Purification of xylosaccharides from eucalyptus residues for l‐lactic acid production by Weizmannia coagulans

Abstract

In this work, phosphoric acid pretreatment (0.6% H3PO4, 160 °C, 40 min) of eucalyptus residues was performed to recover the hemicellulosic fraction for further conversion to l‐lactic acid by fermentation with Weizmannia coagulans DSM 2314 (formerly Bacillus coagulans). The hemicellulosic hydrolysate was composed of xylosaccharides 24.8 g L–1 (mainly xylose, 20.3 g L–1), acetic acid 7.8 g L–1, furfural 0.7 g L–1, and acid‐soluble lignin (ASL) 2.1 g L–1. It was subsequently purified by using anion exchange or adsorption resins. Different liquor‐to‐resin ratios were evaluated to obtain a high concentration of xylosaccharides in the eluate and thorough removal of components that inhibit lactic fermentation. The best performance was observed when using Amberlite‐XAD‐4 resin at a liquor‐to‐resin ratio of 3:1. An eluted hydrolysate was obtained, preserving 80% of the xylosaccharides and effectively removing almost all furfural, 90% of ASL, and 32% of acetic acid. Subsequently, l‐lactic acid production by W. coagulans DSM 2314 was evaluated using concentrated nondetoxified and detoxified hydrolysate obtained with a vacuum oven. For the nondetoxified hydrolysate, 12 g L–1 of l‐lactic acid was obtained after 48 h showing a yield of 0.56 glactic acid gsugar–1 and a xylose consumption of 62%. The detoxification of the liquor significantly improved the fermentation performance of W. coagulans, resulting in a concentration of 16 g L–1 of lactic acid after 24 h, with a yield of 0.73 glactic acid gsugar–1, and almost complete xylose consumption.