Copigmentation effect of phenolic compounds on red currant juice anthocyanins during storage

Copigmentation has been suggested as a main colour stabilising mechanism in plants protecting the coloured flavylium cation from the nucleophilic attack by the water molecule. In this study influence of phenolic compounds addition (catechol, 4-methyl catechol, (+)-catechin and gallic acid) on stability of red currant juice anthocyanins (copigment:pigment molar ratio 50:1 and 100:1) during 30 days of storage at 4 °C was investigated. Stability of anthocyanins was evaluated through determination of anthocyanins, total colour difference (∆E*), kinetic parameters and anthocyanin retention. The initial anthocyanin content of red currant juice was 44.34 mg/100 g. During storage degradation of anthocyanins occurred. After storage anthocyanin content of red currant juice was 38.87 mg/100 mL. However, in samples with addition of phenolic compounds degradation was less pronounced due to formation of pigment-copigment complex (i.e. copigmentation). Anthocyanin content in samples with addition of phenolic compounds ranged from 39.2 to 43.83 mg/100 mL, depending on phenolic compound, its concentration and storage time. The lowest degradation was observed when gallic acid was added. Monitoring only λmax of absorption spectrum of juices, one can get incomplete picture of colour stability of red currant juice. It was important to monitor total colour change (∆E*) with CIELAB colour system since all parameters are taken into account. The lowest ∆E*, after 30 days of storage, had samples with addition of catechol and (+)-catechin (0.83 and 0.86, respectively), while the highest values had samples with addition of gallic acid (1.26).