mannan

A polysaccharide in which the major monosaccharide subunit is mannose. Galactose and glucose are also often present, forming galactomannans, glucomannans, and galactoglucomannans. Mannans frequently occur in hemicellulose. They are also found as reserve polysaccharides in some higher plants, e.g. the ivory palm (Phytelephas macrocarpa), in which the extremely hard endosperm (known as vegetable ivory) is composed of mannans.