1998). A test sample (0.5 mL) was mixed with 1 mL of Folin–Ciocalteu reagent and swirled. After 3 min, 10 mL of sodium carbonate solution(75 g/L) was added and mixed. Additional distilled water was mixed
in thoroughly by inverting the tubes several times. After 1 h, the absor-bance at 750 nm was recorded.