Pro Tip: Determining its structure can help you adjust your formula to get the most of your pea protein.

Pea protein is a trendy form of plant-based protein that is widely commercially available and appears in progressively more baked foods as part of high-protein formulations or more sustainable products. While there are several applications of pea protein, it has shown to be particularly useful in the dessert category, in part because it can form gels, foams, glazes and emulsions that help in replacing egg proteins.

However, incorporating pea protein into baked foods requires some trial and error, as product developers must contend with off-flavors and the sometimes-lacking functionality of the protein. The methods of protein isolation and product formulation impact the protein functionality in important ways.

Pea protein is in the category of pulses, which are low oil content legumes. The protein has a primary structure rich in hydrophobic amino acids; it also contains substantial amounts of lysine and glutamic acid. The secondary structure is comprised of ~40% β-sheet structures, which leads to stabilization of the protein structure through hydrogen bonding. In pea protein, these β-sheet structures form two internal pockets with hydrophobic interiors that can trap compounds that produce off-flavors through oxidation, such as hexanal.

Additionally, pea protein contains appreciable levels of lipoxygenase, which catalyze oxidation reactions, leading to additional off-flavor production during storage and processing. Due to the strong binding between the compounds that produce off-flavors in pea protein and the structure of the protein, producers employ a variety of methods to remove these compounds and deactivate the lipoxygenase enzyme, often as part of the isolation of the protein from pea flour. These include soaking the protein in acidic or alkaline conditions and adding heat to denature unwanted proteins and remove the compounds that produce off-flavors. Decreases in off-flavors can also be aided by defatting the protein. However, these processes also change the structure of the pea protein, impacting key functionalities like protein solubility, which directly impacts its ability to form gels and emulsions.

Figure 1: A – Native structure of pea protein vicilin. B – β-strand (red) region in pea vicilin where some of the compounds that produce off-flavors are thought to bind. C – Pea vicilin structure with Lysine represented in blue and glutamic acid in red. These are the amino acids that transglutaminase crosslinks to form stronger gels.

 

No matter the isolation steps, pea protein has several common features. Pea protein typically denatures around 90°C and has an isoelectric point of ~pH 4.5. This means that in gelling the pea protein, a temperature above 90°C must be reached; this temperature can increase in the presence of high levels of sugar or salt.

The isoelectric point represents the point where pea protein is least soluble, and as the pH increases or decreases from 4.5, the protein becomes more soluble, with good solubility around pH 8.0. This suggests that if it is possible to process baked foods near pH 8.0, the emulsions and gels made from pea protein will be the strongest.

Transglutaminase can also be used to induce stronger gels in pea protein by crosslinking the lysine and glutamic acid in the primary structure of the protein. This may be particularly useful in producing cakes and cookie formulations without eggs where strong gel structures are needed. This point of solubility is also key in producing egg wash glazes from pea protein.

If the protein is solubilized and thoroughly mixed, shiny edible protein films form, which can be used in producing alternative egg washes from pea protein. Glazes like these form best at relatively alkaline pH, but by extracting the protein through methods that minimize heat input and adding sorbitol or glycerol, liquids can be made near a neutral pH which set into shiny coatings when baked.

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.