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Alternative meat: eating microbial protein and others
18th December 2022
Translated from the original article in Catalan (10th December 2022)
PROBLEMS OF ANIMAL PROTEIN PRODUCTION
Most of the protein that we humans consume is meat protein of animal origin produced by industrial livestock farming, be it birds or mammals, and of these mainly ruminants such as beef, whose global production has doubled in the last 50 years. Industrial farm systems, both intensive and extensive, have very negative environmental consequences. As we see schematically in Figure 1, the main disadvantages are:
The area of land occupied by cattle breeding is increasing. Counting the pastureland and vegetable crops to feed the animals —cereals and soybeans in particular—, almost 30% of the land surface is reached, much more than that devoted to crops for human consumption, 13%. In the case of soy, for example, 3/4 of its production is dedicated to feed, and an important part comes from regions of Brazil that were previously jungle or savannah (Hooper 2022).
The fresh water used for the manufacture of any product is called the water footprint (Hidrofilic 2017). In the case of livestock, which includes the cultivation of vegetable feed, water footprint is much greater than any other agricultural crop: 15000 L of water are needed for each kg of beef, 9000 L per kg of sheep meat, 6000 L per kg of pork, while only 300 L is needed for kg of vegetables or 900 L per kg of fruits or about 4000 L per kg of legumes, even less than for animals (Mekonnen & Hoekstra 2010). As we can see (Figure 1), it is estimated that in the USA 30% of the total water footprint is due to industrial livestock.
A third of global greenhouse gas (GHG) emissions are caused by the food system, and within this livestock farming is the main contributor, especially due to the methane gas expelled by ruminants, a result of the metabolism of methanogenic archaea, the final step of rumen fermentation. As a GHG, methane emissions from cattle cause the most environmental impact by far, being about 100 kg of methane for every 100 g of protein produced (Poore & Nemecek 2018).
Finally, it is necessary to take into account the repercussions of land degradation and erosion caused by industrial livestock farming, as well as soil acidification, contamination by antibiotics and eutrophication due to the excessive use of fertilizers (Humpenöder et al. 2022).
Figure 1. Environmental impact of the livestock industry. Image taken from Ecopeanut.com.
It is estimated that by 2050 the world’s human population will be almost 10,000 million (now in 2022 we are 7,800 million), for which we will need about 400 million tons of meat and 800 of dairy products per year, an amount that cannot be achieved by the low efficiency of vegetable protein in feed to animal protein, which is 6 kg of vegetable for 1 kg of animal (Ritala 2017).
All in all, some very concerned environmental activists like George Monbiot believe that agricultural and livestock exploitations lead to destruction, exploitation and economic senselessness that are killing the planet. However, he also believes that there is hope for a more sustainable and healthier world that would go through a consumption of microbes instead of animals (Hooper 2022).
Therefore, this medium-term situation is not environmentally sustainable, and alternatives must be found to replace much of the animal protein with other sources, such as microbial and others.
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THE VEGETABLE ALTERNATIVE
The vegetable protein alternative is well known and forms part of our usual diet (Figure 2). Taking it to the extreme, vegetarians base their diet only on vegetables and exclude meat foods. In India they are 1/3 of the population, but in the rest of the world vegetarians are a minority, 5% in Europe. The reasons for vegetarians – and vegans, who are more strict – are very diverse, such as ethical (animal sensitivity), health, religious, political, fashion, aesthetic, economic, but also increasingly there are the reasons of environmental and sustainability awareness.
Figure 2. Vegetarian diet. Image taken from Salud Blogs Mapfre.
Vegetable protein sources are nutritionally valuable, since they contain fibre —almost non-existent in meat — and antioxidants, but their protein content is always lower than that of meat, which is 45% of the dry extract The vegetable foods with the most protein are soy (35% of dry extract) and legumes such as peas, chickpeas or beans (20-25%). In contrast, wheat, rice and other cereals or potatoes only contain 10% protein. Milk contains 25% and eggs 40% of the dry extract.
The main disadvantage of vegetable protein compared to animal, in addition to the lower total protein content, is the lower nutritional quality in terms of essential amino acids and lower digestibility, with which it is necessary to increase 10-20% of protein if only plant foods are consumed (Petrusán et al 2016). Another disadvantage is the environmental one, partly like the animal protein, due to the needs of large areas of land and a lot of water (Ritala et al. 2017).
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EATING INSECTS ?
Another alternative is the consumption of insect protein, or entomophagy. The protein content of the dry extract of insects is very high, between 35% for termites and 60% for crickets and locusts, and most edible insects have high contents of essential amino acids, and of fibre, minerals and vitamins. Insect “farms” are very suitable for sustainability and the environment, as they require no land, require little water, emit very few GHGs, and are economically advantageous. Therefore, they have very good potential as quality food (Lange & Nakamura 2021). However, consumer acceptance is a major hurdle, especially in Western countries. Instead, they are common in sub-Saharan Africa, Southeast Asia, Australia, and some Ibero-American countries such as Mexico, where “escamoles” are larvae of the Liometopum apiculatum ant very popular since pre-Hispanic times (Figure 3).
Figure 3. Dish of Mexican escamoles. Image taken from Lideresmexicanos.com.
When insects are produced industrially, it is necessary to consider and control possible sources of food safety risks, such as allergens, pathogenic microorganisms that can be transmitted via insects, or mycotoxins from fungi that contaminate insects (Lange & Nakamura 2021).
Currently, most investments in the production of edible insects are for animal feed. It is being produced as a protein powder for domestic animals, in aquaculture and is starting to be introduced as a supplement to livestock feed. In addition, the droppings of insects in the productive phase can be used as fertilizer (Godwin 2021).
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CULTURED OR SYNTHETIC MEAT
Also called “in vitro” meat or “clean” meat or “laboratory meat”, it consists of growing animal muscle tissue in laboratory cultures from stem cells. With this method, which is faster and more efficient than obtaining traditional meat, there is no need to sacrifice animals, nor are there all the mentioned drawbacks of livestock farming.
To obtain cultured meat, a series of requirements summarized in these steps are needed that must work well both from a biological and commercial point of view:
1. Obtain skeletal muscle samples from the appropriate animal
2. Separate the stem cells from the other muscle components and sometimes other cell types
3. Inducing the growth and proliferation of myoblasts in the appropriate physico-chemical conditions and medium, with growth factors
4. Inducing myoblasts to form multinucleated myotubes, in a framework or scaffolding structure, such as collagen
5. Achieve the continued growth of new myoblasts and the differentiation of myotubes into muscle fibres
6. Ensure continued growth throughout scale-up, introducing other components such as adipocytes, with lipids providing palatability
7. Process the resulting product by adding fats, flavourings and other compounds, and shape its physical appearance, all in order to mimic conventional meat products, which is easier with processed products such as minced meat or bacon (Figure 4) (Kadim et al. 2015).
Cultured meat can be just as good and nutritious as conventional meat from farm animals, in addition to the advantages of a drastically lower effect on the environment and on the animal in question. In addition, the yield is clearly greater, since with just one sample of tissue the same amount of meat can be produced as with 80 cows (Bingham 2020).
Although preliminary results so far are very promising, this technology is not yet developed enough for large-scale production, especially in terms of culture media, and consumer acceptance and trust is still very low (Kadim et al. 2015).
Figure 4. “Culturized” meats, made from animal cell cultures, simulating beef fillet (left) or processed meat (right). Images taken from Bingham (2020).
In a similar way, the production of fish fillets and seafood meat with cell cultures is also being developed, this is what is called cell aquaculture. The progressive replacement of caught fish by “farmed fish” would significantly reduce overfishing, eliminate illegal fishing and destruction of marine ecosystems, and these foods would not have potential pathogens or common contaminants such as methylmercury or particulate microplastics.
These farmed fish and shellfish products also have the organoleptic qualities of wild or farmed marine products but with the advantage of being more sustainable, safer, and healthier. Some of the companies that are developing them use techniques similar to organoid cultures or mini organs, which have been used for about 10 years for the study and treatment of diseases and tumours. Cultures are made in three-dimensional structures allowing the cells to form a natural composition of fat and muscle equivalent to that of the animal (VelSid 2022).
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MICROBIAL PROTEIN
It is also known as Single Cell Protein (SCP) because many were originally single-cell microbes such as most bacteria —including cyanobacteria—, yeasts and some single-celled microalgae, but some filamentous fungi and some multicellular algae are also included. Logically, the microbes that have been studied the most in this regard are the ones that contain the most protein. We have a good review of the types, the process of obtaining and applications in the work of Junaid et al. (2020).
We see in Table 1 a summary of the main products that have been developed, most of them since the 1970s, when, with the first energy and environmental crises, alternatives to the production of meat protein were sought, although most of these products have not had great industrial and/or commercial development.
Table 1. Single Cell Protein products, all with at least 45% protein of dry extract. Adapted from Ritala et al. (2017).
| Microorganism | Type | Use | Substrates | Companies (country) | Problems |
| Methylophilus,Methylococcus | Methylotroph and methanotroph bacteria, proteobacteria | Animal feed | Methanol, methane | ICI (UK) “Pruteen” 1970s, Calista Inc. (UK) “FeedKind” from biogas | High content of RNA and DNA (>10%), needs processing |
| Azonexus, Comamonadaceae | H2-oxidizing bacteria, proteobacteria | In perspective, food or feed | H2, CO2, O2, N2 | Startups: Air Protein (USA), Solar Foods (FI), Deep Branch (UK) | Still in R&D |
| Arthrospira maxima, A. platensis | Previously “Spirulina”, bacteria: Cyanobacteria (“microalgae”) | Dietary supplement, food of Aztecs and towns of Chad | CO2, light | BlueBio Tech (D), Cyanotech (Hawaii USA), FEBICO (Taiwan), Parry Nutraceuticals (India) | Possible contamination with toxins (microcystins) from other cyanobacteria, and by heavy metals |
| Aphanizomenon flos-aquae(AFA) | Bacteria: Cyanobacteria | Dietary supplement, positive effects on health | CO2, light | Blue Green Foods (USA), E3Live (USA), Klamath Valley (USA) | Some toxic strains |
| Chlorella | Green microalgae: Chlorophyta | Dietary supplement | CO2, light | TerraVia (USA), Roquette Klötze (D), FEBICO (Taiwan), BlueBioTech (D) | Expensive production: carbonated water. Indigestible cell wall |
| Saccharomyces cerevisiae | Single-celled fungi (yeasts), ascomycetes | Yeast extract: dietary supplement | Molasses, cereals hydrolysate | Bega Cheese (AUS), Flint Hills Resources (USA) | Occasional: tyramine migraines, irregular digestions, intolerance in patients with irritable bowel * |
| Torula utilis | Cyberlindnera jadinii (sin. Candida utilis), yeasts, ascomycetes | Flavouring supplement, alternative to glutamate | Methanol, molasses | Phillips Petroleum Co (USA) until 2002, Provesteen Process (USA) until 1990 | Low profitability of the process |
| Fusarium venenatum | Filamentous fungi, ascomycetes | “Mycoprotein”, cell wall rich in glucans (fibre), positive health effects | Glucose from starch, salts, inorganic N | Marlow Foods Ltd “QuornTM” (UK), Atlastfood (USA), Nature’s Fynd (USA) and others, in operation | Occasional appearance of mutants with highly branched mycelium, which make it necessary to stop the continuous culture every 6 weeks. |
| Paecilomyces varioti | Filamentous fungi, ascomycetes | Animal feed | Sugars from lignocellulosic waste | Finnish paper factories, “Pekilo”, 1970-1990 | It wasn’t profitable, now reviving: https://www.eniferbio.fi/product/ |
As we can see, there are a few products that are microalgae or cyanobacteria, all of them photosynthetic microorganisms, which are interesting for their low production cost as they only need light and a little CO2 and some salts. Of these, we should highlight those known as Spirulina, which are cyanobacteria and have been a food source since the time of the Aztecs and other peoples of Central America, as well as the peoples around Chad. Today it is used as a human food supplement, in the form of tablets or powders (Figure 5) and is also used as a food supplement in the aquaculture and poultry industries. One of the main benefits is the high content of vitamin B12. However, it is necessary to monitor the product well as there may occasionally be contamination with cyanotoxins or the presence of pesticides and other toxic compounds, especially if it is consumed regularly (Grosshagauer et al., 2020).
Figure 5. Supplements in powders and tablets based on “Spirulina”, cyanobacteria. Image taken from Iswari.com.
Many different bacteria, apart from cyanobacteria, have been assayed, such as some Bacillus, Corynebacterium and Rhodopseudomonas, but at an industrial level those that have been most successful as SCP are the methylotrophs and/or methanotrophs (Table 1), which contain a lot of protein (50-80% of the dry weight), are rich in essential amino acids such as methionine, and with relevant amounts of lipids and vitamins. Already in the 1970s, ICI (UK) developed the product “Pruteen” with Methylophilus methylotrophus from methanol, and currently Calysta Inc. (“FeedKind” product) and other companies are producing Methylococcus and other methanotrophs by converting methane, surplus on farms, into bacterial protein (Ritala et al. 2017).
The main problem with bacteria – and fungi – is their high content of nucleic acids, especially RNA, due to their rapid growth and protein synthesis, which requires high rates of transcription and translation. This is not the case with photosynthetics (microalgae and cyanobacteria) which grow more slowly. Ingestion of RNA-derived purines increases plasma uric acid concentration, which can lead to gout and kidney stones. Therefore, it is necessary to partially remove these nucleic acids during the SCP preparation process. The most common method is the combination of mild heat treatment with the use of ribonucleases (Ritala et al. 2017).
A promising case of bacteria are hydrogen-oxidizing chemolithotrophs that are also nitrogen (N2) fixers, such as Azonexus and the Comamonadaceae. They are known as “air-munching microbes” (De Sousa 2021) because they can grow only with N2, O2, CO2 and H2 because they oxidize hydrogen with O2 and fix atmospheric N2 (Figure 6). But since H2is almost non-existent in the atmosphere, it is necessary to provide it, obtaining it by hydrolysis of water with green energies. The main advantage of being N2 fixers is the saving of ammonium, the production of which requires a lot of energy, apart from the yield in protein (Hu et al., 2020).
Figure 6. Scheme of the metabolism of nitrogen-fixing hydrogen-oxidizing bacteria. Taken from Hu et al. (2020).
Fungi and yeasts dominate the global SCP market for human consumption, as yeasts in particular have a long history of acceptance, especially in the form of extracts. Logically, most yeasts marketed as SCP are Saccharomyces cerevisiae, but there are also Torula utilis, Candida and Kluyveromyces. Yeasts and other fungi also have the drawback of nucleic acid content (10%), lower than bacteria, but which also requires processing to reduce them.
The mycelial fungus most used as SCP is undoubtedly Fusarium venenatum, mostly marketed under the name QuornTM by Marlow Foods Ltd. since 1985. In fact, it is the only SCP product used exclusively for human consumption. Like other fungi, apart from the high content of protein (mycoprotein), it is a good source of essential amino acids, vitamins and especially glucans, which contribute to the contribution of fibre to the diet. It is an ascomycete, considered a microfungus (Figure 7) due to the absence of macroscopic fruiting bodies, as are also Penicillium, Aspergillus and many other non-mushroom filamentous fungi.
Figure 7. Electron micrograph (350 x) of the mycelium of Fusarium venenatum on the surface of Quorn product. Image taken from Ugalde & Castrillo (2002).
The production of F. venenatum is carried out in continuous bioreactors with aeration in an aqueous medium with glucose obtained by starch hydrolysis, a source of N, vitamins and minerals. The resulting mycelium is extracted (Figure 8) and treated to remove RNA, and dried.
Figure 8. Preparing a Fusarium mycelium layer. Photo by MyForest Foods Co, taken from Dietrich (2022).
Products with mycoprotein such as Quorn in particular are intended mainly as a substitute for meat and are sold mainly in the form of prepared dishes, with an enormous variety of tastes and textures (Figure 9), logically adding additives. As a curiosity, see Quorn’s advertising website (www.quorn.co.uk), full of recipes and suggestions. Most products contain egg albumin in addition to the fungus, which acts as a binder. Vegan formulations replace the egg with potato.
Figure 9. Examples of products made with F. venenatum: Quorn pseudosausages and Nature’s Fynd non-dairy cream cheese. Images courtesy of quorn.co.uk and Dietrich 2022.
Interest in SCP is growing, and related research and development is increasing greatly, especially in China, where 70% of the world’s SCP patents since 2001 have been registered, often related to the exploitation of agricultural waste such as methane (Ritala et al. 2017).
In any case, microbial protein must be considered as one more of the elements to take into account, in addition to the others mentioned, in the necessary transformation of the agri-food system, combining it with the reduction of food waste, the incentive to eat more healthy, and the marketing of products with less environmental impact than the current ones (Carrington 2022).
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BIBLIOGRAPHY
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Bingham L (2020) Cultured meat: better than the real thing ? Foodunfolded, 10 march 2020.
De Sousa A (2021) How air-munching microbes could grow the fake meat of the future. Bloomberg Europe edition website, 11 October 2021.
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Godwin R (2021) If we want to save the planet, the future of food is insects. The Guardian News website, The Observer Food, 8 May 2021.
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