Commercial plant protein isolates: The effect of insoluble particles on gelation properties

Abstract

Commercial plant protein isolates generally contain a substantial fraction of large insoluble protein particles. We study how these affect the gelation properties of heat-induced protein gels (15% w/w protein, pH 7) and used homogenization as a mean to reduce the particle size of the insoluble fraction before gelation. Three different commercial plant proteins were studied as models for isolates differing in dispersibility and size of insoluble protein particles: Fava bean (FBPI), Pea (PPI) and Mung bean (MBPI). As expected, homogenization (50 MPa, 2 cycles) reduced the particle size and improved the dry matter dispersibility of protein dispersions. We found that the (shear) storage modulus G’ and critical shear strain for fracture of gels obtained after heating were not consistently impacted by homogenization. In contrast, fracture properties in uniaxial compression were sensitive to homogenization, with homogenization leading to gels that are more resistant to fracture. Gels obtained from the isolate with the smallest fraction of insoluble particles and still contained native proteins, FBPI, were the most fracture resistant. Fluorescence microscopy indicated that the insoluble fraction remained well-dispersed in the matrix after heat-induced gelation and that homogenization led to a more homogeneous appearance of the protein networks, with smaller particles being homogeneously dispersed in the continuous background. We conclude that mechanically breaking down insoluble particles in commercial plant protein isolates contributes strongly to their functionality by reducing the number of large insoluble particles that act as effective nucleation points for hydrogel fracture.