Dairy Chemistry And Biochemistry

270 DAIRY CHEMISTRY AND BIOCHEMISTRY

6.7

HO

6.8

6.9

conversion requires about 28 h to convert 50% of previtamin D, to vitamin

D,. Thus, production of vitamin D, in the skin can take a number of days.

Preformed vitamin D, is obtained from the diet. Vitamin D, is stored in

various fat deposits around the body. Regardless of the source of vitamin

D,, it must undergo two hydroxylations to become fully active. Vitamin D,

is transported by a specific binding protein through the circulatory system

to the liver where the enzyme, 25-hydroxylase, converts it to 25-hydroxy-