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Feed and food protein from higher Fungi Mycelia
Feed and food protein from higher Fungi Mycelia
Atanas Torev
Higher Institute of Agriculture, "Vasl
Kolarov", Plovdiv, Bulgaria
Among suggested novel sources of protein are bacteria, yeast, algae, and the mycelia of higher fungi. The latter deserve special consideration, since man has probably consumed mushrooms throughout his evolutionary history, and their flavour is mild and pleasing to most persons. Moreover, unlike human feeding studies with bacteria and yeast, no problems of food allergy have been reported (1). While the cultivation of fungal mycelia has many factors in common with the production of other lower organisms, it has a special advantage in its simple nutrient requirements and a size that makes it easy to separate out by filtration without special equipment requirements.
The organism we have selected is the wood mushroom, Polyporus squamosus-64. The fungal mycelium can be grown on molasses alone, or on other carbohydrate sources such as glucose, sulfite liquor, and whey with the addition of a phosphate and a nitrogen source such as ammonium nitrate or ammonium sulfate. Table 1 shows the nutrient composition of this mycelium. The development cycle varies from seven to 48 hours, depending upon concentration, and can be adapted to batch, semi-continuous, or continuous culture. The final product need only be washed in pure water, filtered, and either pressed or dried.
TABLE 1. Nutrient Composition of Mycelium
| Raw protein | 54 - 58% |
| Pure protein | 44 - 46% |
| Carbohydrates | 22 - 24% |
| Lipids | 4% |
| Mineral composition | 7% |
| Nucleic acids | 6 - 8% |
| Vitamin B1 | 9 mg% |
| Vitamin B2 | 39 mg% |
| Vitamin B12 | 14 mg% |
| Digestibility of protein | 83% |
We produced a molded product industrially in blocks of ten kilograms with a dry matter content of 26 to 28 per cent. It is whitish or slightly grayish in clour, fibrous in structure, and with a slight taste of yeast. When dried to 93 per cent dry matter and powdered, it still has a slightly fibrous structure, a white-to-cream colour, and a taste characteristic of mushrooms or baked flour. In Bulgaria, the cost of the pressed material for addition to sausage is from one-third to one-quarter the cost of the meat and its protein content is roughly equivalent.
The essential amino acid content of the mycelium is given in table 2. In addition, feeding studies in experimental and farm animals were carried out over many years for acute toxicity, carcinogenicity, and teratogenicity with completely negative results and good growth and reproductive performance. Human feeding trials with various mycelial products have indicated that the material is well tolerated, with no allergenicity observed. As a result of these investigations, the higher institutes of food of both the People's Republic of Bulgaria and of the Soviet Union have approved the product for food use.
TABLE 2. Essential Amino Acid Composition of Fungi Mycelium and Selected Protein Sources
| Mycelium PS-64 | Beef | Casein | Soya Flour | |
| Lysine | 8.5 | 8.4 | 8.4 | 6.4 |
| Threonine | 5.3 | 4.0 | 5.0 | 3.8 |
| Valine | 6.0 | 5.7 | 7.4 | 5.0 |
| Isoleucine | 5.1 | 5.1 | 6 2 | 6.4 |
| Leucine | 7.2 | 8.4 | 9.4 | 6.6 |
| Tryptophan | 1.4 | 1.1 | 1.2 | 1.2 |
| Methionine | 1.9 | 2.3 | 2.0 | 0.7 |
| Cystine | 0.9 | 1.4 | 0.3 | - |
| Phenylalanine | 3.9 | 4.0 | 5.1 | 4.8 |
| Tyrosine | 3.4 | 4.0 | 6.4 | 3.1 |
The extensive studies of potential food use of the fungal mycelia have indicated the most important to be: (i) as a partial meat replacement in different sausages and processed meat products; (ii) in the production of different kinds of cheese; (iii) in the enrichment of canned vegetable products, and (iv) as an addition of fish paste and other paste products.
A completely different use is the enrichment of feed grains through solid state fermentation. Corn, barley, and other cereals standard for animal feeding are ground, mixed with added ammonia and phosphate salts, mixed, sterilized, innoculated, and allowed to ferment for 36 hours without added heat because the process itself is exothermic. The result is a fodder mixture with an additional five to seven per cent protein. If corn is the substrate material, the resulting mixture contains more protein than required for feeding swine and calves, and is adequate for feeding poultry without additional protein concentrates. Such a mixture produces equal or better rat growth than found in grains with added soy, yeast, other protein sources.
REFERENCE
1. N.S. Scrimshaw and J. Udall, "The Testing of Single-Cell Proteins for Human Consumption," in: Proceedings of an International Symposium on Single Cell Proteins, 28-30 January, 1981, Paris, France, J. Senez, ed., in press.