Eggs add protein to our diets, as well as various nutrients. They supply all essential amino acids and provide several vitamins and minerals, including vitamin A, riboflavin, folic acid, vitamin B6, vitamin B12, iron calcium, phosphorus, and potassium and choline.
Chicken eggs are graded by size, for the purpose of sales. The United States Department of Agriculture sizing is based on weight per dozen. The most common size of a chicken egg is large and is the egg size commonly referred to for recipes.
Eggs are grades are labeled AA, A and B. There is no difference in nutritive value between the different grades. According to the Incredible Edible Egg website, “All eggs sold at the retail level must meet the standards for Grade B or better. Most eggs sold in supermarkets today are Grade AA or A. Grade B eggs are just as wholesome to eat, they rate lower in appearance. Few Grade-B eggs find their way to the retail supermarket. Most go to institutional egg users such as bakeries or food service operations.”
There are different types of eggs depending on the hen and her surroundings, for example:
Cage-Free Eggs
Eggs laid by hens at indoor operations, sometimes called free-roaming hens. The hens may roam in a building, room, or open area, usually in a barn or poultry house, and have unlimited access to food and water.
Free-Range Eggs
Eggs produced by hens raised outdoors or that have access to the outdoors, as weather allows. In addition to consuming a diet of grains, these hens may forage for wild plants and insects and are sometimes called pasture-fed hens.
Omega-3 Enriched Eggs
Omega-3 enriched eggs are produced by hens fed a special diet that contains 10-20% ground flaxseed. Flaxseed is higher in omega-3 fatty acids and lowers in saturated fatty acids than other grains. The results are eggs produced higher in omega-3 fatty acids. The total fat content and cholesterol level of the egg remain very similar.
Organic Eggs
Eggs produced by hens fed organic feed. The hens must have access to the outdoors and are in a cage-free environment. Organic egg producers cannot use antibiotics. Organic certification also means maintaining basic animal welfare standards.
Brown and White
There is no difference between a brown egg and a white egg except the color and breed of the bird.
When buying eggs, you want a clean egg with no cracks. Proper handling of safety is important. Only buy eggs that are refrigerated. Place them into your refrigerator immediately after arriving home. It is best to store your eggs in their cartons so that you can check the expiration date. Although, eggs are said to be safe to cook with up to 3 to 5 weeks after bringing them home. The expiration date is the date on an egg carton beyond which the eggs should not be sold. Most importantly, eggs can contain salmonella, therefore all eggs should be adequately refrigerated, properly cooked and a sanitary kitchen kept to protect yourself and your family.
http://www.incredibleegg.org/egg-facts/eggcyclopedia/b/buying
