Anthocyanin and antioxidant capacity in Roselle (Hibiscus sabdariffa L.) extract

The relation between antioxidant activity and anthocyanin was determined in Roselle (Hibiscus sabdariffia L.) petals. Petals from Roselle, cultivar F141, were collected and dried in Taitung, Taiwan. Roselle extract was prepared by extracting dried Roselle petals in boiling water. The relation between the anthocyanin color and antioxidant capacity was elucidated by comparing absorbance at 520 nm, with ferric reducing ability of plasma (FRAP), oxygen radical absorbance capacity (ORAC) and total antioxidant status (TAS) antioxidant assays. The results showed that the antioxidant capacity of Roselle extract increased when extraction time or weight of petals increased. The FRAP assay showed a linear relationship with anthocyanin as determined at 520 nm. Comparisons between FRAP and ORAC or FRAP and TAS assays gave a linear relation. These results suggest that anthocyanin is the major source of antioxidant capacity in Roselle extract. Further purification using Amberlite XAD-2 and HPLC indicated that anthocyanin and a brown pigment in the extract account for about 51 and 24% of the antioxidant capacity, respectively. Under different processing temperatures and storage periods, anthocyanin content declines. However, other phenolic compounds increase and overall there is only a relatively small decrease in total phenolic compounds and antioxidant activity. (C) 2002 Elsevier Science Ltd. All rights reserved.