Identification and thermal stability of purple-fleshed sweet potato anthocyanins in aqueous solutions with various pH values and fruit juices

Thirteen anthocyanins were identified in the purple-fleshed sweet potato cultivar Jihei No. 1. The main anthocyanins were 3-sophoroside-5-glucoside derivatives from cyanidin and peonidin, acylated with p-hydroxybenzoic acid, ferulic acid, or caffeic acid. A unique anthocyanin, delphinidin-3,5-diglucoside was also found. The thermal stability of purple-fleshed sweet potato anthocyanins (PSPAs) followed a first-order kinetics model. Aqueous solutions with various pH (2, 3, 4, 5, and 6) and fruit juices (apple, pear, grapefruit, orange, tangerine, kiwifruit, and lemon) were coloured with PSPAs. The enrichment and degradation kinetics of anthocyanins in these matrices were investigated at 80, 90, and 100 °C. A higher stability of anthocyanins was obtained in aqueous solutions with pH 3 and 4 and in apple and pear juices. Moreover, the activation energies for PSPA degradation in aqueous solutions with various pH and fruit juices ranged from 66.56 kJ/mol to 111.57 kJ/mol and 46.76 kJ/mol to 75.68 kJ/mol, respectively.