Improvement of l-lactic acid production from Jerusalem artichoke tubers by mixed culture of Aspergillus niger and Lactobacillus sp.

Aspergillus niger SL-09 and Lactobacillus sp. G-02 were used as a mixed culture in a 7-l fermentor to directly form l-lactic acid from Jerusalem artichoke tubers. The synthesis of inulinase and invertase from A. niger SL-09 was enhanced significantly by the inoculation of Lactobacillus sp. G-02 at 12 h of culture, which reached 275.6 and 571.8 U/ml in 60 h, over 5-folds higher than that of the culture using single strain. In the following simultaneous saccharification and fermentation procedure, the highest l-lactic acid concentration of 120.5 g/l was obtained in 36 h of the fed-batch fermentation with high conversion efficiency of 94.5%.