Thermogelation of nanoemulsions stabilized by a commercial pea protein isolate: high-pressure homogenization defines gel strength

Abstract

The impact of animal-based food production on climate change drives the development of plant-based alternatives. We demonstrate the use of colloidal thermogelation on a real nanoemulsion system to create structured gels that could be of interest for thermo-mechanical processing of next-generation plant-based food applications. We use a commercial pea protein isolate (PPI) without further purification to stabilize a 20 vol% peanut oil-in-water nanoemulsion at pH = 7 by high-pressure homogenization (HPH) and demonstrate the temperature induced gelation behavior of the nanoemulsion as a function of the HPH processing parameters. Bright-field and laser scanning confocal fluorescence microscopy reveals a diverse microstructure of the aqueous PPI dispersions, with a large amount of insoluble protein particles, cell-wall debris particles, and lipid inclusions. Sedimentation of particulates is prevented by HPH treatment and leads to a loss of the dispersion's thermogelation properties. The non-gelling PPI dispersion stabilizes nanoemulsions and the insoluble components of the PPI dispersions persist throughout the HPH processing. We perform a systematic rheological investigation of the effect of HPH processing on thermogelation and demonstrate that the number of HPH passes n and HPH pressure P control the average nanoemulsion droplet size measured by DLS at a 90° scattering angle. We show that the droplet size defines the final gel strength with a strong inverse dependence of the elastic modulus on droplet size. Furthermore, processing can lead to heterogeneously structured gels that yield over a large strain amplitude range.