a film structure. For the wet process,
the selection of solvents is one of the most important factors. Since the film-forming
solution should be edible and biodegradable, only water, ethanol, and their mixtures
are appropriate as solvents (Peyron, 1991). All the ingredients of film-forming mate-
rials should be dissolved or homogeneously dispersed in the solvents to produce film-
forming solutions. The film-forming solution should be applied to flat surfaces using
a sprayer, spreader or dipping roller, and dried to eliminate the solvent, forming a film
structure. Phase separation of incompatible ingredients from the film-forming solu-
tion is not generally desirable unless the phase separation is intentionally designed for
the formation of a bi-layer film structure. To produce a homogeneous film structure
avoiding phase separation, various emulsifiers can be added to the film-forming solu-
tion (Peyron, 1991). This solvent compatibility of ingredients is very important to
develop homogeneous edible film and coating systems carrying active agents. All
ingredients, including active agents as well as biopolymers and plasticizers, should be
homogeneously dissolved in the solvent to produce film-forming solutions. Most
film-forming solutions possess much higher surface tension than the surface energy
of dried films, since they contain excessive amounts of water or ethanol. Therefore, it
is difficult evenly to coat a flat surface that has low surface energy with film-forming
solutions that possess high surface energy using high-speed coating equipment
in
manufacturing. Nonetheless, during the solvent drying process the film-forming solu-
tion is concentrated and its surface energy is decreased due to the loss of solvent. The
viscosity of the film-forming solution also affects the coating process. A lower viscos-
ity accelerates the separation process (coacervation) of the film-forming solution from
the flat surface and causes the uneven coating on the surface, followed by dripping
down of the coating solution from the surface to the floor. Higher viscosity of the film-
forming solution is desirable to reduce this coating phase separation, unless this cre-
ates an uncontrollably heavy coating thickness. If the film-forming solution has a
lower surface tension and higher viscosity, the high-speed coating process is more
likely to form a film layer on the flat surface. However, the lower surface energy of
coated films after drylng makes the peeling process of the film from the flat surfaces
harder, since there is a very high adhesion between the film and the flat surface when
there is a smaller difference of the surface energy between the film and the flat surface
(Figure 15.7). Conversely, this is a desirable phenomenon for the direct coating
process of the film-forming solution onto food surfaces to avoid the peeling problem
of the coated layer.
Edible
films
and
coatings: a review
257
Drying
I,
Peeling
I,
Film peeling roller
Figure
15.7
Effect of surface tension
(yL)
of coating solution on the adhesion of films during a film-forming process.
y,
is the surface
energy of a flat-base solid, such as a drum surface or a conveyor belt.
Feasibility of commercialized system
The production of edible films and coatings may require new processing systems, which
may include extrusion, roll orientation, conveyor drymng, bath coating, pan coating, or
other processes. These new production systems should be economically feasible, and
compatible with current synthetic film production processes and food coating
processes. They will be practicable when simple modifications of synthetic film and
coating processes lead to the production of edible films and coatings without signifi-
cant investments. To satisfy this feasibility of new production systems, the composi-
tion of film-forming materials should be carefully optimized and the film-forming
mechanisms modified (Petersen
et
al.,
1999).
Consumer-related issues
Since edible films and coatings are consumable parts of food products, the potential
uses of edible materials may be significantly affected by consumer acceptance (Petersen
et
al.,
1999).
Consumer acceptance is an integrated index of the subjective preferences
of consumers for the products, and includes organoleptic properties, safety, marketing,
and cultural hesitation regarding the use of new materials. Organoleptic properties
may include favorable flavor, tastelessness, sensory compatibility with coatedpackaged
foods, texture, and appearance (Han,
2002;
Nussinovitch,
2003).
Safety issues relate
to the potential toxicity or allergenicity of the new edible film-forming materials, and
microflora changes of the packagedcoated food products. Marketing factors include
the price of the final products, consumers' reluctance to use of the new materials, and
special attention of consumers to the use of the new packages if special instructions
nnovations in Food Packaging
are required for opening the packages, consuming the packagedlcoated foods, and
disposing of the used packaging materials.
Besides consumer acceptance, there are many limiting factors for the commercial
use of edible films and coatings. They may include the complexity of the production
process, large investment for the installation of new film-production or coating equip-
ment, potential conflict with conventional food packaging systems, manufacturers'
resistance to the use of new materials, and regulatory issues.
Regulatory issues
Since edible films and coatings are an integral part of the edible portion of products,
they should follow all required regulations regarding food products (Guilbert and
Gontard, 1995). All the ingredients of film-forming materials, as well as any functional
additives in the film-forming materials, should be food-grade, non-toxic materials
(Guilbert and Gontard, 1995; Han, 2002; Nussinovitch, 2003). Most GRAS status
ingredients have specific restrictions. For example, when the GRAS notification doc-
ument describes the intended use of a certain material as a surface treatment for poul-
try meat, the use of the same material for red meats, cheese, or other food products
would not be consistent with the GRAS notification.
From a regulatory standpoint, edible films and coatings could be classified as food
products, food ingredients, food additives, food contact substances, or food packaging
materials (Debeaufort
et
al., 1998; Petersen
et
al., 1999). In the case of pharmaceuti-
cal and nutraceutical applications, there may be other regulations regarding their use.
If there is a different viewpoint of categorization between manufacturers and regulatory
agencies, critical mislabeling problems may occur, resulting in mandatory product
recall situations. When food manufacturers formulate film-forming materials and apply
the materials on their food products, they should include all the film-forming ingredi-
ents on the labels of their final products. However, if they use edible film or coating
materials that have been produced by different suppliers, there may be the opportunity
to categorize them as food contact substances or food packaging materials. It is rec-
ommended that the edible film and coating material suppliers obtain no-objection
notifications from related authorizing agencies for the use of their film and coating
products as food ingredients, with careful considerations of proper labeling, including
nutritional information and possible allergenicity (Han, 2001,2002; Krochta, 2002).
Conclusions
Edible films and coatings are promising systems for the improvement of food quality,
shelf life, safety and functionality. They can be used as individual packaging materials,
food coating materials, active ingredient carriers, and to separate the compartments of
heterogeneous ingredients within foods. The efficiency and functional properties of
edible film and coating materials are highly dependent on the inherent characteristics
of film-forming materials, namely biopolymers (such as proteins, carbohydrates,
and
Edible
films
and coatings: a
review
259
lipids), plasticizers, and other additives. Most biopolymers are relatively hydrophilic
compared to commercial plastic materials. For industrial use, it is necessary to con-
duct scientific research to identify the film-forming mechanisms of biopolymers in
order to optimize their properties. It is also suggested that feasibility studies be per-
formed regarding the commercial uses of edible films and coatings by extending the
results of research and development studies to commercialization studies, such as new
process evaluation, safety and toxicity determination, regulatory assessment, and con-
sumer studies.
References
Amarante, C. and Banks, N. H. (2001). Post harvest physiology and quality of coated
fruits and vegetables.
Hort.
Rev.
26,161-238.
Anonymous (1992).
In:
Comprehensive Dictionary of Physical Chemistry
(L. Ulicky and
T. J. Kemp, eds), pp. 15,65. Ellis Horwood, Chichester,
UK.
Anonymous (1997). Edible films solve problems.
Food Technol.
51(2), 60.
Balasubramaniam,
\!
M., Chinnan, M. S., Mallikarjunan, P. and Phillips, R. D. (1997). The
effect of edible film on oil uptake and moisture retention of a deep-fat fried poultry
product. J
Food Process Eng.
20,17-29.
Baldwin,
E.
A. (1994). Edible coatings for fresh fruits and vegetables: past, present and
future. In:
Edible Coatings and Films to Improve Food Quality
(J. M. Krochta,
E. A. Baldwin and M. Nisperos-Carriedo, eds), pp. 25-64. Technomic Publishing,
Lancaster, PA.
Baldwin, E. A., Nispero-Carriedo, M.
0.
and Baker, R. A. (1995). Edible coatings for
lightly processed fruits and vegetables.
Hort. Sci.
30(1), 35-38.
Baldwin, E. A., Nispero-Carriedo, M. O., Hagenmaier, R. D. and Baker, R. A. (1997). Use
of lipids in coatings for food products.
Food Technol.
51(6),
56-64.
Banejee, R., Chen, H. and Wu,
J.
(1996). Milk protein-based edible film mechanical
strength changes due to ultrasound process.
.l
Food Sci.
61(4), 824-828.
Buss, D. D. (1996). Stretching
gum
applications.
Food Prod. Des.
December, 79-94.
Choi, W. S. and Han, J. H. (2001). Physical and mechanical properties of pea-protein-based
edible films.
J
Food Sci.
66(2), 3 19-322.
Cisneros-Zevallos,
L.,
Saltveit, M.
E.
and Krochta, J. M. (1997). Hygroscopic coatings
control surface white discoloration of peeled (minimally processes) carrots during
storage.
J
Food Sci.
62(2), 363-366,398.
Cuq, B., Gontard, N. and Guilbert, S. (1995). Edible films and coatings as active layers. In:
Active Food Packaging
(M. Rooney, ed.), pp. 11 1-142. Blackie, Glasgow, UK.
Dabrowska, R. and Lenart, A. (2001). Influence of edible coatings on osmotic treatment
of apples. In:
Osmotic Dehydration and Vacuum Impregnation: Applications in Food
Industries
(l?
Fito, A. Chiralt, J. M. Barat, W. E. L. Spiess and D. Behsnilian, eds),
pp. 43-49. Technomic Publishing, Lancaster, PA.
Debeaufort, F., Quezada-Gallo, J. A. and Voilley, A. (1998). Edible films and coatings:
tomorrow's packaging: a review.
Crit.
Rev.
Food Sci. Nutr.
38(4), 299-3 13.
Donhowe,
I.
G. and Fennema,
0.
(1994). Edible films and coatings: characteristics, for-
mation, definitions, and testing methods. In:
Edible Coatings and Films to Improve
nnovations in Food Packaging
Food Quality
(J. M. Krochta, E. A. Baldwin and M. Nisperos-Carriedo, eds), pp. 1-24.
Technomic Publishing, Lancaster, PA.
Gennadios, A. (2002). Soft gelation capsules. In:
Protein-based Films and Coatings
(A. Gennadios, ed.), pp. 393-443. CRC Press, Boca Raton, FL.
Gennadios, A. and Weller, C. L. (1990). Edible films and coatings from wheat and corn
proteins.
Food Technol.
44(10), 63-69.
Gennadios, A., McHugh,
T.
H., Weller, C. L. and Krochta, J.
M.
(1994). Edible coatings
and film based proteins. In:
Edible Coatings and Films to Improve Food Quality
(J. M. Krochta, E. A. Baldwin and M. Nisperos-Carriedo, eds), pp. 201-277. Technornic
Publishing, Lancaster, PA.
Gennadios, A., Ghorpade,
V
M.,
Weller, C.
L.
and Hanna, M. A. (1996). Heat curing of
soy protein films.
Trans. ASAE
39(2), 575-579.
Gennadios, A., Hanna, M. A. and Kurth, L. B. (1997). Application of edible coatings on
meats, poultry and seafoods: a review.
Lebensm. Wiss. u. Technol.
30(4), 337-350.
Gennadios, A., Rhim, J. W., Handa, A., Weller, C. L. and Hanna, M. A. (1998). Ultraviolet
radiation affects physical and molecular properties of soy protein films.
.I
Food Sci.
63(2), 225-228.
Good, R. J. (1993). Contact angle, wetting, and adhesion: a critical review. In:
ContactAngle,
Wettability andAdhesion
(K.
L. Mittal, ed.), pp. 3-36. VSP, Utrecht, The Netherlands.
Guilbert, S. (2002). Edible and biodegradable coating/film systems. In:
Active Food
Packaging
(J. H. Han, ed.), pp. 4-10. SCI Publication and Communication Services,
Winnipeg, Canada.
Guilbert, S. and Gontard, N. (1995). Edible and biodegradable food packaging. In:
Foods
and Packaging Materials
-
Chemical Interactions
(P.
Ackermann, M. Jagerstad and
T. Ohlsson, eds), pp. 159-168. The Royal Society of Chemistry, Cambridge, England.
Guilbert, S., Gontard, N. and Gorris, L. G. M. (1996). Prolongation of the shelf life of per-
ishable food products using biodegradable films and coatings.
Lebensm. Wiss. u.
Technol.
29,10-17.
Guilbert, S., Cuq, B. and Gontard, N. (1997). Recent innovations in edible andlor
biodegradable packaging materials.
Food Add. Contam.
14(6-7), 741-75 1.
Han,
J.
H. (2000). Antimicrobial food packaging.
Food Technol.
54(3), 5665.
Han, J. H. (2001). Design of edible and biodegradable films/coatings containing active
ingredients.
In:
Active BiopoIymer Films and Coatings for Food and Biotechnological
Uses
(H. J. Park, R. F. Testin, M. S. Chinnan and J.
W.
Park, eds), pp. 187-198.
Proceedings of Pre-congress Short Course of IUFoST, Seoul, Korea. 10th IUFoST
World Congress Organization.
Han, J. H. (2002). Protein-based edible films and coatings carrying antimicrobial agents.
In:
Protein-based Films and Coatings
(A. Gennadios, ed.), pp. 485499. CRC Press,
Boca Raton, FL.
Han, J. H. (2003). Antimicrobial food packaging. In:
Novel Food Packaging Techniques
(R.
Ahvenainen, ed.), pp. 50-70. Woodhead Publishing Ltd., Cambridge, UK.
Han, J. H. and Krochta, J. M. (1999). Wetting properties and water vapor permeation of
whey-protein-coated-paper.
Trans. ASAE
42(5), 1375-1382.
Han, J.
H.
and Krochta, J.
M.
(2001). Physical properties and oil absorption of whey-
protein coated paper.
.I
Food Sci.
66(2), 294-299.
Edible
films
and coatings:
a
review
261
Hong, S. I., Han, J. H. and Krochta, J. M. (2003). Optimal and surface properties of whey
protein isolate coatings on plastic films as influenced by substrate, protein concen-
tration, and plasticizer types.
J
Appl. Polym. Sci.
92(1), 335-348.
Howard, L. R. and Gonzales, A. R. (2001). Food safety and produce operations: what is
the future?
Hort. Sci.
36(1), 33-39.
Kester, J. J. and Fennema, 0. R. (1986). Edible films and coatings: a review.
Food Technol.
48(12), 47-59.
Krochta, J. M. (1997). Edible protein films and coatings. In:
Food Proteins and Their
Applications
(S. Damodaran and A. Paraf, eds), pp. 529-549. Marcel Dekker,
New York,
NY.
Krochta, J. M. (2002). Proteins as raw materials for films and coatings: definitions, current
status, and opportunities. In:
Protein-based Films and Coatings
(A. Gennadios, ed.),
pp. 1-41. CRC Press, Boca Raton, FL.
Krochta, J. M. and De Mulder-Johnston,
C.
(1997). Edible and biodegradable polymer
films: challenges and opportunities.
Food Technol.
51(2), 61-74.
Lacroix, M. and Ouattara, B. (2000). Combined industrial processes
with
irradiation to assure
innocuity and preservation of food products
-
a review.
Food Res.
Intl33(2), 719-724.
Matk,
J.
I. and Krochta, J. M. (1998). Oxygen uptake model for uncoated and coated
peanuts.
J
Food Eng.
35,299-3 12.
McHugh, T. H. and Krochta, J. M. (1994). Permeability properties of edible films. In:
Edible Coatings and Films to Improve Food Quality
(J. M. Krochta, E. A. Baldwin
and M. Nisperos-Carriedo, eds), pp. 139-187. Technomic Publishing, Lancaster, PA.
Mehyar, G. F. and Han, J. H. (2003). Physical and mechanical properties of edible films
made from high-amylose rice and pea starches.
In:
2003
IFTAnnual Meeting: Book
ofAbstracts,
p. 11 1. Institute of Food Technologists, Chicago, IL.
Micard,
X,
Belamri, R., Morel, M. H. and Guilbert, S. (2000). Properties of chemically
and physically treated wheat gluten films.
J
Agric. Food Chem.
48,2948-2953.
Miller, K. S., Chiang, M. T. and Krochta, J. M. (1997). Heat curing of whey protein films.
J
Food Sci.
62(6), 1 189-1 193.
Miller, K. S., Upadhyaya,
S.
K. and Krochta, J. M. (1998). Permeability of d-limonene in
whey protein films.
J
Food Sci.
63(2), 244-247.
Nussinovitch,
A.
(2003).
Water Soluble Polymer Applications in Foods,
pp. 29-69.
Blackwell Science, Oxford,
UK.
Park, H. J. (2000). Development of advanced edible coatings for fruits.
Trends Food Sci.
Technol.
10,254-260.
Park,
S.
K., Hettiarachchy, N. S., Ju, Z. Y. and Gennadios,
A.
(2002). Formation and prop-
erties of soy protein films and coatings. In:
Protein-based Films and Coatings
(A. Gennadios, ed.), pp. 123-137. CRC Press, Boca Raton, FL.
PBrez-Gago, M. B. and Krochta, J. M. (2002). Formation and properties of whey protein
films and coatings. In:
Protein-based Films and Coatings
(A. Gennadios, ed.),
pp. 159-180. CRC Press, Boca Raton, FL.
Petersen,
K.,
Nielsen,
P.
X,
Bertelsen, G.
et al.
(1999). Potential of biobased materials for
food packaging.
Trends Food Sci. Technol.
10,5248.
Peyron, A. (1991). L'enrobage et les produits filrnogenes:
un
nouveau mode dkmballage.
Viandes Prod. Cares
12(2), 4 146.
262
Innovations in Food
Packaging
Rhim,
J.
M.
(1998).
Modification of soy protein film by formaldehyde.
Korean
1
Food Sci.
Technol.
30(2), 372-378.
Sensidoni,
A.
and Peressini,
D.
(1997).
Edible films: potential innovation for fish products.
Induspie Alimentari
36(356), 129-1 33.
Sothornvit,
R.
and Krochta,
J.
M.
(2000).
Plasticizer effect on oxygen permeability of
P-lactoglobulin films.
1
Agric. Food Chem.
48,6298-6302.
Sothornvit,
R.
and Krochta,
J.
M.
(2001).
Plasticizer effect on mechanical properties of
P-lactoglobulin films.
1
Food Eng.
50, 149-1 55.
Were, L., Hettiarachcky,
N.
S. and Coleman, M.
(1999).
Properties of cysteine-added soy
protein-wheat gluten films.
1
Food Sci.
64(3), 5 14-5 18.
Wu, L.
C.
and Bates,
R.
F!
(1972).
Soy protein-lipid films.
1.
Studies on the film formation
phenomenon.
1
Food Sci.
37(1), 36-39.
Wu, P.
J.
and Schwartzberg, H. G.
(1992).
Popping behavior and zein coating of popcorn.
Cereal Chem.
69(5), 567-573.
Wu, Y., Weller, C. L., Hamouz,
F.,
Cuppett, S. L. and Schnepf,
M.
(2002).
Development
and application of multicomponent edible coatings and films: a review.
Adv. Food
Nutr Res.
44,347-394.
Yildirim, M. and Hettiarachchy,
N.
S.
(1997).
Biopolymers produced by cross-linking soy-
bean
11s
globulin with whey proteins using transglutaminase.
1
Food Sci.
62(2),
270-275.
Agro-polymers for
edible
and
biodegradable films:
review
of
agricultural
polymeric materials,
physical and mechanical
Sttfphane Cuilbert and Nathalie Contard
introduction
........................................................
263
Agro-polymers
........................................................
264
.............................................................
Processing 266
Properties and applications of edible and biodegradable films
.....................
267
Applications of agro-polymer based materials
..................................
270
Market opportunities
.....................................................
273
............................................................
Conclusion 274
.............................................................
References 275
Introduction
Various polymers obtained from products or by-products of agricultural origin are pro-
posed for the formulation of biodegradable materials or edible films. These polymers
(polysaccharides, proteins and lipids, or polyesters) can be used in various forms
Innovations in Food Packaging
ISBN:
0-12-3
1
1632-5
Copyright
O
2005
Elsevier
Ltd
All
rights
of reproduction
in
any
form reserved
264
Innovations in Food Packaging
(coatings, simple or multi-layer films, three-dimensional items, simple materials,
mix-
tures, blends, and composites). The materials obtained from these agro-polymers are
fully renewable and biodegradable (except when severe chemical modifications are
applied). They are non-toxic to the soil and the environment, and when food-grade
ingredients are used to formulate the materials, they can be edible.
In addition, edible and biodegradable coatings or films produced from agro-
polymers provide a supplementary and sometimes essential means of controlling
physiological, microbiological, and physicochemical changes in the food products.
This is achieved by controlling mass transfers between food products and ambient
atmospheres, or between the components in heterogeneous food products. Further-
more, due to some original material properties, they can also be used as an "active
bio-packaging" to modify and control food surface conditions (for example, gas-
selective materials, controlled release of specific functional agents, of flavor
compounds, etc.).
The formulation of bio-plastic or edible films implies the use of at least one compo-
nent able to form a matrix, having sufficient cohesion and continuity. They are poly-
mers which, under preparation conditions, have the property to form crystalline or
amorphous continuous structures. Only polyesters, polysaccharides or proteins are
used for making "materials". Natural lipid compounds are also used, primarily in the
field of edible film and coating applications. Generally they are applied in thin layers,
or as a composite with a polymeric matrix.
Three different techniques using agricultural raw materials (fully renewable raw
materials) are possible to make agro-polymers (Guilbert, 1999):
1.
Agricultural polymers (polysaccharides or proteins) can be extracted and eventu-
ally purified. They can be used alone or in a mixture with synthetic biodegradable
polymers such as polycaprolactone or other synthetic biodegradable polyesters.
2.
Agricultural products can be used as fermentation substrates to produce microbial
polymers (e.g. polyhydroxyalcanoates).
3.
Agricultural products (or by-products) can be used as fermentation substrates to
produce monomers or oligomers which will be polymerized by conventional
chemical processes (e.g. polylactic acid obtained by polymerization of natural lac-
tic acid produced by fermentation of corn).
Edible films or coatings
Agro-polymers that have been proposed to formulate edible films or coatings are
numerous (Cuq et
al.,
1995; Guilbert and Cuq, 1998). Polysaccharide, protein or lipid