A comparison of HPLC and spectrophotometrical methods to determine the activity of ferulic acid esterase in commercial enzyme products and rumen contents of steers

The aim of this study was to compare different methods to determine ferulic acid esterase (FAE) activity in commercial enzyme products and to measure the FAE activity in the rumen of steers fed different diets (A: 5 kg forage and 4 kg concentrate; B: 5 kg forage and 5 kg concentrate; C: 5 kg forage and 6 kg concentrate). FAE activities in seven commercial enzyme products were determined by high performance liquid chromatography (HPLC) at a wavelength of 320 nm and by spectrophotometric assays at wavelengths of 335 and 340 nm. FAE activities varied dramatically among the seven exogenous enzyme preparations. Correlation between the enzyme activities determined by HPLC and spectrophotometric assays was high (r > 0.98), but consistency among the different methods was poor, especially with the spectrophotometrical method (SP) at 335 nm. Therefore, the SP by microplate reader at 340 nm with standard substrate of methyl ferulate (MFA) was recommended for rapid analysis of large numbers of samples. Rumen fluid of steers had low, and different, ferulic acid esterase activity at different times of the day. Furthermore, high diurnal variation occurred for the ferulic acid esterase and other fibrolytic enzymes that were measured. The activity of FAE and other fibrolytic enzymes differed along with the diet compositions and feed intake. Diet C had the highest mean fibrolytic enzyme activity in the rumen, and diet A had the lowest activity of FAE and birchwood xylanase (BX). High correlations occurred between activities of carboxymethyl cellulase (CMC), BX, acetyl esterase (AE) and those of FAE, both with all data and within each diet. As an accessory enzyme, ferulic acid esterase should not be neglected in studies on furthering understanding of biodegradation of plant cell wall in rumen, and impacts of exogenous enzyme products.