Development and Validation of an Analytical Method for Phenolic Acid Extraction from Cereals and Quantification using HPLC-UV

Abstract: Cereals are rich in phenolic acids, a group of secondary plant metabolites that are associated with reduced risk of chronic diseases. The objective was to develop and internally validate a method for extraction and quantification of phenolic acids in cereals using HPLC-UV and to apply this method for quantification of the content of phenolic acids in several species of Swedish cereals. Different procedures for extraction of phenolic acids from cereal grains using acid or base hydrolysis with and without subsequent enzymatic treatment were tested. Both the extraction procedure and the chromatographic conditions for quantification with HPLC-UV were optimized. Phenolic acids from 14 cereal samples, representing different cultivars of rye, wheat, barley, and oat, were extracted and analyzed under optimized conditions. Using the optimized method, 15 phenolic acids could be quantified with limits of detection and quantification ranging from 0.4 to 11.4 µg/g and from 1.3 to 38.0 µg/g, respectively. The hydrolysis procedure and further sample treatment showed a substantial effect on the yield of phenolic acids from cereals. The highest yield was achieved by 90‑minute base hydrolysis at room temperature using sodium hydroxide solution containing ascorbic acid and EDTA. Mean recoveries ranged from 88 to 108%. The following phenolic acids were found in the analyzed cereal grains with ferulic acid being the most abundant one: p‑hydroxybenzoic acid, vanillic acid, vanillin, caffeic acid, syringic acid, ferulic acid, sinapic acid, and 3,4‑dihydroxybenzaldehyde. A further compound was p‑coumaric acid or the co‑eluting syringaldehyde or a mixture of both. The content of phenolic acids in Swedish cereals ranged from 6 µmol/g DM in rye to 3 µmol/g DM in oat and a barley cultivar. In conclusion, a simple and accurate method for extraction and quantification of phenolic acids in cereals was developed and successfully applied.