Lubrication ability of different plant proteins: key factors and mechanisms

Understanding the factors affecting the lubrication properties of plant proteins from different sources and suppliers is essential for optimizing their application in food products. In this study, we investigated the lubrication behavior of four commercial plant protein isolates - pea (PPI), soy (SPI), fava bean (FPI), and potato (POPI). While all tested proteins exhibited relatively poor lubrication ability, pea protein (PPI) showed the lowest friction coefficient, whereas potato protein (POPI) exhibited the highest friction. Surface adsorption analysis revealed that the more viscous and deformable protein film formed by PPI provided better lubrication than the rigid film formed by POPI. For the less dispersible proteins PPI, FPI and SPI, we separated the dispersible and non-dispersible fractions to gain insights into their contribution to lubrication. The dispersible fraction with limited aggregation (particle size <1 μm) exhibited lower friction than the more aggregated, non-dispersible fraction (particle size in the range of 70–100 μm). However, dispersibility was not the only relevant factor, as the well dispersible POPI did not provide the lowest friction. To identify key factors influencing lubrication, we evaluated fat content, particle size, and viscosity. While aggregation seemed to affect friction, principal component analysis (PCA) indicated that fat content was strongly correlated with lubrication performance, while particle size and viscosity showed weaker correlations. Notably, a larger variation in lubrication behavior was observed among proteins from different suppliers of the same source than among proteins from different sources. This highlights the substantial influence of supplier-specific factors. These differences can likely be attributed to differences in processing methods affecting protein quality. Overall, our findings indicate a need to further optimize processing techniques for commercial plant proteins, especially for applications in which lubrication is critical. • The dispersible fraction dominates the lubrication behavior of plant protein dispersions. • Better lubrication for the dispersible fraction was related to a the presence of a more viscous film. • Fat content in plant proteins has a substantial influence on lubrication ability. • More variation in friction is seen for proteins of different suppliers than for different protein sources.