454 THIAMINE 



Thus 1 international unit of thiamine is equivalent to 3 7 of thiamine 

 hydrochloride. 



Afterwards Keresztesy and Sampson- found that this standard prepara- 

 tion was not ideal ; they demonstrated that the preparation contained twice 

 as much thiamine as was indicated in the animal experiments, the animal 

 organism being able to elute only one-half of the adsorbed thiamine. 



Now that the crystalline synthetic thiamine hydrochloride is abundantly 

 available, the pure synthetic preparation itself is taken as a standard, and 

 the quantity of thiamine usually is expressed not in international units but 

 in milligrams of thiamine. 



Before the isolation of the thiamine some authors had recommended 

 units based on rice polish or yeast. Of course these are now obsolete, and 

 a comparison with the pure vitamin is only approximately possible. With 

 this restriction we can say that 1 7 of crystalline thiamine hydrochloride is 

 equivalent to 0.166 Smith curative unit or to 0.666 Chase-Sherman unit or 

 to 0.333 Roscoe unit. 



IX. Occurrence in Food 



B. C. P. JANSEN 



A. OCCURRENCE OF THIAMINE AND ITS PHOSPHATE 

 COMPOUNDS 



In contrast to other vitamins, e.g., the fat-soluble vitamins and ascorbic 

 acid, thiamine has a widespread distribution in food. It is entirely absent 

 only from oils and fats, cassava, and refined sugar. On the other hand we 

 do not know of any foods that are as rich in thiamine as certain fish liver 

 oils are in vitamins A and D. In animal experiments brewer's yeast is used 

 as a rich source of thiamine (and other B vitamins) . 



In connection with this lack of abundantly thiamine-containing foods it 

 is important, as stated by Friedemann et al.,^ that the intestinal absorption 

 of thiamine hydrochloride by normal human subjects is extremely limited. 

 The maximum which could be orally taken without an increase of fecal 

 thiamine is about 5 mg. per day. 



A large part of thiamine in vegetable products is in the form of thiamine 

 itself; in animal tissues it is present largely in the form of its phosphate or 

 pyrophosphate derivative (as cocarboxylase). Witli regard to the nutri- 

 tive value of the food, it does not matter in which foi-m tliiamine is present, 



2 J. C. Keresztesy and W. L. Sampson, Proc. Soc. Exptl. Biol. Med. 36, 6S6 (1937). 

 1 T. E. Friedemann, T. C. Kmieciak, P. K. Keegan, and B. B. Sheft, Gastroenter- 

 ology 11, 100 (1948). 



