Enhancing the potential exploitation of food waste: Extraction, purification, and characterization of renewable specialty chemicals from blackcurrants (Ribes nigrum L.)

Natural colorants were extracted from renewable botanical sources, specifically waste epicarp from the blackcurrant fruit pressing industry. A process was developed which used acidified water extraction followed by a solid-phase extraction (SPE) purification stage which allowed the production of an anthocyanin-rich extract in good yields (ca. 2% w/w based on dry weight of raw material). The components in the extracts were extensively characterized by HPLC, mass spectrometry, IR, NMR and UV-Vis spectroscopy. HPLC confirmed presence of four anthocyanins: delphinidin-3-O-rutinoside (45%), cyanidin-3-O-rutinoside (31%) and the corresponding glucosides at 16% and 8%, respectively. On sequential liquid-liquid aqueous-organic partitioning of the post-SPE sample, monomeric anthocyanins (54.7%) and polymeric anthocyanins (18%) were found in the aqueous layer with 3-O-rutinosides of myricetin (3.1%) and quercetin (3.2%), whilst isopropylacetate achieved selective extraction of caffeic acid (3%), p-coumaric acid (5%), and myricetin (2.5%) and quercetin (3.2%) aglycons. 3-O-Glucosides of myricetin (3.1%) and quercetin (2%), along with nigrumin-p-coumarate (1%) and nigrumin ferulate (0.5%) were selectively extracted from the remaining aqueous fraction using ethylacetate. This allowed for near total quantification of the blackcurrant extract composition.