Processing of Proteins for Plant Based Meat: Current Approaches and Recent Innovations
The vast majority of commercialized alternative meat products are based on wheat and soy protein concentrate (70% protein) or isolate (90% protein) due to the wide availability of these materials as byproducts of other large industries [1,2]. Since commercially available protein isolates are created through processes best suited for the initial industry, they are poorly optimized for application to plant-based meat products.
Conventional processing of plant materials entails the extraction of oil, carbohydrate, and lastly, protein fraction. The specific method can influence the types of protein recovered, the properties of the proteins, and the yield of protein [1]. These approaches can limit the functionality of plant proteins in the emergent plant-based meat space which is driving agri and food tech companies to innovate through optimization of crop selection.
Current Processing Methods
For the production of a realistic plant-based meat product several phases of processing must occur. First the protein concentrate or isolate must be extracted from plant material and then, depending on application, may be further processed to form fibrous structures. These processing techniques can influence protein functionality and solubility to a great degree.
The types of protein reflected in a specific protein isolate depend upon the processing technique used to extract the protein fraction. Conventional fractionation methods employ organic solvents to first extract the oil component, followed by another fractionation step to extract the protein component. Wet, or aqueous, fractionation is a slightly newer approach which involves mixing milled soy flour with water and centrifuging to yield a fat-rich phase, a liquid phase rich in protein, and a pellet containing insoluble fiber [3].
Next, approaches are taken to modify the texture of the protein fraction. Most proteins derived from plant materials, especially soybeans, are globular in structure. Animal muscle and connective tissues, however, are made up mostly of fibrous proteins which are key contributors to texture. Plant materials can be modified to be more fibrous through extrusion based or shear cell technology-based processing methods. Extrusion processes can involve varying levels of hydration combined with heating and mechanical deformation to create fibrous textures. Shear cell technology employs thermal and shear force transmitted through a conical device and is better at delivering large pieces of fibrous structured protein isolate [4].
Protein solubility is a key aspect of the processing phase, especially isolation from wet fractionation, and in downstream applications. Although globular proteins are generally quite soluble, soy proteins are known to have low solubility likely from thermal denaturation occurring during some processing stages [2]. Furthermore, different fractions of proteins can have differing functional properties and solubility as well. Thus, processing methods designed with those limitations in mind may improve yield of desirable protein fractions with minimal denaturation and minimal contamination from organic solvents.
Designing Crops to Minimize Processing
As the plant-based meat industry expands and more companies turn to novel protein sources such as pea, chickpea, quinoa, and others, control over processing methods and the ability to optimize specific protein yield may grow. However, these methods are still energy and water intensive procedures translating to greater monetary and environmental impact [5]. According to Matt Crisp, CEO of Benson Hill, such additional processing of soybeans to create soy protein concentrate could be avoided with high protein varieties of soybeans. Benson Hill has recently developed a soybean that contains 50% more protein content than traditional soybean crops and is gearing commercialization toward the plant-based protein market.
Advances in crop breeding strategies targeted at improving protein content and minimizing downstream processing such as these are on the rise as companies seek to cater to the needs of the growing plant-based meat industry. In addition to Benson Hill’s high protein soybean, Equinom has developed a high protein pea crop [1]. Both claim that downstream processing such as wet fractionation can be avoided with the use of their product.
However, enhancing protein content to reduce downstream processing is only one potential avenue for crop breeding strategies in this space. Other areas can target improvements in nutritional content and reductions in anti-nutrients, the compounds that generate bitter flavors.
Anti-nutrients are secondary metabolites found in legumes and other plant types that are typically removed during downstream processing. They include saponins, tannins, protease inhibitors, and amylase inhibitors [6]. Anti-nutrients are notable as they contribute to bitter flavoring, bind nutrients and minerals reducing bioavailability, and some act as inhibitors to digestive enzymes [6]. Processing such as milling, heating, germination, and soaking can be used to remove anti-nutrients, but these methods can also lead to the loss of desired nutrients like vitamins and antioxidants.
To minimize processing steps involved with anti-nutrient removal, crops could be designed to produce minimal amounts of these compounds. Manipulation of saponin levels in soybean plants through silencing of a key enzyme involved in saponin synthesis has been previously described from an academic lens [7]. One could envision a similar approach to modifying saponin production at the genetic level in soybean plants.
It is important to note, though, that many of these compounds which produce adverse flavors in plants are also beneficial to health. Saponins have been shown to reduce cholesterol absorption, lower body weight, and decrease blood triglyceride levels in addition to acting as anti-microbial and antioxidant agents [8].
Concluding Remarks
As the market for plant-based food grows and demand for high protein and novel protein plant materials increases we will likely see more agricultural tech companies bringing new products to market. Crops that can deliver maximum protein content will alleviate downstream processing requirements, contributing to lower costs and reduced environmental impacts. At some level processing will still be required, but as research into plant protein functionality continues, we will likely see increasing optimization of current methods to improve the quality of the final product.
References
[1] Gaan K. 2020 State of the Industry Report | Plant-Based Meat, Eggs, and Dairy. 2021.
[2] Zayas JF. Solubility of Proteins. Funct. Proteins Food, Springer Berlin Heidelberg; 1997, p. 6–75. https://doi.org/10.1007/978-3-642-59116-7_2.
[3] Geerts MEJ, Dekkers BL, van der Padt A, van der Goot AJ. Aqueous fractionation processes of soy protein for fibrous structure formation. Innov Food Sci Emerg Technol 2018;45:313–9. https://doi.org/10.1016/j.ifset.2017.12.002.
[4] Dekkers BL, Boom RM, van der Goot AJ. Structuring processes for meat analogues. Trends Food Sci Technol 2018;81:25–36. https://doi.org/10.1016/j.tifs.2018.08.011.
[5] Shoup ME. Benson Hill introduces “ultra-high protein” soybean to compete with soy protein concentrate. FoodNavigator-USA 2020. https://www.foodnavigator-usa.com/Article/2020/03/25/Benson-Hill-introduces-ultra-high-protein-soybean-to-compete-with-soy-protein-concentrate (accessed June 1, 2021).
[6] Samtiya M, Aluko RE, Dhewa T. Plant food anti-nutritional factors and their reduction strategies: an overview. Food Prod Process Nutr 2020;2:1–14. https://doi.org/10.1186/s43014-020-0020-5.
[7] Takagi K, Nishizawa K, Hirose A, Kita A, Ishimoto M. Manipulation of saponin biosynthesis by RNA interference-mediated silencing of β-amyrin synthase gene expression in soybean. Plant Cell Rep 2011;30:1835–46. https://doi.org/10.1007/s00299-011-1091-1.
[8] Ku YS, Contador CA, Ng MS, Yu J, Chung G, Lam HM. The Effects of Domestication on Secondary Metabolite Composition in Legumes. Front Genet 2020;11:581357. https://doi.org/10.3389/fgene.2020.581357.
Written by Anna Goddi, PhD Candidate & Helikon Associate
