Four phenolic acids determined by an improved HPLC method with a programmed ultraviolet wavelength detection and their relationships with lignin content in 13 agricultural residue feeds.

BACKGROUND: Lignification-associated phenolic acids are widely distributed in graminaceous plant cell walls. This study developed a rapid and sensitive reversed-phase method for the simultaneous quantification of protocatechuic (PRA), vanillic (VA), ferulic (FA) and p-coumaric (PCA) acids and investigated the relationship between these compounds and lignin contents in 13 fibrous feeds. RESULTS: The phenolic acids were identified at a column temperature of 15 degrees C in a single run, in which the wavelength was programmed at 260 nm for PRA and VA, then switched to 310 nm for FA and PCA determinations. Satisfactory precision, recovery, and linearity were obtained with this method. Among 13 feeds, PCA was most abundant, followed by FA, VA and PRA. Great variations in phenolic acid and lignin contents were found. FA content was much richer than PCA content in maize and wheat brans, and the highest PCA content occurred in maize stalks. Lignin content was correlated with proportions of FA (r = -0.95) and PCA (r = 0.90) in the summed phenolic acids and the PCA : FA ratio (r = 0.91). CONCLUSION: The improved method appears to be useful for simultaneous quantification of target phenolic compounds. Both FA and PCA may be good indicators for plant cell wall lignification associated with feed digestibility. (C) 2012 Society of Chemical Industry