Determination of free and total phenolic acids in plant-derived foods by HPLC with diode-array detection.
A high-performance liquid chromatographic (HPLC) method with diode-array detection (DAD) was used to identify and quantify free and total phenolic acids (m-hydroxybenzoic acid, p-hydroxybenzoic acid, protocatechuic acid, gallic acid, vanillic acid, syringic acid, o-coumaric acid, m-coumaric acid, p-coumaric acid, caffeic acid, ferulic acid, sinapic acid, chlorogenic acid, and ellagic acid) in plant foods. Free phenolic acids were extracted with a mixture of methanol and 10% acetic acid. Bound phenolic acids were liberated using first alkaline and then acid hydrolysis followed by extraction with diethyl ether/ethyl acetate (1:1). All fractions were quantified separately by HPLC. After HPLC quantification, results of alkali and acid hydrolysates were calculated to represent total phenolic acids. Ellagic acid was quantified separately after long (20 h) acid hydrolysis. The methods developed were effective for the determination of phenolic acids in plant foods. DAD response was linear for all phenolic acids within the ranges evaluated, with correlation coefficients exceeding 0.999. Coefficients of variation for 4-8 sample replicates were consistently below 10%. Recovery tests of phenolic acids were performed for every hydrolysis condition using several samples. Recoveries were generally good (mean >90%) with the exceptions of gallic acid and, in some cases, caffeic acid samples.
Mattila
Pirjo
P
MTT Agrifood Research Finland, Food Research, ET-talo, 31600 Jokioinen, Finland. pirjo.mattila@mtt.fi
Kumpulainen
Jorma
J
D002109:Caffeic Acids / Q000032:analysis; D002726:Chlorogenic Acid / Q000032:analysis; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003373:Coumaric Acids / Q000032:analysis; D004610:Ellagic Acid / Q000032:analysis; D005638:Fruit / Q000737:chemistry*; D005707:Gallic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D062385:Hydroxybenzoates / Q000032:analysis*; D014641:Vanillic Acid / Q000032:analysis; D014675:Vegetables / Q000737:chemistry*
D002109:Caffeic Acids; D003373:Coumaric Acids; D062385:Hydroxybenzoates; D004610:Ellagic Acid; D002726:Chlorogenic Acid; C009091:protocatechuic acid; D005707:Gallic Acid; C073734:sinapinic acid; C004999:ferulic acid; C001945:syringic acid; D014641:Vanillic Acid; C040048:caffeic acid