AOAC SPIFAN Stakeholder Program Meeting Book (September 10, 2020)

Analytical methods I

Titration with 2,6-dichlorophenolindophenol

Based upon the reduction of DCPIP (pink in oxidized form) with ascorbic acid in acid media

Advantages: rapid, cheap, suitable for rapid quality control in factory environment

Disadvantages: does not include dehydroascorbic, interferences with coloured extracts and reducing agents are possible. D-isoascorbic acid will react in the same manner. 7

Source of illustrations Lemons: https://www.savibio.fr/fruits/42-citron-jaune.html

Analytical methods II

Fluorimetric

Based upon oxidation of ascorbic acid to dehydroascorbic acid and reaction with o-phenylenediamine (OPDA) to form quinoxaline. Sample blanks are prepared by complexing the oxidized vitamin with boric acid to prevent formation of quinoxaline.

Advantages: includes dehydroascorbic acid, can be applied to coloured extracts and samples containing reducing substances. Disadvantages: D-isoascorbic acid (EA) will react in the same manner. Questions on the applicability to green leaf vegetables (Wills et al. (1983) JAOAC,66,1377) 8

Source of illustrations Lemons: https://www.savibio.fr/fruits/42-citron-jaune.html