Pro Tip: Rheology is everywhere in breadmaking, but the same techniques that provide insight on gluten development can also help understand plant-based protein functionality.
Rheology has more than 100 years of history in understanding the baking process, and it is one of the most widely used techniques in the industry. In its simplest form, rheology studies the relationships between an applied stress and the resulting deformation (strain).
The baking industry uses several rheological instruments, including farinographs to gauge optimal dough hydration, bench top rheometers to study dough formation, or capillary rheometers to understand extrusion like responses of dough. These relationships are often measured using the storage and loss modulus (G’, G”), where the storage modulus is how solid-like a material is, and the loss modulus refers to how liquid-like it is.
Dough is unique because it is viscoelastic, containing both fluid- and solid-like characteristics. Rheological tools are commonly used to characterize gluten strength in flour or how dough behaves with additives such as plant-based protein, and data from rheological equipment directly relates to how dough behaves during processing at nearly every step between mixing and cooling. The reason these techniques are so successful is that stress vs. strain relationships are due to the physical structure of the material being studied, making them well-suited to characterize dough’s interactions including disulfide bonds, hydrogen bonds, electrostatic interactions and hydrophobic forces.
Since rheometers provide insight to the physical chemistry of materials, they are often used to study how gels form in plant-based proteins, such as pea, soy and zein (corn protein). Knowing the types of bonds that make up gel networks allows product developers to add ingredients that modify gel strength and manipulate the texture into creamy gels stabilized by relatively weak forces (hydrophobic/electrostatic), or stronger gels held together by disulfide and hydrogen bonds.
Pea protein, for example, forms a gel when heated above 95°C and cooled back to room temperature. Rheological measurements from bench top rheometers show pea protein gels are relatively weak (low G’) in comparison to gels made from soybeans (high G’). This is because soybeans have more Cystine amino acids that create disulfide bonds. However, both gels can be made significantly stronger by adding salt because salt reduces the repulsive forces of electrostatic interactions. This simple ingredient change strengthens the relatively weak pea protein gel and makes it slightly chewier but not quite as chewy as soy protein.
By manipulating gel interactions, plant-based protein gels can be engineered to mimic textures in fats or eggs, allowing for the reduction or elimination of these ingredients from baked goods.
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.