Eggs and Egg Products PDF

Eggs and Egg products Chapter 6 Dr Mohammad Altamimi Introduction The eggs of various birds are consumed throughout the world; however, the discussion that follows is regarding hen eggs. Eggs are a natural biological structure with shells offering protection for developing ch...

Eggs and Egg products Chapter 6 Dr Mohammad Altamimi Introduction The eggs of various birds are consumed throughout the world; however, the discussion that follows is regarding hen eggs. Eggs are a natural biological structure with shells offering protection for developing chick embryos. Eggs are considered by the World Health Organization (WHO) to be the reference protein worldwide, to which all other protein is compared. The quality and freshness of eggs is important to regulatory agencies, processors, and consumers. Physical Structure of Eggs The Whole Egg An average hen egg weighs about (57 g), which includes the weight of the yolk, white, and shell. The Yolk: An egg yolk comprises approximately 31% of the weight of an egg, all of the egg’s cholesterol and almost all of the fat. containing all of the vitamins known except vitamin C Egg yolks contain all three lipids (triglycerides) fats and oils, phospholipids, and sterols The primary phospholipid is phosphatidyl choline, or lecithin; the most well-known sterol is cholesterol found only in the yolk.  Protein in the yolk is around 10% of total egg protein. The yolk pigments, mainly xanthophylls, also carotene and lycopene, come from animal feed such as the green plants and yellow corn. The White: The egg white, also known as the albumen, comprises approximately 58% of the weight of an egg. Eggs contain a high biological value protein, which is a complete protein, with all of the essential amino acids in a well-balanced proportion. Over half of the protein in whites is ovalbumin. Egg white contains lysozyme, which is able to lyse some bacteria.  Avidin is another egg white protein. If consumed raw, the avidin binds with the vitamin biotin and renders biotin ineffective when consumed. The Shell: The shell contributes the remaining 11% weight of the whole egg. 94% of the shell is calcium carbonate. Thousands of pores run throughout these layers of the shell, with a greater number at the large end. A shell is naturally porous for a potentially developing chick inside. Washing is not recommended as it may remove the shell’s outer cuticle lining or open its pores.  Color: Egg shell color depends on the breed of hen and has no effect on egg flavor or quality, including the nutritive quality of the egg contents. Changes due to Aging: 1. Contents inside the shell shrink and the air cell enlarges due to water loss. 2. the pH rises to a more alkaline level, from 7.6 to 9.6, which allows bacterial growth. 3. Another change with age is that the chalazae cord appears less prominent. Inspections and Grading for Egg Quality: Grading involves an evaluation of the exterior shell, its shape, texture, soundness (not broken), and cleanliness, as well as the interior white and yolk and air cell size. Candling is a technique that allows a view of the shell and inside of eggs without breaking the shell; double yolks. Letter Grades: Letter grades are issued voluntarily. Letter grades are based on candled quality and may appear as shields on the egg cartons. Grade AA Grade A Grade B  Egg Size: The major factor in determining egg size is the age of the hen; an older hen produces a larger egg. Secondary factors influencing size are the breed and weight of the hen. The quality of the feed, as well as henhouse overcrowding and stress, all impact size, perhaps negatively Processing/Preservation of Eggs: Eggs are laid at a hen’s body temperature and require subsequent refrigeration. It is possible to hold an egg for 6 months in cold (0 o C) storage if the shell pores are closed. Mineral Oil: When oil is applied, it partially closes the shell pores and allows less microorganism permeability. It also allows an egg to hold more moisture, retain their CO2, and be protected against a pH rise in storage. Shell eggs may be sprayed or dipped in mineral oil on the same day they are laid. Pasteurization: Pasteurization is a process required by the FDA for all commercial liquid, dry, or frozen egg products that are out of the shell. This treatment destroys microorganisms such as Salmonella bacteria that can travel from the digestive tract and droppings of birds into the egg, causing foodborne illness infection. Eggs are pasteurized at 60-62°C for at least 3.5 minutes. Pasteurization must allow maintenance of the functional properties of the egg. Freezing: Since the eggs are broken open they must first be pasteurized prior to freezing. Uncooked whites retain their functional properties after freezing and thawing, Dehydration: water levels are reduced by techniques such as spray drying or drying on trays (producing a flaked, granular form). The dehydrated whole egg, white, yolk, or blend is then packaged in various sized packages or drums. Egg whites require the removal of glucose prior to dehydration in order to improve storage stability because, otherwise glucose in the whites leads to unacceptable browning and flavor changes. Dried eggs should be kept cold to meet food safety guidelines. Denaturation and Coagulation of egg: Denaturation occurs when a protein molecule (helical shape) unfolds, changing its nature. This is an irreversible process. Denaturation of the protein in an egg may occur due to heat, mechanical action such as beating or whipping, or an acidic pH. eggs change from translucent because light is passed between individual proteins to opaque or white. Coagulation represents the further process that occurs when denatured protein molecules form a solid mass = gel. Coagulation results in the precipitation of the protein and is usually a desirable characteristic = more available protein. Curdling may occur next. Beyond denaturation and coagulation. Egg mixture shrinks or becomes tough.  Effect of Added Ingredients on Coagulation: 1. Sugar: The addition of sugar exerts a protective effect on the egg by controlling the rate of denaturation and ultimate formation of intermolecular bonds. This is seen in the preparation of meringues. Sugar raises the temperature required for coagulation. 2. Salt: When salt is added, it promotes denaturation, coagulation, and gelation. 3. Acid Level: As the pH decreases and becomes more acidic, coagulation of the egg white occurs more readily. An older, more alkaline egg will result in less coagulation.  Egg Products And Egg Substitutes: Egg products include pasteurized, processed, refrigerated liquid, frozen, and dried eggs. Egg substitutes have no yolks and may contain 80% egg white. Generally, the “yolk” is made of corn oil, nonfat milk solids (NFMS), calcium caseinate, soy protein isolate, soybean oil, and vitamins and minerals. The egg substitute also contains no cholesterol, less fat, and more unsaturated fat than whole egg. In processing egg substitutes require less temperature.  Functional use of egg in foods: Nutritive value of egg: Eggs contain vitamins A, D, E, the water-soluble Bs, and minerals such as iron, phosphorus, and zinc as well as iodine, potassium, and sulfur. They are low in calories—75 calories per large egg. Eggs are a complete protein, with a biological value of 100 % Egg yolks contain cholesterol. Protein Digestibility-Corrected Amino Acid Score (PDCAAS) This is a method used to evaluate the quality of a protein source. It takes into account both the amino acid composition of the protein and how easily it can be digested by the human body. Egg Whites and PDCAAS: Highest Score: Egg whites have a PDCAAS of 1.0, the highest possible score. This means that they provide all the essential amino acids in the right amounts, and these amino acids are very easily digested and utilized by our bodies. Complete Protein: This makes egg whites a "complete protein," ideal for meeting our protein needs. Egg safety: Contamination Salmonella Method of production, cages or floor. Inspection