galactomannan

Galactomannan is a class of polysaccharides composed of a linear chain of β-D-mannopyranose units linked by (1→4) glycosidic bonds, with single α-D-galactopyranosyl residues branching off at the O-6 position. The side chains are attached along the backbone, and the degree of branching, galactose-to-mannose ratio, molecular weight, and substitution pattern vary with source. These structural features influence solubility, viscosity, and gel-forming behavior; in aqueous solution galactomannans impart thick, viscous textures and can form gels when used with other polysaccharides or certain cations, depending on concentration and source.

Commercial galactomannans are primarily obtained from legume seeds. The major sources are guar gum (Cyamopsis tetragonoloba), locust bean gum or carob gum (Ceratonia siliqua), and tamarind seed gum (Tamarindus indica). Guar gum typically has a higher galactose content than locust bean gum, affecting hydration and viscosity; locust bean gum has a lower degree of branching and often requires combination with other gums to gel effectively. Tamrind gum exhibits a distinct branching pattern with relatively high galactose content. These gums are widely used as thickening and stabilizing agents in foods, cosmetics, pharmaceuticals, and industrial applications, including oilfield drilling fluids and paper processing.

In fungi, galactomannan is a major cell wall component in species such as Aspergillus, and its presence is exploited clinically as a serological marker for invasive aspergillosis. Dietary galactomannans are not digested by human enzymes but can be fermented by the gut microbiota, contributing to dietary fiber effects.