Fabrication of gel-like emulsions with γ-zein particles using microfluidization: Structure formation and rheological properties

In this work, gamma-zein, which is a type of cysteine rich prolamine in corn, was prepared into particles for fabricating stable gel-like emulsions. The effects of homogenization pressure (0.1-120 MPa) on structure formation and rheological properties of emulsions were systematically studied. Microscopy showed that gamma-zein particles provided stabilization at droplet interfaces, and that excess protein particles provided a particle network in continuous phase, and microfluidization significantly decreased droplet size and induced to form droplet clusters and gel-like network. With an increase of homogenization pressure, protein content adsorbed at droplet interfaces and entrapped within gel-like structure of emulsions increased, and more hydrophobic interactions and disulfide bonds between protein particles were formed. As a result, stronger gel strength of emulsions were observed, for example, apparent viscosity, storage modulus (G'), loss modulus (G "), and G'/ G " crossover strain (gamma co) increased, the frequency dependency of G' (n, G' con) decreased. Also, Lissajous curves were used to further understand the non-linear viscoelastic behavior of these emulsions. Emulsions prepared without microfluidization (control, 0.1 MPa) showed a weak gel structure with viscous-dominating behavior at high strain, while emulsions prepared with microfluidization showed predominantly elastic behavior at low strain, and plastic-dominating behavior at high strain. These findings showed that cysteine rich protein based-emulsion gels with tunable microstructure and rheological properties can be easily produced by controlling the homogenization pressure.