n. (context carbohydrate English) Any of a class of polysaccharides, found in many gums, having a backbone composed of mannose with galactose sidechains.
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 increase the viscosity of the water phase.
Guar gum has been used to add viscosity to artificial tears, but is not as stable as carboxymethylcellulose.