Effect of oil–water colloidal states in liquid feeds on extrudability and textural attributes of high-moisture meat alternatives†

The incorporation of lipids in the extrusion process to produce composite protein–lipid high-moisture meat alternatives is a major challenge due to slip conditions induced by the oil phase. This study investigates the impact of non-emulsified and emulsified liquid feeds – using soy protein isolate and Quillaja saponin as two different emulsifiers – at 6% oil content on the extrudability, visual appearance, textural and structural properties of a soy-based meat alternative. Homogenization pressures from 20 MPa to 140 MPa were used to achieve d_4,3 droplet sizes ranging from 1053 nm to 117 nm, respectively. The emulsions stabilized by soy protein isolate exhibited a larger droplet size at low pressures and a smaller droplet size at higher pressures compared to the emulsions containing Quillaja saponin (1053 nm vs. 659 nm at 20 MPa and 117 nm vs. 243 nm at 140 MPa, respectively). The addition of any kind of lipid feed resulted in a lower specific mechanical energy input compared to the standard with no oil. Non-emulsified oil reduced the directional protein fiber formation and enhanced the protein cross-linking into bulk strips, which resulted in significantly lower mechanical anisotropy compared to the standard. Emulsions stabilized by Quillaja saponin were able to resemble the degree of anisotropy with the smallest mean oil droplet size (243 nm) yielding a slightly higher anisotropic index than the control. Microstructural analyses revealed embedded oil droplets between protein fibers, which increased the visual fibrousness. However, only minor changes in the color measurements were observed among all treatments. The results demonstrate the potential of using emulsified liquid feeds to manufacture high-moisture meat alternatives with an incorporated oil phase by extrusion processing without losing the anisotropic character due to oil slip.