Titratable groups and soluble phenolic compounds as indicators of the digestibility of chemically treated roughages

Methods are presented which evaluate the efficiency of delignification in alkali-treated grass straws. Saponified lignin is soluble in neutral detergent solution and in phosphate buffer, and can be assayed by ultraviolet spectrophotometry of the solutions. Extraction of free phenolic material by means of neutral detergent or phosphate buffer is followed by determination of a saponification number (titratable groups) on the residue. Measurements of phenolic matter in the sodium hydroxide extract of the fibre residue allow assay of the residual, bound lignin in treated straws. The bound lignin is negatively correlated with digestibility of alkali-treated straw. The results provide further evidence that the negative effect of lignin upon digestibility of forages depends on covalent linkage between lignin and the carbohydrate residues that it protects.