Description

Vitamin K refers to a family of fat soluble vitamins which includes phylloquinone (vitamin K1) and menaquinones (vitamin K2). All forms of vitamin K act as cofactors for γ-glutamyl carboxylase, an enzyme which adds Gla residues to certain proteins and are required for the protein to bind calcium. Differences in metabolism of phylloquinone and menaquinones result in phylloquinone being primarily used to help activate blood clotting factors while menaquinones help activate other proteins such as osteocalcin and Matrix-Gla protein. These two proteins have been shown to help fight osteoporosis and heart disease. Increased vitamin K intake has been shown to fight these diseases, but little information is available on the amount of vitamin K in food. To gain more information on the amount of vitamin K in Canadian foods, liquid chromatography-mass spectrometry was used to measure phylloquinone, menaquinone-4 (MK-4), and menaquinone-7 (MK-7) in Canadian cheese obtained from grass-fed cows and conventional supermarket cheese. Samples were homogenized in water, melted in a boiling water bath with HCl and then extracted with hexanes before filtration and injection into the LC-MS. A calibration curve from 0.1 to 1 µg/g was obtained for phylloquinone and MK-4, but was unsuccessful for MK-7. Gouda cheese made from grass-fed cows during the early spring and summer contained very high amounts of phylloquinone and MK-4, as did Maasdammer cheese from grass-fed cows. Vitamin K was not detected in conventional supermarket cheddar cheese and only MK-4 was detected in Gouda from the spring. The extraction procedure likely had a low recovery as the peak area of the internal standards was 10-20x larger in the standards than in the samples. A LC-MS method was successfully used to detect low concentrations of phylloquinone and MK-4, but further optimization of the extraction procedure is required for analysis of a larger number of samples.