VITAMINS — MUNSELL 249 



Losses of vitamin C. — Loss of vitamin-C value from foods may 

 occur as a result of inactivation by oxidation or removal of the vita- 

 min by solution. 



Consideration of losses from oxidation require mention, at least, 

 of factors pertaining especially to this vitamin. Some fruits and 

 vegetables contain substances called oxidases that accelerate the rate 

 of inactivation of vitamin C by oxidation. These substances in turn 

 are inactivated by heat and are destroyed in a short time when kept 

 at the boiling point of water. Small amounts of copper coming from 

 utensils and containers also catalyze, or hasten the oxidation of vita- 

 min C. Some foods also contain within their tissues an amount of 

 oxygen sufficient to be a factor in the oxidation process. 



Deterioration of vitamin C begins in all foods as soon as they are 

 removed from the environment in which they were produced. This 

 is the reason for indicating carefully what is meant by "fresh foods" 

 from the standpoint of vitamin-C content. The rate of inactivation 

 of vitamin C in fruits and vegetables that are allowed to stand seems 

 to depend upon their physical characteristics. Thin leaves like spin- 

 ach lose vitamin C rapidly and may retain no more than 50 percent 

 after standing 2 or 3 days. Peppers having a smooth compact 

 outer covering, show little loss. In apples the loss is gradual and 

 ripe tomatoes may be stored as long as 10 days without detectable 

 change in vitamin-C content. Rate of inactivation in all such prod- 

 ucts increases with increase in temperature so that loss is less when 

 they are kept under refrigeration. 



In plant products inactivation is more rapid when the plant cells 

 have been opened up so that the vitamin is exposed to oxygen. De- 

 crease in vitamin-C content takes place in vegetables that are pre- 

 pared for cooking or canning and then allowed to stand. Foods that 

 are chopped or crushed lose vitamin C rapidly and may contain ap- 

 preciably less of the vitamin after standing only a few hours. The 

 rate of destruction of the vitamin is less, however, at low tempera- 

 tures in such cases. Expressed juices like orange juice and tomato 

 juice may be stored in covered containers at household refrigerator 

 temperatures for as long as 24 hours with no detectable change in 

 vitamin-C content. Rate of destruction after that time depends 

 upon whether the oxidases have been previously destroyed by heat- 

 ing. Canned tomato juice, after the can is opened, shows little 

 change in vitamin-C content after several days' storage in a 

 refrigerator. 



Heat markedly accelerates the rate of destruction of vitamin C 

 and cooked foods are not dependable sources of this vitamin. Toma- 

 toes are a notable exception since they are rich sources to begin with 

 and due to their high acidity they show loss of the vitamin only 



