VII. OCCURRENCE IN FOOD 265 



B. PROCESSED FOODS 



When assessing tlie dietetic value of any foodstuff, consideration should 

 he given to the form in which it is likely to reach the consumer, and the 

 figures given in Talile Y may therefore be misleading unless they are con- 

 sidered in relation to the effect of different methods of preparation. The 

 high solul)ility of ascorbic acid in water and the relative ease with which 

 it is oxidized, either chemically or enzymatically, make this vitamin par- 

 ticularly susceptible to processing conditions, especially when the tissue is 

 broken or when the temperature is raised. Slicing, cutting, or bruising of 

 fruits and vegetables before processing is therefore likely to result in loss of 

 ascorbic acid, especially when associated with high-temperature treatment 



TABLE VI 

 Average Ascorbic Acid Content of Potatoes at Different Times of the Year" 



Average ascorbic acid content, 

 Month mg./lOO g. 



August*" 35 



September'' 35 



October " 23 



November 19 



December 16 



January 12 



February 10 



March and onward 6 



" Taken from table by M. OUiver from "Cooking and Nutritive Value," A. B. Callow, Oxford Clarendon 

 Press, 1945. 



The values for August and September were obtained from freshly dug potatoes, and for October on- 

 ward from stored potatoes. 



in air, water, or steam. Cold-water washing or steeping does not normally 

 leach out any significant amount of the \'itamin, provided that the tissue 

 is not unduly broken. 



1. Boiling, Steaming, and Pressure Cooking 



Investigations into household methods of cooking have shown that, when 

 fruits or vegetables are boiled with water, the ascorbic acid is relatively 

 stable. Significant losses due to oxidation are usually found only in large- 

 scale catering where the bulk addition of vegetables to the cooking water 

 may result in lowering of the temperature to such a degree that the action 

 of the enzymes is temporarily accelerated. Extraction of the vitamin does, 

 however, take place rapidly under normal conditions of boiling and con- 

 tinues until the concentration of \atamin in the liquor approximates to 

 that in the tissue. This point is usually reached after the optimum pala- 



