Single Cell Protein (SCP)

The world's need for animal protein is on a scale that conventional livestock farming alone struggles to meet sustainably: it has been estimated that by 2050 the world would need to produce around 1,250 million tonnes of meat and dairy products every year just to satisfy current consumption levels of animal-derived protein at a larger population — and that scale of meat and dairy production is not achievable sustainably, in part because converting animal feed into meat or milk is inherently inefficient. At the same time, populations in underdeveloped and developing countries already suffer widely from protein malnutrition, which in turn causes a variety of nutritional diseases. Conventional efforts to close this gap use crop improvement, biofertilizers, biopesticides, chemical fertilizers and high-yielding varieties (the Green Revolution approach), but there is also a genuinely non-conventional route: growing microorganisms themselves as a direct source of protein. This idea, called single-cell protein (SCP), was first recognised as valuable during the First World War.

Single-cell protein refers to crude or refined edible protein extracted either from pure cultures of living microbes or from dead or dried microbial biomass. The organisms exploited for SCP include algae, fungi, yeasts and bacteria, all of which have unusually high protein content in their biomass, and — crucially for economics — they can be grown on cheap, often waste, substrates: agricultural residues, wood shavings, sawdust, corn cobs, paraffin, N-alkanes, sugarcane molasses, and even human and animal waste. Specific organisms used for SCP production include the fungi Aspergillus niger and Trichoderma viride; the yeasts Saccharomyces cerevisiae and Candida utilis; the algae Spirulina species and Chlorella pyrenoidosa; and the bacteria Methylophilus methylotrophus and Bacillus megaterium.

During their growth, these microorganisms take up the carbon and nitrogen present in their substrate and convert it into high-quality protein that can supplement both human food and animal feed; besides protein, SCP biomass is also rich in vitamins (including the B-complex), minerals and fats. It is readily used as fodder to fatten calves and pigs, in fish breeding, and in poultry and cattle farming. …