Promotion of nisin production by integrating rare earth salt stimulation and foam separation with fermentation system

Nisin is an antimicrobial peptide which offers potential for the replacement of synthetic preservatives in the food industry. However, nisin is difficult to produce on a large scale due to low synthesis efficiency and severe feedback inhibition. The objective of this work was to promote nisin production by integrating rare earth salt stimulation and foam separation with fermentation system. Experimental results indicated that the addition of 1 × 10^-4 M TmCl₃ into fermentation medium could significantly stimulate cell growth and nisin synthesis. The suitable feeding time of TmCl₃ was the ninth hour after fermentation starting. Multiple characterization methods were used to explore the potential mechanism for TmCl₃ stimulation. The increase in TmCl₃ concentration contributed to improving the permeability of cell wall, but caused the degradation or denaturation of nucleic acids. Moreover, the addition of TmCl₃ could regulate the expression of genes related precursor peptide synthesis and immunity. Finally, foam separation had been used for in-situ recovering nisin from the fermentation system. Under the optimum conditions predicted by using response surface methodology, the recovery percentage of nisin was 93.64 ± 1.31%. Compared with fermentation process without TmCl₃ addition and foam separation, the total nisin titer of 8612.39 ± 140.58 IU/mL was increased by 114.44 ± 8.89%.