Poster Presentation 2-45

Simultaneous Saccharification and Mixed Sugar Fermentation (SSMSF) of Acid Pretreated Rice Straw in Fed-batch Mode by Carbon Catabolite De-repressed Lactobacillus pentosus JH5XP5

Jae-Han Kim,¹ David A. Mills,² David E. Block^2,3 and Sharon P. Shoemaker^1,4*

¹Department of Food Science and Technology

²Department of Viticulture and Enology

³Department of Chemical Engineering

⁴California Institute of Food and Agricultural Research

University of California, Davis

One Shields Ave.

Room 250, Cruess Hall

Davis, CA 95616

Phone: (530)752-2922

Fax: (530)752-6578

E-mail: spshoemaker@ucdavis.edu

Lactic acid, 2-hydroxypropionic acid, is a commodity platform chemical derived from renewable biomass that can be further processed to ethyl lactate, PLA, and organic acids, thereby replacing petroleum-derived reagents and materials. About half of the annual production of lactic acid today is from the fermentation of glucose to lactic acid with glucose being derived from corn starch. In order to consider using lignocellulosic biomass as a commercially viable feedstock in place of starch, there must be further improvement to feedstock properties, separation efficiency, production microorganism(s) and process integration. This paper focuses on the strain and process improvements for the production of lactic acid from rice straw. The carbon catabolite de-repressed strain, Lactobacillus pentosus, a facultative heterofermentative lactobacilli that possesses both homofermentative (for hexoses) and heterofermentative pathways (for pentoses), was selected for the simultaneous mixed sugar fermentation. A newly derived strain, Lb. pentosus JH5XP5, exhibited stable and reproducible co-utilization of glucose and xylose for five consecutive fermentations. During a fed-batch fermentation of media containing 30 g/L glucose, 10 g/L xylose, and 10 g/L arabinose, all three carbohydrates were consumed simultaneously with the concomitant production of 24 g/L acetate, 12.5 g/L ethanol and 67 g/L lactic acid. Importantly, acid-pretreated rice straw, containing similar mixtures of carbohydrates, is readily fermented by Lb. pentosus JH5XP5. Fermentation of 100 g-dry mass/L of rice straw after enzyme hydrolysis was complete within 24 hours. Rice straw hydrolysate contained 23 g/L glucose, 8 g/L xylose and 5 g/L arabinose which were converted to 25 g/L lactic acid, 5 g/L acetic acid and 4 g/L ethanol. In addition, simultaneous saccharification and mixed sugar fermentation using acid pretreated rice straw was performed with cellulase (15 FPU/g-cellulose) and equivalent of cellobiase in the fed-batch mode giving a yield of 95% lactic acid, after depletion of the soluble sugars.