The Incredible Egg
Table of Contents
For centuries, eggs have provided man with a convenient, consistent, nutritious and safe source of food. Convenient, in that the egg is usually readily available, easy to transport, and possesses a relatively long "shelf life".
Consistent, in that the average egg contains approximately 6 grams of fat and 6 grams of protein, the amount and composition of which remains relatively constant from strain to strain, from year to year, regardless of diet composition.
Nutritious, in that the egg is almost completely digestible, contains most nutrients that are not only essential for life but are in a balance that fits relatively close to that required by humans. Indeed, along with milk, eggs are considered one of the almost "perfect foods".
Safe, in that with the egg's protective shell and membranes, the nutrients the egg supplies are almost completely immune to microorganism contamination and thus consumers are assured of a sterile food item. Even in the event of poor handling and /or storage, resulting in significant environmental as well as microbial challenges, the egg can still maintain its nutritional and sterile conditions much longer than many other foods, especially those of animal origin.
While over the years the poultry industry has seen significant changes in the types of birds employed, the diets fed to the birds, and the environment in which the birds have been housed, the average egg produced today is still similar in composition and quality to the egg produced many years ago.
However, there is a potential to alter the composition of an egg and significantly increase specific nutrients that are, and will be, in demand through niche markets for people who are prepared to pay a premium for them.
To date, the main alterations have been with the fat composition of the egg. While the total amount of fat in the egg is difficult to change, various fatty acids making up this fat can be altered to create value added products that, mainly for potential health related problems, have found favour with a significant number of consumers.
In the sixties, when the influence of diet on coronary problems was receiving attention, studies were undertaken in an attempt to increase the polyunsaturated fatty acids in the egg. It was demonstrated by a number of laboratories that the level of linoleic acid, an essential fatty acid for most animals, including humans, could be increased by increasing the dietary level of this fatty acid in the diet. Dr. Sim's laboratory in Alberta, pioneered the work in bringing his "Designer Eggs" to the commercial market in Canada . These eggs found a niche market not only in Canada but also in other places around the world.
Dr. Hulan, in the late 1960's , demonstrated that the level of omega-3 fatty acids could be increased in the fat of broiler chickens by feeding them fish meal. Eventually, work was initiated to try to produce eggs high in these specific fatty acids, which by now had been shown to be good fatty acids for a "healthy heart". Also according to federal government surveys, it was reported that the average Canadian's diet was low or deficient in these fatty acids. Many laboratories were involved in the studies that took place, including researchers from Alberta as well as Drs. Holub and Leeson from Guelph.
It has been shown that flax seed and canola meal were also reasonably good sources of these fatty acids. The result today is that there are a number of eggs produced with a significant increase of omega-3 fatty acids, using in most cases, 10 to 15% of flax seed in laying diets. According to reports from the industry, this niche market is still showing reasonable growth, not only in North America but other countries around the world.
The latest attempt to improve the fatty acid composition of the egg is to produce increase levels of conjugated linoleic acids (CLA). Recent medical data has demonstrated that CLA has been shown to reduce the risk of certain cancer problems as well as associated heart conditions. While the average dietary intake of an adult, as well as the suggested requirement, is not well defined, it is estimated that the average North American's intake of CLA is only approximately 25% of that required for a "healthy diet".
CLA is an acronym for a series of conjugated isomers of linoleic acid. These have the same elements, combined in the same proportions, but differ in chemical and /or physical properties.
Dairy products and the meat from ruminant animals are the richest natural sources of CLA. This is due to the fact that CLA is an intermediary product of rumen biohydrogenation of dietary lipids. The CLA content of some common foods is shown in Table 1.
Table 1. Conjugated Linoleic Acid (CLA) Content of Foods (mg/g of fat)
*(calculated from Du et.al., 1999)
A number of laboratories have conducted research in this area, especially Dr. Sell's laboratory in Iowa. One of the latest papers published from his lab has shown that while the average "regular" egg contains virtually no CLA, feeding laying hens a diet with 5% synthetic CLA resulted in eggs with approximately 15% of the yolk fat being CLA.
There is more work needed to confirm the above findings as well as to study the effect of such high dietary supplements of synthetic CLA on hen performance and "normally accepted " egg quality characteristics. Such studies are underway in several laboratories and before long eggs with relatively high levels of CLA may be available to supply niche market for those people willing to pay a premium in order to increase their intake of these beneficial fatty acids.
Du, M., D.U. Ahn, and J.L. Sell, 1999 . Effect of dietary conjugated linoleic acid on the composition of egg yolk lipids. Poultry Science 78: 1639- 1645.
Dhiman, T.R., 2000. Conjugated linoleic acid: A food for cancer prevention. Feedstuffs, May , 72: 24-32.
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