Recovery of Nisin during Fermentation in Biofilm Reactor

Abstract

Nisin is a 34-amino acid polypeptide with an antimicrobial activity against wide range of Gram positive bacteria. While it is mainly used as a natural food preservative, its applications for medical purposes are promising. Nisin production is limited by many factors, including adsorption of nisin onto producer cells and enzymatic degradation by protease. On-line removal of nisin by silicic acid coupled with a micro-filter module during fermentation was proposed to recover nisin from fermentation broth before those detrimental effects as well as the previously reported product inhibition caused by nisin itself happen. In this study, silicic acid was successfully used to recover nisin from fermentation broth of L. lactis subsp. lactis NIZO 22186. The effect of pH (at 6.8 and 3.0) during adsorption process and several eluents (DI water, 20% ethanol, 1 M NaCl, and 1 M NaCl + 20% ethanol) for desorption were evaluated in a small-scale batch experiment. Higher nisin adsorption onto silicic acid can be achieved when the adsorption was carried out at pH 6.8 (67% adsorption) than at pH 3.0 (54% adsorption). The maximum recovery (47% of nisin was harvested) was achieved when the adsorption was carried out at pH 6.8 and 1 M NaCl + 20% ethanol was used as an eluent for desorption. Nisin production was significantly enhanced (6,701 IU/ml) when comparing to the batch fermentation without the on-line recovery (1,897 IU/ml), possibly as a result of preventing the loss of nisin due the detrimental effects and a higher biomass density achieved during online recovery process.