Comparison of phenolic acids in lignin fractions from forage grasses before and after digestion by sheep

Abstract

Three lignin fractions, dioxane-soluble lignin, alkali lignin and acidolysis lignin, were isolated from Italian ryegrass and orchardgrass hay harvested at the heading stage and from faeces of sheep fed on them and analysed for ester-and ether-linked p-coumaric (PCA) and ferulic acid (FA). Chemical analysis and IR spectra confirmed that the lignin fractions obtained were composed mostly of lignin components and accompanied by little carbohydrate. A comparison between the hay and faecal lignin fractions indicated that ester-linked PCA and FA and ether-linked FA were removed or degraded from the grass lignins during sheep digestion. The faecal dioxane-soluble lignin which was released from the grass cell walls by sheep digestion showed the lowest levels of the bound phenolic acids. The results suggested that removal or degradation of bound phenolic acids by sheep digestion occurred more extensively in the lignin fraction solubilized from the grass cell walls than in the insoluble lignin fraction that remained in the grass cell walls.