Degradation kinetics of anthocyanins from purple sweet potato (Ipomoea batatas L.) as affected by ascorbic acid

Storage (4A degrees C and 25A degrees C, 28 days) and thermal (70A degrees C-90A degrees C, 6 h) stabilities of purple sweet potato anthocyanins (PSPAs) with varying concentrations of ascorbic acid (AA) were investigated in a model soft drink medium. For storage stability, the model drink was sterilized at 85A degrees C for 15 min prior to storage. Zero-order kinetics and first-order kinetics were fitted for storage degradation at 4A degrees C and 25A degrees C, respectively. However, all data for thermal degradation fitted first-order kinetics. The temperature dependence on degradation was modeled after the Arrhenius equation. Storage degradation of PSPAs was increased by the presence of AA (40-360 mg/L). Retarded thermal degradation was be achieved by adding 120 mg/L of AA, while accelerated thermal degradation resulted from 360 mg/L of AA. Heat treatment did not markedly change the DPPH radical-scavenging activity of PSPAs.