Purdue University Agricultural Extension Service Poultry Science Department Lafayette, Indiana
P-54
(Revised Feb., 1957)
Some Factors Affecting Quality Loss in Shell Eggs By J. D. Mitchell, H. J. Korslund, W. W. Marion and Wo J. Stadelman
The term "egg quality” can mean many things. To the grader, it may mean cleanliness of shell, size, color, shape, yolk condition or size of the air cell. However, the most important of the various factors, which not only determine grade but also consumer acceptance, is the condition of the albumen when the egg is broken out. Physical changes which occur in the interior quality of eggs depend to a large extent upon the external influences of temperature and humidity.
When eggs are held at too high a temperature, there is a general breaking down of the structure of the egg white, a weakening of the vitelline membrane surrounding the yolk, and an increased flattening of the yolk. Also, water often evaporates through the porous shell and the air cell enlarges.
Relative humidity of the atmosphere surrounding the shell eggs largely controls the amount of evaporation from the eggs. It is this evaporation of moisture from the eggs which causes a loss in weight and an increase in the size of the air cell. However, excessive moisture in the atmosphere may cause the eggs to become musty and moldy.
To this date, all research and practical investigations show conclusively that low temperatures are necessary for maintaining the interior quality of stored eggs. However, there is some disagreement concerning the effects of various humidities on interior quality maintenance.
Oil treating shell eggs with a light, tasteless, colorless mineral oil tends to seal the pores of the shell. This treatment retards carbon dioxide loss and similarly reduces moisture evaporation from within the egg. When carbon dioxide and water are maintained in the egg, physical and chemical changes are reduced, thus retaining the original quality of the egg for longer storage periods. However, some question concerning the effectiveness of oiling of shell eggs for maintaining quality during short term holding has now arisen.
To obtain more information relative to the effects of temperature, humidity and oiling upon interior quality, a series of studies has been conducted at Purdue University. Data were collected from 1,536 eggs relative to washing, oiling, weight loss and change in albumen quality. All the eggs were subjected to eight temperature-humidity conditions and three shell treatments. Relative humidities of 30, 50, 70, and 90 percent at temperatures of 50 / 1°F. and 74 / 1°F. were maintained with solutions of sulfuric acid and water. The shell treatments Consisted of (a) washed eggs, (b) washed and oiled eggs, and (c) nest clean eggs.
All eggs in the first experiment were trapnested from 24 hens, weighed to the nearest .01 gram, treated, stored in cast iron containers for two weeks, reweighed, and evaluated by Haugh units. Eggs for the second experiment were handled similarly to those of the first experiment except they were weighed to the nearest .1 gram and were not obtained from trapnested hens.