VITAMINS 225 



its reversible oxidation and reduction, as shown in the equation above. 

 These reactions are catalyzed by ascorbic acid oxidase, which, however, 

 has been found so far only in plant tissues. The reducing power of vita- 

 min C has also been utilized in determining by chemical means the amount 

 of ascorbic acid in a given material. This is accomplished by use of a 

 dye, 2,6-dichlorophcnolindophcnol, w4iich is reduced by vitamin C to a 

 colorless form. Hence the quantity of dye that is reduced is a measure 

 of the vitamin potency of the food. The chemical method for determin- 

 ing vitamin C agrees well with the results obtained with feeding experi- 

 ments, and since it takes but a few minutes to make a determination, 

 chemical analysis has largely superseded biological assay. Atmospheric 

 oxygen reacts quite readily with ascorbic acid to destroy it, especially at 

 slightly elevated temperatures and in alkaline solution. 



Occurrence 



Although paprika exhibits the highest individual concentration of vita- 

 min C hitherto observed in nature, as a class, the citrus fruits such as 

 oranges, limes, lemons, and grapefruit, probably deserve to be ranked 

 first in vitamin C content. Other good sources that find extensive use 

 in the diet include tomatoes, strawberries, raw cabbage, fresh spinach, leaf 

 lettuce, turnips, rutabagas, carrots, bananas, apples, and potatoes. The 

 large consumption of potatoes in the average American dietary rather 

 than a high content of vitamin is responsible for its contribution to the 

 total intake of vitamin C. IMilk is too low in vitamin C to furnish an 

 adequate supply, and, hence, pediatricians recommend administration of 

 fruit juices early in the life of a baby to compensate for the deficiency. 

 The bottle-fed baby receives only about one-fourth as much vitamin C 

 from cow's milk as it would from its mother's milk. Meat and eggs con- 

 tain very little vitamin C. Cereal grains likewise contain little, if any, 

 although considerable amounts are formed during germination. 



Because of the ease with which vitamin C is destroyed by oxidation and 

 also because it is water-soluble and therefore lost if the cooking water 

 is discarded, cooked foods are apt to contain much less than the original 

 raw materials. Studies made in a Canadian army camp during World 

 War II revealed that of every 100 mg. of vitamin C in the food brought 

 into the kitchens only 15 mg. reached the table! Boiling cabbage for 

 20-30 minutes and discarding the water may cause the loss of over 80 

 per cent of its vitamin C potency. Even when vegetables such as broccoli 

 or spinach are allowed to remain at room temperature for 24 hours, 50 

 to 70 per cent vitamin destruction occurs. The principles to be followed 

 if loss of this sensitive but vital food factor is to be avoided or minimized 

 may be summarized thus: (1) eat the food raw if possible, (2) if the 

 food is to be cooked, use the minimum amount of water, heat quickly to 



