Freezing: Egg breaking, separation and pasteurization and freezing are the steps involved. Eggs are pasteurized to kill all Salmonella organisms. The usual pasteurization practice for liquid whole egg involves heat treatment at 60oC and 62oC for not less than 3 1/2 minutes. Increasing the acidity of the egg whites before pasteurization seems to protect the proteins from damage to heat.
The functional properties of raw egg whites are not altered by freezing and thawing. Frozen egg yolks become viscous and gummy on thawing unless they are mixed with sugar, salt or syrup before freezing. Freezing process destabilizes the surface of the tiny lipid protein particles (lipoprotein) in egg yolk. The fragments that are liberated then aggregate together on thawing to form a meshy type structure or gel. Cooked egg white is not stable to freezing and thawing. The gel structure of the coagulated protein is damaged by ice crystal formation. Syneresis occurs on thawing.
Cold storage: The optimal temperatures for cold storage of eggs range from 29-32 0 F ( about 0 0C to – 1 0 C). the optimal relative humidity ranges from 75-85 per cent. Good quality eggs can be kept in cold store at 29-32 0 F for about 6 months without deterioration in quality.
Before being placed in cold storage, eggs may be dipped in light mineral oil. The thin film of oil left on the eggs partially closes the pores in the shell, reducing the loss of moisture and carbon dioxide. If the oiling process is done, usually upto 12 hours, the pH of the egg will not rise appreciably on storage. This in turn minimises changes in egg white proteins particularly ovomucin and ovalbumin. It also retards the development of increased permeability in the vitelline membrane that surrounds the yolk.
Eggs can be stored satisfactorily in the home refrigerator for a few weeks. To retard moisture loss, the eggs should be stored in closed containers. Eggs broken out of the shell can be frozen for longer storage.
Drying: It is a satisfactory method for preserving eggs, either whole or as separated yolks or whites. Spray dried egg white and egg yolk has long shelf lives. To retain their functional properties, as well as good color and flavour, dried whites require treatment to remove the last traces of glucose. This helps to control the Maillard reaction during storage. Dried eggs keep best if the initial moisture content is low and if they are kept in a tightly sealed container. Low storage temperatures are also important in maintaining the quality of the dried products. For reconstitution, dried egg should be sprinkled over the surface of luke-warm water, stirred to moisten and then beaten until smooth.
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