Pro Tip: Using zein can aid product developers looking to capitalize on sustainable sources of plant-based protein.

Developers of gluten-free products are still searching for suitable gluten replacements in products like bread and pasta, but no single protein has proven capable of developing the same viscoelastic dough that creates the products consumers love.

This is largely because no single protein has the ability to unfold and create long disulfide bound chains that define the gluten network when mixing wheat proteins in the presence of water.

The search is made even more complicated by other factors in gluten development, such as the role of gliadin, which provides the viscous behavior, or relaxation in wheat dough through non-covalent interactions.

In recent years, however, zein, the predominant protein found in maize (corn), has been the subject of intense research. Zein is one potential alternative in producing viscoelastic dough similar to gluten.

Zein is an attractive choice for product developers looking to capitalize on sustainable sources of plant-based protein. It is comprised of four smaller proteins (α-, β-, γ-, and δ- zein) and is a common by-product of corn starch production. This makes zein environmentally attractive, since it is an upcycled ingredient, or an ingredient which is a waste stream from another current production process.

While zein is not a silver bullet in recreating the gluten network found in wheat, several studies have shown promising results in the functionality of the protein for making viscoelastic dough that can help replace gluten in baked foods.

Figure 1: Representative structures of α-zein (left) and α/β gliadin (right) generated in AlphaFold2. Both are predominantly α-helices and contain high levels of glutamine (green), which are thought to aid in the formation of non-covalent interactions with neighboring protein molecules.

 At the molecular level, zein is mostly made up of α-helical secondary structures, which are converted to β-sheet structures during mixing, similar to the transition that occurs in gluten. This helps zein form a relatively elastic dough that is held together primarily by hydrophobic forces.

Unfortunately, the temperature of mixing must occur above the glass transition temperature (T_g) of the protein, which typically means mixers need to operate above about 95°F. Significant research has gone into different additives and methods that can help reduce the mixing temperature to still make viscoelastic zein dough.

It has been found that hydrating the zein before mixing and adding acetic acid or ethanol, reduces the T_g of zein, which allows researchers to use lower mixing temperatures for their zein dough. This may suggest that the sponge and dough method, which leads to the production of both ethanol and organic acids by yeast, would be the best method for producing gluten free dough using zein.

Loaf volume and crumb structure was also greatly improved by the addition of hydroxypropyl methylcellulose to zein dough formulas. This hydrocolloid increases the viscosity of the dough and also helps retain gas produced by yeast during fermentation, leading to better crumb structure and loaf volume.

While zein is currently still a challenging protein to develop gluten-free products around, it shows significant promise since it leads to a viscoelastic network, unlike many other plant-based proteins. Coupled with the environmental benefits, zein is worthy of additional research from product development teams in the baking industry.

Harrison Helmick is a PhD candidate at Purdue University. Connect on LinkedIn and see his other baking tips at BakeSci.com.

His research is conducted with the support of Jozef Kokini, Andrea Liceaga, and Arun Bhunia.