Agriculture Reference
In-Depth Information
hydrocolloids. Concentrated gum solutions are able to suspend particles and give
soft, spreadable gels with a jam-like consistency. Gum karaya has strong water-
binding ability, enabling it to absorb water and swell to more than 60 times its
original volume. Typical applications include: as a thickener in sauces, particularly
brown sauce; as a stabiliser in aerated frozen desserts (controlling the formation
of ice crystals); as an acid-resistant stabiliser for fruit ices and sherbets; and as a
stabiliser for whipped cream toppings. It is also used to prevent syneresis and
improve the spreadability of cheese spreads, and as a binder for low-calorie,
dough-based products such as pasta and bread.
Gum karaya has been used commercially for about a hundred years. However,
there are limitations to its use - particularly that it has a slight vinegary odour and
taste. This becomes worse during storage, and the powder also loses viscosity on
ageing, limiting its shelf life. In Europe, regulations limit its use to a number of
products, with maximum allowed limits, although it has GRAS (Generally
Recognised As Safe) status in the US (at the time of writing).
8.3.7 Carrageenan
Seaweed (marine algae) is a rich source of gelling agents. Red seaweeds,
Rhodophyceae , contain naturally occurring polysaccharides that fi ll the voids
within the cellulose structure of the plant. This family of polysaccharides include
carrageenan, furcellaran and agar. These three polysaccharides all have a backbone
of galactose, but differ in the proportion and location of ester sulphate groups and
the proportion of 3,6-anhydrogalactose (Imeson 2009). This gives them quite
different rheological properties and therefore application in food.
The main 'farming' areas for carrageenan-containing seaweeds are the costal
waters of the Philippines, Indonesia and Chile (Hazen 2004). Different types of
seaweed grow in the different regions, and each seaweed type contains different
types of carrageenan, either single types or mixtures of the three basic fractions of
carrageenan: kappa, iota and lambda.
After the seaweeds are identifi ed to make a particular extract, they are washed
and then treated with alkali to extract the carrageenan. The carrageenan extracts
are fi ltered and clarifi ed by high speed centrifugation, concentrated and then
precipitated with alcohol before drying, grinding and blending. An alternative
method to the alcohol precipitation for a kappa carrageenan extract is to use
potassium chloride. The potassium chloride and kappa carrageenan interact to
form a gel, which is dewatered under pressure, dried and ground to the required
particle size.
A third process is used for processed Eucheuma seaweed, also known as semi-
refi ned carrageenan and Philippine Natural Grade. This process is carried out on
Eucheuma seaweed harvested around the Philippines and Indonesia, and directly
treated with alkali to modify the carrageenan within the seaweed, thus avoiding
the expensive separation, fi ltration and concentration steps of standard carrageenan
extracts. The processed Eucheuma seaweed material is signifi cantly cheaper than
the purifi ed carrageenan types, but is more limited in terms of functionality and
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