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Plastics As Food Packaging Material
By Th Ibotomba Singh
Introduction: Plastics and polymers have become
a part of our life today. In fact they have
become as essential to mankind as food and
water. We begin our day by brushing our teeth
with nylon bristles. We take bath using plastic
buckets. We wear clothes made from Terylene and
nylon which are man-made polymer fibers. We use
plastic dishes and melamine crockery in the
kitchen. We put on shoes with synthetic rubber
soles. We travel in cars and buses which have a
number of plastic parts. There is no sphere of
human activity in which plastics have not made
their entry ranging from agriculture, chemical
industry, packaging, space exploration or for
that even off-shore drilling. In fact, plastics
now find a place in every field. The ever
increasing use of plastics in our daily life
raises an important question in the mind of any
sensible person. Are plastics harmless enough to
be used in contact with food? Let us seek the
answer of this question.
Common Plastics Used In Food Packaging: The
plastics we generally come across are not
considered to be toxic or harmful in any way.
They are even safe even if they come in contact
with food. In fact, most of the polymers may be
consumed orally without any ill effects, as they
are inert and do not react with the chemicals in
our body. However, one must remember that, even
if a polymer is completely nontoxic, the monomer
from which it is made may not be so. Some
monomers are in fact harmful to human health
particularly styrene (S) and vinyl
chloride (VC). There is always a possibility
that a small amount of
monomer might be present in the plastic in an
uncombined form. Therefore, the level of
unreacted monomer has to be closely monitored in
case of such plastics. Due permission has to be
obtained from the Food and Drug Administration,
Government of India before using any plastics as
food packaging material.
The Indian Institute for Food Packaging, Bombay and the Central Food Technological Research Institute, Mysore have carried out considerable research on this subject and have developed certain standards to be followed while using plastics in contact with food. The samples are tested and permission is granted only if the unreacted monomer present is less than 1 ppm (that is one part of monomer per million parts of plastics by weight), in case of polystyrene or PVC. In general plastics such as polyethylene (PE), polypropylene (PP), oriented polystyrene, Nylon, Polyester, Polyurethane, Saran and polyethylene terephthalate (PET) are used as food packaging material .
Polyethylene (PE): The main requirements of a
packaging material are-
a. To protect and maintain the quality of the
contents,
b. To enhance the aesthetics of the product.
Ethylene, the monomer of polyethylene, is
completely harmless and therefore, polyethylene
is nontoxic even if some ethylene monomer is
present in the polymer. The properties that make
PE film a popular packaging medium are its low
price, toughness, flexibility, pleasing
appearance and softness, chemical inertness,
relatively high oxygen and carbon dioxide
permeability. On the debit side is its low
softening point, poor resistance to greases and
difficult machine handling. The use of high
density polyethylene (HDPE) film improves
softening, temperature and grease resistance,
and stiffness but gives poor clarity. Light
density polyethylene (LDPE) film is used for
packaging of milk, oil, grains, spices, salt and
other eatables. The rigid plastic container used
for coconut oil, vegetable oils, face cream and
other cosmetic products are made from HDPE.
Polypropylene (PP): Polypropylene, the monomer
of which is also non toxic, is extensively used
as packaging material. If PP film were not
quenched rapidly after processing close to the
melting point, the product would be opaque and
have poor impact properties. Rapid quenching of
blown film can be achieved by special techniques
and flat film casting prevents formation of
large spherulites, and transparency is
maintained. PP cast film is more hard and more
transparency than PE film and mainly used in
food packaging where transparency is required.
Oriented Polystyrene (OPS) film: The properties
that make an OPS film a popular packaging medium
are its clarity, rigidity, low cost, thinness
and high gas permeability. An OPS is suitable
for thermoforming (i.e. trays for meat produce,
disposable cup & plate, and containers for
confectionaries), packaging fresh produce and
shrink wrap.
Nylon films: The useful properties of nylon
films are thermoformability, crack and abrasion
resistance, and good low temperature properties.
Its main applications include vacuum packs,
processed meat and cheese, boil-in-pouch.
Polyester film: The main advantages of polyester
films are that they are tough, sterilizable,
very clear, chemical resistant and laminate
base. Its main applications include metallized
films, vacuum and gas packaging, shrink
packaging, cured meat, boil-in-bag,
throw-in-pack food.
Thermoplastic Urethane film: The main advantages
of urethane are that it is very tough and
elastic. The abrasion resistance of
thermoplastic urethane is significantly higher
than other conventional films and sheets. This
property is not only useful in free film package
design, but also imparts excellent wear
characteristics to laminates when this film is
the laminating base film. The impact properties
of these materials are excellent because of
their elongation and puncture resistance. The
main applications of urethane film includes
packaging sharp objects, oil pouches, radiated
food containers and military food
packaging.
Saran film: Recently, some plastics have been
developed specially to be used as food packaging
materials. Saran, a copolymer of vinyl chloride
and vinylidene chloride, is extensively used in
abroad for food packaging. Saran films are
highly transparent and hence food items wrapped
in saran film look very attractive. Moreover,
these films are totally impermeable to air and
therefore, there is a many-fold increase in the
shelf life of the items wrapped in saran.
Polyethylene terephthalate (PET): PET has been
introduced in the Manipur market a few years
back. The transparent bottles in which some
brands of mineral water, cooking oil, fruit
juice, liquor and cola are sold at present are
made from this plastic. Pet bottles are highly
transparent, totally safe and completely
impervious to air. PET is particularly
recommended for bottling cooking oil, since oil
is stored in the bottles for a long time. There
is a chance that due to prolonged contact the
harmful additives in ordinary plastic may
dissolve in the oil, if bottles are made from
cheap plastics. (PET bottle blowing machine is
available at CIPET Imphal and any interested
entrepreneurs can avail the facility for their
commercial production).
Plastic In Packaging Of:
Produce: Owing to perishability, the bulk of
fresh fruit and vegetables are still sold
unpacked at retail or wholesale level in
perforated polyethylene bags or nets. Long term
transport of these materials must remain minimal
to avoid brushing and consequent decay of the
loosely package product. When packaging is
required at the source or when an extended
storage life is desired, the packaging film
should have a high gas permeability and anti-fog
properties. The packaging of fresh vegetables
and fruit provides the largest single use of
printed polyethylene bags. The prepackaging of
potatoes, carrots, onions, parsnips, beets,
radishes etc. for market sales has become an
important aspect of food distribution. Because
of low water vapor permeability of polyethylene
and propylene, both films and bags are sometimes
perforated to allow the product to 'breathe'.
Permeation is the key to extending fresh produce
shelf life.
Fresh Meat: Fresh meat is very perishable and
extending the shelf life a valuable product and
reducing loss of weight by dehydration has
always been the objective of the meat packing
industry. Before one can fully comprehend the
reasoning behind the evolution of meat packaging
concepts, one must understand the meaning of
'fresh meat'. Meat consists of approximately 16
to 18% protein. 18 to 20% fat and the balance is
moisture with less than 1% minerals. Meat
protein is a valuable dietary component and must
be protected from biological attack and
enzymatic detraction. Fat contributes the cooked
meat flavor and texture and must be protective
against oxidative degradation (rancidity). Myoglobin (the protein with iron porphyrin like
structure) is the major purple coloring element
of meat. The meat color as meat 'ages' or
oxidizes. Oxidation of myoglobin leads to the
green porphylene which is an irreversible change
and cannot revert back to the 'red’ form.
Acidity of meat increases with age and certain
proteins undergoes enzymatic degradation into
peptides and amino acids. This process called
'aging' develops the desirable texture and
flavor. However, if this process is not
controlled, the quality of meat rapidly degrades
and becomes unacceptable for human consumption.
One can see that the control of oxygen and
microorganisms is essential to prolonging shelf
life. The best temperature for meat storage is
just above freezing, but investigation of retail
outlets has shown that it is rare that these
temperatures are maintained.
The packaging material should have high oxygen
permeability, to allow the formation of
oxymyoglobin which is responsible for the
desired purple 'bloom' of fresh red meat.
Cross-linked oriented polyethylene,
polypropylene, plasticized PVC are satisfactory
in this respect. Oriented polystyrene films can
be used only on hand-wrapping equipping
equipment and automatic machines to have better
appeal to their sparkle and clarity. Shelf life
can be extended beyond three days with these
films if hygiene and refrigeration are kept
under control. Saran bags have very low gas
permeability and are suitable for vacuum
packaging
where spoilage due to bacteria, surface
oxidation and dehydration may be retarded upto 2
months. Vacuum packaging of fresh meat
constitutes the key to central butchering,
distribution and cost savings. This process of
controlled atmosphere packaging (using gas
mixtures for a flush prior to evacuating and
sealing the bag containing the meat) will allow
individual shops to be supplied with completely
trimmed meat sections ready to be portioned and
prepackaged for sale.
Fresh Fish: Specially designed multiply
shrinkable bag made from ethylene vinylacetate -
vinylacetate vinylidene chloride - Saran (EVA/PVDC-VAC/PVDC-PVC)
have special properties to stabilize and
preserve large sections of fish so that an
entire years supply can be packaged and
distributed during the short fishing season. The
process consists essentially of processing the
fish, vacuum packaging and immediate freezing.
The fish is processed just prior to packaging
and as soon as possible after the catch. The
fresh processed fish is then bagged for
packaging. The bagged fish is then placed in a
vacuum chamber that allows it to inflate (by
vacuum) and deflate (by pressure) to eliminate
the oxygen within the bag. (When the oxygen
(air) is forced out, the bag is completely
formed around the prepared fish. The bag is
clipped to seal the package and finally the
begged fish is conveyed into a hot water spray
shrink tunnel to finish the tightening
(shrinking). This final operation presents a
smooth, formed plastic
shroud. The last step is to immediately freeze
the finished packaged, box it and ship it.
Cured And Cooked Meat: Cured and cooked meat
products are prepackaged under vacuum in
shrinkable bags made of oxygen-impermeable
materials such as Saran and Polyester. Vacuum
and low oxygen permeability are indispensable in
preventing bacterial growth and discoloration
due to a light-induced oxidation of the nitrosomyoglobin. Colored films or film
additives absorbing the critical light waves in
the ultraviolet or blue range have found
customer appeal in the developed countries.
Frozen Foods: Poultry has provided the oldest
market for shrinkable films. The tight cling
between the vapor-impervious packaging film and
the product prevents freezer burn and pockets
where ice may crystallize. The films used for
this application are Saran and Polyester bags
which provide storage life of over one year.
Where shorter periods are feasible, films such
as crossed-linked oriented polyethylene is
satisfactory. The use of polyethylene film in
wrapping
of frozen chickens has created a large business
in printed bags.
Dairy products: All categories of cheese may be
successfully package in shrinkable films,
impermeable to oxygen and preventing moulds from
growing on the surface. In recent years, the
curing of cheese in Saran films and especially
in vacuumised bags made of this polymer had
become very popular, since this curing method
prevents dehydration and ring formation. The
rapid acceptance of film cured cheeses may be
explained by changes in the eating habits of the
consumers, favoring a softer, less salty flavor
in cheeses.
Boxed Goods: Boxes containing toys, housewares
and foods can be over wrapped with heat
shrinkable films such as oriented polypropylene
and cross-linked polyethylene. By engineering
the shrink tension and property controlling it,
the finished package can receive and attractive
appearance, the covering being unwrinkled and
glossy for extended period of time. Trim-sealing
is the more prevalent method of sealing
over-wraps since it eliminates both side folds
or under folds.
Conclusion: The widespread use of plastics as a
food packaging material has, in fact, elevated
the level of public health. Let us remember that
only a few years ago the eatables were wrapped
in old newspapers. This packaging is not
airtight and is vulnerable to the ingress of
disease carrying bacteria. Further the lead used
in the printing ink has also a harmful effect on
living tissues. Thus, packaging of food in
plastic bags represents a phenomenal improvement
over the old method and is much recommended.
(The writer is Manager (Project), CIPET, Imphal)
(Courtesy: The Imphal Free Press) |
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