Pea protein mixtures as structuring agent in edible soft materials

Summary

Plant proteins are considered more sustainable than animal proteins. However, extracting proteins from plant seeds to obtain high purity proteins is resource-intensive since mechanical treatment of seeds, and large amounts of water are needed. Therefore, reducing the focus on high protein purity and using less processing steps could lead to a less resource-intensive protein extraction process. In such an extraction process, proteins are obtained together with non-protein components such as starch, fibers, etc. Therefore, to use the protein mixtures in foods,  their ability to create structures in foods such as forming emulsions, gels should be investigated. Therefore, this thesis aims to understand the structuring ability of pea protein mixtures in emulsion-based model soft food materials. The aim is to link fundamental protein behavior in mixtures containing different amounts of protein from 20 wt%, 50 wt%, and 85 wt% to their emulsifying and structuring functionality. The results show that to be used as emulsifying agents, pea proteins do not need any purification steps. Moreover, we show that the co-presence of starch with proteins provides additional possibilities to structure emulsion-based foods. For instance, when emulsion-gels are formed by heating, starch creates a brittle microstructure as opposed to a paste-like structure when starch is absent. The simultaneous gelation of both proteins and starch leads to an inhomogeneous gel matrix and a brittle gel network. When looking at purified proteins, we show that protein-protein interactions could be modulated using pH changes. In an acidic environment, pea proteins partially self-assemble into particles. So, they exist as both particles and as individual proteins. When such a mixture is used to emulsify oil droplets, the individual proteins stabilize the oil droplets while the particles remain in the water. These protein particles, due to hydrophobic interactions, glue oil droplets together. The gluing of oil droplets paves the way to create 3D printable emulsion materials with elasto-plastic properties. Overall, we show the ability to use pea protein mixtures in structuring soft foods by exploring their natural behavior. The results show that by understanding and exploiting the natural interaction between proteins and proteins and starch, we can expand the structuring ability of plant protein mixtures.