Effect of culture media on the chemical and physical characteristics of polysaccharides isolated from Poria cocos mycelia

Mycelia of a wild strain Poria cocos were cultured in two media differing in one constituent: bran extract or corn steep liquor, and are designated as wb and we, respectively. Six polysaccharide fractions were isolated sequentially from the two mycelia by 0.9% NaCl (PCM1), hot water (PCM2), 0.5 M NaOH (PCM3-I and -II) and 88% formic acid (PCM4-I and -II). Their chemical and physical characteristics were determined by infrared spectroscopy (IR), gas chromatography (GC), C-13 NMR, light scattering (LS) and viscometry. The results indicated that wb-, wc-PCM1, and PCM2 were heteropolysaccharides mainly composed of alpha-D-ghlcose, mannose, and galactose, whereas wb-PCM3-I and wc-PCM3-I were mainly (1 --> 3)-alpha-D-glucans, and wb- and wc-PCM3-II, PCM4-I and PCM4-II were (1 --> 3)-beta-D-glucans. Interestingly, (1 --> 3) alpha- and (1 --> 3)-beta-D-glucans co-existed in the 0.5 M NaOH fraction and were separated individually into the two fractions (PCM3-I and PCM3-II) after neutralizing with acetic acid. The polysaccharides from wc-PCM cultured in media containing corn steep liquor contained relatively more protein. The polysaccharide fractions also existed in conformations including random coil (as in PCM0 and PCM1) and expanded chain (as in PCM3), and differed molecular mass. In addition, two exo-polysaccharides isolated from the two culture media by methanol precipitation (wb- and wc-PCM0) also differed in their monosaccharide composition. (C) 2003 Elsevier Science Ltd. All rights reserved.