Tricin (5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one), a member of the flavonoid family, was recently proved to be a true monomer in grass lignins and probably functions as a nucleation site for lignification. It becomes linked into lignin polymers as an aryl alkyl ether by radical coupling with monolignols (coniferyl, sinapyl, and p-coumaryl alcohols). However, the amount of tricin that incorporates into grass lignin remains unclear. In this study, three common lignin characterization methods, acidolysis, thioacidolysis, and Derivatization Followed by Reductive Cleavage (DFRC), were applied to quantify the tricin content. Their efficiencies at cleaving tricin-(4'–O–β)-ether bonds were evaluated using dimeric model compounds. Thioacidolysis turned out to be the most efficient method with more than 85% of the tricin being liberated. A survey of several plant species for tricin quantitation using thioacidolysis showed that tricin is widely distributed in the lignin of members of the Poaceae family, including maize, oat, wheat, Brachypodium, miscanthus, switchgrass, lemongrass, and others. The amount of lignin-integrated tricin ranged from 0.32 mg/g (miscanthus, based on the whole cell wall) to 7.15 mg/g (oat), most of which is higher than the extractable tricin level (0.05-0.77 mg/g) that was previously reported. The occurrence of tricin in lignin provides an alternative large and valuable source of tricin, and probably reduces the cost, therefore encouraging the study and application of tricin beyond its current roles.

Quantitation of tricin in grass lignins

251st National Meeting (2016)

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