Determination of Phenolic Acids and Hydrolyzable Tannins in Pomegranate Fruit and Beverages by Liquid Chromatography with Diode Array Detection and Time-of-Flight Mass Spectrometry

Abstract

Three phenolic acids (gallic, 3,4-dihydroxybenzoic, and ellagic acids) and four hydrolyzable tannins (punicalin, punicalagins A and B, and corilagin) have been determined in pomegranate beverages and different parts of the fresh fruit and tree by liquid chromatography with diode array detection coupled to electrospray ionization and time-of-flight mass spectrometry (LC-DAD-ESI-ToFMS). For the fruit and tree analysis, the lyophilized sample was submitted to extraction in methanol for 2 h. Centrifuged and filtered beverages were diluted 1:10 with water for the quantification of corilagin and 3,4-dihydroxybenzoic acid and 1:100 for the rest of polyphenols. Calibration against external aqueous standards was used for quantification by liquid chromatography with diode array detection (LC-DAD), achieving detection limits in the 1.8–9.2 ng ml⁻¹ range (0.2–1.1 μg g⁻¹), depending on the compound. Matrix-matched calibration was applied for liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry (LC-ESI-ToFMS), with detection limits ranging between 0.16 and 1.4 ng ml⁻¹ (0.02–0.17 μg g⁻¹). Satisfactory recovery values between 88 and 110 % were obtained for beverages and solid samples spiked in the 5–100 μg ml⁻¹ and 10–100 μg g⁻¹ concentration ranges, respectively, with the two detection modes used. The polyphenols were quantified in the beverages between 0.3 and 325 mg l⁻¹, for corilagin and punicalagin A, respectively, and between 0.04 and 22.82 mg g⁻¹ (as dry matter) for 3,4-dihydroxybenzoic acid and punicalagin A, respectively, in the different parts of the fruit and tree.