glucan

Glucan is a polysaccharide composed of glucose units linked by glycosidic bonds. The term covers a broad class of polymers with varying linkage types and structures, typically categorized by the configuration of the glycosidic bonds (alpha or beta) and by degree of branching. In general, glucans are storage or structural polysaccharides in living organisms and can be soluble or insoluble in water.

Alpha-glucans include starch and glycogen, storage polysaccharides in plants and animals, respectively. They consist mainly of α-1,4-linked glucose chains with α-1,6 branches in glycogen, enabling rapid mobilization of glucose. Bacterial dextrans are also alpha-glucans with predominantly α-1,6 linkages and various side chains.

Beta-glucans are glucose polymers with beta linkages. A prominent example is cellulose, a structural β-1,4-glucan in plants; in fungi and yeast, β-1,3/β-1,6-glucans form cell walls and influence cell integrity. In cereals such as oats and barley, β-glucans occur as mixed linkages (β-1,3 and β-1,4) and contribute to dietary fiber and viscosity, with potential effects on cholesterol and glycemic response. Beta-glucans from fungi and yeast also have immunomodulatory properties that are studied for health applications.

Enzymatically, glucans are degraded by amylases for α-glucans and by glucanases, cellulases, and specific β-glucanases for β-glucans; many glucans have industrial and medical uses as thickeners, stabilizers, or dietary ingredients.