Effects of fed-batch fermentation and pH profiles on nisin production in suspended-cell and biofilm reactors

A biofilm reactor not only shortens the lag phase of nisin production, but also enhances nisin production when combined with an appropriate pH profile. Due to the substrate inhibition that takes place at high levels of carbon source, fed-batch fermentation was proposed as a better alternative for nisin production. In this study, the combined effects of fed-batch fermentation and various pH profiles on nisin production in a biofilm reactor were evaluated. The tested pH profiles include 1) a constant pH profile at 6.8 (profile 1), 2) a constant pH profile with an autoacidification after 4 h (profile 2), and 3) a step-wise pH profile with pH adjustment every 2 h (profile 3). When profile 1 was applied, fed-batch fermentation enhanced nisin production for both suspended-cell (4,188 IU ml^-1) and biofilm (4,314 IU ml^-1) reactors, yielded 1.8- and 2.3-fold higher nisin titer than their respective batch fermentation. On the other hand, pH profiles that include periods of autoacidification (profiles 2 and 3) resulted in a significantly lower nisin production in fed-batch fermentation (2,494 and 1,861 IU ml^-1 for biofilm reactor using profile 2 and 3, respectively) due to toxicity of excess lactic acid produced during the fermentation. Overall, this study suggested that fed-batch fermentation can be successfully used to enhance nisin production for both suspended-cell and biofilm reactors.