New methods for isolation, characterisation and modification of natural colorants

Aronia skin waste contains anthocyanins in high concentrations and has a simpler anthocyanin profile than other anthocyanin-containing berries. Their instability towards pH, heat, hydrolysis etc., limits their application as natural colorants and antioxidants. Anthocyanins were extracted in a simple batch process and a new extraction method, which integrates both extraction and separation in a single process. The new method showed better anthocyanin yield and purity compared to the batch method. Anthocyanins from Aronia skin waste were identified as Cy3gal, Cy3glc, Cy3ara, Cy3xyl alongside its aglycone, contributing up to 44.7% w/w of RASE (Refined Aronia Skin Waste Extract). Neutral polyphenols such as DHBA (3,4-dihydroxybenzoic acid), nCA (neochlorogenic acid), CA (chlorogenic acid), and Q (quercetin) contributed up to 14.2 % w/w of RASE. Polymeric proanthocyanidins contributed up to 39.4% w/w of RASE. Inorganic salts and other harder to observe compounds contributed up to 1.7% w/w of RASE. Anthocyanin salts with carboxylate anions were prepared by applying various milder organic acids during the extraction-purification process. RASE with carboxylate anions were relatively more stable than RASE-chloride. Preserving anthocyanins at milder pH with a more hydrophobic counterion is suggested, especially if used for a longer period (months). The characterisation of flavylium-hemiketal forms mixture for Cy3gal, Cy3glc, Cy3ara and Cy3xyl was obtained by dissolving these anthocyanins in methanol-d4 and analysed by NMR spectroscopy. Hemiketal forms of Cy3gal have been characterised as a single compound through slow evaporation, while nucleophilic addition occurred at the carbon position 2 of anthocyanin by hydration. Overall, a proper structural modification of anthocyanins could increase the physio-chemical properties of anthocyanins with fair antioxidant activity. Mono- and diacylated anthocyanins could maintain the original colour of their precursor. Due to their lipophilic property, acylated derivatives of anthocyanins from Aronia skin waste have a higher potential to be incorporated in lipid-based foods, textiles, cosmetic formulations, and pharmaceutical products than its precursor.