Stability of anthocyanins from grape (Vitis vinifera L.) skins with tannic acid in a model system

The stability of the anthocyanins in nature is assumed to be the consequence of anthocyanins complexing with colourless compounds called copigments. Organic acids, among other substances. can act as anthocyanin copigments. In this study tannic acid was used as a copigment with the anthocyanin crude extract from Cabernet Sauvignon (Vitis vinifera L.) grapes. Anthocyanin stability was investigated with and without the addition of tannic acid under different storage conditions in model and beverage systems. The results revealed that pH, temperature, presence of light and presence of oxygen significantly influenced anthocyanin stability. The addition of tannic acid (1: 1, w/v) significantly (p < 0.01) increased the half-life time of anthocyanin in a model system, with very similar results to those obtained in the rehydrated beverages. The model system kept at pH 3.0, in the dark, in the presence of nitrogen and 4 +/- 1degreesC had longer half-life times and higher colour retention percentage values. When tannic acid was added (1: 1, w/v) to the rehydrated beverage samples at 4 +/- 1degreesC, the half-life time of the anthocyanins increased by 244 hours.