Thermal degradation of anthocyanins and its impact on in vitro antioxidant capacity of downy rose-myrtle juice

Downy rose-myrtle, a well-known edible and medicinal plant, has long been used as a folk remedy for various diseases, is a wild berry mainly distributed in Southeast Asia. Anthocyanins in downy rose-myrtle are of great interest to researchers; and commercial entities due to many health benefits of these compounds. Recently, renewed interest has grown in the stability of anthocyanins during the various processing and extraction methods. Anthocyanins easily degrade and form colorless or unacceptable brown-colored compounds during thermal process. In this study, the stability of anthocyanins in downy rose-myrtle juice was investigated undergoing the influenced of temperature (60, 70 and 80°C) at pH 2-4. The impact of various parameters (temperature and heating time) on the antioxidant activity of downy rose-myrtle juice was also evaluated. Additionally, correlation between the total anthocyanin content and total antioxidant activity of the juice based on thermal treatment using ABTS assay was investigated. The results showed that the effect of temperature and pH on anthocyanins of downy rose-myrtle juice was pronounced, and their contents decreased with the increase of the temperature and pH value. During thermal process, total antioxidant activity of downy rose-myrtle juice decreased and similar trends in anthocyanin content were observed. Data analysis showed first-order kinetics for the evolution of anthocyanin content. According to the Arrhenius model, the calculated values of activation energies (Ea) for pH 2-4 were 63.2, 46.1 and 45.0 kJ/mol, respectively. The total antioxidant activity of downy rose-myrtle juice has positive correlation with the total anthocyanins content in it. The stability of anthocyanins in downy rose-myrtle juice may be improved to some extent by an appropriate thermal process.