Agriculture Reference
In-Depth Information
the setting rate. Alginate suppliers provide the food manufacturer with the best
blend of alginate, calcium salt and sequestrant for their food application. An
advantage for bakery fi llings is that alginate gels are bake stable and gel at a
wide range of sugar levels. Because they are cold setting, alginate gels can be used
in instant bakery fi lling creams. Sodium alginate is also used as the thickening and
structuring agent in low-fat spreads and to control the melting behaviour of ice
cream.
8.3.10 Gelatin
Gelatin is the most widely used gelling agent, but differs from the other natural
hydrocolloids discussed in that it is extracted from animals not plants. While this
has not been a problem in the past, the rise of vegetarianism, along with the
misconception that gelatin may be linked with bovine spongiform encephalopathy
(BSE), has prompted food manufacturers to look for alternative sources of gelatin,
or gelatin alternatives. However, it will be seen that gelatin has some unique
properties that make it very diffi cult to replace in some food products.
On the positive side, gelatin is classed as an ingredient, not an additive, and so
it does not have an E number, making it a good ingredient for additive-free
products. It has traditionally been used as a gelling agent for over a hundred years
and is considered a 'store cupboard ingredient' by many consumers. Along with
pectin, it is one of the best-known gelling agents by consumers, in the Western
world. These factors all lead to its discussion as a natural hydrocolloid. However,
it does have an intensive extraction process using acid or alkali, so it sits in the
grey area of natural.
Gelatin is extracted from collagen, the main source of which is beef or pork
skin, although bones from pigs and cattle can also be used. Newer sources are
poultry and fi sh skins, to give specialist gelatin types. The collagen is fi rst treated
to soften it and break the cross-links, using acid for pig skin and alkali for
beef skin. After washing, the gelatin is extracted using hot water, followed by
fi ltration, purifi cation, sterilisation, concentration, drying and milling (Haug and
Draget 2009).
Gelatin is the only protein-based hydrocolloid discussed in this chapter.
However, due to its structure, it behaves more like the gelling polysaccharides
than other proteins (such as egg and whey protein). Like other proteins, it is made
up of chains of amino acids, with a range of amino acids along the chain.
Unusually, glycine, the smallest amino acid is at every third position, and it
contains signifi cant amounts of the very large amino acids - proline and
hydroxyproline, the latter being unique to gelatin. This arrangement of amino
acids forces the chain into a regular helix shape. The regions rich in these three
amino acids are known as junction zones and are important in the gelling behaviour
of the gelatin. When a solution of gelatin is cooled, two or three gelatin chains
begin to form a helix structure (like the original collagen), using hydrogen bonding
at the junction zones (Fig. 8.3). This produces a slow setting gel that strengthens
over time as the junction zones equilibrate to form more stable structures.
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