Studies on downstream processing of pullulan

Pullulan, an extracellular polysaccharide is obtained by fermentation using a fungus, Aureobasidium pullulan. To obtain the pure biopolymer from the fermentation broth, cell harvesting, removal of the melanin pigments co-produced during fermentation and precipitation of the polymer are essential. The present work reports on some of these aspects. Centrifugation of the fermentation broth (at optimized fermentation conditions) at 800 rpm for 30 min gave a cell pellet that was discarded and a greenish black supernatant containing the melanin pigments. The supernatant was subjected to demelanization by adsorption on activated charcoal, or by use of solvent/solvent blends, or by solvent/salt combinations, all after denaturation of the pullulanases at 80 °C/1 h. Among all these treatments, a combination of ethanol/ethyl methyl ketone in 60:40 ratios was found to be most effective. Melanin separated out in the solvent blend, while the pure pullulan that precipitated out was comparable in colour and texture to that of the commercial sample.