Some aspects of the quantitative/qualitative assessment of commercial anthocyanin-rich extracts

Colour assessment of anthocyanin-rich extracts according to the legal CE normative involves some important limitations: Lack of objectivity in the assessment of samples with different moisture contents and/or absorption maximums, and inability to identify possible fraudulence due to copigmentation phenomena. To overcome these limitations the following corrections were introduced: Colour intensity CI=CIλmax, referred to 1 g dry matter; when Abs780 > 0.001, CI=CIλmax−CI780, followed by determination of total anthocyanins (TA) by any method using a known standard reference. Pigment qualities were best described by the use of spectral colorimetric assessment. Best objectivity was achieved by the use of the homogeneous CIELAB colour space. Separation of anthocyanins as monomer, and red and yellow–brown polymer fractions by open column chromatography gave important information about the structure/quality relationships of the anthocyanin pigments. HPLC analysis contributed to the identification of the extracts with high acylated anthocyanin contents, related to high physicochemical stability. Determination of total dry matter and total soluble and suspended solids gave a good indication of the purity of the anthocyanin pigments and the possible haze contamination of the coloured product, whereas determination of total catechins and condensed tannins were indicative of possible taste alterations. The main drawback, limiting the use of most of the examined qualitative parameters, was the lack of normalized reference data for anthocyanin-rich extracts.