Enhanced lactic acid production from PO-pretreated biomass by domesticated Pediococcus pentosaceus without detoxification.

Expensive cellulase and complex detoxification procedures increase the cost of biomass lactic acid fermentation. Therefore, it is of great significance to develop a robust method to ferment lactic acid using biomass by avoiding cellulase and detoxification. This study demonstrates the advantage of combining mechanocatalytic PO pre-treatment and strain domestication. We show that an enzyme-free mechanocatalytic saccharification process by combining mix-milling of PO with biomass and successive hydrolysis produces a fermentable hydrolysate with much less inhibitory compounds than the hydrolysates obtained by conventional methods; only 5-HMF, furfural and acetic acid were detected in the biomass hydrolysate, and no phenolic inhibitors were detected. Pretreatment of biomass with PO not only avoided cellulase, but also obtained less toxic hydrolysate. Furthermore, the Pediococcus pentosaceus strain gained superior inhibitor tolerance through domestication. It could tolerate 17.1 g/L acetic acid, 12.5 g/L 5-HMF, 11.9 g/L guaiacol and 11.5 g/L furfural and showed activity in decomposing furfural and 5-HMF for self-detoxification, allowing efficient lactic acid fermentation from biomass hydrolysate without detoxification. The lactic acid concentration and conversion rate fermented by domesticated bacteria were increased by 113.5% and 22.4%, respectively. In addition, the domesticated bacteria could utilize glucose and xylose simultaneously to produce lactic acid selectively. The combination of PO pre-treatment and strain domestication to ferment lactic acid is applied to several biomass feedstocks, including corn stalk, corn stalk residue and rice husk residue. Lactic acid concentrations of 29.8 g/L, 31.1 g/L, and 46.2 g/L were produced from the hydrolysates of corn stalk, corn stalk residue and rice husk residue, respectively.