EFFECT OF 2 PRETREATMENTS ON PHENOLIC-ACID YIELD IN 3 FORAGE SPECIES

A direct comparison of two pre-treatments was undertaken to test their effect on the recovery of phenolic acids (PA) from three forage species. Samples of lucerne (Medicago sativa L), reed canarygrass (Phalaris arundinacea L), and switchgrass (Panicum virgatum L) were refluxed with 95% ethanol (EtOH) or neutral detergent solutions (NDS). Subsequently, the resulting ethanol insoluble residue (EIR) and neutral detergent fibre (NDF) were treated with 1 M NaOH, and the extract was assayed for concentrations of p-coumaric acid (PCA) and ferulic acid (FA). In lucerne, the concentration of PCA was 9 times greater in the EIR than in the NDF (0.90 vs 0.11 mg g-1 dry matter, DM), and the FA concentration was 27 times greater in forage treated with EtOH than with NDS (1.89 vs 0.07 mg g-1 DM). In reed canarygrass (RCG), the concentrations of PCA and FA were slightly though significantly higher when the forage was pre-treated with EtOH. No significant differences in PA yield were detected between pre-treatments in switchgrass (SG). Extraction of EIR with hot EDTA (0.025 M, pH = 6.8) removed 80 to 90% of the total PA in EIR in lucerne but less than 5% of the PCA and FA in the grasses. These results indicate that almost all the PA in lucerne, in direct contrast to the grasses, are present in a fraction of the plant that is soluble in NDS. The relatively high PA concentration in the NDS soluble fraction suggests that the structure and composition of the fraction to which PA is esterified influence the degree to which PA affects digestibility.