(643f) Production of Butyric Acid From Sugarcane Bagasse Hydrolysate (SBH) by Clostridial Tyrobutiricum ATCC 25755 (pta-) Immobilized in a Fiber-Bed Bioreactor (FBB)

Plant biomass as a useful and valuable resource of fermentable sugar in the biorefinery industry has generated large interests for use in producing biofuels and chemicals. Sugarcane bagasse, which consists of 42% cellulose, 26% hemicellulose and 20% lignin, is the most abundant and a cheap renewable biomass resource in South China, Cuba and Brazil. It is a heteropolymer of hexose and pentose sugars, with glucose and xylose as two major constituents. Sugarcane bagasse has been successfully used to produce bioethanol by combined acid-enzymatic pretreatment and anaerobic fermentation. The goal of this work was to evaluate the feasibility of using sugarcane bagasse as an inexpensive feedstock for the production of butyric acid, a valuable specialty chemical currently produced predominantly via petrochemical routes. Butyric acid has many applications in the chemical industry as well as food and pharmaceutical industries. Esters of this acid are used as additives for increasing fruit fragrance and as aromatic compounds for the production of perfumes. Butyrate esters, which have similar energy content and properties to biobutanol, can also be used as novel biofuels. The potential markets for bio-based butyric acid and its esters are thus large and awaiting exploration.

A mutant of anaerobic bacteria, Clostridial tyrobutiricum ATCC 25755 (pta-), was constructed to produce high yield of butyric acid with low byproducts concentration in our previous work. The goal of this work was to investigate the potential to produce butyric acid from the concentrated sugarcane bagasse hydrolysate (SBH) in a fibrous-bed bioreactor (FBB), which was connected to a stirred tank bioreactor with pH and temperature controls. The hydrolysate of sugarcane bagasse was prepared by dilute acid digestion (0.1N HCl at 121C for 10 min) followed by enzymatic hydrolysis (ACCELLERASE 1500 at 50C for 44 hours, pH 5.0). The strain of this mutant was cultured in serum bottle to determine the specific growth rate in the medium containing the hydrolysate. In general, the bacterium used both glucose and xylose present in the hydrolysate for growth, with a specific growth rate of 0.036-0.039 h-1 in serum bottles. The FBB, with a large amount of immobilized cells was initially fed with the medium containing 60 g/L glucose, and the concentration of butyric acid reached 29.87 g/L at 138 hours, with a corresponding butyric acid productivity of 0.216 g/L/h. The fermentation broth in the bioreactor was then replaced with the medium containing concentrated SBH. After 326 hours, the butyric acid concentration in the fermentation reached 20.89 g/L, which corresponded to a butyric acid productivity of 0.064 g/L/h. Compared to the fermentation with glucose as the substrate, the hydrolysate gave a lower productivity and there were sugar residues (12.7 g/L glucose and 3.8 g/L xylose) remained in the broth, indicating strong inhibition caused by the high salt concentration and the presence of inhibiting byproducts in the hydrolysate. The fermentation can be improved by optimizing the process of the hydrolysate preparation and adaptation of cells in the FBB to tolerate a higher toxic concentration. This is the first study demonstrating that butyric acid can be produced from sugarcane bagasse by anaerobic fermentation.n.