Lignin impact on fibre degradation. 1. Quinone methide intermediates formed from lignin during in vitro fermentation of corn stover
1996
Sewalt, V.J.H. | Glasser, W.G. | Fontenot, J.P. | Allen, V.G.
Experiments were conducted to determine whether formation of quinone methide intermediates from lignin occurs during ruminal fermentation of corn stover, as indicated by nucleophilic addition reaction with sulphur-containing reducing agents. Corn stover leaf and stem fractions harvested at full maturity were incubated in buffered ruminal fluid without reducing agents or with (NH4)2SO4 (S-control), Na2S.9H2O, cysteine-HCl (cysHCl), or cysHCl plus Na2S.9H2O; and in only buffer with or without cysHCl plus Na2S.9H2O. Mixed reducing agents (cysHCl plus Na2S. 9H2O) enhanced (P < 0.001) in vitro fibre degradation after 48 h, tended to increase solubilisation of fibre (P = 0.07) and dry matter (P = 0.06) in buffer alone, and elevated (P < 0.001) S-content of residual fibre. In vitro incorporation of S into the undegraded fibre was determined for corn stover fractions of varying lignin compositions that were harvested at two maturities (early dent and full maturity) in 2 years. Extent of fibre degradation was correlated with extent of S-incorporation (r= -0.54 P < 0.001), and with lignin methoxyl content (r = -0.84, P < 0.001). The negative association of lignin methoxyl content with digestibility is explained by the relative likelihood of quinone methide intermediate formation from guaiacyl and syringyl units in lignin.
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