4 INTRODUCTION 



As the following chapters will show, between 70 and 80 carotenoids have 

 been found in nature up to the present time. They can all be related to one 

 parent substance, lycopene. By means of simple chemical changes such as 

 cyclisation, double bond migration, partial hydrogenation, introduction of 

 hydroxyl-, keto-, or methoxyl-groups, or introduction of an oxygen bridge, etc., 

 the whole range of pigments can be derived from this parent substance. Their 

 visible Ught absorption comprises a range of about 300 m/u, (ca. 400-700 mju). 

 The carotenoids thus represent one of the most striking examples of the mani- 

 fold variation of a parent substance by the vegetable and animal cell. 



