The extraction and purification technology of Nisin

Nisin is a small molecular polypeptide compound produced by fermentation of some strains of Streptococcus lactis or Lactococcus lactis. The following is the research progress of its extraction and purification technologies:

Ion exchange resin method: This method uses weakly acidic ion exchange resin D113 for static adsorption and dynamic desorption of nisin concentrate. Studies have shown that good results are achieved when the pH is 6, the adsorption time is 90 minutes, the desorbent is a hydrochloric acid-ethanol solution with 1mol/L and V_{hydrochloric acid}/V_ethanol = 1.25, and the desorption rate is 1BV/h. Under these conditions, the obtained Nisin titer can reach 34000IU/mg, with a yield of 67.45%.

Organic solvent method: Methanol and ethanol solutions can be used to extract Nisin from preparations containing nisin. Studies have found that 10% or 50% ethanol can recover about 75% of nisin activity, while ethanol with a concentration higher than 90% has a recovery rate of less than 1%. The extraction effect with 10% or 50% methanol is roughly the same as that with lower concentration ethanol, but the extraction yield of methanol with a concentration greater than 90% is significantly higher.

Membrane separation method: Daoudi L et al. used a hollow fiber membrane with a molecular cut-off of 1000 Daltons to ultrafilter the fermentation broth that had been centrifuged for sterilization. The final concentration rate reached 5, and the yield was 74.2%. However, the membrane separation method has the problem that the membrane surface is easily contaminated, thereby reducing the membrane performance.

Foam separation technology: A preparation method of liquid nisin preservative adopts foam separation technology. First, adjust the pH of the nisin fermentation broth to 1.5-3.0, heat it for 0.5-2 hours to separate it from the bacterial cells, then perform ceramic membrane filtration to remove bacterial cells and macromolecular proteins. Then, in the foam separation equipment, a large number of foams are formed by continuously introducing gas for bubbling. After collecting the foam and defoaming, a high-titer liquid solution of nisin is obtained. The yield of the bubbling concentration process reaches more than 95%, and the concentration multiple is 8-10 times.

Electrodialysis method: Some studies have first used electrodialysis process to purify commercial nisin solutions and compared it with the traditional multi-step centrifugation method. The results show that in one-step purification, electrodialysis has a desalination efficiency equivalent to that of centrifugation (desalination rates are 95.6% and 94.3-99.8% respectively), and the protein recovery rate is higher (83.8% and 12.5-42.1% respectively).

Cation exchange chromatography: In previous studies, nisin was purified by cation exchange chromatography with one-step elution using 1mol/L NaCl at low pH. The optimized purification scheme uses five-step NaCl elution to remove impurities, and the obtained nisin is free of impurities. The nisin-sensitive Lactococcus lactis NZ9000 strain shows high bactericidal activity, and the IC50 of the purified nisin is about 3nM, which is 10 times higher than that obtained by the one-step elution method.