Little known uses for eggs


Introduction

For centuries the egg was known as a perfectly packaged, portion controlled, highly nutritious food providing the most complete, and therefore the highest quality proteins, all necessary vitamins except vitamin C, and minerals. In the 1970s, however, it was identified that serum cholesterol in humans was one of the many causes of cardiovascular disease. Eggs contain dietary cholesterol, and although there has never been any scientific evidence to link egg consumption with heart disease, that link was suggested and accepted by many commentators, some doctors, and by a large percentage of the population.

This perception, exacerbated by changing lifestyle factors and a greater choice of food products, led to a decline in egg consumption. To counteract this, the egg industry invested millions of dollars in research to investigate the real relationship between cholesterol and eggs and heart disease. Recent research has confirmed what had been known for years, that egg is nature's perfect food and beneficial to consumers' health.

This intensive research program, prompted by falling consumption, led to further research into the effects of feeding programs on egg composition. Differentiated diets for laying hens can be utilized to enhance the levels of certain beneficial compounds like vitamins. In addition, studies into compounds which could be extracted from eggs for use in food sciences, nutrition, dietetics, analytical chemistry, phytochemistry, pharmacology, toxicology, biotechnology and clinical sciences also escalated.

The egg, therefore, has been re-born not only as a Functional Food i.e. one which by virtue of the presence of physiologically active components is efficacious in the prevention and/or treatment of disease and the promotion of optimal health, but as a food containing a treasure chest of products which can be utilized in many areas.


Fortified shell eggs

With adjustments to the diets of the laying hen, the profile of fatty acids, fat-soluble vitamins and minerals such as iodine, fluorine, manganese and B vitamins can be changed.

Using a flax-based diet (although others such as rapeseed, and fish oils have been used), eggs can be enriched with omega-3 and omega-6 fatty acids. Omega-3 fatty acids have been shown to reduce plasmatriglyceride levels, and have been associated with a reduced risk of heart attacks and recurrence of myocardial infarction. They also prevent heart disease by decreasing the clotting activity of platelets in the blood. Research has also shown that omega-3 fatty acids in the human diet are essential to brain function and visual acuity and are critical nutrients in neonatal development.

Vitamin E in eggs can also be enriched. In Japan, the iodine level can be enhanced, and in Korea eggs are fortified with ginseng. There is some indication that conjugated linoleic acids (CLA) have anitcarcinogenic properties (3), and research has been done enriching eggs with CLAs.


Egg shells

The use of egg shells as a dietary source of calcium for humans has been investigated. A powdered, purified product has been tested in fortification of breads and confectioneries, fruit drinks, crackers, condiments.

Egg shell calcium has been tested as an oral phosphate binder for use in low phosphate diets for e.g. patients suffering from renal failure.


Egg membranes

The protein from egg membranes adheres to and grows human skin fibroblasts and increases their production of type III collagen which is rich in the skin of infants, presumably softening the skin. This egg membrane protein is being used as an ingredient in many cosmetics.


Egg yolk

Lecithin from egg yolks is a rich source of phosphatidylcholine (PC) which is a major phospholipid component of the cellular membrane. PC also serves as a precursor of acetylcholine, a neurotransmitter. Egg PC in conjunction with vitamin B may slow the progress of, or even prevent Alzheimer's disease.

Choline is a vitamin which research indicates plays an essential role in the development of brain function and memory. Lactating mothers are recommended to increase their dietary choline intake to reduce the severity of memory defects later in life.

Lutein and zeaxanthin are found in egg yolks - their levels depending on the diet of the layers. Research has suggested that these two carotenoids reduce the risk of cataracts and age-related muscular degeneration - the leading cause of vision loss in the U.S.A. Studies also show that the bodies' anility to utilize these compounds from egg yolks is better than from green leafy vegetables.

Egg Yolk Phospholipids (EYPLs) have been defined as a natural cell membrane-refreshing nutrient. They have recently been registered in the European Community as a Novel Food.

Sialic acid derivatives from egg yolk are known to be involved in brain (neuron) functions and are also important in protecting infants from various diseases. These and sialyloligosaccharides attract attention from pharmacalogical and food chemical industries because of their potential biological functions.

Sialyloligosaccharides have been shown to be very high in mothers' milk at the time of parturition, suggesting that they play a significant role in the defence mechanisms against diseases such as pneumonia, diarrhoea, gastritis and ulcers. Sialyloligosaccharides can be extracted from egg yolk. One commercially available product containing sialyloligosaccharides is Sunsial.

Antigen specific immunoglobulins (IgY) By challenging the hen with a specific antigen (e.g. Escherichia coli), the hen will utilize her natural system to create antibodies which will not only protect her but will be passed on to the eggs she lays. Humans or other monogastric animals that eat these antibody enhanced eggs will then have an increase in this particular antibody and an increased ability to counteract the effects of the original antigen: a very effective method of administering vaccine to a population. This is known as passive immunity and it can provide immediate but short lived protection against specific diseases. This is in contrast to active immunity which primes the body to make its own antibodies and confers life-long immunity.

Sim, et al states: 'This new IgY technology opens new potential market applications in medicine, public health, veterinary medicine and food safety. A broader use of IgY technology could be applied as a biological or diagnostic tool, nutraceutical or functional food development, oral-supplementation for prophylaxis, and as pathogen-specific antimicrobial agents for infectious disease control.......This concept could serve as an alternative agent to replace the use of antibiotics, since today, more and more antibiotics are less effective in the treatment of infections, due to the emergence of drug-resistant bacteria.'

Successful results have been obtained by feeding piglets (and rabbits) egg yolk powder containing anti-E. coli antibodies. This serves as a protection against the pathogenic effects of E. coli which causes usually fatal diarrhoea in early weaned piglets.

IgYs from eggs have been used in foods e.g. passive immunization by oral administration of IgY has been effective in preventing dental caries and rotaviral diarrhoea. Some food products e.g. candies, chocolates and gums containing anti-Streptococcus mutans (a cause of tooth decay) have been used in Japan for oral care.

Egg antibodies have also been successfully tested to provide immunity against snake venom in humans, mastitis in cows, Pseudomonas aeruginosa in cystic fibrosis patients and Edwardsia tarda infection of Japanese eel.

Tests indicate that IgYs can be used to counteract some Salmonella spp.

Egg antibodies have also been extracted and used in diagnostics and affinity chromatography applications e.g. antibodies directed against ochratoxin - a mycotoxin widespread in foods and feeds - can be used to detect the presence of ochratoxins.

Work is underway to genetically alter chickens so that they produce eggs containing a large quantity of human serum albumin (HSA), a protein used in saline drips in hospitals. Currently the protein is taken from human blood plasma, but this is very costly. It is estimated that a flock of 100,00 layers could produce 5% of the world's demand for HSA.

Using transgenic chicken, research is also being done in collaboration with a number of companies and research establishments to produce egg antibodies which will fight hepatitis, melanoma and other cancers.


Egg white

Proteins from egg albumen are being researched in the preparation of biological polymer films for use in food packaging.

Cystatin found and isolated in egg white is an inhibitor of sulphydryl proteinases which are involved in muscle activity. Research indicates that cystatin is effective as an antimicrobial, and antiviral agent, and in the prevention of cerebral haemorrhage and cancer cell metastasis.

Avidin is a protein of egg white. When bound with the vitamin biotin it forms an avidin-biotin system which has been extensively used in biotechnological applications, particularly in medical diagnostics. By the 1990s, egg white Avidin had been all but replaced by the bacterial protein Streptavidin (extracted from Streptomyces), but recently a modified egg white Avidin has been created (and manufactured as NeutraLite Avidin TM) which provides a greatly improved product for applied and commercial usage.

Lysozyme is a naturally occurring enzyme which was discovered and characterized in the 1920s as having antibacterial activity against gram-positive bacteria. It attacks the cell wall of gram-positive bacteria leading to cell lysis and death. It is present in many secretions and tissues such as human tears, saliva and mother's milk, as well as viruses, bacteria, phage, plants, birds, eggs, insects, birds, reptiles and other mammalian fluids. The most readily available source is the white of hen's eggs. Lysozyme is effective against a number of bacteria responsible for infections of the human body and for the spoilage of various foods.

One of the most important commercial uses of Lysozyme is in the ripening of certain European-type cheeses. Lysozyme inhibits the growth of Clostridium tyrobutyricum - a bacterium which can be present as a contaminant in milk. The presence of Clostridium tyrobutyricum in the developing cheese has the effect of producing butyric acid which causes an off-flavour, and excess hydrogen and carbon dioxide which causes internal pressures leading to slits and cracks. Lysozyme has been used for over a decade in many European countries and has received GRAS (Generally Recognized As Safe) status from the Food and Drug Administration of the USA.

A more recent use of lysozyme is in wine preparation as a substitute for sulfites. The lysozyme inhibits lactic acid bacteria and development of malo-lactic fermentation can be controlled. This leads to better organoleptic (color and taste) properties and a better tolerance by those consumers who are sensitive to sulfites.

Lysozyme can also form synergies with other antimicrobial compounds such as nisin and the resultant compound will attack gram-negative food spoilage bacteria.

A standardized and refined preparation of Lysozyme is manufactured in Canada under the trade name Inovapure. This is marketed for use in selected processed foods to extend the shelf life by inhibiting or destroying spore forming and non spore-forming spoilage organisms.

Ovotransferrin or Conalbumin is another protein of egg white which has been used as an antimicrobial agent in food applications. More recently research has been in the treatment of HIV and in preventing periodontal disease. Lagarde reports that in Japan, immobilized ovotransferin has been used to remove iron from drinking water, as well as water for brewing, and a company in the Netherlands has filed a patent for a nutraceutical drink containing ovotransferin.

Ovalbumin is the predominant protein in egg white and is utilized in cell culture systems and in the diagnostic industry where enzymes and hormones require stability to maintain their functional integrity. It acts as a stabilizer, binding protein, transport protein and growth media supplement.


Other

For more than forty years, hatching eggs have been used as a culture medium for influenza virus to produce vaccines - particularly influenza vaccines. A small quantity of the influenza virus is injected into the developing embryo. For three days the virus multiplies in the protein-rich medium. The egg is then broken, the fluid extracted and the virus purified and split. This dead virus is used as vaccine.


Conclusion

Listed are some of the non-food products which can be obtained from eggs. Many of these are still being researched. Many are already in production. This is a growth area which will result in the discovery and production of increasing numbers of non-food products from eggs. These will provide new and improved products in many sectors, particularly in pharmaceuticals. Some of these products can be extracted from eggs without altering its fundamental structure, but many utilize the whole egg. In the coming years we can expect to see an increased demand for eggs to provide for non-food products.


Bibliography


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