VII. OCCURRENCE IN FOOD 



2G1 



Assa}' 



Dissolve al)<)ut 40 mg., accuratel}- weighed, 

 in a mixture of 5 ml. of walcr and 5 ml. of 

 dilulc sulfuric acid, and titrate willi 0.01 A' 

 iodine, u.sing mucildtjc of stnrvh a.s indicator. 

 Each milliliter of 0.01 N iodine is ciiuivalent 

 to 0.0008805 g. of CoII«()6. 



II. Occurrence in Food 



M.\MIE OLLIVER 



Investigations into the oocurrence of ascorbic acid in foodstuffs have 

 been facihtated l\v the comparati\'e simplicity of chemical methods for 

 estimation of the vitamin. Unfortunately, however, failure to observe es- 

 sential precautions when applying such methods (see p. 247) has re- 

 sulted, in some instances, in the publication of experimental data of 

 doubtful \'alue. Consequently, discrimination must 1 e used when interpret- 

 ing the conclusions from such work. Nevertheless, a large amount of reli- 

 al)le information relating to the antiscorbutic \"alue of foods is available 

 in the literature, and, indeed, the sources of information are so numerous 

 that it has been foinid impracticable in the present review to attempt to 

 present a comprehensive list of references. 



A. UNTREATED FOODS 



Consideration of the dietetic value of any food must first be directed to 

 the raw material, and, in the case of vitamin C, this is virtually limited to 

 plant tissues, milk, and liver, the other animal tissues used for foods being 

 of relatively little practical importance. Raw liver contains about 30 mg. 

 per 100 g. of ascorbic acid, and liquid milk, as supplied to the consumer, 

 between 13 and 17 mg. per liter. At the present time, synthetic ascorbic 

 acid may be added to some foods either for the purpose of fortification or 

 as a processing aid, e.g., as an antioxidant, and the possibility of such addi- 

 tions should therefore also be borne in mind in dietary assays. 



The distribution of ascorbic acid within one indi\'idual fruit or vegetable 

 is often extremely variable. For instance, the vitamin has been found to 

 be more concentrated in the skins than in the pulp of fruit; the leaves of 

 spinach contain more ascorbic acid than the petioles; and the leaves from 

 a single cabbage may show significantly different antiscorbutic ^'alues from 

 one another. Similarly, individual cabbages of the same variety growing 

 adjacent to one another in the same field may show different average con- 

 centrations of ascorbic acid. Berries on one plant may show similar vari- 

 ation, but this may be partially due to differences in degree of maturity, 



