The effect of chemical preservation of eggs upon the stability of their vitamin contents.

Abstract

The Chinese preserved eggs or “pidan” are produced on a commercial scale from fresh ducks'eggs, and are perhaps as much relished by the Chinese people as cheese is in Western countries. In preserving, each egg is coated with a layer about 7 mm. thick of a mixture containing pure soda 5, burned straw ash 25, table salt 4, slacked lime 40, and boiling water 26. This again is covered with rice husks to prevent sticking. The eggs are laid in earthenware jars, sealed with wet clay, for a month. Both the white and the yolk are then coagulated. The white has turned dark brown and the yolk greenish gray with concentric rings of different shades of gray. These eggs are marketed with their coverings on and are usually consumed within six months of production. The taste of these eggs can only be very imperfectly described as somewhat caustic and piquant and the odor largely ammoniacal.

In the preserved egg there was, according to Blunt and Wang, 1 a marked increase in the ash content and the alkalinity of the ash; and a partial decomposition of the proteins and the phospholipoids resulting in an excessive production of free ammonia and in a diminuation of the yolk-fat. It was believed that these characteristic changes were brought about by the combined action of bacteria and enzymes as well as by the alkali preservative.

It should be of interest, both from the point of view of setting a vitamin value to “pidan” as a food and the point of view of studying the properties of vitamins, to know what effects the preserving agents and the chemical changes have upon the stability of the presumably rich vitamin contents of the ducks' eggs.

Feeding experiments were made on 57 albino rats. Three or four animals were used for each single experiment. It was shown that 3 per cent of the preserved yolk, or 2 per cent of the ether extract of the dried preserved yolk contained sufficient amount of vitamin A to cure this vitamin deficiency disease in the rats. Five per cent of the preserved yolk was as efficacious as 5 per cent of liquid yolk from fresh ducks' eggs in curing Xerophthalmia, and inducing promptly the return of vigorous growbh in rats which had declined in weight on basal diets deficient in vitamin A.