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Galactomannans are polysaccharides consisting of a mannose backbone with galactose side groups (more specifically, a (1-4)-linked beta-D-mannopyranose backbone with branchpoints from their 6-positions linked to alpha-D-galactose, i.e. 1-6-linked alpha-D-galactopyranose).
In order of increasing number of mannose-to-galactose ratio:
- fenugreek gum, mannose:galactose ~1:1
- guar gum, mannose:galactose ~2:1
- tara gum, mannose:galactose ~3:1
- locust bean gum or carob gum, mannose:galactose ~4:1
Galactomannans are often used in food products to viscosify the water phase.
Galactomannans are used in foods as stabilisers. Guar and LBG are comomnly used in ice cream to improve texture and reduce ice cream meltdown. Locust Bean Gum (LBG) is also used extensively in cream cheese, fruit preparations and salad dressings. Tara is seeing growing acceptability as a food ingredient but is still used to a much lesser extent than guar or LBG. Guar has the highest usage in foods, largely due to its low and stable price. Article on LBG
Galactomannan is also attached to and released from the mold Aspergillus during growth. Detection of galactomannan in blood can be used to diagnose invasive aspergillosis infections in humans. This is performed with monoclonal antibodies. An assay from Bio-Rad Laboratories was approved by the FDA in 2003.