Effects of Extraction Conditions on Antioxidant Activities of Roselle (Hibiscus sabdariffa L.) Extracts

The objective of this study was to determine the optimal value of factors affecting the extraction of antioxidant activity of Roselle calyces. The investigated factors included extraction temperatures (30, 40, 50, 60, 70 and 80°C), extraction time (30, 60, 90, 120 and 150 minutes) and solid to solvent ratio (1:5, 1:10, 1:20, 1:40 and 1:50 g/mL). The efficiency of extraction was evaluated based on antioxidant activities which were measured by DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay, ferric reducing antioxidant power assay (FRAP). The results showed that when the extraction temperature range of 70–80°C, DPPH free radical scavenging and FRAP were highest with 677.47–725.81 μmolTE/L and 4186.91–4391.62 μmolTE/L, respectively. For the extraction time from 120 to 150 minutes, the resulting extracts with highest FRAP and DPPH free radical scavenging antioxidant capacity were obtained. Meanwhile, the antioxidant activity tended to decrease as the solvent/solid ratio increased.