VII. OCCURRENCE IN FOOD 267 



\'ariaiits imohed, tliese fi^uios can l)e accepted as indicative of results only 

 for UA'crago and controlled conditions. 



2. Jam (Preserves) 



When frnit is boiled with sugar, as in jam making, the ascorbic acid is 

 remarkably stable, although a significant loss from the original fruit may 

 be entailed if the fruit is soft and broken or pulped or cut and allowed to 

 stand before boiling. The most important factor controlling the vitamin C 

 content of the finished jam is, indeed, the condition of the fruit used for 

 preserx'ation. The rate at which ascorbic acid is destroyed on storage of 

 the jam is associated with temperature of storage but, luider normal con- 

 ditions, only slight loss is to be predicted over several weeks. 



3. Freezing 



The blanching or scalding process given to vegetables which are to be 

 commercially frozen, dehydrated, or canned consists in treating the cleaned, 

 trimmed material at a high temperature for a few minutes in order to in- 

 activate the enzymes. If this procedure is omitted, then off-flavors, dis- 

 coloration, and loss of ascorbic acid may occur during subsequent processing 

 operations and, with frozen and dehydrated vegetables, during post-pro- 

 cessing storage. If hot- water blanching is used, ascorbic acid may be leached 

 from the plant tissues, whereas with steam blanching oxidation of the vi- 

 tamin may occur. To minimize these losses, various precautions are nor- 

 mally taken which include short time-high temperature treatment, serial 

 l)lanching (whereby successive batches of fresh vegetables are passed 

 through the same scalding liquor), and the use of sulfite. 



In the preparation of frozen foods, the actual freezing process appears 

 to have a negligible effect on ascorbic acid content, but post-freezing storage 

 is important and a temperature of not higher than —20° F. has been found 

 necessary in order to retain the maximum content of the vitamin for 10 

 months' storage. Thawing of the food before cooking may result in progres- 

 sive loss of the vitamin, especially if enzymes are present, and indeed it is 

 one of the most important factors affecting the ascoi'bic acid content of the 

 food as eaten. 



By reason of the partial softening of the tissues during ))lanching, the 

 final product needs proportionately shorter cooking time and also less water 

 than when the raw material is cooked. Consequently, when commercially 

 frozen vegetables are given a final household cooking, there is significantly 

 greater retention of ascorbic acid than with the heating of fresh vegetables. 

 This normally offsets the loss of the vitamin which occurs during controlled 

 blanching and results in similar antiscorbutic values for the fresh and pro- 

 cessed material when prepared for the table. 



