Understanding Stabilization of Oil-in-Water Emulsions with Pea Protein─Studies of Structure and Properties.

This study investigates the stability and structure of oil-in-water emulsions stabilized by pea protein. Of the wide range of emulsion compositions explored, a region of stability at a minimum of 5% w/v pea protein and 30-50% v/v oil was determined. This pea protein concentration is more than what is needed to form a layer covering the interface. X-ray scattering revealed a thick, dense protein layer at the interface as well as hydrated protein dispersed in the continuous phase. Shear-thinning behavior was observed, and the high viscosity in combination with the thick protein layer at the interface creates a good stability against creaming and coalescence. Emulsions in a pH range from acidic to neutral were studied, and the overall stability was observed to be broadly similar independently of pH. Size measurements revealed polydisperse protein particles. The emulsion droplets are also very polydisperse. Apart from understanding pea protein-stabilized emulsions in particular, insights are gained about protein stabilization in general. Knowledge of the location and the role of the different components in the pea protein material suggests that properties such as viscosity and stability can be tailored for various applications, including food and nutraceutical products.

Pea protein [Pisum sativum] as stabilizer for oil/water emulsions.

A map of stability for various water/oil/pea protein compositions has been plotted from the numerous reported results. Two clear regions of stability were identified. High internal oil phase emulsions with 70-80%, v/v oil content stabilized by total pea protein concentration <2.5%, w/v showed stability. Low oil content of 10-30%, v/v for a range of total pea protein concentrations >0.5%, w/v have also been identified as stable. Intermediate oil content and pea protein concentrations >4% w/v are unexplored regions and are likely to be areas of fruitful future research. The wide range of stability suggests that different stabilization mechanisms could be important for different compositions and careful consideration has to be taken to avoid oversimplification. Both stabilization with particles, i.e. Pickering emulsions, and protein unfolding have been suggested as mechanisms. The diverse way of describing stability makes it difficult to intercompare results in different studies. A summary of different oil types used have been presented and several properties such as dynamic viscosity, density, the dielectric constant and interfacial tension have been summarized for common vegetable oils. The type of vegetable oil and emulsion preparation techniques were seen to have rather little effect on emulsion stability. However, the different extraction methods and processing of the pea material had more effect, which could be attributed to changing composition of different proteins and to the states of aggregation and denaturing. Careful consideration has to be taken in the choice of extraction method and an increased understanding of what contributes to the stability is desirable for further progress in research and eventual product formulation.