Xylosaccharides purification 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 (mainly xylose, 20.3 g/L), acetic acid 7.8 g/L, furfural 0.7 g/L, and acid soluble lignin (ASL) 2.1 g/L. 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 high 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 non-detoxified and detoxified hydrolysate obtained through vacuum oven. For the non-detoxified hydrolysate, 12 g/L of L-lactic acid was obtained after 48 h showing a yield of 0.56 g lactic acid/g sugar 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 of lactic acid after 24 h, with a yield of 0.73 glactic acid/gsugar, and almost complete xylose consumption.