INTERACTIONS OF NATURAL ANTIOXIDANTS WITH RED GRAPE POMACE ANTHOCYANINS IN A LIQUID MODEL MATRIX: STABILITY AND COPIGMENTATION EFFECTS

The purpose of this study was an examination of 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 degrees Bx, 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 degrees 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 A(520) by 63%, at pH 5.6 and a copigment-to-pigment ratio of 10.