Non-catalytic proteins as promising detoxifiers in lignocellulosic biomass pretreatment: unveiling the mechanism for enhanced enzymatic hydrolysis

Dilute acid (DA) pretreatment of biomass generates multiple inhibitory compounds within the pretreated hydrolysates. These compounds subsequently contribute to the formation of pseudo-lignin on the surface of the substrate, consequently impeding the efficiency of enzymatic digestibility. To detoxify the DA pretreated hydrolysates, post-incubation with non-catalytic proteins (amaranth protein, AP; soy protein, SP; bovine serum albumin, BSA) was performed in the present study. The enzymatic digestibility of DA-pretreated substrates was increased from 40.0% (without non-catalytic proteins) to 64.9, 53.8, and 56.4%, respectively, in the presence of AP (50 mg g⁻¹), SP (65 mg g⁻¹), and BSA (50 mg g⁻¹). The post-incubation of pretreated substrates with non-catalytic proteins led to high hydrophobicity, contact angle, and accessibility, likely due to less formation of pseudo-lignin. Furthermore, gas chromatography/mass spectrometry analysis revealed that AP, SP, and BSA could lower the inhibitor concentrations in the pretreated hydrolysates by 39–100%, 5–100%, and 3–100%, respectively. The detoxification of the pretreated hydrolysates by AP demonstrated superior effectiveness compared to SP and BSA. To assess the affinity between inhibitors and non-catalytic proteins, surface plasmon resonance analysis was conducted, revealing the following affinity rates: AP (18.65 nM) > SP (17.04 nM) > BSA (16.87 nM). Additionally, molecular docking analysis revealed numerous molecular binding sites (i.e., hydrogen, polar, acidic, basic, and greasy contacts) with strong binding affinity ranging from −36.17 to −76.98 kcal mol⁻¹ between the inhibitors and the amino acids of AP. Thus, this study highlights the potential application of AP as a cost-effective strategy for achieving a viable biorefinery. Also, the findings provide valuable insights that can be utilized to advance the development of (hemi)cellulases that exhibit enhanced resistance to lignin and inhibitors.