基于CFD模拟的七烯甲萘醌发酵过程优化

Optimization of Menaquinone-7 Fermentation Process Based on CFD Simulation

摘要:

七烯甲萘醌（menaquinone-7，MK-7）是维生素K2的重要组成部分之一，前期研究发现，摇瓶培养条件下MK-7的最高产量远高于搅拌釜反应器培养条件下的最高产量。为缩小从摇瓶放大至3 L搅拌釜反应器带来的差异，使用计算流体力学（CFD）及动态吸收法对不同转速下摇瓶与搅拌釜反应器内的剪切力及氧气传递性能进行比较，并探讨氧气供应及剪切力对枯草芽孢杆菌BS20菌体生长与MK-7合成的影响。结果表明，充足的氧气供应对菌体生长及MK-7合成有促进作用，但过高的剪切力会对菌体产生破坏作用，降低MK-7的产量。基于上述结果，在3 L搅拌釜反应器中，以较低搅拌转速（400 r/min）保证低剪切力，同时采用通富氧空气（氧气体积分数55%）的方式提高供氧水平，MK-7产量达到296 mg/L，比对照批次（氧气体积分数21%）提高152%，达到摇瓶培养最高水平的79%。本研究在搅拌釜反应器中所采用的降低搅拌转速、提高进气氧体积分数的方法，能够有效提高对剪切敏感且高好氧微生物的发酵性能。

Abstract:

Menaquinone-7 (MK-7) is one of the significant components of vitamin K2. Previous studies found that the highest yield of MK-7 under shake flask culture condition was much higher than that cultured under stirred tank reactor (STR). In order to reduce the differences caused by scaling up from the shake flask to 3 L STR, computational fluid dynamics (CFD) and dynamic absorption method were used to compare the shear stress and oxygen transfer performance of the shake flask and STR at different rotational speeds. The effects of oxygen supply and shear stress on the growth of BS20 and the synthesis of MK-7 were also explored. The results showed that sufficient oxygen supply could promote the growth of BS20 and the synthesis of MK-7, however, excessive shear stress would destroy the bacterial cell and reduce the yield of MK-7. Based on the above results, under the culture condition of the 3 L STR, the lower stirring speed (400 r/min) was used to ensure low shear force, while the oxygen-enriched air (oxygen volume fraction 55%) was used to improve the oxygen supply level. The yield of MK-7 reached 296 mg/L, which was an increase of 152% compared to the control batch (with an oxygen volume fraction of 21%), and reached 79% of the highest level cultured in shake flask. In this study, reducing the stirring speed and increasing the oxygen volume fraction of the supplied air in the STR can effectively improve the performance of the shear-sensitive but highly aerobic fermentation process.