Photosensitizing activity and photostability of <i>Hibiscus sabdariffa</i> calyces

Abstract

The vivid red colour of Hibiscus sabdariffa calyces (Roselle) extract is due to the presence of anthocyanins, which have found uses in food and beverage colouring and other dyeing-related applications. In the present study, stability of the anthocyanins of the methanol extract of Hibiscus sabdariffa calyces was examined by exposing it to light and measuring the decrease in absorption with time. Also, its ability to photosensitize the reaction of a conjugated diene with singlet oxygen was compared to that of methylene blue, which is commonly used. The degradation pattern monitored by absorbance measurement was tested at a significance level of 0.05 and was found to be statistically significant. Its photosensitization was also confirmed by its ability to induce the formation of endoperoxides in the photooxygenation of conjugated cyclohexadiene in ambient light. This was monitored using thin layer chromatography. Thus, Hibiscus sabdariffa calyces extract may be used as a photosensitizer in fine chemical synthesis, and as a natural colorant, however with care in storage and handling.