Pro Tip: Cold extrusion can increase the emulsification abilities of plant-based proteins and produce functional ingredients.
The double-digit growth in the plant-based food market has slowed in the past year. According to MarketsandMarkets, however, the now $13.3 billion market is expected to grow to $19.2 billion over the next five years, representing a compound annual growth rate of 7.7%.
This outpaces other food industry categories and is driven by an increasing number of consumers, particularly younger consumers, demanding high-protein environmentally sustainable products that meet their expectations of flavor and texture.
Plant-based proteins such as peas, lentils and soy meet consumer demand regarding environmental sustainability and protein supplementation. Still, they often lack in terms of texture when compared to animal-based proteins.
In baked goods, plant-based proteins can cause chewy or dense textures from decreases in loaf volume or collapsing cakes. These issues have led to a body of research over the past several years centered on improving the functionality of plant-based proteins.
One processing methodology that may aid in improving texture is cold extrusion, due to its ability to increase the emulsification abilities of plant-based proteins and produce functional ingredients.
Figure 1: Top - Depiction of emulsion coalescence. When oil droplets are present in water without emulsifiers, the droplets come together to form larger droplets, in part, through coalescence. Using emulsifiers can reduce oil droplet coalescence, leading to more stable and texturally appealing baked goods; Bottom - Depiction of pea protein monomers, the assumed state of cold denatured pea protein, coating an oil droplet. The protein’s hydrophobic surface area adheres to the oil droplets, leading to a stable protein layer on the oil droplet. This protein layer is positively charged at pH 3, which prevents the coated droplets from coalescing.
In cakes, muffins and other batter-based baked goods, one of the drivers of collapsing products when adding plant-based protein is poor emulsification.
For the batter to remain stable during the baking process, a homogenous blend of small oil particles must be coated by an emulsifier and evenly dispersed throughout the batter.
This is traditionally accomplished by mixing eggs, oil and sugar before adding other ingredients, where the mixing action separates the oil into small droplets that are coated by the phospholipid lecithin that is naturally present in egg yolks.
If supplementing with plant-based protein at this step, the protein competes with lecithin for interactions at the oil interface. Lecithin and the protein can also interact, decreasing the amount of functional emulsifier available in the batter. This leads to the coalescence of oil droplets and unstable products during processing.
Cold denaturation is a counter-intuitive method of protein unfolding that occurs due to a weakening of hydrophobic forces at low temperatures, leading to denaturation and the exposure of hydrophobic surface area.
This increases the attraction between oil droplets and proteins, leading to more stable emulsions along with increases in the electrostatic repulsive forces of the protein.
In a comparison of emulsions prepared with 1% pea protein solutions at pH 3 and similar solutions that had been stirred at 0.5°C for 30 minutes before emulsifying, the cold-treated protein led to significantly more stable emulsions.
Based on this data, pea protein was tempered to 60% moisture with acidified water and extruded at a barrel temperature of -20°C. It was found that in cold extrusion, pea protein could bind significantly more oil than in hot extrusion conditions; cold-extruded products could also bind more water after grinding into a powder.
These extruded protein-oil conjugates may make an interesting functional ingredient in overcoming some of the textural issues in baked goods formulated with plant-based protein.
If using “pre-emulsified” protein powders with high levels of added lipids, it may be possible to develop plant-based protein products that allow for a distribution of lipids and proteins into batters without the need to emulsify to the same extent during mixing, leading to tender textures in cakes or muffins that are less prone to collapse.
These ingredients could also be useful in formulating high-protein cream-like fillings that retain smooth and creamy textures.
While there is still much research that needs to be done to establish whether cold extrusion could help the baking industry, the preliminary results indicate this technology aids in producing stable emulsions and may find usage in high-protein baked goods or fillings that retain desirable textures that come from using fats in product formulas.
Harrison Helmick is a PhD candidate at Purdue University. You can connect with him on LinkedIn .