Copigmentation Potential of Overripe Seeds from Sun-dried White Grapes on Anthocyanins Colour and Stability by Differential Colorimetry

Abstract

Overripe seeds are wine by-products from grapes submitted to postharvest sun drying, which induce phenolic biosynthesis and polymerisation. Overripe seeds from Pedro Ximénez (PX) and Moscatel (MO) sun-dried grapes were compared as copigments sources to modulate grape anthocyanin (GA) colour and stability in simulated wine conditions. RRLC/MS analysis proved that overripe seeds contain specific phenolic mixtures capable of inducing positive quantitative and qualitative colour changes in GAs, evidenced by differential colorimetry. Copigmentation effects significantly varied depending on the overripe seed variety, related to their qualitative phenolic composition and content. MO extracts richer in gallic acid, catechin and procyanidin B1 led to the stronger colour intensification and perceptible qualitative changes. PX extracts richer in epicatechin, procyanidins B2, B2-GAL and B7 behaved as weak copigments. Overripe seed copigments preserved better GAs colour stability during storage leading to the formation of new anthocyanin-derived pigments, being the stabilising effect stronger with those of MO variety.