Micro-foaming of plant protein based meat analogues for tailored textural properties

Abstract

Meat-like foods based on plant protein sources are supposed to be a solution for a more sustainable sustenance of the world population while also having a great potential to reduce the impact on climate change. However, the transition from animal-based products to more climate-friendly alternatives can only be accomplished when consumers' acceptance of plant-based alternatives is high. This article introduces a novel micro-foaming process for texturized High-Moisture Meat Analogues (HMMA) conferring enhanced structural properties and a new way to tailor the mechanical, appearance and textural characteristics of such products. First, the impact of nitrogen injection and subsequent foaming on processing pressures, temperatures and mechanical energy were assessed using soy protein concentrate and injecting nitrogen fractions in a controlled manner in the range of 0 wt% to 0.3 wt% into the hot protein melt. Direct relationships between related extrusion parameters and properties of extruded HMMAs were established. Furthermore, optimized processing parameters for stable manufacturing conditions were identified. Secondly, so produced HMMA foams were systematically analyzed using colourimetry, texture analysis, X-ray micro-tomography (XRT) and by performing water and Preprint submitted to Innovative Food Science and Emerging Technologies June 17, 2023 oil absorption tests. These measurements revealed that perceived lightness, textural hardness, cohesiveness and overrun can be tailored by adapting the injected N₂ concentrations provided that the gas holding capacity of the protein matrix is high enough. Moreover, the liquid absorption properties of the foamed HMMA were greatly optimized. XRT measurements showed that the porosity at the center of the extrudate strands was the highest. The largest porosity of 53% was achieved with 0.2 wt% N₂ injection, whilst 0.3 wt% N₂ lead to destructuration of the HMMA foam structure through limited gas dispersion and wall slip layer formation. The latter can, nonetheless, be improved by adapting the processing parameters. All in all, this novel extrusion microfoaming process opens new possibilities to enhance the structural properties of plant-based HMMA and ultimately, consumers' acceptance.

Keywords: High moisture extrusion cooking; Micro-foaming; Plant proteins; Tenderness adjustment; Texturization; meat analogue.

Graphical abstract

Fig. 1

Schematic representation of a high moisture extrusion cooking (HMEC) process for the production of high-moisture meat analogues depicting the inlets of soy protein concentrate (SPC) powder, oil, water and nitrogen with arrows. The extruder screw, configured with conveying elements, kneading blocks and gear elements for optimal gas dispersion, is shown in black. The three different heating sections of the cooking process are highlighted in red below the extruder. The temperatures of the two texturing zones in the cooling die are shown in blue. Additionally, the position of pressure transducers and temperature sensors are depicted with circles and the letters P and T, respectively. The subscripts of the sensors give additional information regarding their emplacement, whereby EP stands for the extruder endplate and C1 − 3 for their relative position along the cooling die. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Bottom: Front view of transversally cut high-moisture meat analogue extrudate schematically depicting the position where cylindrical samples were cut out for μCT pore size analysis (red rectangles). Vertical and horizontal symmetry lines are shown by blue dashed lines. Top: Depiction of relative distance from sample surface to the center of the extrudate. The relative distance is a normalized fraction Z of half of the total sample height H. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Evolution of pressure, temperature and specific mechanical energy input for different injected N₂ fractions from 0 wt% to 0.3 wt% at the extruder end-plate as well as along the cooling die as depicted in Fig. 1. Subfigures (a) and (b) show the pressure and the temperatures of the extruded HMMA at the extruder end-plate and in the cooling die. Subfigure (c) depicts the change of the pressure at the end-plate along with the specific mechanical energy input for increasing gas fractions.

Fig. 4

Captures of produced high-moisture meat analogue samples with different N₂ concentrations ranging from 0 wt% to 0.3 wt% ((b) to (f)). The legend is given by the sub-image (a). Top left: Top view of high-moisture meat analogue as seen when it is exiting the cooling die; Bottom: Front view of transversally cut sample; Right: Side view of sample cut in the extrudate center. Flow direction is from top to bottom. The red bar corresponds to 1 cm. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Perceptual lightness, textural hardness and cohesiveness as well as overrun and liquid absorption characteristics of nitrogen foamed SPC-based high-moisture meat analogues. Extruded samples were soaked in tap water and canola oil prior to texture analysis and colour measurements. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 6

Images of XRT scanned HMMA samples foamed with 0%–0.3% nitrogen. Cylindrical samples were cut out at the edge of the HMMA strands as well as in the center of the band exiting the cooling die. Reconstructed 3D representations of the scans are next to 2D cuts, whereby the detected pores are shown in white.

Fig. 7

Equivalent spherical pore diameter of HMMA samples foamed with 0 wt% to 0.3 wt% N₂ during high moisture extrusion. The samples were taken at the edge (yellow box) of the extruded HMMA strand and at the center (empty box) as depicted in Fig. 2 for additional structural information. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 8

Porosity of extrusion foamed HMMA samples with N₂ fractions of 0 wt% to 0.3 wt% in subplots (a)–(e). Filled symbols depict the porosity of samples measured at the edge of the HMMA stands, empty symbols stand for samples measured in the center of the extrudate. The samples were digitally sliced into ten slices representing the relative distance to the surface of the strands. Measured sample thickness values are shown in (f).