Pro Tip: Tensiometers measure the shape of droplets and calculate surface tension, which helps describe and compare emulsifiers.
Making stable emulsions is important in many aspects of the baking industry. After bread dough is mixed and goes into the proof box, it behaves like a foam. As the gluten network expands from carbon dioxide produced by yeast, emulsifiers are needed to keep the air bubbles from collapsing. This is also true in cake formulas, where emulsifiers such as lecithin in eggs are crucial to the stability of the cake while it is rising and before starch has gelatinized.
However, some emulsifiers common in the baking industry, derived from mono- and diglycerides, do not conform to what consumers expect from clean label products, and there is a growing demand for egg-free products. The recent increase in popularity around “plant-based” foods has led many researchers and product developers to replace these emulsifiers with proteins from pea, lentil and other plants to capitalize on this growing market.
The functionality of plant-based proteins, however, is not always comparable to animal-based proteins. What tools exist to help understand why that is and ways that the functionality can be improved? One technique to better understand protein emulsion is tensiometry.
Tensiometers use a camera to record a droplet of solution, often protein in water, and calculate surface tension based on the droplet shape. Lower values of surface tension, especially for oil in water emulsions, are associated with better emulsion stability over time. In emulsions, a protein layer forms around the oil droplets, decreasing surface tension and preventing the oil droplets from coming together (coalescing).
Proteins adsorb strongly to oil droplets, leading to good stability, although this happens at a much slower pace than surfactants like DATEM. The rate of this adsorption can be seen using tensiometer readings.
Figure C shows a representative curve for a protein emulsifier. The end of the rapid decrease in surface tension takes about 10 minutes. This is why the order of addition for ingredients is so important when making emulsions with protein.
For example, if an emulsion is made by blending pea protein and xanthan gum at the same time, it will separate quickly. However, if the pea protein is blended with the oil and water first, then the xanthan gum is added, the emulsion will remain stable. The rate of adsorption can be increased by increasing protein solubility, which is highest around pH 8 in many plant-based proteins, and it can also be sped up by using smaller molecular weight proteins.
In baking with protein-based emulsifiers, it may be helpful to incorporate a pre-mixing stage with your protein-based emulsifiers, oil and water, and then adding that to batter instead of trying to mix everything at the same time.