The Effect of Chemical Preservation of Eggs upon the Stability of their Vitamin Contents.

CHINESE preserved eggs, or "pidan," offer an unusual opportunity for the study of some of the conditions under which the stability of vitamins may be affected. The preserved eggs are more or less chemically changed products of fresh ducks' eggs which are presumably rich in vitamin A, vitamin B, and the anti-rachitic food factor which exhibits certain vitamin-like properties. It should therefore be of interest to know what effects the preserving agents and the chemical changes have upon the stability of these vitamins. Furthermore, such a study would at the same time disclose the vitamin value of "pidan" as a food. This is of practical significance in China where the preserved egg is perhaps as much used on the table as is cheese in Western countries. The method of preservation according to the Chinese Economic Bulletin is the following. Fresh ducks' eggs are selected and washed. For the preservation of 100 eggs, mix 5 ounces of pure soda, 25 ounces of straw ash, and a little less than 4 ounces of table salt with about 20 ounces of boiling water to give a uniform mixture. Then add gradually 40 ounces of slaked lime to make a thick paste. Apply heat if necessary and keep stirring until the ingredients are thoroughly mixed. A layer of this mixture about a quarter of an inch thick is wrapped round each egg and covered with rice husks to prevent sticking. The eggs are then carefully laid in earthenware jars which are sealed with wet clay when full. In about a month the eggs acquire the desired flavour and degree of coagulation and are ready for the table. " Pidan" looks quite different from the fresh egg. The white has not only coagulated but turned dark brown and translucent, not unlike coffee jelly in appearance. The coagulated yolk looks deep green or greenish grey with concentric rings of different shades of grey, brown or dark green. The egg has a peculiar piquant lime taste and a decidedly ammoniacal odour, especially when freshly opened.