Abstract
Phenolic inhibitors generated during alkaline pretreatment of lignocellulosic biomasses significantly hinder bacterial growth and subsequent biofuel and biochemical production. Water rinsing is an efficient method for removing these compounds. Nevertheless, this method often generates a great amount of wastewater, and leads to the loss of solid fiber particles and fermentable sugars. Kurthia huakuii LAM0618T, a recently identified microorganism, was herein shown to be able to efficiently transform phenolic compounds (syringaldehyde, hydroxybenzaldehyde, and vanillin) into less toxic acids. Taking advantage of these properties, a biodetoxification method was established by inoculating K. huakuii LAM0618T into the NH3/H2O2-pretreated unwashed corn stover to degrade phenolic inhibitors and weak acids generated during the pretreatment. Subsequently, 33.47 and 17.91 g/L lactic acid was produced by Bacillus coagulans LA204 at 50 °C through simultaneous saccharification and fermentation (SSF) from 8% (w/w) of NH3/H2O2-pretreated corn stover with or without K. huakuii LAM0618T-biodetoxification, indicating biodetoxification significantly increased lactic acid titer and yield. Importantly, using 15% (w/w) of the NH3/H2O2-pretreated K. huakuii LAM0618T-biodetoxified corn stover as a substrate through fed-batch simultaneous saccharification and fermentation, high titer and high yield of lactic acid (84.49 g/L and 0.56 g/g corn stover, respectively, with a productivity of 0.88 g/L/h) were produced by Bacillus coagulans LA204. Therefore, this study reported the first study on biodetoxification of alkaline-pretreated lignocellulosic material, and this biodetoxification method could replace water rinsing for removal of phenolic inhibitors and applied in biofuel and biochemical production using the alkaline-pretreated lignocellulosic bioresources.
Highlights
Lignocellulose, the most globally abundant renewable bioresource, is attracting increasing attention in the context of biofuel and biochemical production, e.g., lactic acid, biolipids, ethanol, etc., production [1,2,3,4]
K. huakuii LAM0618T was inoculated into yeast extract–peptone–dextrose (YPD) medium containing different concentrations of the phenolic inhibitors syringaldehyde, hydroxybenzaldehyde, and vanillin, which are used as the model chemicals to study the effects of phenolic inhibitors on biofuels and biochemical fermentation from lignocellulosic hydrolysates (Figure 1)
Glucose was completely consumed in the control medium, while more glucose remained in the medium with higher concentration of syringaldehyde (Figure 1c)
Summary
Lignocellulose, the most globally abundant renewable bioresource, is attracting increasing attention in the context of biofuel and biochemical production, e.g., lactic acid, biolipids, ethanol, etc., production [1,2,3,4]. Chemical pretreatments are widely used to dissolve lignin, thereby improving the efficiency of enzymatic hydrolysis and subsequent fermentation [7]. Dilute alkaline, and alkaline peroxide pretreatments were compared, with wheat straw and corncob as substrates. These comparisons revealed that the alkaline peroxide pretreatment is the most appropriate method for ethanol and lactic acid production even without rinsing of the pretreated substrates [8,9]. The alkaline peroxide pretreatment retained more of the hemicellulose than during other pretreatments, and dissolved a portion of the lignin, promoting enzymatic hydrolysis and reducing the inhibitory effect of lignin derivatives on subsequent fermentation [8]
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