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

In this work, phosphoric acid pretreatment (0.6% H 3 PO 4 , 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.