Determination of phenolic compounds in strawberries (Fragaria ananassa Duch.) by high performance liquid chromatography with diode array detection

Abstract

This paper describes a method for simultaneous identification and quantification of phenolic compounds in strawberries followed by a reversed-phase high performance liquid chromatography (HPLC) with diode array detection. The studied phenolics were flavonoids (flavonols: quercentin, rutin, and kaempferol; flavanols: catechin and epicatechin; anthocyanidins: cyanidin and pelargonidin) and phenolic acids (hydroxybenzoic acid derivatives: gallic and ellagic acids; hydroxycinnamic acid derivatives: ferulic, coumaric, and cinnamic acids). The mobile phase consisted in a gradient prepared from formic acid in water (2 %, pH 3) and formic acid in methanol (2 %, pH 3), flow rate 0.7 mL min−1 at 25 °C. Analyses were performed, using methanol as extractant, before and after acid hydrolysis with the aim of determining free and conjugated phenolic compounds in strawberries. The acid hydrolysis conditions (6 mol L−1 HCl, 50 min at 90 °C) were shown to be suitable both for phenolic standards and strawberry extracts. Method validation, using phenolic standard solutions, included: linearity study, limits of detection and quantification, and calibration and analytical sensitivity quantifications. Precision and accuracy were studied in strawberry extracts. The results indicate that the developed method was linear, sensible, precise, and accurate, and the convenience of methanol can substitute acetonitrile as the most commonly used solvent in HPLC. The method was employed for knowing the phenolic profile in seven strawberry cultivars from Italy and Argentina, and besides, total phenolic content was analyzed by the Folin–Ciocalteu method; the total antioxidant activity was investigated using the ABTS method. Good correlations were observed among latter parameters, and total phenolics were obtained as the sum of each phenolic compound analyzed by photodiode array detection-HPLC.