Industrial application of anthocyanins extracted from food waste

Extracts rich with anthocyanin O-glycosides are obtained from sustainable waste food sources; one notable example is delphinidin- and cyanidin-O-glucosides extracted from blackcurrant – after juice production, waste blackcurrant skins are processed and extracted using acidified water, and subsequently purified using Solid Phase Extraction. Analytical HPLC in combination with chemical assays are used to determine the anthocyanin fingerprint, polyphenol and anthocyanin content of the extracts. Preservation of glycosylation in extraction enables advantageous formulation, stability, and application of the anthocyanin extracts in industrial applications. As anthocyanins are pH sensitive, they present some limitations in their applications due to their moderate stability and solubility in aqueous solutions (Pina et al. Chem. Soc. Rev., 2012, 41, 869). Herein, we tackle these limitations by understanding anthocyanin chemistry and exploiting biomimetic approaches. The delphinidin and cyanidin-rich blackcurrant extract can be used as blue semi-permanent hair dye. When dyeing from aqueous acidic medium (pH 3-4), despite λmax in solution being 517 nm for cyanidin and 526 nm for delphinidin (violet colour consistent with flavylium cation), λmax when adsorbed onto hair from aqueous medium is 570-580 nm (blue colour consistent with quinonoidal base); this suggests an in situ neutralisation by basic sites on the hair surface leading to formation of the anhydrobase form. The dyeings are stable over 12+ washes, with minimal colour loss, and no colour change; the systems may be used in combination with other natural dyes to provide a range of shades. In other applications, stable water-soluble and water-insoluble blue pigments may be obtained by combination of anthocyanin O-glycoside extracts with metal salts; pigments are formed using novel “biomimicry” process inspired by plant pigment formation in flowers. We have successfully applied these pigments as blue confectionery colorants and in novel printing methods for obtaining safety codes on eggshell.