The radical scavenging
activity was measured based on the method described by
Thaipong et al. (2006), with some modifications. A stock solution
was prepared by dissolving 24 mg DPPH with 100 mL
methanol and then stored at −20 ◦C until required. The working
solution was then prepared fresh by mixing 10 mL stock
solution with 45 mL methanol to obtain an absorbance at
515 nm of 1.1±0.02. To 0.2 mL of sample, 3.8 mL of working
solution was added and then left under darkness at RT for
3 h before measuring the absorbance at 515 nm using the UV
spectrophotometer. Trolox was used as the standard for a calibration
curve and the results were expressed as g of trolox
equivalents per g of sample (g TE/g).