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Milk Composition & Synthesis
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Milk Composition

Milk contains all the vitamins required by mammals. The fat soluble vitamins, A, D, E, and K, are found primarily in the milk fat; milk has limited amounts of vitamin K. The B vitamins are found in the aqueous phase of milk. Fluid milk in the US is fortified with additional vitamin D. Vitamin A is also added to milk in some other countries.

Vitamins are essential organic compounds required in the diet. Most are not synthesized in the animal (there is some synthesis by the microflora in the intestine). Therefore, milk levels can be influenced by dietary levels. Milk contains all of the B vitamins and fat-soluble vitamins, except perhaps vitamin K.

The fat soluble vitamins (A, D, E, K) are associated with the milk fat globule.

Vitamin A : retinol : Yellow milk fat of Guernsey cows is due to lower efficiency of conversion of ß-carotene to retinol. In some countries milk is fortified with vitamin A.

Vitamin D : antirachitic activity : Involved in bone metabolism, Ca absorption in the intestine, and has other tissue functions. Milk is often fortified with vitamin D.

Vitamin E : tocopherol : Antioxidant, protects lipids. Only low levels are present in milk.

Study Question

This image is of a sample of milk collected from a cow and then centrifued to separate the milk phases. In which fraction of this separated sample would you expect to find most of the vitamin D? In which fraction would you expect to find most of the vitamin B6?

Milk Composition & Synthesis