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Poster Presentation 3-38
Simultaneous Conversion of Hexose and Pentose Sugars to Lactic Acid by Lactobacillus brevis
Jae-Han Kim1, David A. Mills2, David E. Block2 and Sharon P. Shoemaker1
1 Department of Food Science and Technology University of California, Davis and California Institute of Food and Agricultural Research University of California Davis, California 95616
2Department of Viticulture and Enology University of California Davis, California 95616
Telephone: (530) 754-7871; E-mail: jaykim@ucdavis.edu
A prominent goal of biobased chemical production from agricultural waste materials is efficient co-utilization of both the hexose and pentose sugars derived from lignocellulose. A screen of several lactobacilli revealed that the heterofermentative strain, Lactobacillus brevis, can utilize glucose and other fermentable carbohydrates simultaneously without apparent catabolite repression. In this work, we examined the effects of substrates and their ratio on the fermentation kinetic parameters of cell growth and lactic acid production. Fermentations were carried out in MRS media at 30oC with varying concentration glucose and xylose and/or arabinose. L. brevis was shown to metabolize glucose, xylose, and arabinose simultaneously. Moreover, pentose sugars were consumed at similar rates as glucose, though there was some difference between strains. Surprisingly, lactic acid productivity was similar to those obtained with other homofermentative lactobacilli. Though lactic acid production was not significantly affected by sugar substrate, the ratio of two carbon end products (acetate and ethanol) was altered during growth on xylose. While the molecular basis for lack of catabolite repression remains to be determined, simultaneous utilization of both hexose and pentose sugars suggests L. brevis is a good candidate for lactic acid production schemes that employ substrates derived from lignocellulosic matter.
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