Antioxidant activity with the β-carotene bleaching method. The antioxidant activity from the β-carotene/linoleic acid system was carried out according to the method described by Matthaus [16] and by Kang et al. [17]. Briefly, 40 mg of linoleic acid and 400 mg of Tween 20 were transferred into a flask, and 1mL of a β-carotene–chloroform solution (3.34 mg/mL) was added. Chloroform was removed by rotary evaporation at 313.15 K. Then 100 mL of distilled water was slowly added and vigorously agitated to form a stable emulsion. An aliquot of 5mL of this emulsion was added with 0.2 mL of ethanolic black pepper extract solution (1667 mg/mL) and the absorbance was immediately measured at 470nm against a blank consisting of the emulsion without β-carotene. The tubes were placed in a water bath at 323.15 K and the absorbance was measured every 15 min up to 120 min. The absorbance values (mean of the triplicate essays) were converted into percentage of antioxidant activity (% AA).