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Title: Bioactivity of anthocyanins from Hibiscus sabdariffa
Author: Sindi, Hebah Abbas
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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A systematic study on extraction of Hibiscus sabdariffa was carried out for the first time using different solvents (water, methanol, ethyl acetate and hexane) in the presence and absence of formic acid, using different extraction times and temperatures. The extracts were analysed for total phenol content, antioxidant capacity using DPPH, FRAP and TEAC assays, and total monomeric anthocyanin content. In addition, specific anthocyanins were determined using HPLC and LC-MS. The results showed the highest antioxidant capacities were obtained by extracting using water, with or without formic acid, for 10 min at 100 °C. These extracts provided the highest concentrations of cyanidin 3-sambubioside and delphinidin 3-sambubioside. Commercially available herbal teas containing H. sabdariffa were analysed. The study found that contents of total phenols, anthocyanins and antioxidant capacity were higher when using the optimal extraction procedure, suggesting that putative health benefits could be increased by altering processing methods. The partition coefficients (log p) of anthocyanins found in H. sabdariffa, were measured showed that aglycone and glucoside forms of hibiscus anthocyanins behave differently when in the presence of cell wall material. Such behaviour could, in vivo, affect the absorption and bioactivity of these anthocyanins, and therefore, their efficacy. A human crossover study investigated the effect of daily consumption for 8 weeks of a H. sabdariffa juice for 8 weeks on the blood pressure of healthy subjects (n= 29). Cranberry juice was used as the control. A significant reduction was found in systolic blood pressure (but not diastolic) compared to the baseline. No significant effect on blood pressure was seen with cranberry juice. The study suggests that regular consumption of extracts of H. sabdariffa may reduce the risk of cardiovascular disease, on the other hand people with low blood pressure should consumed it very carefully due to hypotensive effect of the extract.
Supervisor: Morgan, Michael ; Marshall, Lisa Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available