β-Glucans (beta-glucans) are polysaccharides of D-glucose monomers linked by glycosidic bonds. Beta-glucans are a diverse group of molecules which can vary with respect to molecular mass, solubility, viscosity, and three-dimensional configuration. They occur most commonly as cellulose in plants, the bran of cereal grains, the cell wall of bakers' yeast, certain fungi, mushrooms and bacteria. Some forms of beta glucans are useful in human nutrition as texturing agents and as soluble fiber supplements, but can be problematic in the process of brewing.
Yeast and medicinal mushroom derived beta glucans are notable for their ability to modulate the immune system. Research has shown that insoluble (1,3/1,6) beta glucan, has greater biological activity than that of its soluble (1,3/1,4) beta glucan counterparts. The differences between beta glucan linkages and chemical structure, are significant in regards to solubility, mode of action, and overall biological activity.
Glucans are polysaccharides that only contain glucose as structural components, and are linked with β-glycosidic bonds.
In general, one distinguishes between α- and β-glycosidic bonds, depending on whether the substituent groups on the carbons flanking the ring oxygen are pointing in the same or opposite directions in the standard way of drawing sugars. An α-glycosidic bond for a D-sugar emanates below the plane of the sugar, whereas the hydroxyl (or other substituent group) on the other carbon points above the plane (opposite configuration), while a β-glycosidic bond emanates above that plane.
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