[The amount of L-dehydroascorbic acid on total-vitamin C of vegetable products (author's transl)].

Spectrophotometric determinations of vitamin C were carried out on different kinds of vegetable products in raw state, after steam-cooking and freezedrying. Indicators used were in part 2,6-dichlorophenol-indophenol (DIP) and in part N-bromosuccinimide (NBS) and starch iodide, which at the same time allows a determination of other reducing interfering substances. The amount of L-dehydroascorbic acid (DAS), which together with L-ascorbic acid (AS) becomes vitamin C or total-vitamin C (VC), proved to be of special interest. During homogenisation of the vegetable samples in oxalic oxid solution AS was not oxidized. Other precautions like cooling or on oxygen-free atmosphere were not required. DAS was not found in raw vegetable products or after cooking. A high proportion of interfering substances especially when estimating VC was considered the cause for the normally measured amount of DAS. In freeze-dried samples of vegetable products a small amount DAS could be identified depending on the freezing process.