Method for extracting pullulan polysaccharide from high-viscosity fermentation broth

A method for extracting pullulan polysaccharide from a fermentation broth having a viscosity of 200-350 mPa·s, wherein the method comprises following steps:

• (1) removal of cells from the fermentation broth, comprising:
• adjusting the fermentation broth to a pH of 3-5 with HCl solution, adding chitosan dissolved in glacial acetic acid, heating to a temperature of 30-50° C., leaving to stand for 10-30 mins at the temperature of 30-50° C. for flocculating, and centrifuging to remove the cells and insoluble substance, so as to obtain a cell-free fermentation broth;
• (2) removal of proteins, comprising:
• adjusting the cell-free fermentation broth to a pH of 8-9 with NaOH solution, leaving to stand for 15-30 mins for precipitating, centrifuging, then adding alkaline protease in supernatant, heating to a temperature of 40-50° C. for 2-3 hrs, deactivating the protease, and centrifuging to remove the proteins;
• (3) decolorization, comprising:
• adjusting a resultant fermentation broth from step (2) to a pH of 3-5 with HCl solution, adding macroporousresin therein, heating to 30° C. for 1.5 hrs under stirring, so as to remove pigments, and then filtering to recycle the macroporous resin;
• (4) removal of ions by an ultrafiltration membrane module, comprising:
• subjecting a resultant fermentation broth from step (3) to ultrafiltration for desalination through the ultrafiltration membrane module, and repeatedly the ultrafiltration until pullulan polysaccharide reaches a concentration of 5-8 g/100 mL;
• and
• (5) drying, crushing and packaging.