VARIATION OF VITAMIN CONTENT OF SHANGHAI FOODS AND THE INFLUENCE OF COOKINGI. VITAMIN C IN VEGETABLES

From previous investigation, it appears that vitamin C content of one variety of vegetable as found in the market may vary considerably. However data on this point are few. Present study investigated the variation of vitamin C content of a number of common vegetables available in the Shanghai market and the influence of different methods of cooking. Harris Olliver method slightly modified was used to determine the ascorbic acid and dehy-droascorbic acid. Roe, Mills, Osterling Dainron method was also used to determine the ascorbic acid, dehydroascorbic acid and diketogulonic acid.The results were as fellows:1.Among 26 different vegetables, the vitamin C of each variety taken at different times of the year showed a variation from less than 1 to 5 times. Generally the variation was from 2 to 3 times. Spinach, green peppers, potato, small onion, aster shoots, foreign cabbage, leeks, string beans showed variation of from 3 to 5 times. Majority of the vegetable showed vitamin C content similar to those in Peking, a few showed values twice as high as those in Peking.2.Dehydroascorbic acid was present in all but 2 of the 35 kinds of vegetable tested. The majority showed less than 10% of the total vitamin C. Eight vegetables showed a presence of 10-20%, seven vegetables 21-50%, and only one vegetable over 50%. Among 32 kinds of vegetable studied, the majority showed an absence of dikitogulonic acid, only a i'ew showed a trace of the acid.3. Four different methods of cooking were used. The loss of ascorbic acid during quick frying (used small amount of oil) was 6.2-48.7%, averaging 25.2%. Dehydroascorbic acid and ascorbic acid showed a total loss of from 7.3-46.8%, averaging 23.4%.Boiling of vegetable caused a loss of ascorbic acid of 4.6-50.6%, averaging 16.2%, while the loss of the sum of ascorbic acid and dehydroascorbic acid was 4.6-40.4%, averaging 15.3%.Steaming of vegetable on the whole caused a destruction of vitamin C more than quick frying and quick boiling. The average loss was 31.9% of ascorbic acid and 23.6% of the sum of ascorbic acid and dehydroascorbic acid.Salting of vegetable for one hour caused an average loss of 24,7% of ascorbic acid and an average loss of 18.1% of the sum total of ascorbic acid and dehydroascorbic acid.Standing for one hour after steaming caused an average loss of about 73% of ascorbic acid, while standing for one hour after quick frying caused only a loss of about 13% of ascorbic acid.