Purification of surfactin in pretreated fermentation broths by adsorptive removal of impurities

An attempt was made to further improve the purity of surfactin in the fermentation broth of Bacillus subtilis ATCC 21332 culture by adsorption or ion exchange after the broth had been treated by a two-stage ultrafiltration process. The commonly used neutral adsorption resin (macroporous XAD-7) and charged ion-exchange resin (AG1-X4) were adopted. Under the conditions tested the impurities in the treated broth such as macromolecules (proteins, polysaccharides, peptides) or smaller molecules (glycine, serine, threonine, alanine) were adsorbed or exchanged more quickly and preferably within 5 h of operation, purification of surfactin was hence achieved by adsorption removal of the impurities. It was shown that XAD-7 resins gave higher purity of surfactin than AG1-X4 resins. The recovery of surfactin from the remaining solution after adsorption using XAD-7 resin exceeded 95% at pH 6.5 and the purity increased from 76% (the feed) to 88%; however, the purity of surfactin reached up to 80% only after ion exchange using AG1-X4 resin. Finally, the breakthrough phenomena of surfactin solutions in a XAD-7 column were tested and discussed.