Galactomannans are polysaccharide

Polysaccharide

Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...

s consisting of a mannose

Mannose

Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose. It is not part of human metabolism, but is a component of microbial cell walls, and is therefore a target of the immune system and also of antibiotics....

 backbone with galactose

Galactose

Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....

 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
  Fenugreek
  Fenugreek is a plant in the family Fabaceae. Fenugreek is used both as a herb and as a spice . The leaves and sprouts are also eaten as vegetables...
  
  , mannose:galactose ~1:1
• guar gum
  Guar gum
  Guar gum, also called guaran, is a galactomannan. It is primarily the ground endosperm of guar beans. The guar seeds are dehusked, milled and screened to obtain the guar gum. It is typically produced as a free-flowing, pale, off-white-colored, coarse to fine ground powder.-Production:Guar gum is an...
  
  , mannose:galactose ~2:1
• tara gum, mannose:galactose ~3:1
• locust bean gum
  Locust bean gum
  Locust bean gum is a galactomannan vegetable gum extracted from the seeds of the carob tree, mostly found in the Mediterranean region. The long pods that grow on the tree are used to make this gum. The pods are kibbled to separate the seed from the pulp...
  
   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.
Galactomannans are used in foods as stabilisers

Stabilizer (chemistry)

In chemistry a stabilizer is a chemical which tends to inhibit the reaction between two or more other chemicals. It can be thought of as the antonym to a catalyst...

.