Fusarium venenatum

Fusarium venenatum is a microfungus of the genus Fusarium that has a high protein content. One of its strains is used commercially for the production of the single cell protein mycoprotein.

Fusarium venenatum was discovered growing in Buckinghamshire in the United Kingdom,^[1] in 1967 by ICI as part of the effort during the 1960s to find alternative sources of food to fill the protein gap caused by the growing world population.^[2] It was originally misidentified as Fusarium graminearum.^[3]

The strain Fusarium venenatum A3/5 (IMI 145425, ATCC PTA-2684) was developed commercially by an ICI and Rank Hovis McDougall joint venture to derive a mycoprotein used as a food.^[1] Because the hyphae of the fungus are similar in length and width to animal muscle fibres^[1] the mycoprotein is used as an alternative to meat and is marketed to vegetarians as Quorn.^[2] It is also suitable as a substitute for fat in dairy products and a substitute for cereal in breakfast cereals and snacks.^[1]

Commercial production

Fusarium venenatum intended for use in Quorn products is grown under aerobic conditions in culture vessels by what is known as the 'Quorn Process'. The vessels are composed of two vertical cylinders, ~50 metres high, connected to one another at their top and bottom, so as to form a continuous loop with a volume of ~150 cubic metres. Ports on the vessel allow the various ingredients involved to be added and removed. The culture broth is composed of 95% glucose, derived by the predigestion of maize starch. Potassium, magnesium and phosphate sources are added as a necessary mineral trace. Both these and the glucose are sterilised prior to use. Additional make up broth can be injected at the base of the vessel as material is removed. The broth is maintained at a pH of 6 and a temperature of between 28 and 30 degrees celsius, with a biomass density of ~15 grams per litre; equating to a total vessel biomass of ~2,250 kilos.

As culture growth occurs, carbon dioxide is produced and released through a vent at the top of the loop. A heat exchanger, located in the union between the towers at their base, allows excess heat generated by the culture to be removed. One tower within the pair contains a sparge bar, also located towards the towers base. Air and ammonia are injected through the sparge bar to provide the oxygen and nitrogen required for respiration and protein production. This sparging action causes the pair of towers to function as an air lift culture vessel. The broth continually circulates between the two towers; as it is driven upwards by the sparge bar in one tower, it falls in the opposing tower. Such a stirring (or circulating) method can be more preferable for biological cultures as it is less likely to cause damage to cell membranes by mechanical compression or abrasion. The denser Fusarium venenatum culture falls to the base of the loop, where it is removed and heated to 64 degrees celsius for 20 minutes. Filtration is used to harvest the Fusarium venenatum, with this then being dried prior to blending with a binder. The majority of Quorn products are bound by rehydrated egg white, which makes them unsuitable for a vegan diet. However, Quorn has been reducing its egg white usage and now offers an egg free alternative.

The complete vessels contain ~230 tons of broth, as glucose is denser than water. 30 tons of the cultured broth are removed per hour. The culture density within the broth at filtration varies from 1.5% (the vessels standard culture density) to 25-30% w/v, equating to a standard production rate of ~292 hydrated kilos per hour, or ~7 hydrated metric tons per 24 hour cycle. Giving a vessel dilution rate of ~13% w/w per hour; the amount of broth and culture mass being removed and then made back up per hour, with respect to the total mass in the vessel. The dry mass contains, 25% cell wall, 48% protein, 12% soluble carbohydrate and 12% fat. The total protein content varies from 43-85%.

Comparison with animal based farming

Broiler chickens reach a slaughter mass of between 1.8 to 3 kilos within 5 to 7 weeks; averaging 2.4 kilos over 6 weeks, or 42 days. Within this period, a 'Quorn Process' culture vessel will produce ~294 tons of hydrated culture, which equates to ~122,727 slaughter mass chickens. Intensive broiler chicken sheds contain 25 to 60 thousand birds. Large facilities, with multiple sheds, can house around 300,000 birds. The area packing density of intensively farmed, non-caged broilers is around one chicken per 250 to 500 square centimetres at slaughter mass, with 300,000 birds occupying 15,000 square metres (3 to 4 acres) by the latter density; 750 square centimetres per bird are required for caged broilers.

According the US Department of Agriculture, as of 2013, pork forecasting remained unchanged at 107.4 million tons, beef forecasting had fallen to 57.5 million tons and broiler forecasting had risen to 84.6 million tons; 249.5 million tons in total, globally, per annum. It would require ~97,651 'Quorn Process' culture vessels (14.6 million cubic metres of broth volume) to match this production rate, mass wise, based on the estimates given in the production section. In OSP (Olympic Swimming Pool) units, with one pool having a nominal depth of 2 metres and containing a standard 2,500 cubic metres of water, 5,859 pools worth of volume would be needed, which would cover an area of 7.3 square kilometers. If the pool was instead the depth (or height) of a 'Quorn Process' culture vessel (that being 50 metres as opposed to the 2 metre nominal depth of an olympic swimming pool), this would occupy an area of 0.3 square kilometers. Central Park (NY, USA) and the Royal Botanical Gardens, Kew (London, UK) have areas of 3.4 and 1.2 square kilometres, respectively.

Assuming all broilers produced globally weigh ~2.4 kilos at slaughter and are grown at the maximum area packing density of 250 square centimetres per non-caged broiler, they alone would require ~880 square kilometers of shed area.

Regulation

In the United Kingdom the Ministry of Agriculture, Fisheries and Food approved mycoprotein for sale as a food in 1985.^[1][3]

See also

• History of biotechnology
• United Nations Food and Agriculture Organization

References