2.4.3. Total antioxidant activity
The total antioxidant activity was determined according to the
method of Kim, Lee, Lee, and Lee (2002). AAPH (2,20-Azobis(2-
methylpropionamidine) dihydrochloride, Sigma–Aldrich) 1.0 mM
was mixed with 2.5 mM ABTS (2,20-Azino-bis(3-ethylbenzothiazoline-
6-sulfonic acid) diammonium salt, Sigma–Aldrich) in phosphate
buffered saline (PBS) solution (100 mM potassium
phosphate buffer (pH 7.4) containing 150 mM NaCl). The mixture
was heated at 68 C for 1 h and mixed every 15 min. The resulting
blue-green ABTS solution was then filtered (No.1 Whatman filter
paper) to remove the undissolved AAPH and the absorbance adjusted
to a value of 0.8 ± 0.02 at 734 nm. 0.05 ml of the filtered
sample (cheese cloth) was added to 2.45 ml of radical solution
and the mixture incubated, protected from light, in a water bath
at 37 C for 10 min. The decrease of absorbance at 734 nm was
measured after exactly 10 min. A control consisted of 0.05 ml of
distilled water and 2.45 ml of ABTS solution. Standard Trolox
solutions were also evaluated and the ABTS radical scavenging
activity of the juice was expressed as Trolox Equivalent Antioxidant
Capacity (TEAC) (mM).