Ascorbic acid (AA) content was measured by using a UV–VIS
spectrophotometer according to the literature procedure of
Durust et al. (1997).The spectrophotometer was adjusted to zero
by using distilled water. The absorbance of mixing of 1 ml of oxalic
acid solution with 8 ml of DCPI solution (12 mg of DCPI in 1000 ml
of distilled water) and 1 ml of acetate buffer solution (300 g of
anhydrous sodium acetate in 700 ml of distilled water with
1000 ml of glacial acetic acid) was recorded at the end of 15 s. This
value was recorded as X1. Then, the absorbance of the standard
ascorbic acid solution (1 ml) with the acetate buffer solution
(1 ml) and DCPI (8 ml) was recorded as X2. X1 was the absorbanceof all DCPI, and X2 was the absorbance value of the remaining DCPI,
after its reaction with AA. X2 values were similarly recorded for the
other standard AA solutions (20, 30, 40, and 50 ppm). X1 X2 values
were the absorbance of each working standard. The calibration
graph was constructed by plotting the absorbance values versus
the concentration (ppm) of standard AA solutions (r2 = 0.9951).
For the absorbance measurements of the sample extracts, the
same procedure was applied. First, an autozero operation for the
instrument was performed. Then, the absorbance of 1 ml of the
sample extract with 8 ml of distilled water and 1 ml of acetate buffer
solution was recorded at the end of 15 s. This was the X2 value
of the sample solution. X1 X2 values represented absorbance of
the sample. From the calibration graph, the AA concentration of
the sample was determined. All of the measurements were
recorded at 520 nm. All determinations were performed in triplicate
(n = 3).