Numerous beverages, such as multivitamin juice and sports drinks, are enriched with vitamins. These beverages may not be listed on a label as "enriched" or "fortified" with a particular vitamin supplement unless the vitamin is present in "significant amounts", which are defined in Annex XIII to Regulation (EU) No 1169/2011. For beverages, this amount is set at a minimum of 7.5 % of the NRV (nutrient reference values) per 100 ml or 15 % of the NRV per portion for individual portions.
Quantities recommended for the daily dietary intake of vitamins:
Determination of ascorbic acid by enzymatic means
This analysis is suitable for wort, beer, beer-based beverages and NAB
L-Ascorbic acid (ascorbate) as well as the reducing substances (X-H2) reduce the tetrazolium salt MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] in the presence of PMS (5-methylphenazinium methosulfate), which mediates electron transfer, at a pH of 3.5 to a formazan:
L-Ascorbate (X-H2) + MTT+ \(^\underrightarrow{PMS}\) dehydroascorbate (X) + MTT formazan +H+
Of all the reducing substances present in the blank, only the ascorbic acid portion of the sample is oxidatively removed by ascorbate oxidase (AAO) in the presence of oxygen. Dehydroascorbate is produced in the reaction and does not react with MTT/PMS:
L-Ascorbate (X-H2) + ½ O2 \(^\underrightarrow{AAO}\) dehydroascorbate (X) + H2O
The absorbance of the sample minus the absorbance of the blank is equivalent to the quantity of ascorbic acid in the sample. MTT formazan serves as the measured variable, and its absorption can be determined photometrically in the visible part of the spectrum at 578 nm.