Determination of plasmalogen molecular species in hen eggs

Miyazawa T, Higuchi O, Sogame R, and Miyazawa T. (2024) Determination of plasmalogen molecular species in hen eggs. Molecules

Plasmalogens are an important class of phospholipid that contain a vinyl-ether bond at the sn-1 position. This double bond causes a more compact structure and also cause these lipids to have unique characteristics and roles including scavenging radical oxygen species, membrane structure and fluidity, and vesicular fusion. A deficit or reduction in plasmalogens is associated with many diseases including Rhizomelic chondrodysplasia punctata, multiple sclerosis, Parkinson’s disease, Gaucher’s disease, and Alzheimer’s disease. It is theorized that an increase in plasmalogen levels could prevent progression of these diseases or reduce their symptoms, therefore some researchers have been looking into dietary plasmalogens. Plasmalogens can be found in a number of different foods including mussels, brown algae, beef, chicken, fish, pork, salmon, scallop, and eggs however the levels range between foods. As hen eggs are consumed all over the world, are a rich source of lipids, and are relatively inexpensive, Miyazawa et al focused on the use of hen eggs as a source of plasmalogens.

To measure the fresh weight of either component, a metal egg separator was utilized then the egg white and the yolk were determined to weigh 35.4 ± 1.9 g and 20.5 ± 1.4 g, respectively. Dry weights of the egg yolk and egg white were determined by separating the two components, freezing them at -30°C then freeze drying in a vacuum freeze dryer, and weighing. Since the egg white is 90 wt% water, its dry weight was 3.9 ± 0.3 g and the yolk was 9.8 ± 0.6 g. Using the dry weight of the egg yolk and egg white, total lipid weights were determined by extraction. The egg white had very low lipid levels at 0.2 ± 0.1 g/100 g powder egg white, while the egg yolk had 35.5 ± 0.4 g/ 100 g powder egg yolk. Because of this, the authors opted to determine the amount of each lipid type for only the egg yolk since the lipid content of the egg white was minimal. Of the total lipids in egg yolk, phospholipids made up 6.2 ± 0.3 g/100 g total lipids; glycolipids made up 0.5 ± 0.1 g/100g total lipids; and neutral lipids made up 73.9 ± 3.4 g/100g total lipids.

Electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) was used to determine the plasmalogen species within the phospholipid fraction from the egg components. Three species of ethanolamine plasmalogens (PE-Pls), 18:0/18:1-PE-Pls, 18:0/20:4-PE-Pls, and 18:0/22:6-PE-Pls, were measured. In the yolk, the most abundant species was 18:0/22:6-PE-Pls with this comprising 75.6 wt% with the total amount measured being 1292.1 ± 320.8 µg/100 g fresh weight egg yolk. In egg whites the same three PE-Pls were quantified as well as a choline plasmalogen (PC-Pls), 18:0/20:4 PC-Pls. Of the species analyzed, 18:0/20:4 PE-Pls made up 49.6 wt% and 18:0/22:6 PE-Pls were 19.2 wt% with the total amount of plasmalogens measured being 31.4 ± 10.2 µg/100 g fresh weight egg white. Using the amount of plasmalogens determined from the fresh samples and the fresh weights of the whites and the yolk components, the authors calculated that a person would ingest about 0.276 mg of total plasmalogens from one hen egg.

Miyazawa et al were interested in measuring the amount of plasmalogens that is ingested in a hen egg. Eggs have been well established as an excellent and relatively cheap source of protein and important lipids, therefore they wanted to determine how much plasmalogens are ingested when eating an egg. The authors found that, unsurprisingly, the egg white had very little plasmalogen content at 11.1 µg/35.4 g fresh weight of egg white while the egg yolk had higher levels at 264.6 µg/20.5 g fresh weight of egg yolk, totaling about 0.276 mg of plasmalogen in one egg. The research looking at whether egg consumption improves cognition is not consistent with some results showing a significant association between their consumption and improved cognition, and some depicting no association at all. One thing to note is that 0.276 mg per egg not a very large amount of plasmalogens and it has been previously demonstrated by other researchers studying beef* that cooking reduces plasmalogen levels therefore the amount consumed after preparing the eggs is likely less. Although it could prove more beneficial to intentionally consume foods with higher plasmalogen levels, especially eggs which also fulfill other nutritional needs, to achieve a clinically meaningful “dose” of plasmalogens a person would need to eat a very large volume of food. Not only would this be impractical to the person, but the population of many of these species with higher plasmalogen levels could not be sustained to provide for the entire diseased group. There are some plasmalogen supplements on the market, however they too have low reported plasmalogen levels. Another option that would offer higher plasmalogen levels are synthetic plasmalogen treatments and these would not depend on a person consuming a great amount of specific foods daily.

*Wu Y, Chen Z, Chiba H, and Hui S. (2020) Plasmalogen fingerprint alteration and content reduction in beef during boiling, roasting, and frying. Food Chemistry