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 g_{lactic acid} g_sugar^–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 g_{lactic acid} g_sugar^–1, and almost complete xylose consumption.