Analysis of recalcitrant phenolic lignin structures to understand the impact of pretreatment and feedstock selections on enzyme digestibility

Nearly all the leading pretreatment technologies would result in certain modifications of original lignin structures. It is known that both acid pretreatment and stream explosion would break down lignin and generate more phenolic units with the increase in pretreatment severities. In the present study, we investigated enzyme digestibility of various pretreated substrates by chemical analysis of recalcitrant phenolic lignin structures. The substrates were subjected to periodate oxidation for total phenolic group analysis and cupric oxide oxidation for changes of S/V ratios and lignin condensation reactions. The results showed that there was a good correlation between enzyme digestibility and total phenolic units from periodate oxidation. In addition, S/V ratios and the yield of syringlaldehyde and vanillin could indicate if certain feedstock was more recalcitrant than others or if the substrate was under or over-pretreated