Using the acetyl bromide assay to determine lignin concentrations in herbaceous plants: Some cautionary notes

The acetyl bromide assay was developed to provide a rapid and sensitive met hod for quantifying lignin in woody plant species. The original procedure c autioned against prolonged reaction times and advised keeping the reaction temperature at 70 degrees C to prevent excessive carbohydrate degradation t hat would skew the absorption spectra. Characterization of the reaction con ditions revealed that the acetyl bromide reagent readily degrades xylans, a prominent polysaccharide group within all lignified plants. This degradati on results in increased absorbance in the 270-280 nm region that is used to quantify lignin. The degradation of xylans is temperature dependent and is exacerbated by the addition of perchloric acid. Lowering the reaction temp erature to 50 degrees C and increasing the reaction time from 2 to 4 h allo ws complete lignin solubilization but minimizes degradation of the xylans.