Development of a continuous cell-recycle fermentation system for production of lactic acid by Lactobacillus paracasei

Experimental devices for stimulating productivity of lactic acid fermentation were installed and an electromagnetic flow-meter and a pneumatic diaphragm pump were employed to alleviate the fouling of the membrane and to improve the durability of membrane cell-recycle bioreactors (MCRBs). In this case, the continuous fermentation using a 5 L automatic fermentor lasted stably over 150 h, and could repeat periodically with simple intermittent on-line cleaning and sterilization of the membrane filtration system. Maximum value of OD620 of 98.7 was obtained, six times greater than that of the fed-batch fermentation. Meanwhile, maximum productivity of 31.5 g/(L h) was recorded, 10 times greater than that occurred in the fed-batch fermentation. Compared with conventional MCRBs, the MCRB system with a diaphragm pump and tangential flow-rate controlling was more stable and durable. The tangential velocity of membrane module could be monitored and controlled on-line, and the possibility of contamination due to hose rupture could be eliminated.