Three methods were compared in the estimate of lignin cell wall contents in different fractions of seven forage species. The methods for assaying lignin were: acid detergent lignin, permanganate lignin and acetyl bromide soluble lignin. The lignin extracted from the forage sample through the acetyl bromide reagent was employed as a reference standard for the spectrophotometric method. There was no agreement among the three methods; in general, the ABSL yielded higher values than the two other analytical procedures while the ADL method yielded the lowest values. For most samples, lignin concentration was higher for the mature plant cell wall in relation to the young plant; similarly, lignin concentration was higher for the stem fraction as compared to the leaf fraction. Legumes tended to show higher lignin values obtained through the gravimetric methods than grasses, regardless of maturity stage; however, this trend was not observed for the ABSL method, particularly at mature stage. The cell wall preparations were fermented "in vitro" and the data correlated with lignin concentrations obtained through the three methods. The spectrophotometric method exhibited the lowest correlation coefficients for the majority of samples, which strongly suggests that this method must be better evaluated.
acetyl bromide lignin; acid detergent lignin; cell wall; digestibility; potassium permanganate lignin; spectrophotometric method
