Effects of process parameters in microwave-assisted extraction on the anthocyanin-enriched extract from Rhodomyrtus tomentosa (Ait.) Hassk and its storage conditions on the kinetic degradation of anthocyanins in the extract

Rhodomyrtus tomentosa (Ait.) Hassk (RTH) is a plant distributed mainly in Southeast Asia that has long been used as a food or a folk remedy for various ailments. Anthocyanins extracted from RTH have received the attention of researchers as well as manufacturers in exploiting the application of this plant for commercial purposes. Several extraction methods have been performed, however, concerns about new extraction methods, extraction conditions as well as stability of anthocyanins during storage are issues that need to be evaluated. In this study, the process of extracting anthocyanins by microwave method and the stability of anthocyanins in RTH extraction were investigated. For the extraction method, the influence of solvent concentration (30-70%), application ratio (10:1-1:1 mL/g), microwave power (100-500W), and time (1-9 min) have been evaluated. A first-order kinetic model was also used to evaluate the variation of anthocyanin content during storage at different conditions, including 5 °C (refrigerator), 30 °C (room temperature), and 45 °C (incubator). The study results showed that the anthocyanin content had the greatest value of 137.54 mg/L when extracted with 50% ethanol solvent with the material/solvent ratio of 1:3 (g/ml) microwave power is 200W for 5 min. The first-order decomposition kinetics model showed that the t_1/2 values of the RTH extract were 69.64, 28.66, and 19.8, respectively, for the storage temperatures of 5 °C, 30 °C, and 45 °C, respectively. During storage, anthocyanin content tends to decrease more rapidly under high-temperature conditions. In addition, a close correlation between anthocyanin content and antioxidant capacity was recorded at a high significance level R² > 0.98.