Comparison of methods of extraction of phenolic compounds from american cranberry (Vaccinium macrocarpon L.) press residues

American cranberries (Vaccinium macrocarpon L.) contain significant quantities of various phenolic compounds. Most of these compounds are recovered when berry juice is produced. However, a considerable part of polyphenols remain in berry press residues and are discarded as food industry waste. The aim of the study was to compare the methods of extraction of polyphenols (ultrasound, microwave-assisted, Soxhlet) from press residues of American cranberry. The impact of main extraction parameters (e.g., extraction time, solid/solvent ratio, solvent type) on the yield of extracted polyphenols. Ultrasound-assisted extraction showed the highest potential from all studied methods, given its fast, convenient use and low cost. Aqueous ethanol and methanol in the presence of acid (anthocyanin extractions should be assisted with trifluoroacetic acid, polyphenol extractions – with HCl) were assessed as the best solvents for extraction. The obtained extracts were characterised using the Folin-Ciocaulteu method for determination of total phenolics and the pH-differential method for determination of total anthocyanins, and UPLC–PDA was used to determine the content of individual anthocyanins. Cyanidin-3-O-arabinoside, peonidin-3-O-galactoside, peonidin-3-O-glucoside and peonidin-3-O-arabinoside were identified as the main anthocyanins in cranberry press residue extracts.