Biological detoxification and metabolism of inhibitors in corncob acid hydrolysate using Aspergillus niger

Abstract

Background The complex structure of lignocellulosic raw materials requires pretreatment and enzymatic hydrolysis to convert them into monosaccharides for further microbial utilization. During pretreatment, the main inhibitory compounds produced are acetic acid, furfural, and 5-hydroxymethylfurfural (HMF), which are significant factors limiting the microbial growth and fermentation of lignocellulosic materials. Biological detoxification is an efficient, gentle, and environmentally friendly method for removing fermentation inhibitors in lignocellulose hydrolysate. Results Aspergillus niger (A. niger) M13 efficiently metabolizes acetic acid, furfural, and HMF at concentrations of at least 7.50, 1.81, and 1.02 g/L, respectively. Among these inhibitors, furfural exerts the strongest inhibitory effect on cell growth. Both M13 spores and mycelial balls can completely remove the major inhibitors in the hydrolysate, with spores exhibiting a higher removal efficiency than mycelial balls. The detoxification rates of acetic acid, furfural, and HMF by M13 spores were 0.1566, 0.1125, and 0.015 g/L/h, respectively. This strain prefered to consume furfural first, followed by HMF, and then simultaneously consumes acetic acid and glucose. Finally, M13 spores can produce a small amount of citric acid (about 6 g/L) directly from the non-detoxified hydrolysate. Conclusions Using A. niger M13 spores for detoxification is a highly feasible option. These spores can completely remove the main inhibitory substance from the hydrolysate within 1–2 days while retaining the carbon source for subsequent fermentation production. Biodetoxification by A. niger M13 provided a fast and efficient biodetoxification method for removing inhibitors generated during intensive lignocellulose pretreatment, and its advantages made it possible for potential industrial application.