Towards understanding the mechanism of fibrous texture formation during high-moisture extrusion of meat substitutes

• Published in: Journal of food engineering Vol. 242; pp. 8 - 20
• Main Authors: Sandoval Murillo, J.L., Osen, R., Hiermaier, S., Ganzenmüller, G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2019
• Subjects: High-moisture extrusion; MPM; Phase separation; Simulation; Structure formation; High-moisture extrusion; MPM; Simulation; Structure formation; Phase separation
• ISSN: 0260-8774; 1873-5770
• DOI: 10.1016/j.jfoodeng.2018.08.009

This paper investigates the physical mechanisms of structure formation during high-moisture extrusion of vegetable proteins. Our model starts from the observation that extrudates with fibrous, meat-like structures exhibit water-rich and protein-rich domains. The origin and structure of these domains is attributed to a spinodal phase-separation process which occurs upon cooling of the extrudate. We investigate the process using continuum-mechanics simulations, considering the combined effects of viscous flow, thermal diffusivity, and the mixing thermodynamics of water and protein. This multi-physics problem is numerically solved using an unconventional mesh-free approach, the material point method (MPM), combined with the Cahn- Hilliard model of phase separation. The method incorporates both Eulerian and Lagrangian aspects, and is well suited to model multicomponent flows of history-dependent materials. Our simulations show that fiber-like structures are obtained when the ratio of phase separation rate, heat conduction rate, and flow rate are matched within a narrow window. Our results predict that the shape of the temperature profile within the cooling channel determines the structure of the phase-separated state. These findings suggest that the physical mechanism which causes fibrous structure formation is given by spinodal phase separation under the influence of a temperature gradient. •This paper investigates how extrusion-cooking of vegetable proteins leads to fibrous meat-substitute products.•A thermodynamic model of phase separation is proposed and simulation is used to explain the resulting fibrous structure.•We show that both shear flow and cooling are necesary in this process for structure formation.•Our findings explain the experimentally observed narrow window of process parameters which lead to fibrous structures.