Ascorbic acid content was determined according to the modified
2,6-dichlorophenolindophenol (DIP) method (Klein and Perry, 1982).
Freeze-dried samples were extracted with 1% metaphosphoric acid
(0.1 g/10 ml) and centrifuged (3000×g/15 min) (SORVALL Legend RT,
Germany). An aliquot of 0.5 ml of the supernatant was added to
4.5 ml of 0.05 mM DIP, mixed for 15 s and measured colorimetrically
at 515 nm. L-ascorbic acid was used as a standard (0–400 μg/ml).