食物系統佔了全球三分之一溫室氣體排放量，反芻動物肉類生產是最大的單一來源，PIK 研究員 Florian Humpenöder 說：這是因為越來越多儲存大量碳的森林被清除用於放牧或種植飼料，以及畜牧業進一步排放溫室氣體。部分解決方案可能是現有的生物技術：由真菌等微生物通過發酵產生的富含蛋白質的營養豐富的生物質，具有類似肉類的質地，科學家稱為「微生物蛋白質」。
來自德國和瑞典的研究團隊將微生物蛋白納入計算機模擬模型，以檢測整個糧食和農業系統背景下的環境影響，而不是之前在單一產品層面的研究。他們的前瞻性情景一直持續到 2050 年，並解釋了未來的人口增長、糧食需求、飲食模式以及土地利用和農業的動態。由於未來肉類消費量可能會繼續上升，越來越多的森林和非森林自然植被可能注定會因牧場和農田而滅絕。
我們發現，如果到 2050 年，我們用人均 20% 的反芻動物肉替代，與一切照舊的情況相比，土地利用變化導致的年度森林砍伐和二氧化碳排放量將減少一半。牛數量的不僅減少，Humpenöder 說：因此用微生物蛋白代替碎紅肉將是減少當前有害影響的一個很好的開端。
肉類類似物大致分為三組，PIK 研究員 Isabelle Weindl 解釋說：有以植物為基礎的，如大豆漢堡肉餅，以及在培養皿中培養的動物細胞，也稱為培養肉，迄今為止非常昂貴，但最近受到了很多公眾的關注。還有發酵衍生的微生物蛋白，我們認為最有趣。如今，它已經在超市中以多種形式出現，例如在英國或瑞士，它可以在很大程度上與農業生產脫鉤。我們的結果表明，即使將糖作為原料，與相同蛋白質供應的反芻動物肉相比，微生物蛋白質所需的農業用地要少得多。
微生物蛋白是在特定的製程中產出，就像啤酒或麵包一樣。這些微生物以糖和穩定的溫度為生，生產出一種富含蛋白質的產品，這種產品的味道、感覺和紅肉一樣有營養。基於百年曆史的發酵方法，它是在 1980 年代開發的。美國食品和藥物管理局 （FDA）在 2002 年批准了一種微生物蛋白肉類替代品（真菌蛋白）是安全的。
Fungi-based meat alternatives to help save Earth’s forests
Author：Potsdam Institute for Climate Impact Research （PIK）
“The food system is at the root of a third of global greenhouse gas emissions, with ruminant meat production being the single largest source,” says Florian Humpenöder, researcher at PIK and lead author of the study. That is because more and more forests that store a lot of carbon are cleared for cattle grazing or growing its feed, and because of further greenhouse-gas emissions from animal agriculture. Part of the solution could be existing biotechnology: Nutritious protein-rich biomass with meat-like texture produced from microbes like fungi via fermentation, what scientists call “microbial protein.”
“The substitution of ruminant meat with microbial protein in the future could considerably reduce the greenhouse gas footprint of the food system,” says Humpenöder. “The good news is that people do not need to be afraid they can eat only greens in the future. They can continue eating burgers and the like, it’s just that those burger patties will be produced in a different way.”
Sustainable burgers: replacing minced red meat with microbial protein
The team of researchers from Germany and Sweden included microbial protein in a computer simulation model to detect the environmental effects in the context of the whole food and agriculture system, as opposed to previous studies at the level of single products. Their forward-looking scenarios run until 2050 and account for future population growth, food demand, dietary patterns as well as dynamics in land use and agriculture. As meat consumption will likely continue to rise in the future, more and more forests and non-forest natural vegetation may be doomed to extinction for pastures and cropland.
“We found that if we substituted 20 per cent of ruminant meat per capita by 2050, annual deforestation and CO2 emissions from land-use change would be halved compared to a business-as-usual scenario. The reduced numbers of cattle do not only reduce the pressure on land but also reduce methane emissions from the rumen of cattle and nitrous oxide emissions from fertilizing feed or manure management,” says Humpenöder “So replacing minced red meat with microbial protein would be a great start to reduce the detrimental impacts of present-day beef production.”
Microbial protein can be decoupled from agricultural production
“There are broadly three groups of meat analogues,” Isabelle Weindl, co-author and also researcher at PIK, explains. “There are plant-based ones like soybean burger patties, and animal cells grown in a petri dish also known as cultured meat, which is so far very expensive but got a lot of public attention recently. And there’s fermentation-derived microbial protein, which we consider most interesting. It is available in a large variety already today in supermarkets, for example in the UK or in Switzerland, and, importantly, it can be largely decoupled from agricultural production. Our results show that even accounting for the sugar as feedstock, microbial protein requires much less agricultural land compared to ruminant meat for the same protein supply.”
Microbial protein is made in specific cultures, just like beer or bread. The microbes are living on sugar and a steady temperature, and getting out a very protein-rich product that can taste like, feel like and be as nutritious as red meat. Based on the centuries-old method of fermentation, it was developed in the 1980s. The US Food and Drug Administration（FDA） greenlighted a microbial protein meat alternative（mycoprotein） as safe in 2002.
Green biotechnology needs to be fuelled by green energy
“Biotechnology offers a promising toolbox for a number of land-related challenges from ecosystems preservation through improving food security,” says co-author Alexander Popp, leader of the Land Use Management group at PIK. “Alternatives to animal proteins, including substitutes for dairy products, can massively benefit animal welfare, save water and avert pressure from carbon-rich and biodiverse ecosystems.” However, there are crucial questions attached to shifting more and more production from livestock to fermentation tanks — most importantly the energy supply for the production process.
“A large-scale transformation towards biotech food requires a large-scale decarbonisation of electricity generation so that the climate protection potential can be fully developed,” Popp adds. “Yet if we do this properly, microbial protein can help meat-lovers embrace the change. It can really make a difference.”