Liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS/MS) was applied to the analysis and authentication of fruit-based products and fruit-based pharmaceutical preparations. A Kinetex C18 reversed-phase column under gradient elution with 0.1 % formic acid aqueous solution and methanol mobile phases was used for the simultaneous determination of 26 polyphenols, allowing an acceptable separation in less than 22 min. Instrumental quality parameters such as limits of detection (LOD, values between 12-14 µg/L for 19 of the 26 analyzed polyphenols), linearity (r2 > 0.991), run-to-run and day-to-day precisions (RSD values lower than 9.9 and 13.5 %, respectively), and accuracy (relative errors lower than 8 %) were established. A simple extraction method, consisting of a sample sonication with acetone:water:hydrochloric acid (70:29.9:0.1 v/v/v) and centrifugation, was proposed. Two calibration procedures, external calibration using standards prepared in water and standard addition, were evaluated for polyphenol quantification in several grape and cranberry fruits and processed fruit products. For a 95 % confidence level, no statistical differences were observed between the two calibration methods (p values between 0.06 and 0.95), denoting that external calibration was suitable enough for the quantitative analysis of polyphenols in fruit-based products. The proposed LC-ESI-MS/MS method was then applied to the analysis of polyphenols in 23 grape-based and cranberry-based natural products and pharmaceutical preparations. Polyphenolic concentration data was then analyzed by principal component analysis (PCA) to extract information of the most significant profile data contributing to authentication of natural extracts according to their fruit of origin.