Rye Straw Lignin as a Promising Source of Tricin: Varietal Differences and Its Release Using Deep Eutectic Solvents

Lignins isolated from the straw of six rye (Secale cereale) varieties (Cl 98, Slapske, Zidlochovicke Panis, Ceske Normalni, Bates, and SU Stakkato) were comprehensively characterized by advanced analytical techniques to assess their structural features and valorization potential. Rye straws contained ∼15% of lignin, which was primarily constituted by guaiacyl (∼52-61%) and syringyl (∼35-45%) units, with minor amounts of p-hydroxyphenyl units (∼3%). The lignin backbone was enriched in β-O-4' alkyl-aryl ether linkages (77-79%), followed by β-5' (10-12%) and β-β' (4-6%). All the lignins from the rye straws were enriched in tricin, with the Cl 98 variety having the highest content, reaching up to 26.2 g/kg straw. Since tricin is incorporated exclusively through 4'-O-β ether linkages, an environmentally benign deep eutectic solvent (DES, choline chloride/lactic acid, 1:10), which is known to efficiently cleave such bonds, was evaluated for its selective release. DES treatment of Cl 98 straw yielded 1.92 mg of free tricin/g straw, confirming the effective cleavage of β-O-4 linkages. This study highlights rye straw lignin as a tricin-enriched, renewable biopolymer, emphasizing its potential as a sustainable source for high-value tricin recovery and supporting the valorization of cereal crop residues within lignocellulosic biorefineries.