VITAMINS — MXJNSELL 245 



Glandular organs, other than liver, contain fairly large amounts of 

 the vitamin but, like liver, they are available in limited quantities. 

 Lean muscle meats contain only small quantities of vitamin A. 



Losses of vitaniin-A value. — Vitamin A and its precursors are not 

 greatly affected by any of the processes connected with food preser- 

 vation and preparation unless there is considerable chance for oxi- 

 dation. Foods that are stored show a loss only after prolonged stor- 

 age. This is greatest in foods that have been dried preparatory to 

 storing, such as dried grasses and dried fruits. Even though such 

 foods were good sources to begin with, they may lose as much as 50 

 percent of their vitamin-A value in a few months' time. Boiling and 

 steaming cause practically no diminution in vitamin-A content. 

 Losses have been noted as a result of baking but they are not serious ; 

 in roasting, destruction of vitamin A is appreciable. 



As would be expected there is little or no loss of vitamin A when 

 foods are canned. During storage the vitamin-A content of canned 

 foods may decrease but this change takes place gradually and usually 

 is not appreciable up to 9 months. 



VITAMIN Bi (THIAMIN) 



Properties. — ^Vitamin Bi is a white crystalline material that is solu- 

 ble in water. In plants it seems to exist in relatively simple combina- 

 tion and may be removed fairly easily by extraction with water. In 

 animal tissue it is present in more complex form combined with 

 phosphate. 



Vitamin Bi is described as heat-labile — that is, unstable when 

 heated. Inactivation depends entirely, however, upon conditions 

 under which it is treated. In acid solution it is relatively stable but 

 in neutral or alkaline solution it is readily broken down, the rate of 

 destruction being higher with increase in alkalinity, temperature, 

 and time of heating. The rate of destruction of the vitamin is also 

 higher when it is heated in solution or in mixtures that are moist 

 than when heated in dry mixtures. 



Food sources. — ^Vitamin Bi occurs in practically all foods derived 

 from plants with the exception of fats and oils, but there are very 

 few concentrated sources. Vitamin-Bi values of foods seem to be less 

 subject to the influence of conditions of production and are therefore 

 somewhat more constant than other vitamin values. 



The relatively low concentration of vitamin Bi in foods and the 

 lack of sensitivity of the methods for measuring it have not made it- 

 possible to determine its distribution in the different parts of plants 

 as closely as in the case of some other vitamins. Seeds, including 

 grains, nuts, and legumes, are known to be among the richest sources. 

 In grains, the vitamin is concentrated in the embryo and outer cover- 



