Stabilisation of the colour of anthocyanins in solutions by admixture with phytocomponents from apple

Abstract

SummaryThe colour of anthocyanins can be enhanced by planar chemical complex formation, or stabilised by the formation of adducts. We investigated these properties using fruit extracts. Delphinidine and its glucoside, myrtilline, at 0.1 mM were mixed with 10 mM caffeoylquinic acid (CQA; chlorogenic acid) or 6 mM ferulic acid (FeA). In a second experiment CQA, ferulic acid, and a CQA-rich apple extract were added in variable concentrations to a blackcurrant pigment preparation and incubated at 37°C in 0.02 M citrate buffer at pH 1.5, pH 3.0, or pH 4.5. The colour change was followed by measuring the absorbance at 540 nm and the composition of the solutions was assayed by HPLC using diode array detection. Deglycosylation of anthocyanins leads to a loss of colour and chemical stability. It is therefore of major importance that the enzyme preparations used during juice extraction be devoid of glycosidases. Addition of phenolic acids to an anthocyanin solution increases and stabilises the colour, which is accompanied by an acceleration of the loss of the native anthocyanins and the formation of coloured adducts, presumably based on the pyranoanthocyanin structure. The glycosyl residue in anthocyanins is necessary for colour stabilisation, which appears to be due to the formation of new pigments. Caffeoylquinic acid appeared to be more efficient than ferulic acid, and a CQA-rich extract from apple also resulted in stabilisation of the colour of a blackcurrant extract.