With the global population currently at 7.7 billion and expected to hit the nine billion mark by 2050, it comes with no surprise that there will most likely be an increase in food demand. In addition, the Food and Agriculture Organisation forecasts at least a 70% increase in food stocks will be required to fulfil the dietary needs of the growing world population. As a result, this places a great amount of pressure on the animal meat production industry.
Meanwhile, the increasing animal welfare, health, and environmental concerns have driven significant changes in consumer behaviour over the past few years, in which there has been an increased appetite for animal-free, plant-based products. What’s more, Informa Agribusiness Intelligence predicted that the sales for both meat analogues and milk-alternatives will grow by 25% and 43%, respectively, in the UK by 2021 as they continue to rise in popularity.
With that being said, let’s hope that you are “hungry” to learn because this article will briefly introduce you to the developments of alternative protein!
What are alternative proteins?
In essence, alternative proteins are basically proteins that are extracted from non-animal-based sources such as plants, cell cultures, fermentation products, or even insects! Besides that, these proteins can even be artificially produced in laboratories.
You probably would have come across these proteins at some point in your lives. Asia, for instance, offers a myriad of options such as tofu, tempeh, and/or seitan. And to put it simply, the alternative protein industry is currently growing at a rapid pace as many organisations are beginning to invest in the development of innovative food products which can effectively replace animal meat. Beyond Meat, Impossible Foods, and Gardein are simply one of the many examples of such companies.
How are alternative proteins made?
One of the key goals of the manufacturing stage at the moment is to develop a product that has a similar fibrous texture to that of animal meat, and in order to do so, some texturising techniques will be required.
To give you a better understanding of why this processing step is critical, let’s use legumes as an example. Legumes are a type of plant from the Fabaceae plant family, whereby the common edible variants of them include lentils, peas, chickpeas, and soybeans.
Crucially, their proteins occupy a globular conformation in their native state. Therefore, we will need to use certain processing methods to denature and unfold them so that we can restructure these proteins into the desired fibrous filamentous structures.
Figure 1: A simplified representation of globular and fibrous filamentous structures. To generate alternative proteins from legumes (e.g. soy and pea), whose proteins naturally have a globular structure, the processing is required to generate a filamentous structure so that it mimics the texture of animal meat. As you can see, globular conformations possess a spherical shape, whilst filamentous structures are elongated and consist of multiple protein strands.
How are they processed?
You can process proteins using a variety of techniques such as wet spinning, electrospinning, and thermoextrusion.
Wet spinning
Wet spinning produces edible protein fibres by first passing a polymer solution through a spinneret, which is a piece of equipment similar to a spider’s spinneret that aids the formation of polymer fibres. After that, the polymer solution is sent into a coagulation bath where polymer fibres are formed. Once that step is completed, the protein fibres formed are collected and dried. On certain occasions, factories may put these polymer fibres through multiple coagulation baths to enhance their overall quality in terms of molecular alignment and orientation.
Interestingly, wet spinning has been pretty successful at converting soy, pea, and faba bean proteins from their native globular state to a fibrous structure.
Figure 2: This figure illustrates the general set-up for the wet spinning procedure. You’ll usually find apparatuses such as the polymer solution within the syringe pump, which is released through the spinneret into the coagulation bath. The polymer fibres are then formed within the bath before they are collected by a take-up device and dried eventually. This figure has been modified from DeFrates et al. (2018)’s “Protein-Based Fiber Materials in Medicine: A Review”.
Electrospinning
Electrospinning is a production method that uses electrostatic forces to produce super thin fibres from polymer solutions.
It begins with the polymer solution being forced through a syringe whilst simultaneously being placed under a high voltage potential. This creates a large difference in the voltage between the hollow hole of the syringe and the fibre collection site. In addition to that, the high voltage also induces charged ions into the polymer solution and they, in turn, move towards the electrode with an opposite charge. As a result, these charged ions help to transfer tensile forces to the polymer solution, generating thin fibres during the process.
Despite the higher quality protein fibres produced by this technique, the applications of electrospinning in the formation of plant-based alternative proteins are limited. And that’s because this procedure has a lot of strict requirements.
For example, the polymers need to be extremely soluble as well as be in a random coil conformation. Other than that, the polymer solution needs to have the right level of surface tension, viscosity, and conductivity. If any of these conditions are not met, you won’t get any of the highly fibrous proteins that you want.
On that note, it would therefore be really difficult to electrospin plant proteins because they often fail to tick all the boxes. As you may also recall from our discussion earlier, plant proteins typically have a globular structure - this property itself makes it harder for them to interact with others during the spinning process so that they entangle.
Figure 3: An illustration of the electrospinning process. The polymer solution comes out of the syringe through a hollow hole or spinnerette whilst being placed under a high voltage supply to generate thin fibres. This figure has been modified from Nieuwland et al. (2014)’s “Reprint of "Food-grade electrospinning of proteins”.
Thermoextrusion
Thermoextrusion basically involves forcing the material through an extruder - which requires conditions of high pressure and elevated temperatures - before pushing the final product out of a shaped hole (called the “cooling die”) to form the shape of our desired food product. Some examples of common food products produced via this technique include pasta, cereals and more recently, plant-based alternative proteins.
In fact, thermoextrusion is the most widely utilised technique in the alternative protein industry for it is capable of producing plant-based alternative proteins at a low cost and high productivity rate whilst remaining versatile and energy-efficient.
We can even segment thermoextrusion into three categories, namely low-moisture extrusion, intermediate-moisture extrusion, and high-moisture extrusion. In all three categories, the dry blend of proteins is placed into an extruder for processing. The extruder is a device that mediates the formation of protein fibres via a forward pumping action generated by single- or twin-rotating screws. Typically, twin-rotating screws are better at “meshing up” the protein mixture more effectively, thereby inducing a greater amount of protein denaturation by shear stress. Following that, we arrive at the cooling die that sits towards the extruder’s long-slit end. As its name suggests, the cooling die is used to cool down the final product and promote greater protein-protein interactions that aid the formation of the fibrous structures (check out Figure 4).
Importantly, the overall texture and structure of the restructured protein are dependent on the moisture levels during the restructuring process. In particular, having more moisture during the thermoextrusion process generates more fibrous proteins with branched structures in comparison to a procedure with reduced moisture.
Figure 4: A simple example of a high moisture thermoextrusion system with a twin-screw extruder. This system can be used during the production of plant-based alternative proteins, whereby it restructures a dry protein mix into fibrous protein chunks. The general processes involved are indicated by steps one to five. This figure was modified from Liu & Hsieh (2008)’s “Protein–Protein Interactions during High-Moisture Extrusion for Fibrous Meat Analogues and Comparison of Protein Solubility Methods Using Different Solvent Systems”.
How is the meaty taste replicated?
Besides mimicking the texture of animal meat, we still need to take taste, appearance, as well as the nutritional components of our alternative protein products into consideration as well. Scientists would typically incorporate other non-protein components known as additives (such as vitamins, seasoning, fats, minerals, and colourants) into the protein mix.
An excellent example of this would be leghemoglobin. Leghemoglobin is a recently approved food colourant additive derived from soy legumes. It has actually been used by Impossible Foods in its products to replicate the appearance and taste of regular animal meat. And interestingly, it is also similar to myoglobin, which is a type of protein that affects the colour and taste of traditional meat.
What kinds of challenges remain?
Generally speaking, we have actually accomplished quite a lot in terms of our technological capabilities to produce “mock” meat. Nevertheless, we still have loads of room for improvement as we haven’t exactly created a meat analogue that offers the precise level of juiciness, bite, and fibrous structure that we all cherish when eating a real piece of animal meat.
Furthermore, diversifying from the dominant use of soy in many plant-based protein alternatives would be desirable. This is because some researchers have found soy to cause allergic reactions in many individuals, and apparently, it also has some antinutritional factors!
What could the future of food look like?
As the global population and the demand for protein continue to grow, food security will soon become an inevitable issue that we will need to face. Meanwhile, more and more individuals are becoming open to the incorporation of alternative protein products into their diets. Henceforth, we can definitely expect the alternative protein industry to be receiving increasing attention over the years to come.
However, despite the values-driven mission fueling the development of these products, there is still a lot of uncertainty surrounding their actual benefits. In particular, we are still not entirely sure as to what extent these alternative proteins resolve the environmental and ethical issues surrounding the consumption of regular meat. Besides that, many remain sceptical of whether these products can effectively substitute real animal meat as a proper source of protein.
But, to look at things from the brighter end, it is still good to remember that this is just the beginning. Overall, we can definitely expect future technological advancements to follow suit as the increasing popularity of alternative proteins would incentivise researchers and companies to venture into this space.
If you are interested…
These are some of the companies that are offering plant-based alternative proteins in the market:
Author
Stephanie Ho
BSc Biochemistry
Imperial College London