Colour, pH stability and antioxidant activity of anthocyanin rutinosides isolated from tamarillo fruit (Solanum betaceum Cav.)

Changes in colour and stability of anthocyanins have been evaluated over pH range 2.0–8.7. The study was made on crude extract (XAD-7 Amberlite-retained fraction) as well as on the following pure pigments isolated from tamarillo fruit (Solanum betaceum Cav.): delphinidin 3-O-(6″-O-α-rhamnopyranosyl-β-glucopyranosyl)-3′-O-β-glucopyranoside, delphinidin 3-O-(6″-O-α-rhamnopyranosyl)-β-glucopyranoside, cyanidin 3-O-(6″-O-α-rhamnopyranosyl)-β-glucopyranoside and pelargonidin 3-O-(6″-O-α-rhamnopyranosyl)-β-glucopyranoside. The relationships between the colour and the hydroxylation degree of the B ring and the pH have been studied for the first time on rutinosides. The peel extract showed much more colour stability than the jelly extract at all the pH values studied. The replacement of the 3′-OH with a glycosyl group increased the stability of the colour to pH changes, although this substitution yields a less colourful (higher L  ∗ and lower Cab∗) compound (Dp 3-rut-3′-glc), having both hypsochromic and hypochromic shifts relative to the non-glycosylated molecule (Dp 3-rut). Moreover, the influence of the hydroxylation degree of the B ring on the quality and stability of colour, as well as on the antioxidant activity, was determined.