Purified Beta-13/16-Glucan. Suitable For Vegetarians. Beta glucan is a complex polysaccharide composed of glucose molecules extracted and purified from the cell wall of common baker's yeast Saccharomyces cerevisiae. Beta glucan is used to maintain or stimulate the effectiveness of the immune system. . Animal and human cell culture studies have shown that beta glucan can stimulate several aspects of immune function such as phagocytosis and interleukin production. Source Naturals Beta Glucan uses a purification process that removes the mannoproteins and yeast residues that may reduce the effectiveness of beta glucan.