The Incredible Edible Egg

Eggs are among the most nutritious foods on earth owing to its high proportion of calories to nutrition. An average egg has about 75 calories and has long been revered as a great source of protein along with 13 other essential nutrients. However, eggs have also been implicated in serious food borne illnesses associated with Salmonella. According to the FDA, an estimated 118,000 illnesses per year are caused by consumption of eggs contaminated with Salmonella. Here we will look at what can be done to keep eggs safe from farm to fork.

What is an egg?

A single hen produces approximately 250 to 300 eggs per year.

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The major food safety concern with eggs in recent years is the fear of Salmonella enteritidis ( Se). The bacterium is commonly found among chickens and can wind up on the outside of the egg very easily. This is the reasoning for washing and sanitizing eggs at the processing plant. Another concern is the bacteria getting inside of the egg. This can occur when the egg is forming inside of the hen’s ovary before the shell has been formed. In these cases, the bacteria grow and thrive in the nutrient rich yolk of the egg. Scientists cannot rule out the possibility of Salmonella being found in the whites either, so it is just as important to thoroughly cook the whites as well as the yolk.

Production and Quality of Eggs

Eggs come in several varieties based on color and size. The color of eggs comes from pigments in the shell, and is not any indication of quality or nutritive content. Different breeds of laying hens lay differently colored eggs. Eggs come in five sizes: small, medium, large, x-large, and jumbo. Egg size has no effect on quality, only the quantity of the liquid interior is affected.

Eggs can be purchased Organic or Free-Range, as well as conventionally raised. Organic eggs are eggs from hens fed rations having ingredients that were grown without pesticides, fungicides, herbicides or commercial fertilizers. Free-range eggs are from hens that are given access to the outdoors, either all or part of the time. No layer hen is ever hormonally treated.

The United States Department of Agriculture grades eggs on quality on a three level scale. Eggs receive a grade of AA, A, or B based on a set of criteria as shown in this table (Source: USDA).

Egg Quality

	Grade AA	Grade A	Grade B
Break Out Appearance	Covers a small area.	Covers a moderate area.	Covers a wide area.
Albumen Appearance	White is thick and stands high; chalaza prominent.	White is reasonably thick, stands fairly high; chalaza prominent.	Small amount of thick white; chalaza small or absent. Appears weak and watery.
Yolk Appearance	Yolk is firm, round and high.	Yolk is firm and stands fairly high.	Yolk is somewhat flattened and enlarged.
Shell Appearance	Approximates usual shape; generally clean,* unbroken; ridges/rough spots that do not affect the shell strength are permitted.		Abnormal shape; some slight stained areas permitted; unbroken; pronounced ridges/thin spots permitted.
Usage	Ideal for any use, but are especially desirable for poaching, frying and cooking in shell.	Ideal for any use, but are especially desirable for poaching, frying and cooking in shell.	Good for scrambling, baking, and as an ingredient in other foods.

*An egg may be considered clean if it has only very small specks, stains or cage marks. Source: USDA

	•	Grade AA: A 'Grade AA' egg will stand up tall. The yolk is firm and the area covered by the white is small. There is a large proportion of thick white to thin white.
	•	Grade A: A 'Grade A' egg covers a relatively small area. The yolk is round and upstanding. The thick white is large in proportion to the thin white and stands fairly well around the yolk.
	•	Grade B: A 'Grade B' egg spreads out more. The yolk is flattened and there is about as much (or more) thin white as thick white.

Candling: Egg processors use light to inspect eggs while in the shell. This process is called “candling,” as candles were originally used as the light source. Candling can detect such problems as blood spots, developing embryos, or other imperfections, and these eggs can then be removed from production.

Eggs begin to degrade in quality shortly after being laid. Gases can diffuse through the shell, causing the interior to oxidize and later dry out. In addition, osmosis between the yolk and the white can cause the yolk to flatten and the white to become thin and watery. To delay this from occurring, eggs are gathered after laying as soon as possible. They are immediately washed to remove dirt and microorganisms from the shell, and are dipped in hot mineral oil to provide a barrier to gas exchange. Eggs are stored below 40ºC at 80-90% humidity to further prevent degradation of the interior. Recently, egg producers have begun storing eggs in a controlled atmosphere, in carbon dioxide. This gas does not diffuse through the shell, and therefore does not cause the egg to oxidize.

Eggs must be kept below 40ºC and at 80-90% humidity throughout transport. In addition to this, the fragile nature of eggs must also be taken into account. This presents several challenges for egg producers. Eggs are typically packed in recycled paper or styrofoam cartons, which protect the eggs from breakage.

What about Salmonella?

Salmonella Enteritidis is a bacterium that's found commonly in the environment. It can penetrate through egg shells, and can also be found in the reproductive tracts of layer hens. Salmonella thrives in the nutrient rich yolks of eggs. Scientists estimate that 1 in 20,000 eggs is infected with salmonella. If ingested, Salmonella can cause an intestinal infection called salmonellosis.

Salmonellosis is an infection of the intestinal tract caused by Salmonella. Sufferers of salmonellosis may experience diarrhea, fever, abdominal cramps, headache, nausea, and vomiting. Children, the elderly and persons with weakened immune systems are most vulnerable, but salmonellosis is infrequently fatal.

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What about my safety?

Egg Safety: Governmental Regulations

As stated before, Salmonella Enteritidis illness is of the greatest concern in terms of food safety and eggs. Governmental agencies take several measures to prevent contamination of eggs, dividing the egg into parts and allowing different aspects of the government to regulate the food safety practices of the eggs. Below are the specific duties each group upholds, but together they work towards a common goal through implementing the Egg Safety Action Plan. This plan has an overall goal of eliminating SE illnesses from eggs by 2010, through identifying certain systems and practices that must be followed by egg producers.

US Food and Drug Administration (FDA): Shell eggs

Agricultural Marketing Service (AMS): This agency performs voluntary egg-quality grading program for egg shells and carries out the egg shell surveillance program which ensures all eggs in the marketplace are as good as or better than U.S Consumer Grade B. To ensure that egg handlers and hatcheries follow the requirements, AMS visit these places four times per year. They then put a grade mark on the egg carton to show consumers that the eggs were processed following the USDA’s sanitation and manufacturing processes.

Animal and Plant Health Inspection Service (APHIS): This agency is responsible for reducing the risk of disease in flocks of laying hens. They do this through implementing the Voluntary National Poultry Improvement Plan which certifies poultry breeding stock and hatcheries that are free from certain diseases; this certification is necessary for producers to be able to ship interstate or internationally.

United States Department of Agriculture (USDA): Egg Products

Food Safety and Inspection Service (FSIS): This agency is responsible for imported shell eggs from all countries and educates consumers about safe handling of eggs.

Agriculture Research Service (ARS): This agency performs food safety research in order to study other methods of preventing the contamination of eggs. Examples include an oral vaccine for chickens to prevent infection.

What Can I do at Home?

Certain steps can be taken to prevent salmonella infection in the home.

Cracked or dirty eggs should be discarded, and not used for consumption. Eggs should not be eaten raw, and should be cooked until the whites are firm and opaque.

To prevent cross contamination, utensils used for preparation of eggs should not be used to prepare other foods.

Eggs should also be stored below 40ºC to ensure freshness and to prevent the growth of microorganisms.

Some egg producers have begun to use lasers to print an expiration date directly on eggs. This can help consumers tell which eggs are still fresh and safe.

Biosecurity Program: This program outlines the overall measures taken to reduce the chances of egg contamination reaching the consumer; it applies to all grounds and facilities.

On the farm:

Limit visitors on the farm and in the houses, restrict movement of equipment between houses, restrict movement of people between houses, and prevent stray animals from entering the houses and grounds.
Rodent and Pest Control: Due to the presence of SE in rodents, it is very important to follow appropriate monitoring methods and riding any populations of pests if and when necessary.
Cleaning and Disinfection of Houses: Proper cleaning and disinfecting are required at depopulation when an egg of house test positive. To do this the house must be clean of visible manure, dry cleaned, wet cleaned, and then disinfected with appropriate chemicals.
Refrigeration: If held on the farm for more than 36 hours after laying, eggs must be kept at 45 F or lower. This is because refrigeration has been shown to minimize the growth of SE that may be present in the eggs.

The following sources were used for reference

www.aeb.org

http://hgic.clemson.edu/