Self-Supporting
Edible Films:
A Field of Interest in Modern
Food Science
Madhusweta Das and Satish Bal
Edible films are defined as a thin layer
of edible materials formed on food as a coating or a self-supporting
thin layer placed (pre-formed) on or in-between the food
components, and in both cases consumed along with the food.
Though edible films in the form of coatings are traditionally
used to extend the shelf life of food and maintain its quality
by inhibiting the migration of moisture, oxygen, carbon
dioxide, aromas and lipids, development of the self-supporting
form has been the subject of tremendous research since the
last decade. The worldwide interest on such films is evident
from increasing number of publications1,2 mentioning various
properties of the developed films.
The self-supporting films have been prepared
by casting solutions of proteins, carbohydrates and lipids,
in different combinations and compositions. Their properties
are found to be affected considerably by different factors
at different stages in the process. Table 1 gives a comprehensive
view on this aspect. The raw materials those have received
attention include polysaccharides (e.g., cellulose, modified
cellulose, starch, agar, carageenan, alginate, pectin, dextran,
pollulan, curdlan, etc.), proteins (e.g., zein, gluten,
collagen, gelatin, ovalbumin, myofibrillar proteins, etc.)
and lipids (e.g., carnuba wax, bees wax, lauric acid, palmitic
acid, stearic acid, etc.)3,4.
The properties of the edible films those
have been mostly evaluated are mechanical properties, like
ultimate tensile strength (UTS) and percent elongation at
break (EL) and the barrier properties, like water vapour
permeability (WVP) and oxygen permeability. Although most
of the developed films show desirable oxygen permeability,
their moisture barrier and mechanical properties are poor
in comparison to the synthetic polymeric films5-7. Table
2 gives qualitative information on some edible films prepared
from different biopolymers. Inclusion of lipids in the film
in emulsified form or following the technique of formation
of a composite bilayer has been found to improve the moisture
barrier property of the films8. Nevertheless, the mechanical
strength of the edible films appear to be quite reasonable
for making casings, wrappers or using as a septum in some
heterogeneous fabricated food items. Table 3 highlights
some possible applications of the edible films.
In addition to their usefulness as edible
coatings when applied externally, self-supporting films,
can control the diffusion of different ingredients from
one part to other within the food when applied as a septum
in between the layer of a fabricated heterogeneous food.
Additionally, self-supporting edible films can carry antioxidants,
antimicrobials in very specific area of a multicomponent
food system without unnecessarily incorporating the same
throughout. Traditional packaging materials can not compete
in these aspects.
Self-supporting edible films can conveniently
be used as wrapper for low moisture and confectionary items.
Films with considerable mechanical strength could be used
for making small pouches. In food packaging usually multibarrier
functionality is needed which is normally achieved with
the help of a laminated multilayer synthetic package. Such
disposed packages are difficult to recycle and ultimately
become a potent pollutant to the environment. Pouching of
foods with edible film will definitely contribute its inherent
barrier capacity and convert the need of conventional multilayer
laminated packages to simpler, even a single layer synthetic
package; the edible pouch could be used as a part of the
food, if liked, or as feed. Although the concept of total
replacement of synthetic packaging materials remains doubtful,
such simplification will certainly reduce the consumption
of the petroleum-based raw materials to a considerable extent.
Moreover the simplified synthetic package, if it is a single
layer one could conveniently be recycled. More important
practical aspect is the prevention of environmental pollution
through the reduction of the amount of synthetic plastic
in the package disposal.
Additionally, when fabricated from highly
dissolvable material, self-supporting films could be used
for making instant soluble pouches for soup mix, flavouring
components, leavening agents, etc. Such packets get dissolved
in the mix and could release the contents just at the time
of mixing. Ideally, there is no need to dispose off the
package. Thermoforming, overwrapping, and shrinkwrapping
of foods with self-supporting edible films is also conceivable.
On a broad perspective, edible films (which
are otherwise completely biodegradable too) with appreciable
mechanical strength could also find applications as packaging
materials or wrappers for some non-food items for protection
from various environmental contamination during their handling,
storage and distribution. Thus, the favourable aspects of
edible films can be summarised as follows.
(1) The films are completely biodegradable.
(2) The films can be a part of a food/used
as feed.
(3) The films can reduce the consumption
of naphtha-based polymeric films
Therefore, development of edible films
with good mechanical and barrier properties is undoubtedly
a challenge in the modern food science. Information on commercialisation
has recently been available with the film made from hydroxypropyl
cellulose (marketed by Watson Foods, West Haven, Conn)1.
These films are used to form pouches that allow processors
to add pre-measured amounts of additives such as colorant
and vitamin pre-mixes directly without further handling.
Although this developmental work is very
active at the international level, this is still at a rudimentary
stage in India. Since recent past, some scientist at Post
Harvest Technology Centre, IIT, Kharagpur, is persuading
on the development of starch-based edible films. The films
are quite appealing in appearance; their mechanical and
moisture barrier properties are comparable to many reported
protein-based edible films. Recently, one work has been
published9 on development of edible film from shark meat
by the scientists working at Bhaba Atomic Research Centre.
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The authors are faculty members at Department of Agricultural
and Food Engineering, IIT, Kharagpur
