Dairy Chemistry And Biochemistry

266 DAIRY CHEMISTRY AND BIOCHEMISTRY

(RNI) is the quantity of a nutrient sufficient to meet the needs of 97% of the

population. Nutrient intakes equal to the RNI thus pose only a very small

risk of deficiency. United Kingdom RNI values (Department of Health,

1991) are also quoted below.

6.2 Fat-soluble vitamins

6.2.1 Retinol (vitamin A)

Vitamin A (retinol, 6.1) is the parent of a range of compounds known as

retinoids, which possess the biological activity of vitamin A. In general,

animal foods provide preformed vitamin A as retinyl esters (e.g. 6.5, which

are easily hydrolysed in the gastrointestinal tract) while plant foods provide

precursors of vitamin A, i.e. carotenoids. Only carotenoids with a /3-ionone

ring (e.g. p-carotene) can serve as vitamin A precursors. p-Carotene (6.6)

6.1 3

6.2

6.3

6.4