Production of extruded meat substitutes based on textured soy protein

Term Paper (Advanced seminar), 2021

18 Pages, Grade: 1,0


Table of Contents

1. Introduction and aim of the study

2. Soy protein as meat substitute
2.1. Structure and function
2.2. Protein fractions
2.3. Advantages of soy protein in extrusion

3. Manufacturing processes of protein isolates, concentrates and flours

4. Extrusion process
4.1. Basics of extrusion
4.2. Extruder construction

5. Conclusion and further considerations

6. References

7. Figures

8. Tables

1. Introduction and aim of the study

Due to the steadily growing world population and the rising wealth in developing countries, the demand for proteins is increasing (Vázquez-Rowe 2020). However, it is difficult to cover the demand for proteins only with animal proteins. Furthermore, various customers attach great importance to their well-being and health, and therefore avoid eating meat for ecological, ethical and social reasons. Hence, it is of great interest to access domestic plants with protein-rich seeds for the market of meat alternatives.

On the food industry side, a trend towards the production of plant-based, protein-rich products for human consumption is emerging. In the first quarter of 2020, sales of meat substitutes in Germany increased by 37% compared to the first quarter of 2019 from just under 14.7 thousand tons to 20 thousand tons (Statistisches Bundesamt 2020).

To make consumers choose the plant-based alternative, these products need to imitate the techno-functional and sensory properties of animal products. In the 1960s, the first meat analogues using an extruder were produced from common proteins like soybean protein (Osen et al. 2014). However, extrusion is a very complex process in which numerous parameters interact with each other. The effects of different material, machine and process parameters on the physical properties of the end product are very difficult to predict. For this reason, food extrusion is still carried out according to the "trial-and-error" principle (Schuchmann and Danner 2000). Among other things, this leads to a high loss of raw materials and efficiency.

The aim of this work is therefore to provide the fundamentals of extrusion. This includes an in-depth understanding of the structure and composition of plant proteins. Based on this, the production of the raw materials is discussed, as this has a great influence on the final product. In the last step, the difference between high moisture extrusion and low moisture extrusion is explained, as well as the general set-up of an extruder.

2. Soy protein as meat substitute

Along with carbohydrates and fat, proteins make up a large part of our diet as they provide the necessary building blocks for protein biosynthesis. Plant proteins are often used as the basis for meat substitutes. Sales are not only driven by environmental and ethical considerations, but also by health effects. The World Health Organization (WHO) has classified red meat as potentially carcinogenic to humans. Processed meat has been linked to diabetes or diseases of the cardiovascular system. A general shift to a plant-based diet high in legumes and whole grains could reduce the global mortality rates by 6 - 10%. (Godfray et al., 2018)

Meat and fish substitutes can help to enable this transition. These products usually contain so-called textured vegetable protein (TVP) and have a protein content of 50 - 95%, depending on the source. Commonly, such products are made from soy, wheat or pea, but there also exist other native grains, oilseeds or legumes that can provide a rich source of protein. (Belitz, 2008)

Besides contributing to flavor and color, proteins provide important techno-functional properties promoting the product quality of food applications. They are able to stabilize gels or foams and form fibrillar structures. To enhance the above-mentioned physical properties and increase the nutritional content, proteins can be applied as flours, concentrates or isolates. In this way, they are used in the production of fish or meat-like foods. (Belitz, 2008)

2.1. Structure and function

Proteins, as macromolecules, play a central role in the functionality of foods and in biological systems. They are composed of amino acids linked by peptide bonds. The sequence of the amino acids determines the unique three-dimensional structure of each protein and its specific function (Khan, Siddiqi, & Salahuddin, 2017). Above a certain molecular weight, or more than 100 amino acids, it is no longer called a polypeptide but a protein (Vasudevan, Sreekumari, & Vaidyanathan, 2011).

Protein molecules take over all important structural and functional work in the body. In addition, from a nutritional point of view, there are two further reasons for the relevance of proteins. On the one hand, a varied diet covers the need for essential amino acids that cannot be synthesized by the human organism itself. For example, a high concentration of vital lysine is found in legumes. On the other hand, the supply of nitrogen ensures the formation of non-essential amino acids. Other nitrogen-containing compounds, such as nucleic acids and creatine, also depend on a regular supply of nitrogen. (Young & Pellet, 1994)

The side groups of the individual amino acids are decisive for the multitude of protein structures with the most diverse properties and functions. These are responsible for the three-dimensional molecular structure of the proteins through various interactions with each other. The basis is the so-called primary structure, thus the linear sequence of amino acids and the position of existing disulfide bonds. (Khan et al., 2017)

The primary structure is followed by the secondary structure. This is the spatial structure of the amino acid chain, which arises as a result of hydrogen bonds between neighboring functional groups. A distinction is made between the spiral α-helix and β-helical structures. Helical structures are mainly formed by amino acids with no or small side chains. However, in the β-sheet structure, the β-strands fold over each other. (Whitford, 2005)

The tertiary structure refers to the three-dimensional conformation of the entire protein. In this type of structure, amino acids are far apart in linear sequence, but are close to each other in three-dimensional view. This three-dimensionality between the individual parts of the molecule is maintained by non-covalent bonds, such as hydrophobic interactions, electrostatic interactions, or van der Waals interactions. In this context, the tertiary structure in the native protein is always the most thermodynamically stable. (Khan et al. 2017; Vasudevan et al. 2011)

When two or more peptide chains assemble to form a protein, this is known as the quaternary structure. These subunits can be similar or different, resulting in homogeneous or heterogeneous quaternary structures, respectively. The hydrophobic bonds make the greatest contribution to stabilizing the protein molecule. The interactions within the protein largely define the conformations and properties. (Khan et al. 2017; Vasudevan et al. 2011) The preceding explanations of the various protein structures are depicted in Figure 1.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1: Different levels of protein structures (Vasudevan et al., 2011, p. 31)

During the extrusion process, the bonds are broken by shear and high temperatures, resulting in a change in the tertiary and quaternary structure. During this denaturation, new bonds can be formed between the proteins as side groups come to the surface and crosslink with each other. Partial unfolding and stretching of the globular proteins result in an arrangement of the protein strands in the direction of flow. This leads to new functional properties of the proteins. (Kristiawan et al. 2018; Belitz 2008)

2.2. Protein fractions

Proteins are divided into four Osborne fractions according to their solubility behavior. A distinction is made between water-soluble albumins, globulins, which can be extracted with a sodium chloride solution and alcohol-soluble prolamins. All the proteins remaining in the residue are classified as glutelins. The storage proteins albumins and globulins originate to a large extent from the cytoplasm or other subcellular fractions, whereas prolamins and glutelins are storage proteins. (Belitz, 2008)

However, it must be mentioned that the classification of proteins according to this scheme depends on the conditions of production or seed pretreatment as well as on the type of fractionation. (González-Pérez & Vereijken, 2007)

Fractions can be separated into their major components by chromatography or ultracentrifugation. They vary in molecular weight and have different isoelectric points (IEP). This leads to a different behavior under thermomechanical stress. The solubility of the proteins is lowest at the IEP since the same amount of positive and negative charges is present there. As a result of the lack of electrostatic repulsion, the proteins aggregate via intermolecular hydrophobic bonds, insofar as sufficient exposed hydrophobic groups are present. (Belitz, 2008) The molecular weights and IEP of soy protein are presented in Table 1.

Table 1: Protein Fractions in Soy Protein

Abbildung in dieser Leseprobe nicht enthalten

The proteins of soy can be divided into three fractions: albumins, globulins and glutelins. Globulins represent the largest fraction, accounting for 70% of the total protein content (Boye et al., 2010). Two main globulins exist in all legume species, with few exceptions, and are classified based on their sedimentation coefficient as vicilin (~ 7S) and legumin (~ 11S) (Belitz, 2008; Freitas, Ferreira, & Teixeira, 2000). Legumin has a significantly higher molecular weight of 340 - 360 kDa than vicilin with 175 – 180 kDa (Swanson, 1990). These proteins generally have minimal solubility at the pH values between four and five (IEP) (Boye et al., 2010). In contrast, for example, Swanson specifies the isoelectric point of pea albumin at a pH of 6.0 (Swanson, 1990).

For basic extrusion research, it is generally important to know the IEP of the different protein fractions, since protein solubility analysis according to Morr must be performed to determine the protein binding types. The successful performance of this analysis is strongly dependent on the IEP. It is not recommended to choose the isoelectric point to perform protein solubility analysis. At this point, protein solubility is at its lowest due to increasing protein interactions, as the electrostatic forces are at their minimum and less water can interact with the protein molecules. Therefore, the protein cannot be completely dissolved in the buffer substance, which leads to a falsification of the results.

2.3. Advantages of soy protein in extrusion

In addition to extrudability, other factors must be considered for the suitability of a raw material for efficient application as a meat substitute. From an economic point of view, the market price and availability play a major role. However, the final product must also be accepted by the consumer. More and more value is placed on regionality, ecological cultivation methods and non-genetically modified plants.

For people who do not want to consume animal proteins for ethical, religious or ecological reasons, soy offers the possibility of becoming an important protein source. Soy protein convinces through its abundant worldwide availability, high nutritional quality and its diverse functional properties (Wang et al., 2004). It is an excellent source of protein and contain fiber, vitamins and minerals, while being low in sugar, sodium and fat (Kristiawan et al., 2018). Furthermore, there are many scientific studies on extrusion with soy protein and it is already widely used to make vegan substitutes without bringing a strong inherent taste like pea protein, for example.

Protein powders from soy can be divided into three different purity grades. A precise classification is made in the next chapter, but soy protein concentrate is available at lower cost than soy protein isolate due to its lower protein content and is therefore mostly involved as a main ingredient in a number of food applications (Cheftel, Kitagawa, & Quéguiner, 1992). However, soy faces an increasing consumer rejection due to its association with rainforest deforestation and the existence of several genetically modified varieties. In addition, its high allergenic potential excludes a certain group of consumers.

3. Manufacturing processes of protein isolates, concentrates and flours

The selection of the protein fractionation has a great influence on the final product. In general, a decision is drawn between three degrees of purification. A distinction is made between protein flours with less than 70% protein in dry matter (DM), protein concentrates with at least 70% protein in DM and protein isolates with at least 90% protein in DM (Eldridge 1982). In comparison to a protein concentrate with 3.5% fiber content, a protein isolate has a much lower fiber content of 0.2% (Belitz 2008). During extrusion, in some cases, higher fiber contents can have a negative effect because they block bonds between protein macromolecules (Riaz 2000).

When selecting a raw material, financial concerns also play an important role. Soy protein concentrates and isolates are more expensive than soy protein flours due to further extraction steps. They are rarely used as the exclusive ingredient to produce textured vegetable protein (TVP). However, adding concentrate or isolate can optimize the product by improving the water holding capacity and protein content of TVP. It should be noted for process parameters, that a higher fat content of the raw


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Production of extruded meat substitutes based on textured soy protein
University of Applied Sciences Weihenstephan
Catalog Number
ISBN (Book)
Extrusion, Englisch, Sojaprotein, Proteinfraktionen, Fleischersatz, Fleischersatzprodukte, Extuder, Proteinisolat, Proteinkonzentrat, Soja, soy protein, soy, protein fraction, Proteinstruktur, Hausarbeit, Studium, Food Biotechnology, Biotechnologie, meat substitute
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Naomi Albiez (Author), 2021, Production of extruded meat substitutes based on textured soy protein, Munich, GRIN Verlag,


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