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Alternative Proteins include cultured meat, plant-based meat, insect protein and single-cell protein. Here, the technological, safety and environmental aspects of these protein sources are described.
2. Technological Aspect
Cultured meat, also known as in vitro, lab-grown or cell-based meat, is derived from animal stem cells that are cultivated in controlled settings. Currently, the two main stem cells considered to be the most suitable for culturing meat are embryonic stems cells or satellite cells . The main steps involved in the production of cultured meat include the isolation of stem cells from an animal biopsy, followed by the proliferation and differentiation of these isolated stem cells into desired tissues (for example, skeletal muscles) in a cell culture medium . In the process, the growing cells can be attached to scaffolding materials, such as collagen-like gel polymers, which serve as a support network for the tissue development  —potential polymers to be used as scaffolds are listed elsewhere . Trecapitulation of complex meat structures via tissue engineering needs to include skeletal muscles (myogenesis), extracellular matrix (fibrogenesis), microvascular networks (vascularization) and intramuscular fats (adipogenesis) . Thus, there are practical advantages of using pluripotent stem cells, especially the induced pluripotent stem cells (iPSC) derived from adult cells .
Texturized vegetable proteins (TVP) can be used as a potential replacement of conventional meat and are commonly derived from soy proteins , or to a lesser extent, from wheat glutens  and legume proteins (for example, pea and chickpea) . Currently, plant-based meats are mainly produced through thermoplastic extrusion . This process can be categorized based upon the amount of water added, i.e., low moisture (20–35%) or high moisture (50–70%) . Both product types are made in three main steps: (1) pre-conditioning of the raw materials outside of the extruder; (2) heating and compression inside of the extruder; (3) cooling of the die and processing of the final product (for example, cutting to desired pieces) . Shear technology has also been used to structure vegetable proteins .
Insects have been a part of the human diet for centuries, particularly in Asia and Africa . According to the Food and Agriculture Organization of the United Nations (FAO), there are over 1900 insect species consumed around the world . This practice of eating insects, also known as entomophagy, is sustainable due to the high amounts of protein and polyunsaturated fatty acid contained in edible insects, although there are variations across species . Insects are also more effective in converting feed into edible body mass than farm animals . These have made them an attractive option for expanded production to improve global food security. Most edible insects are harvested from the wild, but they can also be semi-domesticated through habitat manipulation or reared in farms for a mass-scale production . Similar to other animals, insects require macronutrients (lipids, proteins and carbohydrates) and micronutrients (essential sterols and vitamins), which can be derived from animals, plants and yeast . In particular, polyunsaturated acids, essential amino acids and sterols must be supplied in the feeds, given that insects lack the ability to synthesize these compounds in sufficient amounts . In addition to adequate nourishments, rearing conditions (for example, temperature, humidity and population density) need to be optimized .
Single-cell proteins, also known as microbial proteins, are commonly derived from microalgae, fungi or bacteria. In their review article, Ritala et al. summarized available studies on potential fungal, microalgal and bacterial species for application in the production of single-cell proteins, including patents from the years 2001 to 2016 . These include green algae (Chlorella vulgaris), Haemotococcus pluvialis, Dunaliella salina and spirulina (Arthrospira maxima or Arthrospira platensis) , Fusarium venenatum A3/5 (previously known as Fusarium graminearum A3/5)  and Methylcoccus capsulatus .
3. Safety Concerns
Briefly, cultured meat grown in fetal bovine serum-based media can be exposed to viruses or infectious prion, in addition to other safety risks associated with the use of genetic engineering. Plant-based meat may contain allergens, anti-nutrients and thermally induced carcinogens. Microbiological risks and allergens are the primary concerns associated with insect protein. Single-cell protein sources are divided into microalgae, fungi and bacteria, all of which have specific food safety risks that include toxins, allergens and high ribonucleic acid (RNA) contents. The environmental impacts of these alternative proteins can mainly be attributed to the production of growth substrates or during cultivation. Legislations related to novel food or genetic modification are the relevant regulatory framework to ensure the safety of alternative proteins. Detail explanations are provided in the original version of this article.
4. Environmental Impact
|Protein Type||Energy Use
(kg CO2-eq/kg Product)
|Water Use or Eutrophication a||Land Use
|Minced beef 1||26–33||1.90–2.24||0.36–0.52 m3/kg meat (W)||0.19–0.23|||
|CHO 2||106||7.5||7.9 g PO4-eq/kg meat (E)||5.5|||
|Beyond Burger®||54.15||3.35||28.84 m3/kg meat (W)||3.97|||
|Impossible Burger®||NA||3.5||0.11 m3/kg meat (W); 1.3 g PO4-eq/kg meat||2.5|||
|Mealworm (T. molitor and Zophobas morio)||33.68||2.65||NA||3.56|||
|Black soldier fly (H. illucens)||21.20–99.60||1.36–15.10||NA||0.032–7.03|||
|Cricket (G. bimaculatans and A. domesticus)||NA||2.29||0.43 m3/kg cricket (W); 0.00047 kg P-eq and 0.020 kg N-eq/kg cricket (E)||NA|||
|Spirulina tablets (A. platensis)||7.88–12.7||5.05–7.71||0.015–0.022 kg N-eq/kg tablet (E)||NA|||
|Micoalgal protein (A. platensis)||1225.6–3338.3||78.1–196.3||3.2–3.3 m3/kg protein meal (W); 49.2–85.3 kg N-eq/kg protein meal (E)||1.7–4.3|||
|Microalgal protein (C. vulgaris)||217.1–4181.3||14.7–245.1||0.3–3.9 m3/kg protein meal (W); 40.6–105.3 kg N-eq/kg protein meal (E)||1.9–5.4|||
|Bacterial protein (Cupriavidus necator)||NA||0.81–1||0.0001–0.0038 m3/kg protein (W); 0.000333 kg P-eq/kg protein (E)||0.029–0.085|||
|Bacterial protein (hydrogen-oxidizing bacteria)||200||8||2.5 m3/kg protein (W);
0.0025 kg P-eq/kg protein and 0.00035 N-eq/kg protein (E)
5. Future Outlook
This entry is adapted from 10.3390/foods10061226
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