engleski

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 of 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 storage at 4 °C for 30 days was investigated. Stability of anthocyanins was followed through anthocyanin determination and investigation of total colour change (ΔE*). 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 g. 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 g, depending on phenolic compound, its concentration and storage time. The lowest degradation was observed when gallic acid was added. Copigmentation effect was proven by bathochromic shift (Δλmax) for the samples with addition of phenolic compounds. Δλmax were 3 nm for catechol and 4-methyl catechol, 4 nm for gallic acid and 5 nm for catechin. 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 (ΔE*) with CIELAB colour system since all parameters are taken in account. The lowest ΔE*, after 30 days of storage, had samples with addition of catechol and catechin (0.83 and 0.87, respectively), while the highest values had samples with addition of gallic acid (1.26).

anthocyanins; phenolic compounds; copigmentation; storage

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