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Sequential extraction of black currant residues produces anthocyanin-rich extracts containing anthocyanin dimers


BACKGROUND: Annually, the EU processes ~750 000 M tonnes of black currants to juice with a substantial production of waste material. This pomace is currently disposed but could be exploited as a source of polyphenol antioxidants, bioactive components and flavour components. OBJECTIVE: This study investigates the amount and composition of polyphenol components extractable from black currant residues, with a focus on anthocyanin components. METHODS: Polyphenol levels in laboratory derived juice, successive water-extracts and methanol-extracts of black currants were compared. Similar extractions were carried out on commercial black currant pomace. Differences in polyphenol composition were examined using liquid chromatography mass spectrometry analysis. RESULTS: Extracts obtained with methanol after juice removal and water washing had considerably higher anthocyanin content and a higher proportion of anthocyanidin glucosides. The methanol extracts also contained putative C-C linked anthocyanin dimers not previously identified in berries. Similar ethanol extraction of commercial pomace also released an anthocyanin-rich fraction with elevated levels of anthocyanidin glucosides. CONCLUSIONS: Sequential alcohol extraction of black currant residues produced anthocyanin-rich fractions which contained components that may be tightly bound to the residues. These included putative anthocyanin dimers. Compositional differences in extracts from laboratory residues and commercial pomace may be related to the use of cell-wall-lyzing enzymes during juicing.