Macrophage stimulating activity of exo-biopolymer from submerged culture of Lentinus edodes with rice bran

To find a new utilization of rice bran, nine higher fungi were examined for the production of exo-biopolymer with macrophage stimulating activity from rice bran. Among the exo-biopolymers produced from submerged cultures, Lentinus edodes showed the highest activity, followed by Grifola frondosa, Schizophyllum commune, and Coriolus versicolor. L. edodes also had the most potent macrophage stimulating activity in a liquid culture rather than in a solid culture. In order to improve rice bran utilization and the yield of exo-biopolymer with macrophage stimulating activity, the treatment of Rapidase effectively increased the macrophage stimulating activity (about 30% increase), whereas the other enzymes (Econase, Viscozyme, Ultraflo, Celluclast, and Thermylase) treatments did not increase the macrophage stimulating activity. Exo-biopolymer with macrophage stimulating activity from L. edodes contained mainly neutral sugars (58.7%) with considerable amounts of uronic acid (32.2%) and a small amount of proteins (9.1%). Component sugars of exo-biopolymer consisted of mainly arabinose, galactose, glucose, mannose, and xylose (0.95:0.81:0.96:1.00: 0.39, respectively). When the exo-biopolymer was treated with NaIO₄, NaClO₂, and pronase, the NaClO₂ treatment and pronase digestion had little effect, whereas NaIO₄ oxidation significantly decreased the macrophage stimulating activity (47.6% reduction at 100 μg/ml). Therefore, the carbohydrate moiety in exo-biopolymer from L. edodes plays an important role in the expression of the macrophage stimulating activity.