MYCOPROTEIN

Mycoprotein is a food material derived from the mycelium of a species of the fungus Fusarium.

[In fact in 1998 it was proven to be Fusarium venenatum. (See YODER, W.T. & CHRISTIANSON (1998). Species-specific Primers Resolve Members Of Fusarium Section Fusarium. Taxonomic Status of the Edible "Quorn" Fungus Re-evaluated. Fungal Genetics & Biology, 23, 62-80.)]

(Misleadingly, it is sometimes referred to as an example of single cell protein (SCP)).

Background
Fusarium graminearum is the conidial stage of the Ascomycote fungus Gibberella zeae. The fungus exists mainly as a saprobiont in soil, although it is capable of parasitising wheat and other cereals. It has a mycelium of narrow, branched and septate hyphae. This basis for a naturally fibrous (and therefore 'chewy') texture has been exploited in the formulation of meat analogues.

The material is marketed under the brand name QuornTM. Teachers are recommended to obtain the useful teaching pack, available from the QuornTM Education Service.

Mycoprotein fermenter

The fermenters currently being used to manufacture mycoprotein are 40m high (similar in height to Nelson's column). The fermenters run continuously for six weeks, after which there is a two week period for cleaning and preparing the fermenter for the next run. During the six week run, there is a steady input of nutrients and a corresponding output of medium containing the product.

Mechanical agitation is not used; the fermenter is not of the paddle-stirred type but is an air lift or 'loop' fermenter, in which circulation of the broth is achieved by pumping compressed air into the system. Introduction of this air at the base reduces the density of the broth, which therefore rises. Gases, including carbon dioxide produced by fungal respiration, leave the. broth at the top and are pumped out. The broth, now with increased density, descends in the other limb of the vessel thus the air supply both agitates the broth and supplies oxygen for the aerobic process.

Apart from oxygen, a source of carbon is required; this is provided as a syrup, containing approximately 95% glucose, derived from enzymic and/or acid hydrolysis of maize starch. Nitrogen is also needed; this is supplied as ammonia.

Other mineral ions, including potassium, magnesium and phosphate, are also supplied, as well as trace elements.

Stringent precautions are taken to avoid contamination with unwanted organisms which would ruin the product and compete with Fusarium for the substrate. These include the initial sterilisation of the fermenter, using steam. The incoming nutrients are heat sterilised and a filtered air supply is used. Conditions within the fermenter are monitored by means of probes. Adjustments to pH, temperature, nutrient concentration and oxygen supply can be made as required to secure the optimum growth rate. After emerging from the fermenter, the mycoprotein is subjected to a temperature of 65C, a treatment which triggers the breakdown of most of the fungal nucleic acid, the level of which would otherwise exceed health and safety limits.

The material is then dried in huge centrifuges. It emerges from the dryer looking rather like pastry and has a slight mushroom-like smell. It is then processed into food products which usually contain added flavourings and other ingredients.

Mycoprotein production represents an efficient use of a cheap and readily available energy source. The harvested product readily absorbs a wide variety of flavourings and colouring, whilst its fibrous texture (arising from its mycelial origin) makes it easy to formulate into products which 'chew' like meat and fish.

It is relatively easy for students to construct and use a simple bioreactor which illustrates the air lift principle; a commercial kit for such a bioreactor (not a fermenter in this case) is available (see Resources, page 40.).

Advantages of using mycoprotein

The material has high all-round nutritive value:

Candidates should be aware of the potential health benefits of these features in terms of the roles of nutrients in a balanced diet (core syllabus, page 9) and also in terms of the control of body mass and the lower risk of heart disease.

QuornTM is suitable for vegetarians, but not for vegans, since a small amount of egg white is added during processing of the harvested product.

Nutritional analysis of freshly-harvested QuornTM mycoprotein:

Constituent Mass (g per 100g)
Protein 11.8
Dietary fibre 4.8
Fat3.5
Carbohydrate2.0
Sodium0.24
Cholesterol 0.0
Water75.0

(The remaining mass includes a wide variety of minerals and vitamins, particularly zinc and vitamin B 12, as well as compounds such as nucleic acids).

Recall of this data is not required but candidates may be expected to use information of this type, as well as data comparing the nutrient content of mycoprotein products with that of other foods, in assessing the value of mycoprotein.

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