250 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



after prolonged heating. In foods that contain oxidases destruction 

 of vitamin C during cooking is very rapid at first or until the tem- 

 perature is reached at which the oxidase is destroyed when it pro- 

 ceeds at a much slower rate. To preserve vitamin-C content during 

 cooking, foods should be cooked quickly. They should also be 

 served immediately since cooked foods lose vitamin C more rapidly 

 when allowed to stand than do raw ones. 



When foods are boiled some of the vitamin C they contain may 

 dissolve in the cooking water. This dissolved vitamin may be con- 

 served, obviously, by using the water. The proportion of vitamin C 

 destroyed in foods that are boiled averages 20 to 25 percent while 30 

 to 40 percent may be present in the cooking water depending upon 

 the amount used. 



Foods that must be cooked at temperatures higher than that of 

 boiling water do not retain enough vitamin C to require 

 consideration. 



Reduction in vitamin-C content from canning is less than in foods 

 cooked by other methods since air is largely excluded during proc- 

 essing. Decrease in vitamin-C content is greater in foods that are 

 preheated in an open kettle before they are put into the can than in 

 those canned by the cold pack method. Blanching may cause some 

 loss of vitamin C through solution, but this procedure at the same 

 time effects inactivation of any ascorbic acid oxidase present. 



Canned foods may be stored several months without showing 

 serious decrease in vitamin-C content, but when deterioration once 

 begins it proceeds rapidly. Inactivation of vitamin C in canned 

 goods is directly and specifically related to the size of the bead space, 

 hence, this should be kept as small as possible. Conditions of stor- 

 age do not seem to be closely related to rate of loss of vitamin C in 

 canned foods. The question as to whether loss is greater in foods 

 canned in tin or in glass is still in the controversial stage. 



In considering canned foods as sources of vitamin C, one impor- 

 tant point must be kept in mind. Such foods have been cooked at a 

 fairly high temperature and the cellular structure is largely broken 

 down. If they are allowed to stand after removal from the can or 

 are heated and then allowed to stand they will not have very 

 much vitamin C. Tomatoes are an exception since they retain vita- 

 min C well under most conditions because of their high acidity. 



Drying of foods is very destructive of vitamin C. Some dried 

 products — fruits — have been reported as containing small quanti- 

 ties, and sulfured foods are supposed to contain more than others; 

 but the amounts left even in foods that have just been dried are so 

 small that it seems safer on the whole to disregard dried foods as 

 probable sources of this vitamin. 



