Accurate nutrient composition is valuable for the egg industry
Ever more eggs are being processed nowadays, rather than being sold fresh in shell.
In 2005, the American Egg Board (AEB) funded an updated analysis of egg products, which it published under the title Egg Products Reference Guide. I presented the results of this study at this year's International Egg Commission meeting in London.
Nine egg products were analysed including liquid/frozen whole eggs, liquid/frozen salted whole eggs, liquid/frozen yolk, liquid frozen sugared yolks, liquid/frozen salted yolks, liquid/frozen whites, dried whole eggs, dried yolks and dried stabilised whites.
Samples analysed were collected from major processors in different parts of the USA. Each product included samples from three different processors. The samples included three different lots, which were pooled. Egg products were analysed for proximate composition and cholesterol (see table) as well as vitamins, minerals, fatty acids and amino acids. Egg chemistry data including pH, fat, protein, ash, solids, and free glucose were also presented.
With respect to proximate analyses, moisture and protein content was quite comparable to previously reported values. Total fat was determined rather than total lipids. Total fat is defined as the quantitated fatty acids expressed as triglycerides. For labelling purposes, the US Food and Drug Administration requires reporting total fat. (Code of Federal Regulations 101.9). Previous analyses reported total lipids, which includes phospholipids and cholesterol. Thus, total fat of yolk, for example, will be about 3% lower than total lipids (AOAC acid hydrolysis method).
Cholesterol content of whole egg and yolk was similar to that reported previously. In a recent review of factors affecting yolk cholesterol, it was indicated that feeding reductase inhibitors (statins) to laying hens could reduce as much as 46%. However, there were concerns with the effect on nutrient composition and potential transfer of drugs to the egg. Previously, I reported that two-thirds of the cholesterol could be extracted using supercritical carbon dioxide extraction but costs were found to be excessive. Therefore, lowering of cholesterol in the egg by various approaches has not been practical. Since dietary cholesterol does not significantly affect heart disease, the cholesterol issue has become less important.
AEB's report found that fatty acid composition was comparable to previous reported data, with a 1.8 ratio of unsaturated fats to saturated fats. Egg yolk is a good source of unsaturated fats. Trans-fats in egg yolk averaged 0.24%, which means egg products can be labelled 0% trans-fats.
Vitamin content was found to be quite uniform among all processors. Lutein and zeaxanthin are two pigments that have been found to be important for preventing the eye condition, macular degeneration. Lutein and zeaxanthin in egg yolk have been observed to be more available than from vegetables such as broccoli. Choline and folic acid, which are high in eggs, have been observed to be important for memory function and foetal brain development.
With respect to mineral content, values were again found to be quite uniform. One exception was selenium. Selenium content can vary since some areas of the USA have more selenium in the soil. Amino acid analyses continue to show that eggs contain all of the essential amino acids needed in our diet. Eggs are used as a standard for measuring protein quality.
When considering egg chemistry, egg solids have been a continuing concern to processors. It is known that in-line systems may have a lower percentage of solids than off-line systems. Also, age of the hen, strain and storage may affect egg solids.
Accurate nutrient composition of eggs is valuable for our industry. Consumers are demanding more information about the composition of the foods they consume.