New analytical aspects of vitamin D in foods

A comprehensive study of vitamin D in foods was undertaken during 1991–1994 in Finland to develop high-performance liquid chromatographic (HPLC) methods for analysing cholecalciferol, ergocalciferol and their 25-hydroxylated metabolites in fish, egg yolk, meat, milk, edible mushrooms and fortified foods, and to evaluate which vitamin D compounds should be analysed to estimate the total vitamin D contents in these foods. The procedures included saponification, extraction and purification using one or two chromatographic steps prior to quantification by HPLC using internal standard methods. Ergocalciferol was used as an internal standard for cholecalciferol and vice versa, and, as first presented in the present study, 25-hydroxyergocalciferol was used as an internal standard for 25-hydroxycholecalciferol and vice versa. The methods developed were well suited to determining the contents of ergocalciferol, cholecalciferol and their 25-hydroxylated metabolites in food. Good estimates of the vitamin D content of fish or edible mushrooms are obtained if only cholecalciferol or ergocalciferol, respectively, are determined. On the other hand, in addition to cholecalciferol 25-hydroxycholecalciferol should also be determined from egg yolk, meat and milk.