3. Gelatin is a translucent brittle solid substance,
colorless or slightly yellow, nearly tasteless and
odorless, extracted from the collagen inside
animals' connective tissue. It has been
commonly used in food, pharmaceutical,
photography, and cosmetic manufacturing.
Substances containing gelatin or functioning
in a similar way are called gelatinous. Gelatin
is an irreversibly hydrolyzed
form of collagen. Gelatin is
also known as E number
E441.
Gelatin is a protein produced
by partial hydrolysis of collagen
extracted from connective
tissues of animals such as the domesticated
bovines, porcines and equines. The natural
molecular bonds between individual collagen
strands are broken down into a form that rearranges
more easily. Gelatin melts when heated and
solidifies when cooled again. Together with water it
forms a semi-solid colloidal gel. birefringence.
4. Application
Common examples of foods that contain gelatin are:
- jellies
- desserts
- candies
- trifles
- aspic
- marshmallows
- gummy bears
5. Gelatin may be used as a stabilizer, thickener, or texturizer in foods
such as:
- Ice cream
- Jam
- Yoghurt
- Margarine
Gelatin is used for the clarification of juices, such as apple
juice, and of vinegar. Isinglass, from the swim bladders of fish,
is still in use as a fining agent for wine and beer.
6. Technical uses
- Gelatin typically constitutes the shells of pharmaceutical capsules in
order to make them easier to swallow. Hypromellose is the vegetarian
counterpart to gelatin, but is more expensive to produce.
- Animal glues such as hide glue are essentially unrefined gelatin
- It is used to hold silver halide crystals in an emulsion in virtually all
photographic films and photographic papers. Despite some efforts, no
suitable substitutes with the stability and low cost of gelatin have been
found.
- Gelatin is closely related to bone glue and is used as a binder in
match heads and sandpaper.
7. Selected Raw Materials for the Manufacture of Gelatin
Pig and cattle skin
In the skin processing
industry, the skin of
slaughtered animals is
first thoroughly washed.
The layer of connective tissue on
the meat side of the skin is then
removed by machine and the skin
horizontally split. The intermediate
layer, so called hide split, consists
mainly of collagen and is thus
excellently suited to the
manufacture of gelatin. The hide
split is preserved using salt or
calcium hydroxide, which keeps it
fresh until it is used in the gelatin
manufacturing process.
8. Bone chips.
In meat processing, fresh bone is a by-product
that is used in the production of gelatin.
However, before it is used, it is subjected to a
stringent pretreatment process. As a first step,
bone is reduced to pieces of between 5—10
mm. These are then degreased with hot water,
dried and separated into various particle sizes.
Potential bone adherent tissues are removed in
the degreasing process. The bone chip
material is then stored in silos until required
for production purposes.
Demineralization of bone chips.
Treatment of this intermediate product with
dilute hydrochloric acid at low temperature
over several days using the reverse flow
process removes any phosphate contained in
the bone. This process is known as
"maceration" and the demineralized bone
chips as "ossein". The surplus acid is then
removed from the ossein by thorough
washing.
9. Raw Material Pretreatment.
Acid processing.
For gelatin of type A (acid), pigskin is
normally used as starting material. Pigs, in
contrast to cattle, are slaughtered at a
relatively young age. Since the skin of
such young animals is not as highly cross-
linked, a more gentle process than the
tedious alkaline process can be used; in
this case, acid is used. All that is required
is a one-day treatment with dilute acid,
and the collagen of the pigskin is rendered
soluble in warm water, a precondition for
the subsequent extraction process. Any
superfluous acid is partly neutralized and
the remaining salts washed out with
several washings of water. Ossein can also
be processed to gelatin using this method
with appropriate acid concentrations and
treatment times. However, gelatin
produced in this way is relatively
unimportant.
Alkaline processing.
Gelatin of type B (basic) is produced from
ossein pretreated with alkali or from
washed and cut hide splits. In this process,
the raw materials are treated for a period
of up to three months with calcium
hydroxide, which is renewed several times
during the period. In this process, the
collagen bonds are partially separated and
any noncollagenous proteins and related
substances removed. As an alternative
process, the raw material can be treated
over a period of one to two weeks with
dilute sodium hydroxide solution instead
of calcium hydroxide. Subsequent to this
process, the treated raw material is washed,
neutralized by adding acid, and washed
again to remove any residual salts.
