2.2.5. Vitamin C
For vitamin C determination the titrimetric method with 2,6-
dichlorophenolindophenol reagent (AOAC-Association of Official
Analytical Chemists, 1995) with some modifications was applied.
1 g of freeze-dried peel was mixed with 100 mL of a solution of
oxalic acid (4%). The mixture was homogenised and filtered. 5 mL
of filtrated solution were diluted to 10 mL with 4% oxalic acid solution.
This solution was titrated with 0.01% of 2,6-dichloro-phenolindophenol
solution. The end point was considered to be when the
solution had attained a pink colour which persisted for 15 s. The
calibration of 2,6-dichlorophenolindophenol solution was performed
with 0.05% ascorbic acid solution. Results were expressed
as mg of ascorbic acid equivalents per 100 g of DW.