Measurement of antioxidant activity under these conditions showed a strong correlation to anthocyanin concentration, declining with temperature and time. However, overall antioxidant levels do not decrease substantially (a few percent), presumably because of the contribution from the formation of polymeric phenols (data not shown). Overall, Roselle petals are a good source of antioxidants and this activity is relatively stable over a storage period, although provided by different compounds.
The nutritional benefit of Roselle as an antioxidant will ultimately depend on the bioavailability of the anthocyanins. Preliminary studies show that delpinidum 3-sambubioside and cyanidin-3-sambubioside are rapidly absorbed from the gastrointestinal tract when fed to rats. Further studies are underway to confirm this finding.