Experimental cookery

Enzyme action. Balls and Swenson report that trypsin, a proteolytic enzyme, is found only in the thick white. Its action, i.e., protein splitting, which reduces the proportion of thick white in the egg, is speeded up by increase in temperature, its greatest activity occurring near body tempera- ture. Sharp has found that the weakening of the yolk membrane is greater in 2 days at 98.6°F. for eggs stored in air containing ordinary amounts of carbon dioxide and at 80 per cent humidity than after 5 days of storage at 77°, or 20 days of storage at 60.8°, or 100 days of storage at 35.6°F. Likewise a />H of about 9.25 may be reached in 2 days at 37°C., in 5 days at 16°, and in 10 days at 2°C. Or, in other words, carbon dioxide escapes more slowly and enzyme action is also slower at lower temperatures. The reaction of trypsin is also speeded up as the reaction becomes more alkaline, the optimum activity according to Swenson, Slocum, and James occurring at pH 8.4 to 8.8. Thus with loss of carbon dioxide from the egg, the action of the trypsin is increased. Balls and Swenson found that the action of the trypsin is decidedly speeded up by injecting enterokinase into the thick white, which also gives proof that the enzyme is trypsin, since enterokinase activates only trypsin. The thin white contains an anti-trypsin which inhibits the action of the trypsin. Therefore, when the thick and thin white are mixed together the action of the trypsin is inhibited. This mixing of the thick and thin white before freezing may be one reason for the claim made by many users of frozen eggs that frozen eggs are superior to and more uniform in quality than fresh eggs. Balls and Swenson state the amount of trypsin varies greatly in individual eggs of the same lot. Alkaline hydrolysis. Alkaline hydrolysis of proteins, the breaking down of the protein into smaller units, is also speeded up as the egg becomes more 330 EGG COOKERY alkaline by loss of carbon dioxide and as the temperature increases. Alkaline hydrolysis of protein occurs independently of enzyme action. Chemical changes and changes due to bacterial action. Slow chemical breakdown may cause off flavors and changes in eggs, but true rotting of eggs is caused by microorganisms. Eggs which are infected with a large number of molds and bacteria ordinarily do not keep well. Microorganisms cannot always be detected in eggs in the shell, yet the eggs deteriorate in storage. But, in general, eggs with clean shells are comparatively free from bacteria. Reetger found that not over 4 per cent, and usually a smaller number, of eggs with clean shells were infected with bacteria. Egg shells vary in porosity and some eggs have a few very large pores. Infection with bacteria is easier through these large pores. Eggs having dirt on the shell are most easily infected. Bryant and Sharp report that washing of such eggs is not the cause for deteriora- tion, if they are handled properly after washing. The deterioration of washed eggs is caused by bacterial infection of the egg from the dirt on the shell.