beta-Glucan in Foods and Its Physiological Functions

beta-Glucans are a class of polysaccharides consisting of D-glucose units that are polymerized primarily via the beta-1,3 glycosidic bonds, in addition to the beta-1,4 and/or beta-1,6 bonds. They are present in various food products such as cereals, mushrooms, and seaweeds and are known for their numerous effects on the human body, depending on their structures, which are diverse. The major physicochemical properties of beta-glucans include their antioxidant property, which is responsible for the scavenging of reactive oxygen species, and their role as dietary fiber for preventing the absorption of cholesterol, for promoting egestion, and for producing short-chain fatty acids in the intestine. Dietary beta-glucans also exert immunostimulatory and antitumor effects by activation of cells of the mucosal immune system via beta-glucan receptors, such as dectin-1. In this review, we elaborate upon the diversity of the structures and functions of beta-glucans present in food, along with discussing their proposed mechanisms of action. In addition to the traditional beta-glucan-containing foods, recent progress in the commercial mass cultivation and supply of an algal species, Euglena gracilis, as a food material is briefly described. Mass production has enabled consumption of paramylon, a Euglena-specific novel beta-glucan source. The biological effects of paramylon are discussed and compared with those of other beta-glucans.