Mass Spectrometry Exposes Undocumented Lignin-Carbohydrate Complexes in Biorefinery Pretreatment Stream

The presence and effects of lignin carbohydrate complexes (LCCs) in biorefinery processes are largely unknown. Recently identified in a significant hydrothermal pretreatment process stream (autohydrolyzate), these molecules likely influence not only downstream processing but also product purity and performance. However, without an understanding of their structures, it is impossible to analyze and cope with their effects. To identify and elucidate LCCs in autohydrolyzate, a new method employed chloride doping and tandem mass spectrometry. The results showed complexes ranging in mass from 326-714 Da with evidence of xylose and glucose units. Further analysis revealed lignin-like levels of unsaturation, considering the number of carbons present. These results suggest that, although the complexes contain one or two carbohydrate units, their primary structures are closer to lignin compounds. This method provides a glimpse into the structures of LCCs in a biorefinery process stream, laying the foundation for easier identification and continued structural elucidation of these enigmatic complexes.