Study On Production Of Vitamin K2 By Microbial Fermentation

Vitamin K2 is a liposoluble compound with extremely high biological activity in its all-trans configuration.Menaquinone-7(MK-7)is a type of vitamin K2 that plays an important role in preventing osteoporosis,cardiovascular disease,and cancer,among other conditions.Therefore,MK-7is highly valued in the fields of medicine and functional foods.Currently,chemical synthesis of MK-7 is plagued by problems such as high toxicity of reagents,high levels of byproducts,low yields,and high pollution,among others.In contrast,microbial synthesis of MK-7 has the advantages of being environmentally friendly and producing a high proportion of all-trans MK-7.However,it also faces challenges such as a long fermentation period and low yield.Therefore,the screening of high-yielding vitamin K2-producing strains and the optimization of fermentation and product extraction processes are urgent issues to be addressed.The results of this study are as follows:(1)In this study,a structure-similarity-based resistance strategy was employed to screen out five strains of bacteria capable of producing vitamin K2 from a soil-derived library containing 2,300 strains.Among them,Bacillus amyloliquefaciens GSA-184 exhibited the highest ability to synthesize MK-7with a yield of 18.1 mg/L.After optimizing the fermentation medium,the production of MK-7 was increased to 23.5 mg/L,providing a foundation for subsequent fermentation process optimization.(2)After screening nine surfactants and optimizing the concentration and timing of their addition,it was found that adding 0.2 g/L of polyethylene oxide(POE)24 h after fermentation could increase the yield of MK-7 to 34.2 mg/L,greatly promoting the synthesis of MK-7 by strain GSA-184.(3)Optimization of p H,temperature,agitation speed,and aeration rate revealed that the optimum initial p H was 7.0,the optimum fermentation temperature was 37℃,the optimum agitation speed was 400 rpm,and the optimum aeration rate was 2 vvm.Batch feeding fermentation was conducted for 144 h under the optimized conditions of p H 7.0,resulting in a MK-7 yield of 45.1 mg/L.(4)By optimizing the extraction process of MK-7,including cell disruption methods,organic solvent selection,and extraction methods,a feasible method for directly extracting MK-7 from the fermentation broth was determined.Compared with the previous methods of extracting intracellular and extracellular products separately,the concentration of MK-7 extracted was slightly increased to 45.9 mg/L,while the amount of organic solvent used was reduced by 30%.The data presented in this study provide some basis for the industrial production of vitamin K2 by microbial methods.