Eggs are among the most commonly used ingredients in some bakery preparations, and their functionality can be challenging to replace in certain cases. In this entry, we will analyse their composition, functionality, and the various forms in which these products can be found in the market.

Morphology and Composition

We are all familiar with eggs, and we can clearly distinguish three parts. Firstly, there is an outer shell that envelops and protects them. This shell must be removed and is not used in the baked goods industry. Inside the shell, we find a more watery and transparent part, commonly known as the egg white which covers a central, more yellowish and oily zone, called the yolk. If you find a more complete diagram showing the morphology of the egg, you will see some other parts, either separation zones between the parts we are talking about, or structures to hold them together, or small areas included in these. But composition and functionality analyses tend to focus on the areas we have mentioned, and the egg products we find on the market also correspond to these areas. You can also find some treatises that differentiate different areas of the egg white, depending on their viscosity and proximity to the central part, but as we mentioned, these are not usually separated for marketing.

The composition of eggs can change depending on the size and feed of the hens, and the age and type of the hens. But roughly speaking, a size L egg usually has approximately 10% shell, 58% white and 32% yolk. In terms of nutritional composition, we must distinguish between egg whites and yolks, as their composition is very different. The egg whites are mainly made up of water (around 87-89%). However, if we dry them, we can see that most of their composition corresponds to proteins (more than 80%). Yolks, on the other hand, have a water content slightly higher than 50%, and a percentage of around 25% (50% in dry weight) of fat or lipids. If we take into account the percentages of both, the whole egg (excluding the shell) contains 75% water, 12-13% protein and 10% lipids, with very low percentages of carbohydrates, less than 1%. The yolk is also much richer in minerals, such as calcium, iron and phosphorus than the white, but has somewhat lower values of sodium and potassium. In general, the yolk contains a higher level of mineral salts than the white.

Functionality of Eggs in Baked Products

Due to their different compositions, the functionality of egg whites and yolks varies significantly and should be discussed separately.

As mentioned earlier, yolks have a high lipid content, and their functionality is similar to other lipids with similar melting ranges. They contribute to moistness in products where they are incorporated and possess emulsifying properties that aid in the formation of mixtures between fat and water. However, the most crucial functionality of yolks is often associated with providing colour and flavour to the products. Yolks impart a pleasant yellow-orange colour, enhancing the crumb colour in cakes and other baked goods. The flavour of yolks is also typically well-received. To substitute egg yolks in products, one might need to use blends of lipids, emulsifiers, colorants, and flavours to replicate these characteristics successfully.

On the other hand, egg whites, being predominantly composed of proteins, contain unique proteins with specific functionalities that are challenging to find in other protein sources. Egg white proteins have excellent foaming properties, crucial for entrapping air in the form of small bubbles during whipping. This functionality is essential in the preparation of angel cake or sponge cakes, which incorporate a substantial amount of air during whipping and generally include minimal or no leavening agents. The expansion of gases inside these cakes during baking is usually sufficient to achieve good volume and a tender, airy texture. The foaming property is also vital in making meringues, where the incorporation of small air bubbles during whipping is necessary to create an airy structure.

Apart from their foaming property, egg white proteins tend to coagulate with heat, significantly increasing their consistency. This coagulation is crucial for stabilizing foams, ensuring that meringues and batters retain air over time. The coagulation occurs during baking, contributing to the stability of these products and preventing collapse in the later stages of baking or during cooling. In products like layer cakes, pound cakes, or muffins with a fat base, the coagulation of egg proteins, along with starch gelatinization and changes in other proteins, also helps achieve the final structure and prevents collapses.

In gluten-free products, where the absence of gluten leads to crumbly and fragile textures, the inclusion of egg whites or their proteins helps achieve more cohesive textures. The binding ability of egg whites is utilized in certain cookies and other batters, such as crepe batter, although it is not always necessary. However, excessive amounts of egg white protein can result in products with an overly tough texture.

The stability of foams or batters also depends on the pH of the medium and the presence of acidic salts. Manufacturers can manipulate these parameters to achieve products with distinct functionalities. While adjusting the pH in a given formulation is often challenging, changes can influence these characteristics.

It’s important to note that egg white protein is highly soluble and has limited thickening power compared to most plant proteins. These proteins also exhibit a certain emulsifying ability. Additionally, egg white is considered to have a humectant effect, reducing moisture loss in cakes.

Both egg white and yolk, whether alone or mixed with other substances such as salt or milk, are used to add gloss to certain products by spraying or “painting” them, typically before baking. The final colour of the products depends on the type of egg product used and the specific blends employed. Egg white is also an effective “glue,” used to help other substances like nuts or seeds adhere to the surface of dough or final products.

Issues in Egg Usage

The primary concern with using eggs lies in the potential for microbial and toxic contamination. The eggshell is a permeable layer that allows the passage of gases, and certain microorganisms can enter the egg through this membrane. While the egg is a complex system that can inhibit microbial growth through pH changes and certain antimicrobial properties in egg white proteins, contamination with specific microorganisms can lead to their development in products where eggs are incorporated, depending on the pH and temperature of the environment. Salmonella is a particular concern in these cases due to its toxicity, leading to salmonellosis. Consequently, national regulations have sought to limit the use of raw eggs in certain types of preparations. Small bakeries often use eggs, provided that the product incorporating eggs undergoes a heat treatment ensuring the complete elimination of salmonella. For industrial uses, ensuring pasteurization is often preferred to guarantee this elimination.

The main challenge with pasteurization and other heat treatments lies firstly in the coagulation capacity (increased consistency) of egg white. Temperatures not excessively high are sufficient for this coagulation process, and any residue from this process could block the pipes or plates through which eggs circulate during their thermal treatments. Secondly, it’s important to consider that heat treatments modify the functional properties of eggs, affecting their functionality in the products they are incorporated into. In the next entry, we will explore how these problems can be addressed or at least managed.

The second major issue with eggs is their negative nutritional reputation and the presence of certain groups of people who need or prefer to eliminate them from their diets. Despite the excellent nutritional quality of egg proteins, the cholesterol content in egg yolks has always conditioned their consumption. While egg whites do not contain cholesterol, recent studies suggest that blood cholesterol is less influenced by dietary cholesterol than previously believed. In general, moderate egg consumption should not pose a problem for cholesterol levels, considering the amount of eggs used in baked products and the daily consumption of these products, unless otherwise advised by specialized medical professionals.

Egg proteins, like many proteins, can cause allergic reactions in some individuals. Those with egg allergies must exclude eggs from their diets, and manufacturers aiming to produce egg-free products must consider not only removing eggs from formulations but also eliminating the possibility of cross-contamination. In Spain, at least, the presence of egg or egg products and the potential for cross-contamination must be indicated on labels.

There is also a growing group of individuals who prefer to eliminate eggs from their diets for various reasons or beliefs, whether nutritional or environmental. Vegans, who seek to remove all animal-derived foods from their diets, are a prominent subgroup within this category. Within the vegan community, there are various groups based on their tolerance to the consumption of certain animal products, and some do not advocate for strict elimination, such as flexitarians.

Lastly, there is a group more concerned with environmental issues, being more sensitive to egg production systems, the well-being of hens, or aspects related to ecological production. While these aspects are often regulated, and it is possible to obtain organic eggs or eggs from farms where hens are not caged, for instance, using these eggs, typically more expensive, requires effectively communicating these issues to environmentally conscious consumers. It is necessary to build a significant community of potential consumers who value these issues enough to justify these practices.

It’s evident that producing egg-free products poses a challenge, especially in cakes and products like meringues. However, overcoming this challenge can attract new consumer groups, although it is currently a niche and relatively small market. In the next entry, we will discuss the different egg products available in the market.