Turning everyday eggs into powerful nutrient delivery systems

From hen food to human health, researchers are uncovering the biological pathways that turn everyday eggs into powerful nutrient delivery systems.

Study: Egg-based nutrient delivery system: advances in omega-3, antioxidant and micronutrient enrichment. Image credit: sergey kolesnikov/Shutterstock.com

Eggs are nutrient-dense and nutrient-dense foods. A recent review published in the journal Frontiers in Nutrition examines egg enhancement approaches that could lead poultry farmers and poultry feed producers to produce functional eggs.

Import

Eggs are a very popular, relatively cheap food of animal origin with increasing global consumption. They are an excellent source of high-quality, easily digestible protein, as well as lipids, carbohydrates, vitamins and minerals.

Egg yolk and albumin are emulsifiers and can be whisked to produce foam. They also help produce gels and improve flavor, making eggs essential for many culinary and industrial processes.

Eggs efficiently transport fat-soluble and water-soluble compounds, making them ideal nutritional delivery systems for bioactive molecules. The egg yolk is a complex lipid-rich matrix that acts as an optimal carrier for multiple lipids, micronutrients and fat-soluble vitamins.

Functional eggs are enriched with one or more functionally important compounds, such as polyunsaturated fatty acids (PUFAs) such as omega-3 fatty acids, carotenoids and essential trace elements such as selenium. They could help improve nutrition at the population level, although proven health outcomes depend on dietary context and intake patterns.

Current knowledge on egg enrichment is scattered in many areas, including different types of nutrients, feeding protocols and biological outcomes. The review aims to provide a more comprehensive understanding of nutrient deposition in eggs, from absorption to yolk deposition, with antioxidant and potential health benefits largely inferred from mechanistic and observational evidence.

Egg structure

Eggs have a shell with membranes, the albumin protein, and the yolk, comprising ~10%, 63%, and 28%, respectively. About 74% of the egg is water, with proteins and lipids making up 12% each.

Proteins such as lysozyme and ootransferrin are present in both the white (albumin) and the yolk. They escape complete breakdown in the gut and provide antioxidant and antimicrobial action to the body.

Fats are concentrated in the yolk, which contains 65% triacylglycerols and 30% phospholipids such as phosphatidylcholine and phosphatidylethanolamine. These phospholipids are >90% bioavailable. They are rapidly incorporated into plasma high-density lipoproteins (HDL, “good cholesterol”) and are key regulators of fat metabolism.

Hens lack the enzymes required to efficiently convert the precursors into PUFAs. Food enrichment with omega-3 fatty acids and other bioactives (carotenoids such as lutein and fat-soluble vitamins A, D, E and K) leads to their deposition in the yolk.

Factors that make eggs unique functional delivery systems for such compounds include:

• Rapid dose-dependent response of yolk to manipulation of chicken feed
• Balanced yolk lipid profile
• Stable lipid matrix that holds lipophilic nutrients in stable solution, enhancing their digestibility and distribution
• Preserved bioavailability, stability and physiological activity of enriched compounds
• Egg fortification may improve nutrient bioavailability compared to individual dietary supplements, although results vary by nutrient and composition
• Eggs are already staple foods with high acceptance and culinary versatility, ensuring their high absorption

Omega-3 fatty acids

Omega-3 fatty acids, such as α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are cardioprotective and neuroprotective and support cardiometabolic health, based on established biological mechanisms and epidemiological evidence.

Fish oil, flaxseed and algae are excellent sources of these fatty acids, with varying enrichment yields, aesthetic properties and oxidation resistance.

Fish oil can change the taste, unlike algal oil, and enhance oxidation, although it is the most effective source of DHA. Flaxseed is rich in ALA, which, however, is inefficiently converted to omega-3 fatty acids.

These can increase omega-3 fatty acid levels in the yolk by two to tenfold when added to poultry diets, improving the ratio of pro-inflammatory omega-6 to anti-inflammatory omega-3 fatty acids. However, excessive levels of omega-3 fatty acids can worsen lipid oxidation, causing the yolk to be enriched with antioxidants.

Lipase-mediated hydrolysis of triglycerides in the intestine produces monoacylglycerols (MAGs) and free fatty acids. Omega-3 fatty acids are much better absorbed as MAG than as free fatty acids.

After absorption, omega-3 fatty acids reach the liver and are preferentially incorporated into specific lipoproteins during assembly. Selective transport to ovarian follicles is followed by receptor-dependent yolk uptake and deposition. Fatty acid composition of the yolk reflects the lipoprotein profile of the liver, explaining the rapid response of the yolk to food enrichment.

DHA deposition is favored among dietary fatty acids due to its resistance to oxidation and its higher esterification to phospholipids, particularly phosphatidylcholine. This stays longer in the liver, promoting its packaging into lipoproteins that target the ovaries. Ovarian receptors take up DHA, mainly in yolk phospholipids, until saturation.

Antioxidants

Dietary supplements with vitamin E, folate, carotenoids, and plant-derived polyphenols increase oxidation resistance and nutritional value, potentially improving cardiovascular and cognitive health by enhancing antioxidant capacity rather than through direct therapeutic effects.

Carotenoids, including lutein, zeaxanthin, β-cryptoxanthin, and β-carotene, occur in a highly bioavailable form in eggs, compared to plant sources. They make up <1% of yolk lipids, but are responsible for the color of the yolk and the antioxidant properties of the egg.

Carotenoid enrichment of eggs can provide up to 15 times higher carotenoids in the body. The egg matrix also enhances the bioavailability of plant-based carotenoid-containing accompanying foods.

Enrichment sources include microalgae such as Spirulinayeast, bacteria, plants like marigold and basil, and carrot and tomato by-products. Crabmeal is another rich source, as is biofortified corn and other crops.

Eggs also provide about 1.1 mg of vitamin E, at 8.5% of the recommended daily allowance. Fortification can yield up to 150% of the RDA.

Antioxidant minerals such as iodine and selenium also accumulate in yolk proteins and lipids. Selenium is a component of glutathione peroxidase, a key antioxidant regulatory molecule, while iodine regulates thyroid hormone synthesis. Fortification with iron, chromium, zinc and manganese is also being investigated.

Unlike lipids, mineral deposition in yolk is a one-time event, although other individual-level factors influence its efficiency. Micronutrient deposition is also affected by mineral form, feed composition and composition, production system and hen type. More evidence is needed to support the use of micronutrient-fortified eggs for consistent clinical benefit at the population level, particularly from long-term human studies.

Future work is essential to ensure standardization of egg enrichment in bioactive deposition, feed formulation, chicken biology and production facilities. This would facilitate regulatory and research efforts and aid commercialization.

Artificial intelligence, digital feed handling and careful monitoring of chicken health could support data-driven adjustments to nutrient inputs for accurate feeding and efficient enrichment. Microbiome-related strategies such as probiotics, prebiotics, and dietary fiber could help enhance egg nutrient deposition through the gut-egg axis.

Conclusion

The authors of this review offered a mechanistic view of egg nutrient enrichment. This highlights “the potential of next-generation functional eggs as effective vehicles to improve nutrient intake and promote preventive and precise nutrition”, while emphasizing that translation into clinical outcomes requires further validation.

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