How to evaluate plant proteins functional properties?

The demand for plant-based products is leading companies all over the world to invest more in research, developing products with a texture and taste that meet consumer needs. When using vegetable proteins, such as soy, pea and fava bean, it is important to know their functional properties, such as the physical-chemical features that influence the behavior of proteins when processing and consuming food. They are related to the amino acid composition, structure and conformation of proteins and other conditions such as pH and temperature.

How to properly evaluate the functional properties of plant proteins?

In the scientific literature you can find different ways, generally similar to each other, which are performed in laboratory.

Taking solubility as the first functional property, it refers to the amount of protein that dissolves in water. This functional property is very important because it affects other properties such as emulsion, foaming and gel. To measure the solubility, the protein flour is dispersed in water and subjected to a shaking condition. Then the mixture is centrifuged, separating the supernatant, liquid containing the proteins, from the flour. The solubility is then tested at different pHs, in order to understand the best condition for the proteins to pass more easily into solution. A protein with high solubility can be used to formulate drinks, such as protein shakes or children’s drinks.

On the other hand, the water holding capacity (WHC) is measured as grams of water retained per gram of flour. To evaluate this property, the protein flour is weighed and dispersed in water, approximately ten times its initial weight.  The mixture is then shaken for a fixed time, to allow the complete dispersion of the flour in water. Then it is centrifuged, in order to separate excess water which has not been absorbed by the flour. After centrifugation the flour that has absorbed the water is weighed. The water holding capacity is then calculated as the difference between dry and wet flour. The oil holding capacity (OHC) is also measured in the same way, simply by replacing oil with water in the analysis. These functional properties are intrinsically linked to the texture and mouthfeel of the food (water and fat/oil absorbtion of proteins are related with texture, mouthfeel and flavour retention of food). For example, in the formulation of pasta or bakery products the use of a high-WHC protein will be preferred to keep the dough elastic and moist, while in the creation of a meat substitute the use of an ingredient with high OHC will be better for giving the sensation of juiciness on the palate.

The emulsion capacity of a protein is its ability to create and stabilize systems made of oil and water. An emulsion can be defined as a suspension of two immiscible liquids, where one liquid is dispersed as globules in the constant phase of another liquid. The emulsion capacity of proteins can be measured as both emulsion capacity and emulsion stability. To measure the emulsion-making ability of a given protein flour, the flour is dispersed in water. Next we add a drip of oil, shaking in a vigorous and mechanical way using a high speed homogenizer. At the end, the mixture is transferred to a test tube and centrifuged, finally measuring the emulsified layer from the non-emulsified one. The emulsion capacity is given by the proportion between the volume of emulsion after centrifugation and the initial volume of emulsion after the homogenization. To measure its stability, the emulsion is subjected to a heat treatment, and after that its volume is measured.  An ingredient with a high emulsion capacity can be used in different food preparations, such as vegetable drinks, sauces, and desserts.

Foaming capacity measures the ability of a protein to form a foam and its stability over time. To assess the foaming capacity of a given protein flour, the flour is dispersed in water and then subjected to mechanical agitation. A high speed homogenizer can also be used to test this functional property. After transferring the mixture into a graduated cylinder, the foaming capacity is measured as a percentage of the volume increase. The stability over time is then evaluated based on the decrease in foam volume. A high-foaming capacity protein is recommended for many applications, for example in desserts such as mousses, whipped cream, meringues or ice cream.

Finally, the gelling capacity is measured by mixing water and flour together at different concentrations. The test tubes receive a heat treatment to help protein denaturation. During this process the proteins take on a linear structure and form networks capable of trapping water. After letting the tubes cool down, we will be able to see at what concentration the gel formation occurs. A protein having a high gelling capacity can be used for example in gluten free preparations, to replace the gluten mesh.

Did you know about the functional properties of vegetable proteins?

Protilla Finder can help you identify which plant protein best suits the formulation you want to create, associating the functional properties to the desired application.