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:
Analysis for determining the amount of added folic acid by means of the microbiological microtiter plate test
This analysis is suitable for NAB, juice and other foods.
The VitaFast® microbiological assay for folic acid is carried out on microtiter plates and is suitable for the determination of total amount of folic acid in foods and beverages.
The beverage is sterile-filtered and diluted with sterile water for the determination of added folic acid.
The sample must be digested through enzymatic hydrolysis in order to measure the total content of folic acid (naturally occurring and added).
The diluted sample and the folic acid assay medium are added to the wells of the microtiter plate, which are coated with Lactobacillus rhamnosus. Lactobacillus rhamnosus requires folic acid to grow. After an addition of folic acid, the microorganism exhibits growth until the vitamin is completely utilized. The plates are incubated at 37 °C for 44–48 h.
The growth of Lactobacillus rhamnosus is dependent upon the concentration of folic acid and is determined through measuring the turbidity. These results are compared with those obtained from a series of standard concentrations. The measurement is performed with a microtiter plate photometer at 610–630 nm (alternatively at 540–550 nm).