BACKGROUND: Simultaneous xylose isomerization and fermentation was investigated to improve the lactic acid production from xylose by Lactobacillus pentosus in a novel two-in-one bioreactor constructed by packing the immobilized xylose isomerase (65 g) in a fixed bed reactor (diameter 56 mm × 66 mm, packing volume 154 mL) with a permeable wall, which was installed inside a conventional fermenter (2 L) and rotated along the axis together with the mechanical stirrer of the fermenter.
RESULTS: Xylose (20 g L−1) was completely consumed within 24 h in the novel bioreactor, compared with 72 h needed for the control without packed enzyme. The maximum cell density (17.5 g L−1) in the novel bioreactor was twice that in the control and the lactic acid productivity (0.58 g L−1 h−1) was 3.8 times higher. Repeated use of the immobilized enzyme showed that the lactic acid productivity and yield obviously dropped after the first batch fermentation but maintained almost unchanged afterwards.
CONCLUSION: Simultaneous xylose isomerization and fermentation significantly improved lactic acid production from xylose by Lactobacillus pentosus. The novel bioreactor made it easier to recycle and reuse the immobilized enzyme. © 2012 Society of Chemical Industry