Production, purification and tumor necrosis factor-α (TNF-α) release capability of exopolysaccharide from Laetiporus sulphureus (Bulliard: Fries) Bondartsev & Singer in submerged cultures

The optimal culture conditions of exopolysaccharide (EPS) productions in submerged culture by Laetiporus sulphureus were determined in flask cultures. Optimal medium composition was determined as follows (g/l): glucose 10, yeast extract 5, KH2PO4 3. The optimal temperature and initial pH for EPS production were 31 °C and initial pH 4.0, respectively. The optimal culture medium was then cultivated in a 5-l and a 20-l stirred tank fermenter at 1 vvm (volume of aeration per volume of bioreactor per min) aeration rate, 150 rpm agitation speed, controlled pH 4.0 and 31 °C. In the optimal culture medium, the maximum EPS production in a 5-l and a 20-l stirred tank fermenter was 367 and 356 mg/l, respectively, resulting in a 57% and 51% enhancement of EPS fermentation production compared with those from the basal medium cultures. Two main fractions, Fr-I and Fr-II, of crude EPS extracted from optimal L. sulphureus culture were obtained by a Sepharose CL-4B column chromatography. The high-performance gel-permeation chromatography (HPGPC) analysis exhibited that the number average molecular weight (Mn) of two polysaccharides were 4290 and 1120 kDa, respectively. The protein contents of two fractions were 36.98% and 12.31% (w/w), respectively. All polysaccharide fractions showed significantly higher tumour necrosis factor-α (TNF-α) release capability on macrophage cells. The results obtained are useful in optimization of L. sulphureus culture for efficient production of a potent immunostimulating EPS in the submerged culture.