Subsequently, the mixtures were incubated at 50 ◦C for 20 min.
1.0 mL of 10% TCA was added to the mixture. After centrifuged
(5000 rpm/min for 15 min), the mixture (2.5 mL) was mixed with
0.15 mL of 0.1% FeCl3. The absorbance was measured at 700 nm.
Increased absorbance of the reaction mixture demonstrated the
increase of reducing ability. Ascorbic acid (Vc) was served as positive
control.