The Science of Egg pH: Egg Whites vs. Yolks
Understanding the pH of an egg requires looking at its two main components separately: the white (albumen) and the yolk. The American Egg Board clarifies that these two parts have different pH levels that also change over time.
- Egg White (Albumen): A fresh egg white is naturally alkaline, with a pH of approximately 7.6. As the egg ages, it loses carbon dioxide through the shell's pores. This loss causes a chemical reaction that increases the alkalinity of the egg white, pushing its pH up to as high as 9.2. This process is the reason why older egg whites whip more easily and have a less firm structure than fresh ones.
- Egg Yolk: In contrast to the white, a fresh egg yolk is slightly acidic, with a pH of about 6.0. As the egg ages, the yolk's pH also increases, though only slightly, reaching levels near neutral (6.4 to 6.9). This slight change is accompanied by the yolk absorbing water from the albumen, causing it to flatten and weaken the vitelline membrane.
When a whole egg is combined, its overall pH is influenced by the differing values of its parts. Because the egg white makes up about two-thirds of the total egg by volume, a whole blended egg typically falls into a neutral to slightly alkaline range, around 7.2 to 7.9.
How Egg Storage Affects Alkalinity
Proper storage is critical for maintaining an egg's freshness and, by extension, its pH. The rate at which an egg's pH changes is largely dependent on temperature.
- Refrigeration: Storing eggs in a refrigerator significantly slows down the loss of carbon dioxide. This helps preserve the quality of the thick egg white and reduces the rate at which its pH increases. A study on the effect of storage found that eggs stored under refrigeration had more stable pH values compared to those stored at warmer, ambient temperatures.
- Ambient Temperature: At room temperature, eggs lose CO2 much faster, and the albumen's alkalinity increases rapidly. For this reason, eggs are typically refrigerated in many countries to maintain quality and extend shelf life.
Comparing Different Types of Eggs
While chicken eggs are the most common, other types, like duck eggs, are sometimes noted for different pH properties.
- Chicken Eggs: As a whole food, chicken eggs are often categorized as mildly acid-forming in the body according to the Potential Renal Acid Load (PRAL) score, though they are an excellent source of complete protein. This mild acidity is balanced by consuming plenty of fruits and vegetables in a healthy diet.
- Duck Eggs: Some proponents of the alkaline diet suggest that duck eggs are more alkaline-producing than chicken eggs. Duck eggs also have a thicker shell and a higher yolk-to-white ratio, and they are sometimes used by people with chicken egg sensitivities.
The Alkaline Diet and Eggs: A Reality Check
The alkaline diet is a popular eating plan that categorizes foods as either acid-forming or alkaline-forming based on their effect after digestion. However, it is important to understand that your body's pH is tightly regulated by your kidneys and lungs and is not significantly altered by the foods you eat. The perceived health benefits of an alkaline diet are more likely a result of its emphasis on nutrient-dense foods like fruits and vegetables and its discouragement of processed foods.
Nonetheless, understanding the pH of foods like eggs can be useful for those curious about food chemistry or following specific dietary approaches. The takeaway is that while egg components have different pH values, the impact on overall body pH is negligible for most healthy individuals.
Comparison Table: Egg Components and Type
| Feature | Egg White (Albumen) | Egg Yolk | Whole Egg (Chicken) | Duck Egg |
|---|---|---|---|---|
| Initial pH | ~7.6 | ~6.0 | ~7.2-7.9 (blended) | Reportedly higher initial pH |
| pH After Storage | Rises up to 9.2 | Rises slightly to ~6.8 | Increases overall | Stays fresher longer due to thicker shell |
| Alkalinity | Naturally alkaline | Naturally acidic | Slightly acidic (metabolic effect) | Considered more alkalizing (metabolic effect) |
| Protein Source | High-quality protein | Contains protein and fats | Complete protein source | Higher in protein and fats |
Conclusion
In summary, egg whites are the only part of a chicken egg that is naturally alkaline, and their pH increases with storage. Egg yolks are acidic, though they become more neutral with age. While whole chicken eggs are often considered slightly acid-forming metabolically, the human body effectively regulates its internal pH regardless of diet. For those interested in maximizing alkaline intake, some believe duck eggs offer an advantage over chicken eggs. The most health-conscious approach is to enjoy eggs as part of a balanced diet rich in alkaline-forming fruits and vegetables, rather than focusing solely on the pH of one food item. National Cancer Institute on Alkaline Diet
