Application of an HPLC assay for the determination of folate derivatives in some vegetables, fruits and berries consumed in Finland

The folate content of 30 commodities of vegetables, fruits and berries, including a few processed products, was determined by high-performance liquid chromatography (HPLC). HPLC was used with a combination with fluorescence and ultraviolet detectors to analyze folate monoglutamate derivatives and their distribution after extraction at pH 6.0 and deconjugation with hog kidney deconjugase at pH 4.9. 5-Methyltetrahydrofolate was the main derivative in all foods studied, but tetrahydrofolate, 5-formyltetrahydrofolate and 10-formylfolic acid were also detected. The sum of the monitored folate derivatives (as μg folic acid) in vegetables ranged from 9 to 114 μg per 100 g and that of berries and fruits from 3 to 36 μg per 100 g. The variation in folate content, which was studied by analyzing raw potato, carrot and cabbage bought from retail shops three times a year, was small. Some of the studied processed vegetable foods were also reasonably good sources of folate. The results obtained with HPLC are rather similar to the previously reported values for vegetables determined by a microbiological method. Several measures for method improvement and quality control of the analysis allowed reliable determination of the main folate forms, particularly 5-methyltetrahydrofolate, in a wide range of plant-derived foods.