Gluten's role in baking: a fun and unique chemistry lesson

You’re here because you want to bake without gluten. Well, in order to successfully replace it, we have to really deep dive into its chemistry to truly understand gluten's role in baking. Let’s get to it!

Modeling gluten's proteins

Gluten is a protein in wheat, rye and barley. We’re gonna focus on wheat here, because wheat flour is what we’re most interested in replacing/mimicking. So wheat flour is about 16% protein, the main protein being gluten. That’s a bit of a misnomer though... the proteins in wheat are actually gliadin (45%) and glutenin (35%), which interact together when mixing/kneading to form this network of proteins we call “gluten.” (The other 20% protein content comes from other proteins).

Let’s back up a little bit to discuss the structure of a protein. A protein is a chain of amino acids connected together through peptide bonds. A peptide bond is a type of covalent bond that happens between the carboxyl group (-COOH) of one amino acid and the amino group (-NH₂) of another. As you can see in my diagram below, a biproduct of two amino acids bonding together to form a peptide bond is water. That’s called a dehydration reaction.

Organic chemistry diagram showing the COOH group of an amino acid and the NH2 group of another undergoing a dehydration reaction to form a peptide bond.

Gliadin is a fairly small protein, containing about 100-200 amino acids. Neighboring gliadin proteins interact by intramolecular disulfide bonds. This actually contribute to decreasing gliadin’s solubility in water, making some part of the protein hydrophobic. Being “scared” of water causes gliadin to fold and coil on itself.

Glutenin is a larger protein, 2000-20,000 amino acids long and will form aggregates as large as 10 million glutenin units! It presents itself as an elongated chain.

Model showing the two proteins in gluten. Small pink gliadin molecules are coiling, and purple glutenin molecules are linear and long.

Yeast fermentation and gases

Okay let’s take a breath! That’s a lot of information and what does it have to do with gluten's role in baking? Well, when we bake bread for example, we use yeast to make the bread rise. Yeast is a single cell organism, and like all living things, it needs food to thrive. It feeds on sugar and starch that’s in bread through a process called fermentation. Here’s the chemical equation for fermentation:

C₆H₁₂O₆ --> 2 CH₃CH₂OH + 2 CO₂

That means glucose (in the form of sugar, and broken down starches) gets eaten by yeast, and there’s ethanol and carbon dioxide gas being released. In beer brewing, we care about the ethanol. However, in bread baking, the alcohol just evaporates! What we care about is the release of carbon dioxide gas.

Gluten's role in bread making

Okay let’s go back to our two protein friends glutenin and gliadin. Let's also keep in mind this release of carbon dioxide gas. When you bake a traditional loaf of bread, you have to knead the dough to “develop the gluten.” Whatever does that mean?

The gluten structure is formed through kneading; the process keeps rearranging and aligning gliadin and glutenin until they are able to form intermolecular forces between each other’s amino acids, as well as stronger disulfide bonds between their protein complexes.

Well let’s draw a picture.

Model of pink coiled gliadin and purple elongated glutenin forming a cohesive and structural network after kneading. The gluten structure looks like an organized chess board.

If we now go back to carbon dioxide being produced during yeast fermentation, and we look at this gluten structure that was formed through kneading, we can understand how bread rises! Carbon dioxide bubbles become trapped in the gluten structure, which causes the structure to expand and rise, giving bread a beautiful airy crumb!

Model of gluten's role in baking. The gluten structure is expanding when carbon dioxide is trapped inside; next to it is a real picture of bread showing air bubbles in the crumb.

I have only just begun touching about how complex it is to replace gluten's role in baking. It is not just about choosing a gluten-free flour that has a similar protein content, like brown teff flour (15% proteins). It’s about finding flours with proteins that will interact with one another in the same way that gliadin and glutenin do. We need to replace this highly organized cohesive network that can trap carbon dioxide. In case of bread baking, we are going to have to look beyond flours for an adequate gluten replacement, towards polymers called hydrocolloids, or even deglutenized wheat starch.

If you would like more information, please check out my sources below. If you have questions or anything to add, please comment below!

Gliadin - an overview | ScienceDirect Topics

Attack of the Gluten - American Chemical Society (acs.org)

Comprehensive Comparison of Clinically Relevant Grain Proteins in Modern and Traditional Bread Wheat Cultivars - PMC (nih.gov)