In keeping with the pace of progress, changing food habits, demand for foods of animal origin and the health problems associated certain kinds of foods, food industry is evolving itself into an exciting area of functional foods which can be defined as those providing health benefits beyond basic nutrition and include whole fortified, enriched or enhanced foods having potentially beneficial effects on health when consumed as part of a varied diet on a regular basis at effective levels. Traditionally, eggs have not been regarded as a functional food because of their perceived link with adverse effects on blood cholesterol. However, research over the last 3 decades has shown that dietary cholesterol only has a small effect on plasma cholesterol levels and has little relationship to heart disease incidence. The egg is a nutritious food and is now regarded as an excellent, inexpensive, convenient and low calorie source of high quality protein and several important nutrients such as riboflavin, selenium, choline and vitamin B12.
Public demand for food products of superior health quality has generated interest in modifying fat composition and enriching poultry meat and eggs with beneficial nutrients. Meeting consumer demands is a constant challenge for the animal based food industry. Many consumers desire somewhat distinct products with respect to safety, healthfulness, freshness, taste, color, etc. To tap this market, feed companies have developed poultry feeds to produce several designer eggs which have appeared on store shelves. Modified or enriched eggs or super eggs are those in which the content has been modified from the standard eggs. These eggs may be classified as nutritionally enhanced eggs, value added eggs or processed eggs. The most commonly available modified eggs are vegetarian eggs and eggs with modified fat content. Vegetarian eggs may be produced from hens fed on grain based diets free of animal fat and by-product. However, modified fat content of the eggs are marketed as a reduced amount of cholesterol, less saturated fat, elevated amount of omega-3 fatty acid, higher vitamin E and iodine content. The level of cholesterol in modified fat eggs is 110 mg per egg in comparison to 253 mg in generic eggs, however, the organic and free range eggs are marketed as value added eggs. The nutritional content of the organic eggs will be equal to the generic eggs if the feed is of similar quality.
Strategies for nutrient enrichment of eggs
For nutrient enrichment of egg, the following factors should be considered
(a) Efficiency of nutrient transfer from feed to the egg
(b) Availability of commercial sources of effective feed forms of the nutrient
(c) Possible toxic effects of nutrients for the laying hens (vitamin A and D are toxic for birds at high levels)
(d) Amount of nutrient delivered with an egg in comparison with recommended dietary allowance (RDA)
e) Established health promoting properties of nutrients and their shortage in a modern diet.
(f) Possible interactions with assimilation of other nutrients from the egg
(g) Nutrient stability during cooking
(h) Effect of nutrient enrichment on appearance and taste (vitamin E, carotenoids and selenium do not affect egg taste but help prevent fishy taste in ω-3 eggs)
(i) Possibilities to claim health benefits by supplying vitamin E, omega-3 fatty acids, low cholesterol etc.
Each 100 g of egg contains 76.15 g moisture, 12.56 g protein, 9.51 g total lipids, 0.72 g carbohydrate, 56 mg calcium and 143 Kcal energy.
Omega -3 (ω-3) fatty acids enrichment
In the recent past, eggs have gained attention as an alternative to fish and oilseeds as a source of ω-3 fatty acids. Generally, people tend to avoid egg yolk but only yolk contains ω-3 fatty acids. The total fat content in the egg yolk cannot be altered; but its fatty acid composition can be altered by changing the type of oil used in the hen’s diet. Omega-3 is an essential fatty acid with lot of health benefits. It is found naturally in marine micro algae (Crypthecodinium cohnii) and fishes which consume these microalgae and some plants. Omega-3 is a building block for foetal development, vision and brain function. In adults, ω-3 lowers risk of heart disease and cancer of the breast, colon and prostate. Its anti-inflammatory properties help decrease occurrence of asthma and pain associated with rheumatoid arthritis. One normal egg contains only 50- 100 mg of ω-3 fatty acids which can be increased to 500 mg or more with dietary modifications in the hen’s diet. Flax seed (linseed), marine algae, fish oil and rape seed oil are added to chicken feed to increase the ω-3 fatty acid content in the egg yolk. This n-3 PUFA in egg yolk has decreased the serum triglycerides and increased the serum HDL-Cholesterol levels and also found to decrease incidence of atherosclerosis and hypertension. Studies show that by using designer eggs, the n-6 / n-3 PUFA ratio is decreased to about 1.5 from as much as 20 in regular eggs. This favourable change in designer eggs will supply about 50% of the daily requirement of n-3 PUFA to the consumers. Hence, for all especially those who don’t eat fish will probably find the most in ω-3 enriched eggs in their diet.
Diseases related to inadequate supply of ω-3 fatty acids in the diet
The diseases associated with inadequate dietary ω-3 PUFA are as follows. The imbalance of dietary ω-6: ω-3 can cause:
Atherosclerosis (hardening and narrowing of arteries due to deposits in arterial walls)
Thrombosis (blood clot within heart/blood vessels impeding blood flow)
Arrhythmia (irregular heartbeats)
Hypertension (elevated blood pressure)
Rheumatoid arthritis (degenerative disease of joints)
Visual acuity reduced (impaired vision)
Brain development affected (learning difficulties)
Cancer (breast, colon, pancreas, prostate)
Atopic dermatitis, lupus, psoriasis, migraine, multiple sclerosis
Bronchial asthma, diabetes mellitus and ulcerative colitis
Modification of fatty acid profile of eggs
The fatty acid composition of hen egg yolk can be modified through alterations in the diet. Feeding poultry with sources rich in long-chain (LC) or short chain (SC) ω-3-fatty acids increases the content of these fatty acids in egg yolk. Omega-3 PUFA like alpha linolenic acid (LNA) is found in canola oil, soybean oil, and flaxseed, walnut, spinach and mustard greens. Supplementation with ω-3 from plant sources results in much lower concentrations of LC ω-3 in the egg as this is due to oxidation of the alpha linolenic acid and its low conversion to DHA.
Herbal enriched super eggs
In these days, many eggitarians like herbal enriched eggs. Phytobiotics or plant-derived products containing several plant secondary metabolites can be used in poultry feed to improve the performance of hen and to produce herbal enriched super eggs. Chicken feed can be supplemented with herbs like garlic/onion leaves, spirulina, basil leaves, turmeric powder, citrus pulp, flaxseed, red pepper, fenugreek seeds etc. These super eggs will have a lower LDL cholesterol, immunomodulatory, antioxidant, anticarcinogenic properties and higher ω-3 fatty acids etc. For example, a normal egg has vitamin E content of 90-100 µg/g yolk whereas herbal supplemented egg has 220-240 µg/g yolk which adds to its increased antioxidant property. Therefore, overall health promotion in hens as well as possible health promotion in humans is possible by popularization of herbal enriched eggs.
Reduction in cholesterol content
Even though the dietary cholesterol is insignificantly correlated with the serum cholesterol levels, the consumers are scared of high content of cholesterol in eggs. A large egg contains about 250 mg of cholesterol and chicken meat contains about 60 mg per 100 g. Research towards lowering egg cholesterol has centred mostly on dietary and pharmacological interventions. Chromium, copper, nicotinic acid, statins, garlic, basil (tulasi), plant sterols, n-3 PUFA supplementation to chicken feed will reduce the yolk cholesterol levels significantly. The cholesterol contents can be reduced upto 110 mg by giving flax seed, methi and chromium containing diet.
Similarly, dietary linseed oil level of 2-4% or fish oil (body oil and not liver oil) 1-2% or garlic 0.5% or basil 0.3% or spirulina 0.2% or bay leaves 0.5% or nicotinic acid 200 mg/kg or neomycin 10 ppm or statins of yeast 0.5-1% or guar gum 1%, grape seed pulp/tomato pomace (lycopene) 2-5% or citrus pulp (nirangenin) 2-5% or chelated copper 200 ppm, organic chromium 2 ppm or Roselle seeds 0.5% and many more herbs in chicken diets will reduce the yolk and body cholesterol levels by 10-25%. Moreover, these substances are having synergistic effect in reducing the cholesterol levels. Hence, a combination of these supplements will be more beneficial.
Increment in antioxidant level in eggs
Egg is a rich source of natural antioxidants like vitamin-E, selenium, carotenoid pigments, flavinoid compounds, lecithin and phosvitin. These compounds will protect the fat-soluble vitamins and other yolk lipids from oxidative rancidity but their levels are not sufficient in n-3 PUFA eggs. Hence, it is essential to increase the anti-oxidant levels in the designer eggs.
The advantages of enrichment of the egg with anti-oxidants include:
- Decreased susceptibility to lipid peroxidation
- Prevention of fishy odour to the product
- Designer foods could be a good source of antioxidants in human diet
- Prevents destruction of fat-soluble vitamins
- Prevents denaturation of natural fat-soluble pigments
- Promotes the overall health of the consumers
For designer egg production, vitamin E and organic selenium can be added as anti-oxidants at levels of 200-400 mg/kg and 0.1-0.3ppm, respectively. Besides these, other anti-oxidants as chemicals and herbs may be added to prevent oxidative rancidity.
Vitamin-E enriched designer eggs
Vitamin E enriched eggs can be produced by feeding hens on diet high in vitamin E. The higher contents of vitamin E can be obtained by supplementation of poultry feed in the form of natural sources found in butter, milk, vegetable and nut oils. The extra addition of vitamin E in the diet of hens leads to the following advantages:
Vitamin E reduces free radicals in blood
Decreases risk of cancer and ageing process due to the reduction in the formation of the free radicals formation
May reduce the risk of heart disease since it is an antioxidant
Vitamin E acts as an antioxidant that results in delay of the development off odours
Immunomodulating egg production
The eggs naturally contain certain specific compound like lysozyme (G1-globulin), G2 and G3 globulin, ovomacro globulin, antibodies etc. The globulin antibodies are natural antimicrobials and immunostimulants in the egg that can be utilized in the cure of immunosuppressed patients like AIDS patient. Chicken egg is abundant in antibodies like “IgY” which is cheaper and better than mammalian immunoglobulin “IgG”. The IgY level in the egg can be increased by dietary manipulations. The functional feed rich in ω-3 fatty acids and anti-oxidants itself will increase the IgY level in the egg. Herbal supplementation will further boost the IgY level in the egg. Among the herbs, Basil leaves (Tulasi) at 0.3-0.5 % dietary level is having the highest ability to boost the IgY level in the egg. Other herbs like rosemary, turmeric, garlic, fenugreek, spirulina, aswagantha, arogyapacha etc. also possess immune-modulating properties.
Pigment enrichment of yolk and skin
The color of the yolk is a reflection of its pigment content. Natural carotenoid pigments like carotenes, xanthophylls, cryptoxanthin, zeaxanthin, lutein present in alfalfa, corn gluten meal, blue green algae – spirulina, marigold petal meal and capsicum will impart rich yellow and orange colours to the yolk. Some of the pigments are having vitamin A activity.
Most of these natural pigment sources are used in feeds at 1-5% levels to increase the yolk colour. Turmeric powder at 0.5 kg along with red chilli powder at 1 kg/tonne of feed not only improve the yolk colour but also act as anti-microbial agents and anti-oxidants. The beneficial effects of pigment enrichment in the yolk include:
It assists in preventing muscular degeneration
It is responsible for attractive colour of yolk
It acts as antioxidant and anti-carcinogenic agent
Lutein safeguards retina
Pharmaceutical designer eggs cure ailments in human beings
Researchers are producing genetically modified chickens through the genetic manipulation which are capable of producing certain pharmaceutical compounds and those compounds can be harvested through eggs like insulin which are used for treatment of diabetes. The hen, like all animals, produces antibodies to neutralize the antigens (viruses, bacteria etc.). These antibodies circulate throughout her body and are transferred to egg as protection to the developing chick. Specific antigens are now being selected and injected into hens to develop antibodies against them. In future, designer eggs may be produced which shall result in a range of antibodies for treatment against snake venoms to the countering of microorganisms which cause tooth decay.
Trace mineral enriched designer eggs
Trace minerals can also be enriched in designer eggs. Among these selenium, iodine chromium and copper have been tried. This can be achieved by the dietary manipulation of hen’s diet. These trace minerals are very important for human health because the deficiency of these trace minerals lead to development of certain deficiency disease. Normally, a hen egg contains almost about 53 μg iodine/100g of their edible portion, which is the 33% of the approximate dietary intake. However, supplementation with potassium iodide i.e., KI at the @ of 5 mg of their feed level increases the iodine content from 26 to 88 μg in 60 g hen egg and does not affect the performance of the hen.
Selenium enriched designer eggs: Now a days, selenium enriched eggs are available in about 25 countries in the world. Selenium content of eggs can be easily modified by the supplementation of organic selenium rich feed to the hens. Selenium exists in the eggs mainly in the firm of selenomethionine and the trace mineral is an important constituent of a number of functional seleno-proteins which is mandatory for normal health. Selenium deposited in eggs can decrease the incidence of cancer in humans and may help in betterment of semen quality in sub-fertile men and enhances the probability of successful conception.
Iodine-enriched designer eggs: In developing country like India, Africa, China and in many other countries of the world, some people are suffering from iodine deficiency diseases, therefore, iodine enriched eggs could be a good source of iodine in human diet. A typical egg of this type includes approximately 700 μg iodine. Eggs enriched with iodine can also reduce plasma cholesterol in humans and laboratory animals. However, these eggs may not be effective when used in low fat and low cholesterol diet by hyperlipidemic people. There are some indications of anti-inflammatory and anti-allergic properties of such eggs. To avoid this situation, apart from iodine, the eggs should be enriched with vitamin E as well.
Development of an egg enriched with Omega-3 PUFA, selenium, carotenoids and vitamin E
By manipulating the feed of laying hens, it is possible to enhance the levels of Se, vitamin E, lutein and DHA. A single designer egg could, therefore, contain 50% of the RDA of Se, 100% of the RDA of long chain n-3 PUFAs, and 150% of the RDA of vitamin E. It would also supply 1.91 mg lutein.
The major advantages of the combination of DHA and anti-oxidants in the egg yolk are:
- Vitamin E, lutein and Se protect DHA from oxidation during absorption and metabolism thereby preventing a ‘fishy’ taste formation
- Egg yolk lipids are necessary for the efficient absorption of vitamin E and lutein in human intestine (6 g lipids in the egg yolk is sufficient amount of lipids needed for an efficient absorption of vitamin E and lutein in the human intestine)
- Lutein interacts with vitamin E and phospholipids while improving egg yolk’s anti-oxidant potential and egg storability
Epilogue
The poultry sector is the most advanced sub-sector of the livestock sector in India and it has remained competitive due to adoption of the most modern production technologies including breeding, feeding and management systems. Over the last decade, designer eggs especially ω-3 enriched eggs have made substantial progress into supermarket shelves in developed countries as well as in developing countries like India. The ability to enrich eggs with ω-3 PUFA, vitamin E and selenium have provided the local egg industry with a unique opportunity to produce an innovative, premium quality and value-added product for the domestic and export market. Continued investigation in the areas of efficiency of dietary nutrient transfer, sensory evaluation and product stability are needed if significant improvements in the health quality of foods available to the consumer are to be made. Nutrient enriched poultry eggs and meat can thus play an important role as functional food for consumers. If we want to develop an industry with modified or enriched eggs it is utmost important to consider the safety and quality of such products. Such types of eggs hold a very good promise as functional foods.
Dr. J.P. Sehgal* and Dr. Chander Datt**
Dairy Cattle Nutrition Division, National Dairy Research Institute (NDRI)
