Lactic Acid Production from Steam-Exploded Sugarcane Bagasse Using <i>Bacillus coagulans</i> DSM2314

Abstract

This work aimed at producing lactic acid (LA) from sugarcane bagasse after steam explosion at 195 °C for 7.5 and 15 min. Enzymatic hydrolysis was carried out with Cellic CTec3 and Cellic HTec3 (Novozymes), whereas fermentation was performed with Bacillus coagulans DSM2314. Water washing of pretreated solids before enzymatic hydrolysis improved both hydrolysis and fermentation yields. The presence of xylo-oligosaccharides (XOS) in substrate hydrolysates reduced hydrolysis efficiency, but their effect on fermentation was negligible. The presence of fermentation inhibitors in C5 streams was circumvented by adsorption on activated carbon powder with no detectable sugar losses. High carbohydrates-to-LA conversions (Yp/s) of 0.88 g·g−1 were obtained from enzymatic hydrolysates of water-washed steam-exploded materials that were produced at 195 °C, in 7.5 min, and the use of centrifuged-but-never-washed pretreated solids decreased Yp/s by 16%. However, when the detoxified C5 stream was added at a 10% ratio, Yp/s was raised to 0.93 g·g−1 for an LA productivity of 2.55 g·L−1·h−1. Doubling the pretreatment time caused a decrease in Yp/s to 0.78 g·g−1, but LA productivity was the highest (3.20 g·L−1·h−1). For pretreatment at 195 °C for 7.5 min, the elimination of water washing seemed feasible, but the use of longer pretreatment times made it mandatory to eliminate fermentation inhibitors.

Keywords

• sugarcane bagasse
• steam explosion
• enzymatic hydrolysis
• fermentation
• lactic acid