Eggs are used in various forms apart from just hard boiling or frying for food. In fact, the forms that eggs can be used are very many and they have very important industrial applications.
Furthermore, eggs are not always handled in the form they were laid with the shell intact, and because they are perishable or easily contaminated, proper storage is essential.
This article will examine the issues raised above with a focus on the most important processing and storage methods.
Egg Processing Methods
Eggs have very important attributes that make the industrial application possible. These attributes are thermal coagulation, foaming ability, and emulsifying effect.
Thermal coagulation: Egg white coagulates at about 62oC and yolk at about 65oC, and therefore could serve as a thickening or binding agent such as in the manufacture of custard.
Foaming ability: When the egg white is mixed together quickly (beaten/whipped) it forms a foam, which entraps air. Therefore, it is used as a leavening agent (helps introduce air) in many baked food products and salad dressings.
Emulsifying effect: Egg yolk emulsifies (breaks large oil droplets into very small or fine droplets and allows mixing with water) when mixed with oil and water and is used in the production of mayonnaise. Mayonnaise contains egg yolk, olive oil, lemon juice, vinegar, and seasonings.
Industrial egg products are manufactured in liquid, frozen, and dried forms using either whole egg (white and yolk) or white or yolk. Therefore, you can have liquid or frozen or dried whole egg; liquid or frozen or dried egg white; and liquid or frozen or dried egg yolk.
The initial preparation for any of the egg products is almost the same involving the use of fresh eggs, which are washed, dried, cracked, and the contents and shell separated before processing into the specific product whether whole, yolk, or white.
Regardless of the type of product, all are mixed properly for a uniform consistency (homogenization), purified by centrifuging, and sugar is removed in case of dried egg to prevent browning.
Dried egg products or powdered eggs are eggs that have been dehydrated (usually dried in a spray dryer) and made into a simple powder, with a texture similar to that of powdered milk.
As mentioned before the product could be powdered whole egg, yolk, or white and other ingredients may be added to enhance the flavor or the texture of the eggs.
Powdered eggs have a longer shelf life than fresh eggs and can be stored for almost 10 years it is not necessary to store the eggs under refrigeration; all that is required is a cool to moderate temperature and a dark environment.
Powdered eggs are also easier to transport, and handle (no breakage), and occupy less storage space than fresh eggs.
Frozen eggs are whole, yolk, or white that is frozen at very low temperatures after purification. The specific product is frozen at between -23 to -25oC and subsequently stored at -15oC.
This can keep for between eight to ten months. It is important to note that the composition of the yolk is such that freezing will thicken the yolk and render it useless for use later when it is thawed.
To circumvent this problem, the whole and yolk can be pre-treated with proteolytic enzymes such as papain, or a small amount of salt or sugar is added and then homogenized into a smooth consistency.
Containers used for freezing the eggs should be airtight in order to prevent having a product of low value when about to be used.
After purification, eggs to be used for liquid eggs have to be pasteurized because of pathogenic (disease-causing) microorganisms most especially Salmonella. Salt and sugar are not added to the liquid egg because it tends to increase the resistance of microorganisms to heat treatment.
Therefore, the pasteurized liquid egg is preserved by the addition of ascorbic or benzoic acid. The liquid egg can be stored under refrigeration but they have a very short shelf life of about six days.
In some countries, the egg industry is not well developed and is rudimentary. The egg products mentioned above are not produced in the country, and they have to be imported by food, confectionery, and pharmaceutical companies that may require such products.
The high cost of equipment and lack of infrastructure to process eggs industrially probably present a strong barrier to its takeoff.
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Egg Preservation and Storage Methods
Fresh eggs deteriorate rapidly during storage under ambient conditions. The reason for this rapid spoilage is that the shell is porous, which can allow the escape of carbon dioxide and moisture and entrance or contamination by bacteria, insects, etc.
Although a fresh egg is highly perishable, the shell is naturally protected by a surface coating of mucilaginous matter, which prevents for a time the entrance of these harmful organisms into the egg depending on the climate and storage conditions.
However, if this coating is removed or softened by washing or any other means, the keeping quality of the egg is much reduced.
These facts explain why many methods of preservation have not been entirely successful, and suggest that the methods employed should be based upon the idea of protecting and rendering more effective the natural coating of the shell, so that air bearing the germs that cause decomposition may be completely excluded.
Coating of the shell with a white paraffin base mineral oil containing antifungal and bacteriostatic agents have been found to aid in maintaining the quality.
A technique that has been developed preserves the eggs by a combination of washing and coating using egg washing powder and egg coating oil.
The egg washing powder has a combined detergent and sanitizing action. It lowers the bacterial load and increases shelf life, sale value, and consumer acceptability.
The egg coating oil formulation preserves the shell eggs for about 4 weeks at 25°C to 30°C and 10 days at 38°C. Eggs keep well for 12 weeks at 13°C and 24 weeks at 7°C. The primary concern is to prevent Salmonella infection.
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General methods of preservation, cleaning, handling, and storage are:
Collect eggs in an easy-to-clean container like coated wire baskets or plastic egg flats. This will prevent stains from rusted metal and contamination from other materials which are difficult to clean and disinfect.
Never cool eggs rapidly before they are cleaned. The eggshell will contract and pull any dirt or bacteria on the surface deep into the pores when cooled. Try to keep the temperature relatively constant until they are washed.
Wash eggs as soon as you collect them. This helps limit the opportunity for contamination and loss of interior quality. Washing eggs with water 10o (degrees) warmer than the egg will make the egg contents swell and push the dirt away from the pores of the egg.
If you have extremely dirty eggs, a mild detergent approved for washing eggs can be used. Never let eggs sit in water. Once the temperature equalizes the egg can absorb contaminants out of the water.
Cool and dry eggs quickly after washing. Store eggs small end down in an egg carton to keep the air cell stable and at 10-12°C and 70-75% relative humidity. Never hold eggs at or above room temperature or at low humidity more than necessary.
If eggs sit at room temperature (25°C) they can drop quickly in quality daily. Leaving eggs in a warm, dry environment will cause interior quality to drop quickly.
Do not stack (place them one above the other) eggs too high. If collecting in baskets do not stack eggs more than five layers deep. If using plastic flats do not stack more than six flats. If you stack eggs too deep you will increase breakage.
Never store eggs with materials that have an odor. Eggs will pick up the odors of apples, fish, onions, potatoes, and other food or chemicals with distinct odors.
Sell the oldest eggs first and try to use or sell all eggs before they are three weeks old.
In conclusion, the opportunity for industrial application to egg processing increases its importance as a food source. Corresponding development of processing capacity in developing countries as developed countries will be significant in contributing to solving serious food shortages existing there.
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