6 OCCURRENCE, DETECTION, ESTIMATION I 



been found that part of the pigments is excreted unchanged, while the re- 

 mainder is absorbed. The absorbed carotenoids are either deposited in the fat 

 tissues, nerve tissues, inner organs, etc., or converted into other substances 

 which often fulfil important physiological functions in the animal organism 

 (e.g. vitamin A). In the animal organism, the carotenoids either occur dissolved 

 in fats or combined with protein in the aqueous phase. Colloidal solutions are 

 also observed^. 



A typical example of a carotenoid-protein complex is the astaxanthin 

 proteid, ovoverdin. This water-soluble chromoproteid occurs, for example, in 

 the green eggs of the lobster and in many other Crustacea (cf. p. 230). Asta- 

 xanthin occurs as the fat-soluble carboxylic acid ester in the red hypodermis 

 of the lobster, and the retina of the chicken also contains at least two different 

 esters of this pigmenf^. 



JuNGE^ has recently carried out investigations on the pigments of insects 

 and has observed that many of these appear to be carotenoid-protein complexes. 

 Thus, phytoxanthins (e.g. xanthophyll) as well as epiphasic carotenoids (e.g. 

 jS-carotene) have been found to be constituents of such chromoproteids. 



The mode of occurrence of carotenoids in blood serum is also of importance. 

 The present view is that the carotenoids here occur in the aqueous phase com- 

 bined with lipoids and proteins^. 



Von Euler and Adler^'' have estabhshed the occurrence of carotene in 

 the retina. According to experiments by Brunner and collaborators^\ the 

 pigment here occurs in the colloidal state. 



3. detection and estimation 



In order to establish the presence of carotenoids in natural sources, the 

 dried materials (e.g. leaves or blossoms) are treated with certain reagents (e.g. 

 concentrated sulphuric acid), which produce characteristic colourations. Ac- 

 cording to MoLiscH^^^ -j-i^g polyene pigments are best detected by first destroying 

 the surrounding substances, e.g. fats, and only then applying the colour tests. 

 In practice, the material is first treated with concentrated aqueous alcoholic 

 alkali, which dissolves the fats and sets free the carotenoids. At the same time, 

 the phytoxanthin esters* are hydrolysed and the phytoxanthins are liberated. 

 In this way, crystalline carotenoids are often obtained and can be recognised 

 under the microscope. Their presence can also be shown by colour reactions. 

 Recently, however, it has become increasingly usual to isolate the carotenoids 

 first and to characterise them subsequently. For this purpose the micro- 

 method of KuHN and Brockmann^^ ^g often employed. It must be emphasised. 



In nature, phytoxanthins often occur esterified as colour waxes, e.g. physalien, 

 helenien. 



References p. 8-g. 



