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Rural Industries Research & Development Corporation
High value opportunities from the chicken egg
by Dr Craig Davis and Reg ReevesAugust 2002
RIRDC Publication No 02/094 RIRDC Project No DAQ-275A
Components or properties of eggs and eggshells that show potential for commercial development include:
Egg White Products
Low allergenic egg white - by removal of ovomucoid, the
major factor causing allergic reactions to egg white. A novel method using
ethanol precipitation has been developed for producing a low ovomucoid
egg white preparation that retained much of its whippability and foam stability
characteristics. This product would thus be applicable as a new processed
food for ovomucoid-sensitive people.
Edible films - polymerised egg white protein and egg white protein can be reacted with other materials (including specific egg yolk fractions) to produce edible films.
Functional egg white - the functional properties of dried egg white can be significantly improved following heating of proteins in a dry state at 80 o C for several days. The combination of dry heating and deamidation at controlled pH offers a new approach to improve the functional properties of food proteins. Other techniques can produce egg white protein products with reduced coagulation on heating.
Egg White Proteins
Ovalbumin - a key reference protein in biochemistry.
Ovokinin - a peptide recently shown to have a vasorelaxing function that can be used in the treatment of hypertension.
Ovotransferrin - can be used to produce iron-fortified food products and has bactericidal properties (e.g. has been shown to have therapeutic properties against acute enteritis in infants).
Lysozyme Ś is used as an antimicrobial agent in various foods, either as a preservative or to control microbial processes in cheese, beer and wine production, and in antibacterial food packaging films. The dimeric form of lysozyme exhibits therapeutic, antiviral and anti-inflammatory properties.
Ovomucin - has been shown to inhibit haemagglutination by viruses, the â -subunit from ovomucin was shown to have a cytotoxic effect on cultured tumour cells.
Ovoinhibitor - this is a trypsin inhibitor that inhibits bacterial and fungal serine proteinases and chymotrypsin.
Cystatin - medical applications include antimicrobial, antiviral and insecticidal effects, the prevention of cerebral haemorrhage and the control of cancer cell metastasis. The use of cystatins results in less severe side effects than synthetic analogues. The greatest problem in utilising cystatins for medical treatments is their high cost.
Avidin - binds biotin and has been widely used in molecular biology, affinity chromatography, molecular recognition and labeling, Enzyme Linked ImmunoSorbent Assay (ELISA), histochemistry and cytochemistry.
Egg Yolk Products
Low-fat, low-cholesterol dried egg yolk - can be made
by extracting fat and cholesterol from dried egg yolk using supercritical
CO2. The by-product of this process (egg oil), which contains 4% cholesterol
and triacylglycerols with a high content of monounsaturated fatty acids,
has potential use in pharmaceutical products, cosmetics and aquaculture.
Liposomes - have a range of uses involving distribution of water-soluble substances, (e.g. vitamins, antioxidants, enzymes, etc.) in an oil based environment such as emulsification, as a transport system or as a sustained release delivery system, including pharmaceutical emulsions, pesticides, functional foods, vaccines, cosmetics and topical treatments. They can also be used as vehicles for targeting specific sites such as inflamed joints in arthritis patients.
Antibodies - eggs contain antibodies against all challenges to which the hen has been exposed.
Therefore, hens can be exposed to specific challenges to induce specific antibodies. Chicken antibodies are attractive for use in humans and animals since they do not cause inflammatory responses. They have been shown to be useful in providing protection against enteric infections, particularly in patients whose own immune system is impaired, and some inflammatory conditions. Conjugation of antibodies and drugs may be an important agent for cancer treatment.
They are also useful as biochemical reagents. If they are chemically removed and encapsulated, they are particularly resistant to pH and digestive enzymes. Some food products including candies, chocolates and gums containing anti-Streptococcus mutans IgY have been launched in the Japanese market for oral care. Antibodies produced against cholecystokinin or its receptor have been shown to increase muscle protein and decrease body fat. Although this is particularly suited for food animals, it is applicable to all animals and humans, and particularly those suffering from malnutrition, gastrointestinal disorders, eating disorders and famine.
Egg Yolk Lipids
Lecithin - recently, the demand for lecithin and phospholipids
has been increasing because of their recent cost-effective large-scale
production. The general phospholipid application areas include confectionery,
snack foods, fast foods, noodles, bakery products, margarines, dairy products,
ice cream, yoghurt, milk drinks, and meat and poultry processing. Recently,
utilisation of phospholipids has been increasing in non-food products such
as soaps, detergents, dyes, fertilisers, leather, paints, papers and textiles.
Since egg yolk phospholipids are regarded as the best quality, they are
generally used in pharmaceutical products. Egg yolk lipids are used as
a multifunctional source of arachidonic acid, docosahexaenoic acid and
cholesterol for dairy products and infant formulas. Lecithin also has antioxidant
properties.
Choline - recent trends to reduce fat in the diet have resulted in low intakes of essential phospholipids and choline. Eggs are an excellent dietary source of choline. Choline and folate are also routinely added to commercial infant formulations.
Cholesterol - intake during early infancy may be crucial for proper cell function and lipoprotein metabolism in the developing child. When cholesterol is added to infant formula the plasma cholesterol concentration and fatty acid pattern of the red cell membranes of the infants more closely matches those of breast-fed infants.
Sphingolipids - while there is no known nutritional requirement for sphingolipids, they are hydrolysed throughout the gastrointestinal tract to the same categories of metabolites that are used by cells to regulate growth, differentiation, apoptosis and other cellular functions. Studies with experimental animals have shown that feeding sphingolipids inhibits colon carcinogenesis, reduces serum LDL cholesterol and elevates HDL, suggesting that sphingolipids represent a ‚functional™ constituent of food. Additional associations among diet, sphingolipids and health are certain to emerge as more is learned about these compounds.
Phosvitin - has emulsification properties higher than those of other food proteins and also is a potent natural antioxidant. The conjugation of egg yolk phosvitin with galactomannan produces a novel macromolecular antioxidant with significantly improved emulsifying activity and emulsion stability. Phosvitin phosphopeptides were shown to be effective for enhancing the calcium binding capacity and inhibiting the formation of insoluble calcium phosphate. This suggests a potential application of phosvitin peptides as novel functional oligophosphopeptides for the prevention of osteoporosis.
Egg Yolk Carbohydrates
Sialyloligosaccharides - are likely to play their most
important role in the defence mechanisms against diseases caused by pathogenic
microorganisms including pneumonia, diarrhoea, gastritis and ulcers. Sialic
acid derivatives (gangliosides) are known to be involved in brain function
and are also important in protecting infants from various diseases. Recently,
sialic acid and sialyloligosaccharides have attracted attention from pharmacological
and food chemical industries because of their potential biological functions.
The development of a variety of industrial preparations from egg yolk has
resulted in the production of various grades of products for use in infant
formula, health foods and nutritional supplements.
Egg Yolk Pigments
Lutein and Zeaxanthin - egg yolk is a highly bioavailable
source of lutein and zeaxanthin (derived from the chicken diet), which
are antioxidants and are active in protecting against macular (eye) degeneration.
Egg Shell Proteins
Egg shell membranes - protein products which are stable
in water have been prepared from hydrolysed egg shell membrane. The growth
of normal human skin fibroblasts on egg membrane protein-coated tissue
culture dishes increased in relation to increasing egg membrane protein
concentration. The eggshell membranes contain several bacteriolytic enzymes
and other membrane components which may alter the thermal resistance of
Gram-positive and Gram-negative bacterial pathogens. A reduction in the
thermal resistance of microorganisms might lead to the use of more moderate
processes (lower heating temperatures, shorter times) resulting in lower
processing costs and improved product quality and nutrition.
Collagen - bovine and to a lesser extent human collagen are becoming relatively commonly used in a variety of applications, especially in the biomedical field. Research to produce skin and tissue replacement products made from collagen is continuing. The cost of such collagen-based products is very high but is considered economically acceptable in medical applications. However, a proportion of the population is allergic to bovine collagen and concern over the risk of mad cow disease creates a need for private, well-isolated and expensive herds. The egg shell membrane comprises about 10% collagen.
Egg Shell Minerals
Eggshell powder - is considered a good source of highly
bioavailable calcium and can also contain significant quantities of strontium,
which increases bone density in humans. The low levels of lead, aluminum,
cadmium and mercury that normally occur in egg shell may be an advantage
of eggshell powder over other natural calcium sources. Levels of microelements
(e.g. strontium and selenium) in eggshell can be improved and controlled
via the feeding of the chickens.
Calcium - in addition to its normal dietary requirement, calcium has been used as an oral phosphate binder. Patients suffering from renal failure often require oral phosphate binders to supplement other treatments to prevent hyperphosphataemia. Eggshell calcium was shown to be more efficient as an oral phosphate binder than calcium carbonate.
Egg Shell Carbohydrates
Glycosaminoglycans - have a wide range of applications
in the pharmaceutical, cosmetic and food industries, including moisturisers
in cosmetics, treatment of osteoarthritis and as an emulsifying agent in
mayonnaise and dressings.
Designer Eggs
Designer eggs produced to date include eggs enriched
in:
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