3. Results and discussion
Preliminary studies were carried out to determine the conditions needed for the extraction of antioxidant activity. The antioxidant activity was low over the first minute of extraction, but then increased rapidly and remained at the same level for 3–5 min (Fig. 1A). This indicates that an incubation of 3 min gives essentially complete extraction. It was also shown that antioxidant activity increased proportionally to the weight of Roselle petals used (Fig. 1B). For a series of standard samples, a linear relationship existed between FRAP and TAS (R2=0.9411, Fig. 2) or ORAC (R2=0.9288, Fig. 3). This suggests that any of these methods will give an accurate measurement of antioxidant status.