Blending Proteins in High Moisture Extrusion to Design Meat Analogues: Rheological Properties, Morphology Development and Product Properties

Abstract

High moisture extrusion (HME) of meat analogues is often performed with raw materials containing multiple components, e.g., blends of different protein-rich raw materials. For instance, blends of soy protein isolate (SPI) and another component, such as wheat gluten, are used particularly frequently. The positive effect of blending on product texture is well known but not yet well understood. Therefore, this work targets investigating the influence of blending in HME at a mechanistic level. For this, SPI and a model protein, whey protein concentrate (WPC), were blended at three different ratios (100:0, 85:15, 70:30) and extruded at typical HME conditions (55% water content, 115/125/133 °C material temperature). Process conditions, rheological properties, morphology development, product structure and product texture were analysed. With increasing WPC percentage, the anisotropic structures became more pronounced and the anisotropy index (AI) higher. The achieved AI from the extrudates with a ratio of 70:30 (SPI:WPC) were considerably higher than comparable extrudates reported in other studies. In all extrudates, a multiphase system was visible whose morphology had changed due to the WPC addition. The WPC led to the formation of a much smaller dispersed phase compared to the overlying multiphase structure, the size of which depends on the thermomechanical stresses. These findings demonstrate that targeted mixing of protein-rich raw materials could be a promising method to tailor the texture of extruded meat analogues.

Morphology Development and Flow Characteristics during High Moisture Extrusion of a Plant-Based Meat Analogue

“…At 95 • C, the structure was still dough-like, while at 125 • C, more pronounced structures were visible. An influence of temperature on the product structure could be observed for various other material systems in HME as well [11,14,15,24,55,56]: the temperature increase also resulted in more pronounced structures or led to improved textural properties (e.g., higher anisotropy index). The morphology of the extrudates was studied by cryo-imaging and is displayed in Figure 5.…”

“…Dead-stop experiments, in which the extruder is abruptly stopped and then samples are taken from different points in the extruder, could show that the formation of anisotropic structures takes place at the beginning of or in the die section [7,8]. The large influence of the die section becomes clear when the shape or orientation of the anisotropic structures is considered: these usually exhibit the V-shape of a laminar flow profile [9][10][11][12][13][14][15], which is attributed to the laminar flow (Re < 1) in the die section.…”

“…The anisotropic structures in HME were shown to originate from a multi-phase system in the extrudates [11]: according to the theory of Tolstoguzov [16,17], the thermodynamic incompatibility of the involved biopolymers, i.e., proteins and polysaccharides, leads to a phase-separated system, in which the phases differ in their biopolymer composition and local water concentration. Separated phases were found in various systems of highlyconcentrated food biopolymers [15,[18][19][20][21][22][23], also when only one raw material component was used [10,11,[23][24][25].…”

“…Based on the hypothesis that phase separation only occurs when the material cools in the die section, it was shown that the process conditions in the die section (e.g., temperature distribution) have a very large influence on the anisotropic structures in the product. Studies on the morphology development in HME are largely limited to the analysis of product morphology, whereby the clear influences of, e.g., temperature [11,24], screw speed [10], or raw material composition [10,15] could be shown. The morphology development in the process, i.e., at different points in the extruder, has only been investigated by a recently published study [7] on the HME of peanut protein biomass.…”

Comparison of the Rheological Properties of Plant Proteins from Various Sources for Extrusion Applications

“…A closed cavity rheometer has been proposed for this task [34][35][36] as it overcomes many of the limitations of conventional methods for this purpose. This device has already been applied to measure the rheological properties of diverse plant-based protein-rich raw materials [3,34,[36][37][38][39][40][41][42][43][44][45]. These studies were limited to conventional protein sources, such as soybean, wheat, and pea.…”