198 THE VITAMINS 



scorbutic properties, though extensive, was less complete than might 

 have been expected from the results at lower temperatures.* 



Applying these results to a discussion of methods of cooking vege- 

 tables, Delf pointed out that slow cooking at a low temperature is likely 

 to be more deleterious than more rapid cooking at high temperature. 

 The prolonged cooking of vegetables in a fireless cooker might thus 

 be more destructive of vitamin C than actual boiling for a short time. 

 Contrary to the results of Hoist and Frolich with cabbage and of 

 Harden and Zilva with lemon juice, the addition of dilute citric acid 

 to the cabbage before boiling did not prevent the destruction of vitamin 

 C. In view of these results and previous observations of the instability 

 of vitamin C to alkalinization, Delf concluded that in cooking vege- 

 tables it is better to add neither acid nor alkali to the water in which 

 they are cooked. 



Delf and Skelton (1918) found a loss in antiscorbutic potency of 

 more than 93 per cent when cabbage was dried at a low temperature 

 (60° C.) and stored subsequently for two to three weeks at laboratory 

 temperatures. This loss increased with prolonged storage until at the 

 end of three months nearly all the protective value of the fresh mate- 

 rial was lost. By plunging the cabbage into boiling water before drying, 

 the residual amount of antiscorbutic factor was distinctly greater, indi- 

 cating that "killing the cells" (coagulation of protoplasm with destruc- 

 tion or inactivation of enzymes including oxidases) by heat before 

 drying is beneficial in lessening the loss of vitamin C taking place 

 during drying, 



Givens and Cohen (1918) reported that cabbage dried in a blast 

 of air at 40° to 52° C. retained some of its antiscorbutic value, but 

 heated in an oven for 2 hours at 75° to 80° C. and then dried at 65° 

 to 70° C. afforded no protection. Ellis, Steenbock, and Hart (1921) 

 attempted to prevent the destruction of vitamin C in cabbage on dry- 

 ing by heating the material in a vacuum oven in an atmosphere of 

 carbon dioxide at 65° C, the process requiring 35 hours. Practically 

 no protection was afiforded by the dried cabbage when fed to guinea 

 pigs in 1.5 grams daily amounts. 



In recent studies by Clow, Marlatt et al. (1929) fresh raw sauer- 

 kraut was found to contain about half as much vitamin C as the cab- 

 bage from which it was prepared. An extension by Qow, Parsons, and 

 Stevenson (1930) of these studies to six brands of commercially canned 

 sauerkraut put up in tin showed wide variations in the content of 



* From the point of view of newer knowledge, briefly summarized in the section on 

 chemical behavior (beyond), the interpretation of these results should also take account of 

 oxidation potentials and of possible destruction of oxidases. 



