Comparative analyses of copigmentation of cyanidin 3-glucoside and cyanidin 3-sophoroside from red raspberry fruits

Cyanidin 3-glucoside (Cy 3-glu) and cyanidin 3-sophoroside (Cy 3-soph) from red raspberry extracts were selected as pigments, and five phenolic acids as copigments. The influences of pH, temperature, structure of anthocyanins and copigments, and molar ratio of anthocyanins to copigments on the copigmentation effect were analyzed with a UV–Visible spectrophotometer. The reaction was thermodynamically defined in terms of ΔH0, ΔG0 and ΔS0 values.The maximum copigmentation effect for Cy 3-glu and Cy 3-soph with ferulic acid was observed around pH 4. Sinapic acid and ferulic acid had stronger copigmentation effect than the other three phenolic acids investigated. The strongest immediate copigmentation was observed at an anthocyanin/copigment molar ratio of 1:100. Lower temperatures favoured the copigmentation reaction. Moreover, the calculated thermodynamic data indicated that the copigmentation reaction was more favourable at pH 4.0 than at pH 3.2 for the same anthocyanin, and more favourable for Cy 3-glu than for Cy 3-soph at the same pH.