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Gelatin is
a substantially pure protein food ingredient, obtained
by the thermal denaturation of collagen , which is the
structural mainstay and most common protein in the animal
kingdom. Today gelatin is usually available in granular
powder form, although in Europe, sheet gelatin is still
available. |
There are two main types of
gelatin. Type A, with iso-electric point of 7 to 9, is
derived from collagen with exclusively acid pretreatment.
Type B, with iso-electric point of 4.6 to 5.4, is the
result of an alkaline pretreatment of the collagen. However,
gelatin is sold with a wide range of special properties,
like gel strength(bloom), viscosity to suit particular
applications.
Gelatin forms thermally reversible gels with water, and
the gel melting temperature (<35¡ÆC) is below body temperature,
which gives gelatin products unique organoleptic properties
and flavour release. |
Gelatin is produced from the fibrous protein, collagen,
from beef hides , pig skins and bones. Collagen is the
most abundant of all proteins, making up one-third or
more of the total body protein.
Beef hides for gelatin production can
be fresh, chilled or preserved (salt or caustic treatment).
Pigskin can be used fresh, chilled or
frozen.
Beef bones(ossein) resulting from the
bone processing are usually used in producing gelatin. |
Boiling in an aqueous system hydrolyses the collagen,
and converts it into gelatin, which is essentially a mixture
of polypeptides with molecular weights ranging from below
100.000 to more than 700.000 Daltons.
Gelatin is the purified protein derived by the selective
hydrolysis of collagen. Collagen forms the largest organic
component of the bones and skins of mammals. In practice,
the most commonly used raw materials are porcine and cattle
hides as well as the bones of these animals. |
There are basically two processes:
 The
liming process (B-type gelatin)
The liming process produces a gelatin with a rather narrow
iso-electric point (IEP) range of 4,6-5,4. In practice,
the hides or demineralised bones are placed in liming
pits and soaked in a lime suspension over a period of
14 days. The lime suspension is replaced periodically.
At the end of this treatment, the raw material is washed
thoroughly to remove residual lime
¤ýAlkaline process (gives type B gelatin)
using beef hides or bones as raw materials.
The
acid process (A-type gelatin)
The acid process produces a gelatin with an iso-electric
point (IEP) range of 7-9. In practice, the bones or skins
are treated in a vessel containing a dilute solution of
acid for a predetermined period of time. Afterwards, the
acid is washed out with cold water.
¤ýAcid process (gives type A gelatin)
using pigskin as raw material
The actual processes consists of a several steps including
chopping/crushing the raw materials, alkali/acid treatment,
washing, neutralization, hydrolysis , extractions, filtering,
evaporation, sterilization, chilling, drying, crushing,
testing, blending to desired performance. |
Gelatine is a protein, i.e. gelatine is a polymer composed
of amino acids,
The shaded area is common to all amino acids, and R is
a side chain group, which is different for all the existing
20 amino acids. As with all proteins, the sequence and
type of the amino acids in the chain determines the functionality
of the chain
The major amino acids in the gelatine structure is glycine
(around 30%) and proline/hydroxyproline (around 25%) and
frequently occuring sequences are -glycine-X-proline-,
-glycine-proline-X- and -glycine-X-hydroxyproline-, where
X may be any of the other 20 amino acids |
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Aspartic acid
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4.8
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Threonin
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2.0
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Leucin
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2.5
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Glutamic acid
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10.3
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Alanin
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10.4
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Hydroxylysin
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0.9
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Hydroxyprolin
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11.4
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Prolin
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12.0
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Phenylalanin
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1.1
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Serin
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3.4
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Tyrosin
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0.4
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Lysin
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2.9
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Glycin
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23.2
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Valin
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2.2
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Histidin
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0.8
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Methionin
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0.7
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Arginin
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10.0
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Isoleucin
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1.0
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Iso-electric
Point
As all other proteins, gelatine
has an Iso-electric point (IEP), i.e. the pH at which
the total surface charge of the molecule is zero. The
IEP is different for the two types of gelatine as seen
in the figure below.
The properties of Type A and
Type B gelatine are fairly identical. However, caution
in selection should be taken when undesired interactions
with other anionic polymers, such as carrageenan, can
take place. In such situations only Type B gelatine should
be used
Solubility
Swelling of gelatine in (cold)
water depends on the temperature, the presence of salts
and pH with maximum swelling away from IEP.
Solubilisation of gelatine takes place at temperatures
above 40 oC.
Gelation
Gelation starts when a hot gelatine
solution is cooled to temperatures below 30-35 oC, at
which temperatures viscosity starts to increase. Maintaining
the temperature at 10 oC will cause a continuing increase
of the rigidity of the gel, reaching maximum after 15-20
hours. Kept at refrigeration temperatures (+5oC), maximum
gel strength will be reached after 5-8 hours.
The Bloom Value is used to describe the strength of a
given gelatine product. The bloom strength is defined
as the force needed to make a 4 mm depression in a 6,67%
concentration gelatine gel under well defined conditions
(British Standard: BS 757).
Gelatine does not, like many polysaccharides, require
the presence of salts or a certain pH range and high sugar
levels in order to gel, but the rigidity of gelatine gels
is affected by temperature, presence of salts and other
ingredients.
Gelatine gels are thermo reversible.
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For optimal functionality gelatine has to be dissolved
completely without lump formation. In order to avoid hydrolysis,
i.e. loss of functionality, over heating (boiling) and
dissolution in the presence of acids should be avoided.
Actual methods of dissolution and recommended type of
gelatine (e.g. mesh size) depends on type of finished
product, available equipment and process.
In order to avoid lump formation, gelatine can be dispersed
in water under conditions of minimum swelling, i.e. in
cold water or mixed with other dry materials followed
by heating to 60 oC. In this way gelatine solutions without
air bubbles can be made.
Concentrated gelatine solutions (e.g. for the Confectionery
Industry) can be made by adding coarse mesh gelatine to
90 oC water under proper agitation. Maintaining the solution
for some time at 60 oC with gentle agitation, will allow
air to escape. |
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