374 RIBOFLAVIN 



Von Euler^ had proposed a unit which consisted of 5 7 of riboflavin, the 

 amount which produced an increase in weight of 0.8 to 1.0 g. per day in 

 young rats. A Cornell unit^ was defined as the growth effect on chicks 

 equivalent to that produced by 1 7 of riboflavin. 



The need for standards of biological activity continues to exist, especially 

 in the study of derivatives of riboflavin. As an example, consider the assay 

 of a very water-soluble riboflavin derivative prepared by Stone. ^ Fluoro- 

 metric assay of the material yielded a value of 57.2% riboflavin; micro- 

 biological assay by the U.S. P. XIII revision method yielded a value of 

 33 % riboflavin. The biological assay by the standard rat growth method 

 indicated the riboflavin potency was almost nil. 



IX. Occurrence in Food 



M. K. HORWITT 



The best sources of riboflavin are milk, egg white, Uver, heart, kidney, 

 and growing leafy vegetables. Beef muscle, veal, apricot, tomato, and 

 poultry muscle are good sources. Fish muscle, unenriched grains, and leg- 

 umes, although relatively poor sources, supply important minimal amounts 

 to the average regimen. Yeast, the richest natural source of riboflavin, is 

 not normally a major component of non-therapeutic diets. 



The primary factors to be evaluated in a consideration of the stabiUty 

 of riboflavin in food products are the effects of heat, light, elution, and the 

 intracellular reactions which take place during storage. 



The relative heat stability of riboflavin is a fortunate property which 

 favors its preservation by ordinary cooking procedures.^ Even the addition 

 of bicarbonate to a pH of 8.8does not appreciably increase the loss of ribo- 

 flavin during short cooking procedures.^ The major losses which occur dur- 

 ing home cooking or commercial canning operations are probably attribu- 

 table to the extraction of the vitamin by the water used in the cooldng or 



3H. von Euler, P. Karrer, E. Adler, and M. Malmberg, Helv. Chim. x\cia 17, 1157 



(1934). 

 ^ H. von Euler, Institut international di Chimie Solvaj^ Sixieme Conseil de Chemie, 



rapport et discussions sur Les Vilamines et les Hormones, p. 198. Paris, 1938. 

 * L. C. Norris, H. S. Wilgus, A. T. Ringrose, V. Heiman, and G. F. Heuser, Cornell 



Univ. Agr. Exptl. Sta. Bull. 660, 3 (1936). 

 6G. B. Stone, Science 111, 283 (1950). 



1 H. Levine and R. E. Remington, J. Nutrition 13, 525 (1937). 



^ C. H. Johnston, L. Schauer, S. Ra])aport, and H. J. Deuel, Jr., J. Xutrition 26, 

 227 (1943). 



