Interactions of natural antioxidants with red grape pomace anthocyanins in a liquid model matrix: Stability and copigmentation effects

Abstract

The purpose of this study was an examination on the stability and colour enhancement of red grape pomace anthocyanins in a juice model matrix, and the effect of the addition of natural antioxidants. The approach was based on a juice-like liquid medium (10.1?Brix, pH 3.48), which was used as the model matrix to test the effect of the addition of natural antioxidants (L-cysteine, ascorbic acid, catechin and quercetin) on the degradability of anthocyanin pigments, extracted from grape pomace. It was found that treatment of the model solutions at 80?C induced anthocyanin decomposition, which obeyed first order kinetics. Addition of increasing amounts of antioxidants, including L-cysteine, ascorbic acid, catechin and quercetin, did not provoke a proportional impact, either positive or negative, with regard to anthocyanin stability. The best stabilising effect was seen after addition of ascorbic acid and catechin at concentrations of 4 and 2 mg L-1, respectively (P < 0.001). Quercetin, however, was demonstrated a very efficient co-pigment, inducing an increase in A520 by 63%, at pH 5.6 and a copigment-to-pigment ratio of 10.