Nisin's environmentally friendly production technology

The environmentally friendly production technologies of nisin mainly focus on using waste as fermentation substrates and optimizing fermentation processes to reduce energy consumption and pollution. The following are the relevant research progresses:

I. Production of Nisin by Fermentation Using Waste

Acid whey: Lactococcus lactis can produce nisin using acid whey as a substrate. By adding yeast extract as a nitrogen source and sucrose as a carbon source, the yield of Nisin can be significantly increased, with the maximum yield reaching 2.6×10⁵ AU/mL. This not only realizes the reuse of whey, reduces wastewater discharge, but also lowers production costs.

Distiller's grains from Baijiu production: Using distiller's grains from Baijiu production as raw materials, microcrystalline cellulose is first prepared by a compound enzyme method. The wastewater generated during the preparation can replace distilled water for the culture medium of Lactococcus lactis for nisin production. After optimization, by adding appropriate amounts of yeast powder, peptone, sucrose and other components to the wastewater-based medium, the titer of nisin can reach 732.52 IU/mL, realizing the resource utilization of distiller's grains and the reduction of wastewater emissions.

Skim milk: Studies have found that Lactococcus lactis has high activity in fermenting and producing nisin in diluted skim milk. Using skim milk as a low-cost growth medium enables large-scale production of Nisin, while also providing a way to utilize milk by-products.

II. Optimization of Fermentation Processes

Co-culture technology: A co-culture strategy of enterobacteria and Lactococcus lactis has been developed. By adjusting the inoculation ratio and time, the yield of nisin is increased by 85% compared with the single culture of Lactococcus lactis, reaching 6260 IU/mL. During co-culture, the pH of the fermentation broth is relatively high and the lactic acid yield is low, which is more suitable for Lactococcus lactis to produce nisin. Meanwhile, it can also change the crystallinity of bacterial cellulose.

Coupling of rare earth salts and foam separation technology: In the process of nisin production by Lactococcus lactis fermentation, adding an appropriate amount of rare earth salts (such as TmCl₃) can promote bacterial growth and nisin synthesis. Under optimal conditions, the nisin titer of the fermentation broth is 5643.23 IU/mL. Coupling foam separation with fermentation helps to increase the dissolved oxygen in the fermentation broth, recover metabolites in situ, reduce their degradation, and improve production efficiency.

III. Genetic Engineering Technology

Through gene cloning technology, the nisin synthesis gene cluster is introduced into host strains to achieve high-efficiency expression in host cells, which can increase the nisin yield of recombinant strains by 2-3 times compared with the original strains. In addition, gene editing technologies such as CRISPR/Cas9 can be used to modify genes related to its synthesis, enhance their transcriptional activity, and thereby improve Nisin yield.

IV. Cell-Free Protein Synthesis Platform

The research group led by Professor Liu Tiangang from Wuhan University has developed a cell-free protein synthesis (CFPS) platform. Targeting nisin, this platform identifies the rate-limiting steps in its biosynthesis and accurately guides the metabolic modification of industrial strains, resulting in a 60% increase in its yield. This provides a universal, rapid, and efficient method for high-yield nisin production.