Pro Tip: No single ingredient will simultaneously recreate gels, emulsions and flavors imparted by eggs, but breaking down each functionality separately allows ingredient blends to start building back egg functionality for applications in baked goods.
Eggs are a staple ingredient in baked goods that serve a variety of functions, including emulsification from lecithin (a phospholipid found in the yolks), gelation from proteins found in egg whites, or color and flavor from the yolks.
However, due to the volatile and rising cost of eggs, along with concerns about their environmental impact and status as a Big Nine allergen, many bakers are working to remove eggs from their products.
Since eggs serve so many functions in baked goods, it is unlikely that a single ingredient will be able to replace eggs directly. Gelation in eggs is primarily caused by proteins in the egg whites, and if egg-free cakes using plant-based protein are dense or caving during baking, understanding the structure and interactions that occur between egg proteins during gelation is an excellent place to start solving these problems.
Egg whites make up about 58% of an egg by volume and are comprised of about 88% water, 10% protein, 0.5% carbohydrates and 1.5% of other minor soluble components.
In egg white protein, ovalbumin, ovotransferrin and ovomucoid make up about 77% of the total protein content. Ovalbumin and ovomucoid both contain 6 Cys residues, while ovotransferrin contains 30 Cys residues that can form disulfide bonds. When these proteins are heated above ~60 to 75°C (temperature of denaturation range for all three), such as during baking, these bonds break. Upon cooling, the disulfide bonds form in new organized patterns that lead to strong gels.
Gelation is also caused by hydrophobic interactions between the denatured proteins and hydrogen bonding, though these physical interactions lead to weaker gels than those which rely on disulfide bonds, such as egg whites.
When searching for suitable egg white replacers, proteins that form relatively strong and springy gels are a good place to start. These proteins are largely stabilized by disulfide bonds, and plant-based protein such as soy and hemp both contain relatively large numbers of disulfide bonds in the proteins that comprise most of their structure.
Recent work studying egg white gelation has also highlighted the importance of ovomucin, a protein that has a carbohydrate structure bound to it (glycosylated) and makes up about 1.5% of the total protein in eggs.
While ovomucin is not an abundant protein, egg white gels made without it form weak fluid gels instead of the hard-set gels egg whites are known for. It is hypothesized that the long carbohydrate that is bound to the protein allows ovomucin to form an internal scaffolding that other proteins then interact with to form a rigid and opaque gel, as you might see while frying an egg in a pan. This may suggest that identifying other glycosylated proteins that contain high levels of Cys residues for disulfide bonding could serve as a good foundation to start building gels in baked goods.
Proteins such as these may exist naturally and could be found using bioinformatic software, or ingredient companies could specifically design glycosylated pea or soy protein, functionalizing it to achieve more realistic textures in egg-free baked goods.
While no single ingredient will simultaneously recreate gels, emulsions and flavors imparted by eggs, by breaking down each functionality separately, ingredient blends can start to build back egg functionality for applications in baked goods.
(Alvarez-Ramirez, et al., 2018; Aydemir & Yemenicioğlu, 2013; J. Boye, et al., 2010; J. I. Boye, et al., 2009; Kaur & Singh, 2007; Sánchez-Vioque, et al., 1999)