Microbial (1 → 3)-β-D-glucans, their preparation, physico-chemical characterization and immunomodulatory activity

(1 --> 3)-beta-D-glucans have the ability to stimulate the immune system and are classified as biological response modifiers (BRMs). Glucans from two technologically important species, baker's yeast Saccharomyces cerevisiae and filamentous fungus Aspergillus niger were isolated and characterized. Water-insoluble yeast glucan has a low branched structure with a ratio of the glucose units in the side chains and the backbone of 1:8. Using ultrasonic treatment and subsequent chemical derivatization, water-soluble derivatives (carboxymethyl and sulfoethyl) of yeast glucan were obtained with high yield. The glucan isolated from A. niger forms a complex with chitin and is relatively resistant to solubilization. The yield of its carboxymethylated derivative was only 30%. A method of determination of the relative ratio of alpha-and beta-glycosidic linkages in the glucans using FTIR spectroscopy has been developed as well as a method for ultrasonic purification of the isolated glucans. Using ultrasonic treatment, glucan derivatives with decreased molecular weight (90-100 kDa) have been prepared, which show broader application possibilities in comparison with the initial high molecular-weight derivatives (300-600 kDa). It has been found that the derivatives prepared reveal high mitogenic and comitogenic activities, as well as radioprotective and antimutagenic effects. (C) 1999 Elsevier Science Ltd. All rights reserved.