Menaquinone-7 Fermentation Process Optimization Based On CFD Simulation

Vitamin K2 is an essential fat-soluble vitamin for human body.Menaquinone-7（MK-7）,as one of the most important components of vitamin K2,is favored in the fields of functional food and medicine.In the previous study,it was found that the highest concentration of MK-7in shake flask was much higher than that in stirred tank reactor（STR）.In order to reduce the difference caused by scale-up from 250 m L shake flask to 3L STR,computational fluid dynamics（CFD）and dynamic absorption method were used to compare the shear stress and oxygen transfer performance between shake flask and STR at different rotational speeds firstly,and then different culture conditions of the shake flask culture was carried out as scale-down model to explore the effects of oxygen supply and shear stress changes on the growth of Bacillus subtilis BS20 cells and the production of MK-7.Finally,by optimizing the culture conditions of the 3 L STR,the oxygen supply level was increased and the production of MK-7 was increased.The main findings are as follows:（1）Comparing the apparent mass transfer coefficient of the shake flask determined by the dynamic absorption method under different conditions with the real mass transfer coefficient of the shake flask simulated by the CFD model,it was found that the mass transfer coefficient of the shake flask increases with the increase of the rotating speed,during the culture process,the resistance of sealing conditions is much greater than the resistance of gas-liquid mass transfer.The existence of sealing film plays a major role in restricting oxygen mass transfer.Among them,the oxygen permeability of cotton plug sealing film is the best,and the oxygen permeability of five-layer sealing film is the best.Difference.（2）Shake flask culture under different culture conditions is used as the basis for reducing the model.Sufficient oxygen supply can promote the growth of the bacteria and the production of MK-7,but excessive shear stress will cause damage to the bacteria,reducing the production of menadione heptaenone.Finally,the batch with baffle shake flask,cotton stopper sealing,and rotating speed of 120 r·min^-1had the highest production of MK-7,reaching 375 mg·L^-1.（3）The CFD model was used to compare the flow field characteristics of the shake flask and the STR at different speeds.It was found that the shear rate of STR at 400 r×min^-1was approximately consistent with that of the best batch of shake flask culture.In the STR,the speed of 400,600,and 800 r×min^-1and the oxygen concentration of 21%,42%,and 55%of the intake air were used.Finally,on the premise of using a lower stirring speed,the production of MK-7 can be greatly improved by using oxygen-enriched air or microporous aerator to supply oxygen,which can respectively reach 296 mg×L^-1and 192 mg×L^-1,reducing the gap between with shake flask batch.The method of reducing the stirring speed and increasing the oxygen concentration of the gas supply in the STR in this study can effectively improve the performance of the shear-sensitive but high aerobic fermentation process.