Protein and fat compositiOn and vitamin content of () luteus mycelium produced in submerged culture

Mar j a L i is a Hat t u l a and H. G. G y ll e n b e r g Department of Microbiology, University of Helsinki

Man has utilized fungi as food for cen­ lium in submerged culture. Agaricus cam­ turies. Agaricus spp. and Boletus spp. of the pestris was the first which was inten­ Basidiomycetes and spp., the morel sively investigated. HuMFELD (1948, 1952 ), of the Ascomycetes have been the HuMFELD & SuGIHARA (1949, 1952), SuGIHARA most common types consumed (LITCHFIELD, & HuMFELD ( 1954) etc. have investigated the 1964) . The idea of growing fungi for their growth factors and methods of growing A. mycelium rather than their fruiting bodies campestris. JENNISON and his co-workers developed because of, or at least was stimu­ (1955, 1957 ) investigated the submerged lated by, the success of deep tank or sub­ cultivation of 42 different kinds of fungi. In merged fermentation in the field of the large a series of patents SzuEcs and YoNKERS (1950, scale production of antibiotics (RoBINSON & 1954, 1956, 1958 ) disclosed methods for pro­ DAVIDSON, 1959). Man has grown various ducing essence of fungal mycelium in sub­ microorganisms on an industrial scale since merged culture and for enhancing the flavor World War I when yeasts were produced to of the mycelium. The main trend in present supply a .source of dietary fats in Germany. day research in this field seems to be myc­ During World War II several kinds of micro­ elium production as a source of flavor rather organism were grown for human food pur­ than as a source of protein. poses. Food preparations were made from In this paper experiments on submerged strains of Fusarium, Candida, Oospora, cultivation of Boletus ( Suillus) luteus are Endomyces and Rhizopus. The main purpose described. Boletus luteus is a quite common was to produce fats and protein. There is in Finland but its great water one particular reason, however, why fungal content and its susceptibility to insect larvae mycelium can be given preference to other make it less acceptable (RAUTAVAARA, 1947). microbial preparations. The edibilities of The taste of the mushroom is slightly sour different fungi are known by tradition and and the smell recalls that of fruits (HINTIKKA experience, and moreover there is no religious & SArmo, 1942 ) . The main purpose of this taboo against fungi. Thus, if a natural pre­ investigation was to develop methods for judice toward new and unusual food ma­ growing the mycelium of Boletus luteus in terials can be overcome, there seems to be no submerged culture and to compare the vi­ reason why the use of fungi for food should tamin, fat and protein content with the not increase repidly (GILBERT & RoBINSON, corresponding values of the fruiting bodies. 1957). Boletus luteus was selected as the test orga­ Over the past 20 years a number of in­ nism because it seemed to be rather easy to vestigators have directed their attention grow in big laboratory fermentors ( 14 liters ). toward the mass propagation of fungal myce- Later experiments (cf. HATTULA & GYLLEN-

46 BERG 1969 ) have shown that a number of ot­ 40°C until they were e~.:.sy to grind to fiPe her fungi show better adapta:bility to sub­ powder. The powder, the colour o.f which was merged growth. dark brown, was kept in a closed vessel in the refrigerator.

Materials, methods and results Analytical methods Cultural methods: The culture used in the The vitamins: submeraed growt experiments was kindly Of the water soluble vitamins thiamine, ri­ supplied by Professor P. Mikola. (J?ept. of boflavin, nicotinic acid and vitamin B,, were Silviculture, University of Helsmki). The analysed quantitatively and of the fa•t soluble stock culture of Boletus luteus was grown on vitamins vitamin D was determined. agar slant of the Modess' agar (:MonEss, Thiamine was extracted according to the method 1941 ), the composition of which is presented of A.O .A.C. (39 025, 1960 a). The solution was in the accompanying paper (HATTULA & refined free from other fluorescent compounds GYLLENBERG, 1968 ) 0 according to STROHECKER & HENNING ( 1963 a). The Two agar slants of B. luteus (2 weeks old) determination was made by the A.O.A.C. method were inoculated into 80 ml of sterile 5 % (39·025, 1960 a). The thiamine content of the malt extract in a 250 ml Erlenmeyer flask. mycelium was 12 .3 fJ-/g dry mycelium and that of The flask was incubated one week in a rotary the fruiting 4 fl-g/g dry powder. shaker operated at 280 rpm. The grown Riboflavin was extracted according to the met­ mycelium was washed with sterile ?estilled hod of A.O.A.C. (39 033, 1960 b). The method of water and was transferred to a 2 bter fer­ STROHECKER & HENNING ( 1963 b) was used for mentor. In the two-liter fermentor one liter refining the solution. The determination of the of Reusser's synthetic medium (REussER & vitamin was performed according to the method al. 1958 a; for the composition of this medium of A.O.A.C. (39 033, 19•60 b) . The riboflavin cf. HATTULA & GLYLLENBERG, 1969) was used. content of the mycelium was 41.0 fl-g/g dry myce­ The aeration rate was one liter air/min/1 lium and the corresponding value for the fruiting medium· agitation was 300 rpm and the tem­ body was 57.0 fA-g. perature' 28°C. After one week the mycelium Nicotinic acid (Niacin and Nicotinamide) was was transferred into a 14 liter fermentor determined according to the method of A.O.A.C. which contained 10 l of Reusser's synthetic (39 037, 39· 038, 1960 c) . The nicotinic acid con­ medium. Aeration was adjusted to 0.8 vol. tent of the mycelium was 214 fA-g whereas the air/minfvoL of the medium, agitation was content of the fruiting body was 1560 fl-g/g dry 280 rpm and the temperature kq~t at 28°C. powder. Synthetic Naphco was used as antrfoam. The Determination of the vitamin B, was made using growth was controlled by taking daily samples a microbiological method with Escherichia coli for determination of sugar (Bertrand-met­ ( DmrNG 19·5 2) . The extraction of the vi tam in hod; GROSSFELD, 1935 ) and ammonium from the material was performed according to the nitrogen (Conway method; CoNWAY, 1957) . method of STROHECKER & HENNING ( 1963 c). The When all the sugar was consu~ed, 9 1 of the vitamin B12 content of the fruiting body was found culture was removed and one hter was left at to be 55 mfl-g/g and the corresponding vitamin the bottom of the vessel as inoculum. New B,, content of the mycelium 62 mfJ-g/g dry powder. sterile medium was conducted into the fer­ The analytical data concerning the water soluble montor, and this was repeated four times. vitamins are summarized in Table 1. The mycelium was separated by Biichner­ filtration and was washed with distilled water. The mycelium was then dried at 40°C and Table I. The water soluble vitamins of Boletus the dry material as ground to fine powder. luteus. Vitamin content fl-g/g dry mushroom. The colour of the fresh mycelium was white and the aroma pleasant. The dry powder was Vitamin Mycelium Fruiting body yellow and almost odourless. Thiamine 12.3 4.0 Fruiting bodies of Boletus luteus :vere Riboflavin 41.0 57.0 collected from a pasture! and for companson; Nicotinic acid 214.0 1560.0 the were scraped clean of sand and dried at Vitamin B,, 0.062 0.055

47 The fat soluble vitamins were extracted from conceming the total fatty acid composition of the unsaponified fraction of the fat according to Boletus luteus are given in Table 2. The fatty acid PAWH & TRACEY ( 1955). The qualitative analysis composition of yeasts cultivated on mineral oil was made by thin layer chromatography (STAHL, hydrocarbons is represented for comparison. 1962) . Only the vitamin D was analyzed quantita­ tively. In the mycelium as well as in the fruting Table 2. The fatty acid composition of Boletus bodies small amounts of ~-carotene were detected. luteus compared with the fatty acid composition The attempts to demonstrate the presense of a­ of yeasts cultivated on mineral oil hydrocarbons. tocopherol and vitamin K failed. The itamin D Fatty acid Boletus luteus Yeasts was analyzed quantitatively according to STRO­ mycelium fruiting (ALENTYEVA HECKER & HENNING ( 1963 d) . The vitamin D body & a!., 1968) content of the mycelium was 2.2 ftg/g dry mycelium c1o- c1s 8.5 0.8 0.3

compared with the 9.2 ftg/g dry fruiting body. C14 :0 3.6 0.1 0.1 Fats: The total fat of the mycelium and the cl4:1 0.1 fruiting body preparations was extracted according cl5 2.8 0.5 3.2 to the method of A.O.A.C. (22 032, 1960 d). The c1s 14.8 10.6 14.5 rough analysis of the fat was made by thin layer cl6:1 1.3 1.7 3.7 chromatography (HATTULA, 19·65). The following cl7:o 1.7 0.4 26.3 lipid fractions were found in both preparations: cl7 : 1 23.2 phospholipids, sterols, triglycerides, free fatty acids c1s 7.5 19.3 9.1 and sterolesters. Although some difference in the cls:1 20.4 16.9 14.7 fatty acid composition of these fractions occured cls=2 22.6 29.1 4.3 the total fatty acid composition (of the unfractio­ cl9 1.6 0.8 nated fat) may provide a representative picture. cls:3 0.4 The fatty acid methyl esters were analyzed using unidentified 18.3 19.8 0.5 a Perkin Elmer Gas Chromatograph. The results Total% 100.0 100.0 100.0

Table 3. The amino acid content of Boletus luteus compared with the amino· acids of potato, beef and algae (Spirulina maxima). Gram of amino acid/ 16 gram of nitrogen.

Amino acid Boletus luteus Potato Beef Spirulina maxima fr. body mycel. (BELITZ & SCHORMULLER, (CLEMENT & a!., 1967) 1967)

Aspartic acid 6.06 7.15 11.5 9.7- 9.9 8.60 Threonine 3.39 3.60 2.5 4.8 4.56 Serine 3.47 3.88 2.6 4.1- 4.5 4.20 Glutamic acid 10.52 8.50 7.4 15.8-16.2 12.60 Proline 3.43 3.23 3.0 3.0- 4.1 3.90 Glycine 3.59 3.61 1.9 4.6- 6.1 4.75 Alanine 4.26 4.89 6.1 6.1- 6.3 6.80 Valine 0.13 4.3 4.8- 5.5 6.49 Cystine 4.02 5.87 0.6 1.3- 1.5 0.40 Methionine 0.18 1.08 2.5 4.1- 4.5 1.37 a-e-diaminopimelic acid 20.02 15.46 Isoleucine 6.39 5.9 5.2 6.03 T yrosine 2.47 3.86 2.5 3.8- 4.0 8.02 Phenylalanine 2.63 4.25 3.6 3.8- 4.5 4.97 y-aminobutyric acid 4.69 1.16 Ornithine 0.30 0.30 Lysine 2.67 8.39 3.7 9.2- 9.4 4.59 Tryptophan 1.74 3.72 1.0 1.40 Histidine 2.15 2.35 1.2 3.7- 3.9 1.77 Arginine 4.18 4.70 7.1 5.3- 5.5 6.50 Ammonia 11.58 8.21 1.24

48 Amino acids: Only the total amino acids of and the mycelium are comparable to good Boletus luteus were analyzed; the free amino acids vegetable and animal protein except for were not analyzed separately. An Autoanalyzer valine and methionine. The amount of oys­ (Technicon) was used for the determinations and tine is, however, remarkably high and cystine the preparative and analytical methods are descri­ can substitute for methionine in the diet up to bed in detail in the accompanying paper of HAT­ 80 o/o. Accordingly, the low valine content is TULA and GYLLENBERG (1969). the only real deficiency of B. luteus protein. Table 3 shows the total amino acid composition However, in the mycelium of Boletus luteus of Boletus luteus . .Some data referring to the amino no isoleucine could be detected, but the acid compostion of vegetable, animal and micro­ amount of this amino acid was sufficient in bial protein have been included for comparison. the fruiting body. The amounts of leucine, phenylalanine, lysine and tryptophan are high Discussion enough in the mycelium of this fungus but in the fruiting body the amounts of lysine and The main components of Boletus luteus are leucine are quite small. On the whole the summarized in Table 4. The results show amino acid content can be regarded good. that the cannot be considered The contents of different water soluble vi­ of great nutritional value because of their tamins in Boletus luteus are good. 100 g dry smaH amount. As to the fatty acid compo­ mycelium contains the same amount of thia­ sition of B. luteus, the high content of linolic mine as 220 g pork or 250 g wheat meal acid contributes significantly to the nutritio­ (whole grain). As to the riboflavin content nal value. The results for amino acids given of the mushroom 100 g of the dry fruiting in Table 3 show that both the fruiting body body corresponds to 370 g pork or 190 g veal ( TURPEINEN & RorNE, 196 7) . The Table 4. The main components of dried Boletus amount of nicotinic acid is also considerable. luteus. In our opinion Boletus luteus seems to constitute a good supplement for other foods, Component Fruiting bodies Mycelium especially with regard to the protein and Carbohydrates the water soluble vitamin content of the (soluble) 5.00 5.15 mushroom. Mo-reover, it is obvious that the Fats 5.50 4.30 submerged cultivation of mycelium does not Protein (N X 6.25) 24.60 23.80 cause losses in nutritionally valuable consti­ Moisture 3.44 6.51 tuents as compared with the fruiting bodies Ash 5.85 4.25 produced under natural conditions. In fact, Insoluble material as shown above, the artificially grown my­ (cellulose, etc.) 55.61 55 .99 celium, in certain respects may possess an Total % 100.0 100.0 even higher nutritional value.

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50