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ABSTRACT
Propionibacteria produce tetrahydromenaquinone-9 [MK-9 (4H)] as a major menaquinone (vitamin K^sub 2^). This study aimed to determine the MK-9 (4H) concentration in commercial propionibacteria-fermented cheese. The MK-9 (4H) concentration was quantified using an HPLC instrument with a fluorescence detector after postcolumn reduction. Among the various cheese samples, the MK-9 (4H) concentration was highest in Norwegian Jarlsberg cheese, followed by Swiss Emmental cheese. In contrast, the MK-9 (4H) concentrations in Appenzeller or Gruyère cheeses were extremely low or undetected. Likewise, the concentrations in Comte and Raclette cheeses were lower than those in Jarlsberg and Emmental cheeses. In the present study, the MK-9 (4H) concentration in cheese showed a correlation with the viable propionibacterial cell count and propionate concentration. This implies that the increase in propionibacteria contributed to the generation of MK-9 (4H) in cheese. We presumed, based on these results, that Swiss Emmental and Norwegian Jarlsberg cheeses contain a meaningful amount of vitamin K because of their high MK-9 (4H) concentrations (200 to 650 ng/g).
Key words: vitamin K, menaquinone, Propionibacteria, cheese
INTRODUCTION
Vitamin K exists naturally in 2 forms, namely, vitamin Ki (phylloquinone) in green plants and vitamin K2 (menaquinone) in animals and bacteria. Vitamin K is an essential cofactor for the formation of γ-carboxyglutamic acid residues in proteins (Shearer, 1990). The γ-carboxyglutamic acid-containing proteins bind calcium ions and influence blood coagulation and tissue calcification. Vitamin K deficiency has been implicated in several clinical ailments such as intracranial hemorrhage in newborn infants (Purves, 2005) and possible bone fracture resulting from osteoporosis (Iwamoto et al., 2004). To decrease the risk of these diseases, therefore, vitamin K food composition data are required. Further, to appropriately counsel patients taking the antithrombotic medicine warfarin, a vitamin K antagonist, accurate food composition data are of importance.
Early food composition data regarding vitamin K used chick bioassays that were more qualitative than quantitative. Recently, the development of reliable chromatographic procedures has resulted in greater sensitivity and accuracy of vitamin K measurements in foods (Koivu-Tikkanen et al., 2000; Schurgers and Vermeer, 2000). These quantitative analyses have revealed that vitamin K2 occurs in foods in various molecular forms, such as menaquinone (MK)-4 and MK-7. Therefore, more reliable data are needed on the menaquinone contents in foods.
Numerous types of cheeses...