268 ascorbic acid 



4. Dehydration 



The loss of ascorbic acid in controlled modern methods of dehydration, 

 whereby the blanched tissue is rapidly dried, is small compared with the older 

 drying processes which destroyed most of the vitamin. Some oxidation does 

 take place, however, and this, in conjunction with blanching loss, may mean 

 that, for instance, in cabbage only some 50 to 60 % of the original ascorbic 

 acid is retained. However, since no further loss is to be anticipated on storage 

 of the dehydrated tissue in nitrogen over a period of several months and 

 since reconstitution again brings about no further degradation of the vi- 

 tamin, the product as eaten is likely to be of only slightly less antiscorbutic 

 value than freshly harvested material after household cooking. 



5. Canning and Bottling 



During the canning or bottling of fruits and vegetables, there is very 

 little destruction of ascorbic acid, but leaching into the liquor takes place. 

 On account of the relatively lower ratio of liciuid to solid than in household 

 saucepan cooking, less vitamin is extracted and therefore less loss occurs 

 when the vegetable licjuor is discarded. Destruction of ascorbic acid gradu- 

 ally takes place on storage of the processed material, the rate of loss being 

 accelerated with increasing headspace, by high-temperature storage, and, 

 when jars are used, by the action of light. With vegetables, these storage 

 losses have to be considered alongside losses due to blanching. In general, 

 however, the total loss is usually offset by the stability of the ascorbic acid 

 during the reheating process. Consequently, canned fruits and vegetables 

 which have been stored for a few months under normal conditions may 

 be accepted as having a comparable antiscorbutic value in the diet as sim- 

 ilar material prepared by open saucepan cooking. 



6. Assessment of Ascorbic Acid Content of Diets 



Unless conditions of processing of the foodstuff are known, it is almost 

 impossible to predict the vitamin C content of a diet from a knowledge of 

 the fruits and vegetables consumed, and chemical assays must be used. If 

 information about such processing, and especially the final household treat- 

 ment, is known, however, then over a period of several weeks it is possible 

 for the average daily intake of ascorbic acid to be determined, with a rea- 

 sonable degree of accuracy, from a knowledge of the quantities of different 

 fruits and vegetables which have been eaten. Household cooking is likel}'' 

 to prove not only the most important but also the most unpredictable 

 factor in determining the antiscorbutic value of the diet, and any assess- 

 ment by calculation should always be substantiated by chemical assay of 

 a proportion of the individual components of the diet. 



