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The role of the extruder in creating palatable meat alternatives

31 January 2021

Dr Anubha Garg Dinis discusses the challenges of feeding a growing global population and the role that alternative proteins has to play and the importance of engineering technologies in making them palatable for consumers. 

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Today’s global food supply systems are very complex, comprising of multiple steps, from the farm to storage, transport, processing, retail and ending eventually at the plate of the consumer. This food system puts a huge burden on the planet, up 70% of the world’s available fresh water is used within agriculture, in addition to a tremendous amount of energy, and contributing to nearly a quarter of global green-house gas emissions. Despite this, one-third of all produced food is eventually wasted.

Parallel to this there is a growing consumer trend towards more balanced and protein-rich diets, resulting in a tendency towards putting as much protein on the plate as possible. Looking at our existing protein value chain, it is estimated that with livestock farming, 45% of protein produced worldwide is lost during the conversion step of plant to animal protein. Beyond these inefficiencies, the over-production of animal-based protein for humans has been the leading cause of the most recent pandemics – from Covid-19 and SARS to Swine Flu and Bird Flu.

Consumers are now looking for alternative sources of proteins and expect more choice in the products available. Researchers around the world are therefore looking for novel proteins sources which could be valorised for human consumption. In this race, plant-based proteins top the charts. Employing twin-screw extrusion technology, it is possible to use plant-based protein sources to create products that mimic animal-based meat such as chicken chunks, burgers, pulled pork, tuna, etc.

It is expected that by 2040 the global protein market share will be dominated by alternative proteins, including both plant-based and cultured meat leading to a reduction in traditional meat products. This has intrigued many companies from the traditional meat and dairy industries, encouraging them to diversify their portfolios and cater to the needs of the market. According to the 2019 ‘US State of the Industry Report’ by the Good Food Institute (GFI), there was a 31% increase in the retail sales of plant-based meat substitutes, compared to only 5% for actual meat products, between the years 2017 and 2019 and this explains the entry of food giants like Nestlé, PepsiCo and Kraft Heinz into the plant-based meat substitute segment. Additionally, many traditional meat producers, such as Tyson and Hormel, have launched their own plant-based meat brands. 

The traditional meat industry can provide expertise from the processing of animal meat to create familiar cuts, shapes and forms out of plant-based meat substitutes, which can improve the meat mimicking process. Additionally, the same equipment can be used to produce different product categories, with diversified textures, by simply altering the extrusion settings. This is typically not the case with handling traditional meat products. For example, a company that has expertise in producing plant-based beef can now enter the plant-based seafood market, simply by optimising the process. Hence, it is a huge opportunity for traditional meat companies to diversify their product portfolios.   

The role of technology 
Despite the existing concerns in the food system, and especially in the protein value chain, it is a challenge for consumers to fully shift to plant-based diets. People enjoy the sensory experience involved in eating meat – not only from the flavour but also from the texture of the product. The biting quality and the chewiness that is provided by a meat product is missing in traditional plant-based meat substitutes. 

However, with the advent of high moisture extrusion in food technology, it is now possible to more closely mimic meat products. Plant proteins in their raw state are typically globular in structure. As they are processed inside the extruder, the shear forces and the increase in temperature lead to a denaturing of these plant-proteins, allowing them to be re-aligned into long fibres. The cooling die is a vital attachment at the extruder die. As the restructured protein melt flows through the cooling die, the phase separation results in a fibrous and layered structure, which is then cooled to a solid product exiting the cooling die. This meat substitute – typically a rectangular slab due to current cooling die designs – can then be further processed to create a diverse variety of products such as minced meat, pulled pork, burger patties and chicken chunks.

Dry extrusion
In addition to high moisture extrusion, there have been improvements in the dry extrusion process to produce meat substitutes. Dry extrusion uses plant-based protein sources which can be turned into fibrous structures using shear and heat, similar to high moisture extrusion. However, in this process, the temperature profile of the extruder is higher which results in flash evaporation of moisture as the product exits the extruder die. The product after the extruder is then cut into various shapes using a continuous cutter and dried to reach a stable shelf-life condition. 

Both high moisture and dry extrusion have their own advantages and can be used to produce meat substitutes with specific characteristics. Specialising in both dry and high moisture extrusion, Bühler can help its customers to find solutions with customised recipes in order to achieve the most desirable layered and fibrous textures. 

Bühler’s application centers located in USA, Switzerland, China and very soon in Singapore, enable customers to carry out trials for recipe and process optimisation with the support of Bühler’s technology team. 

In order to cater to the growing demand, plant-based meat producers also need to increase the throughput of their processes. Bühler’s solution for a cooling die throughput of 500kg/hr offers a solution to this need. In addition to extruder systems and cooling dies, Bühler can provide solutions for pre-processing of the material using pre-conditioners. These pre-conditioners can provide an additional residence time for the raw ingredients which might be needed to stimulate certain physico-chemical reactions, improving the functionality of the recipe components. 

Today’s plant-based meat substitutes are mostly produced from soy protein or pea protein-based recipes. As an example for high moisture extrusion, one can formulate basic products by mixing 33% soy protein concentrate with 66% water, or 45% pea protein isolate with 55% water in the recipe. The extrusion conditions will differ depending on the recipe. Typical temperatures would reach up to 145-150°C when extruding soy protein concentrate, while for pea protein isolates, temperatures in the range of 130-145°C are used. The configuration of the screw elements must be adjusted depending on the protein sources in order to provide the necessary amount of shear force inside the extruder. These process parameters are best optimised with access to experience and scientific understanding. 

New protein sources gaining popularity more recently include chickpea, lentil, potato, fava bean, and mycoprotein, which all have great nutritional properties and can be used to produce meat-like structures. With the furthering of fermentation technology, single-celled proteins such as algae, yeast, and bacteria will also become more important in the near future. 

In conclusion, scientists and industries around the world are exploring the nutritional and functional aspects of alternative protein sources in order to make the protein value chain more efficient. Meat substitutes present a great opportunity for sustainability in food systems and extrusion technology has an important role to play in this movement.

Dr. Anubha Garg Dinis is a plant protein processing specialist at Bühler.

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