Effects of pinewood extractives on bioconversion of pinewood

Abstract Extractives are a wide range of compounds that make up a small fraction of lignocelluloses, but they can profoundly affect the bioconversion processes of these materials. To investigate the effects of extractives on these processes, pinewood extractives were extracted by water and ethanol as solvents. The composition of extractives was analyzed by GC/MS, and the phenolic contents of extractives were determined by Folin-Ciocalteu assay. Pinewood and extractives-free pinewood were subjected to enzymatic hydrolysis, simultaneous saccharification and fermentation (SSF), and anaerobic digestion in the presence of different concentrations of pinewood water extractives (PWE) and pinewood ethanol extractives (PEE). It was found that PWE and PEE contained 122.7 and 57.9 mg gallic acid equivalent (GAE)/g extract of phenolics, respectively. The GC/MS results revealed that 4-benzyloxy-4- [2,2-dimethyl-4-dioxolanyl] butyraldehyde and abietic acid were the most abundant components of PWE and PEE, respectively. The addition of 100 g/L PWE decreased enzymatic hydrolysis glucose yield from 23.3 to 16.8%, and a linear relationship between inhibition and the concentration of PWE was found. Whereas, the addition of 100 g/L PWE decreased the SSF ethanol yield from 16.8 to 4.6%. Accumulated biogas was declined from 107.4 to 16.7 mL/g VS with the addition of 80 g/L of PWE in anaerobic digestion. By increasing the concentrations of PWE from 0 to 80 g/L, accumulated methane also decreased from 91.7 mL/g VS to nearly zero. On the other hand, adding 100 g/L of PEE improved ethanol yield from 15.3 to 28.6%. An increase in the level of PEE from 0 to 40 g/L decreased accumulated biogas from 140.2 to 62.8 mL/g VS. However, it had no significant effect on glucose yield in enzymatic hydrolysis. Although extractives are minor components of lignocellulose, they affect its bioconversion severely, especially biogas production.