Edible protein containing substances

This invention is for improvements in or relating to the production of edible protein containing substances.
It has particular reference to a process for reducing the nucleic acid content of microfungi.
Our Specification No. 1,210,356 describes and claims a process for the production of an edible protein-containing substance which comprises incubating and proliferating, under aerobic conditions, an organism which is a non-toxic strain of a microfungus of the class Fungi Imperfecti, in a culture medium containing essential growth-promoting nutrient substances, of which carbon in the form of assimilable carbohydrate constitutes the limiting substrate in proliferation, and separating from the assimilable carbohydrate exhausted medium the proliferated organism which constitutes the edible protein-containing substance.
Our application No. 8977/70 (Ser. No. 1,331,471) describes and claims a process for the production of an edible protein-containing substance which comprises incubating and proliferating, under aerobic conditions, a non-toxic strain of Penicillium notatum or Penicillium chyrsogenum or a variant or mutant thereof, in a culture medium containing essential growth-promoting nutrient substances, of which carbon in the form of assimilable carbohydrate constitutes the limiting substrate in proliferation, and separating from the assimilable carbohydrate exhausted medium the proliferated organism which constitutes the edible protein-containing substance.
Our application No. 8978/70 (Ser. No. 1,331,472) describes and claims our specific novel strain of Penicillium notatum-chrysogenum IMI 138291 and variants and mutants thereof.
Our application No. 30584/70 and cognate No. 10466/71 (Ser. No. 1,346,062) describes and claims a process for the production of an edible protein-containing substance which comprises incubating and proliferating, under aerobic conditions, a non-toxic strain of the genus Fusarium or a variant or mutant thereof, in a culture medium containing essential growth-promoting nutrient substances, of which carbon in the form of assimilable carbohydrate constitutes the limiting substrate in proliferation, and separating the proliferated organism comprising the edible protein-containing substance. The corresponding U.S. Patent is U.S. Pat. No. 3,937,654.
Our British specification contains the following disclosure:
The present invention relates to a process for the production of edible protein-containing substances and has particular reference to the production of fungal protein by microbial action.
Our Specification No. 1210356 relates to a process for the production of an edible protein-containing substance which comprises incubating and proliferating, under aerobic conditions, an organism which is a non-toxic strain of a microfungus of the class Fungi Imperfecti, in a culture medium containing essential growth-promoting nutrient substances, of which carbon in the form of assimilable carbohydrate constitutes the limiting substrate in proliferation, and separating from an assimilable carbohydrate exhausted medium the proliferated organism which constitutes the edible protein-containing substance.
Our copending application No. 8977/70, Ser. No. 1,331,471, claims an edible protein-containing substance comprising fungal mycelium possessing a high net protein utilisation value on rat assays of at least 70 based on the .alpha.-amino nitrogen.
It is also an object of the present invention to provide an edible protein-containing substance comprising non-toxic fungal mycelium possessing a high net protein utilisation value on rat assays of at least 65 preferably at least 70 based on the .alpha.-amino nitrogen and containing a non-toxic strain of the genus Fusarium or a variant or mutant thereof. The non-toxic mycelium possessing a high net protein utilisation value of at least 70 based on the .alpha.-amino nitrogen may contain a non-toxic strain of the species Fusarium graminearum.
According to the present invention there is provided a process for the production of an edible protein-containing substance which comprises incubating and proliferating, under aerobic conditions, a non-toxic strain of the genus Fusarium or a variant or mutant thereof, in a culture medium containing essential growth-promoting nutrient substances, of which carbon in the form of assimilable carbohydrate constitutes the limiting substrate in proliferation, and separating the proliferated organism comprising the edible protein-containing substance.
The separated proliferated organism comprising the edible protein-containing substance may be incorporated into a foodstuff for human or animal consumption.
The substrate employed in the incubation stage may be of vegetable origin, for example starch, starch containing materials or products of their hydrolysis, sucrose, sucrose containing materials or hydrolysed sucrose i.e. invert sugar or mixtures thereof. Thus the substrate may comprise hydrolysed potato, molasses, glucose, maltose, hydrolysed bean starch or cassava. Alternatively substrate of animal origin comprising whey may be employed.
The non-toxic strain of Fusarium may be a strain of Fusarium graminearum.
The preferred non-toxic strain is our strain of Fusarium graminearum Schwabe, which is described and claimed together with variants and mutants thereof in copending United Kingdom application No. 23452/70 (Ser. No. 1346061), has been deposited at the Commonwealth Mycological Institute, Kew, and assigned the number IMI 145425. It is non-pathogenic to wheat.
Our copending United Kingdom application No. 23452/70 (Ser. No. 1346061) also describes and claims specifically five variants of our strain of Fusarium graminearum Schwabe IMI 145425 namely I-7, I-8, I-9, I-15 and I-16 deposited with the Commonwealth Mycological Institute and assigned the numbers IMI 154209, IMI 154211, IMI 154212, IMI 154213 and IMI 154210 respectively.
The temperature of incubation is in general between 25.degree. and 34.degree. C., preferably around 30.degree. C.
Inoculation resulting in commencement of the process is carried out by a pregerminated seed stage comprising for example from 2% to 10% of inoculum, usually in the range 5% to 10% of inoculum based on final fermented operating volume.
The pH of the substrate medium during incubation is preferably kept within a suitable range supporting maximum growth, for example, between 3.5 to 7.
The period of growth in batch culture under the above-mentioned conditions is usually found to range from 20 to 48 hours. In both batch and continuous processes aeration and agitation should be carried out to provide a sufficient level of dissolved oxygen to overcome deficiency which can be a limiting growth factor.
As will be well understood by those skilled in the art sufficient quantities of essential growth nutrients such as nitrogen, sulphur, phosphorus and other trace elements are maintained in the substrate medium so that growth of the substrate is limited only by the carbohydrate available to the fungus.
In addition to the nutrients stated above the presence of one or more vitamins such for example as biotin may be desirable to maintain maximum growth rate.
It is also desirable to add a non-toxic anti-foaming agent to the substrate medium to control foaming during the fermentation.
The substance produced according to the present invention may be isolated in any suitable manner known in the art. Thus the resulting mycelium may be recovered by separation, washing, filtration and drying. In this connection, however, it has been found that if the moisture content of the substance is reduced below a critical level of about 50% (w/w) by filtration under pressure the subsequent drying methods employed are not subjected to such stringent temperature limitations which is an important factor in the economic processing of these materials. The method of drying must not cause damage to the nutritional value of the mycelium and may be drying in a current of air at 75.degree. C. or freeze drying.
The fungal mycelium produced by the process of the present invention shows very good water binding capacity and may be useful as a thickening and gelling agent. Not being an isolate, it retains its vitamins as well as other nutritionally available materials such as lipids and some carbohydrates. Fungal mycelium has satisfactory baking characteristics which are of value in protein enriched breads, breakfast foods and food snacks. The fungal mycelium, because of its filamentous structure, can be baked, fried or puffed and presented to many communities as a food comparable in appearance and acceptability with conventional foods which they are accustomed to eating.
Following is a description by way of example of methods of carrying the invention into effect.
Culture medium or medium percentages given are as weight per unit volume (w/v) or volume per unit volume (v/v) for solids and liquids respectively
Definitions:
NPU=net protein utilisation
NPUop=net protein utilisation: operative
.mu.: a specific growth rate which is the rate of increase/unit of organism concentration ##EQU1## .mu..sub.max. is the growth rate constant (the maximum value of .mu. at saturation levels of substrate).
Yield Factor: weight of organism formed/weight of substrate used.
Examples 1-4 are of batch culture.

EXAMPLE 1
10 Liters of the following culture medium were prepared and sterilised as described in a stirred fermenter vessel.
______________________________________Cane molasses to provide 6% w/v sugarAmmonium sulphate 1.2%NaH.sub.2 PO.sub.4 0.25%Sterilised 30 minutes 15 psigCaCO.sub.3 0.5% w/vSterilised 3 hours 15 psig______________________________________
The medium components were added aseptically and attemperated to 30.degree. C. An inoculum equivalent to 5-10% by volume of the culture medium and grown either on a glucose/corn steep liquor medium or other suitable materials in shake flasks was inoculated with a spore suspension of the organism comprising our strain of Fusarium graminearum Schwabe IMI 145425, for 18-24 hours at 30.degree. C. on a rotary shaker, and added aseptically to the fermenter.
The fermenter incubated at 30.degree. C. was then stirred at 800 rpm with a 6 bladed disc turbine (0.5D) in a full baffled vessel and 1 VVM of sterile air passed through. After 35 hours, the grown mycelium was removed from the fermenter, centrifuged, washed with water and dried in a warm air band drier, air temperature 75.degree. C.
The dried product had the following composition:
______________________________________Total Nitrogen 8.0%Ash 5.3%Lipid 2.7%NPUop. 52 based on Total Nitrogen______________________________________
EXAMPLE 2
10 Liters of the following culture medium were prepared and sterilised as described, in a 14 liter New Brunswick, Microferm, fermenter.
______________________________________ Final %______________________________________Solution 1 Glucose pH 3.0 3.0Solution 2 Ammonium sulphate 0.7Solution 3 Potassium di-hydrogen pH 5.0 1.0 phosphateSolution 4 FeSO.sub.4 7H.sub.2 O pH 2.5 0.001 MnSO.sub.4 4H.sub.2 O 0.0005 CuSO.sub.4 5H.sub.2 O 0.0001 MgSO.sub.4 7H.sub.2 O 0.025Solution 5 Na.sub.2 MoO.sub.4 2H.sub.2 O 0.0001 CoCl.sub.2 6H.sub.2 O 0.0001 CaCl.sub.2 2H.sub.2 O 0.0015Solution 6 NaOH 0.1______________________________________
All the above solutions were sterilised by heat for 15 minutes at 15 psig. Solution 7 Vitamins and/or amino acids as described below sterilised by filtration.
The solutions were added aseptically to the vessel.
An inoculum was grown and added as in Example 1 except that the final concentration in the fermenter was adjusted so as to provide 0.5 gm/l dry wt. of mycelium.
The conditions of growth were temperature 30.degree. C.; aeration 1 VVM, stirrer speed was adjusted to maintain a level of dissolved oxygen above 25% of the saturation value in the culture medium, measured by a New Brunswick Inc. DO probe. Sterile anti-foam, polypropylene glycol 2000, was added as required to suppress foam and pH was maintained between 6.0-6.3 by the addition of sterile potassium hydroxide solution.
______________________________________ Growth rates (hr..sup.-1)______________________________________(i) Omitting solution 7 (Minimal medium) very slow(ii) Solution 7 such that the final 0.2 concentration of Biotin in the culture medium was 50 .mu.g/l(iii) Solution 7 such that the final 0.25 concentration of Biotin in the culture medium was 50 .mu.g/l; Choline chloride 30 mg/l and Methionic 300 mg/l______________________________________
EXAMPLE 3
Medium and conditions were as in Example 2, but the glucose was replaced with maltose.
______________________________________(i) Solution 7 as Example 2 (ii) 0.18(ii) Solution 7 as Example 2 (iii) 0.21______________________________________
EXAMPLE 4
100 Liters of the following culture medium were prepared and sterilised as described in a 130 l stainless steel fermenter.
______________________________________ % final concentration______________________________________Glucose 4.0Corn steep liquor (50% Total 0.8Solids)Ammonium sulphate 0.2Potassium di-hydrogen phosphate 0.2MgSO.sub. 4 7H.sub.2 O 0.025ZnSO.sub. 4 7H.sub.2 O 0.0005FeSO.sub. 4 7H.sub.2 O 0.0005MnSO.sub. 4 4H.sub.2 O 0.0001______________________________________
The medium was sterilised at pH 3.0 at 15 psig for 30 minutes and on cooling to 30.degree. C. adjusted to pH 5.0 by the sterile addition of ammonia.
Biotin sterilised by filtration to give 40 .mu.g/l final concentration, was added aseptically.
The vessel was inoculated with 10 liters of culture grown in a sparged vessel, for 18 hours, at 30.degree. C., on a medium containing: Glucose 2%; tryptone ("Oxoid") 0.4%; yeast extract ("Oxoid") 0.1%; ammonium sulphate 0.15%; potassium di-hydrogen phosphate 1%; sodium hydroxide 0.1%; magnesium sulphate 0.025%; ferrous sulphate 0.001%; zinc sulphate 0.001%; manganese sulphate 0.0005%; copper sulphate 0.001%; anti-foam, polypropylene glycol 2000 0.05% and sterilised for 45 minutes at 15 psig, inoculated with a spore suspension of our organism Fusarium graminearum Schwabe IMI 145425. The word "Oxoid" is a Registered Trade Mark.
The conditions for growth were temperature 30.degree. C., aeration adjusted to provide dissolved oxygen concentrations above 10% of the saturation value for the culture broth. Sterile anti-foam, polypropylene glycol 2000, was added to suppress foaming, and the pH was maintained at 5.0 by means of sterile ammonia additions. Samples of the mycelium were taken at intervals over the period of batch culture, filtered, washed with water and dried. On dry weight basis analysis gave Total nitrogen 8.0-8.6%; .alpha.-Amino nitrogen 6.4-6.6%. The initial growth rate in this complex medium derived from both the batched culture medium and inoculum was approximately 0.3 hr..sup.-1.
The following examples 5 and 6 are of continuous culture.
EXAMPLE 5
Culture medium of the following composition was prepared:
______________________________________ Final %______________________________________Solution 1Glucose 3.0Ammonium sulphate 0.25Potassium di-hydrogen phosphate 0.3Magnesium sulphate 0.025Anti-foam, polypropylene 0.01glycol 2000Sterilised at pH 3.0 for30 minutes at 15 psigSolution 2MnSO.sub.4 4H.sub.2 O 0.0005FeSO.sub.4 7H.sub.2 O 0.0005ZnSO.sub.4 7H.sub.2 O 0.0005CoCl.sub.2 6H.sub.2 O 0.0001CuSO.sub.4 5H.sub.2 O 0.0001NaMoO.sub.4 2H.sub.2 O 0.0001Sterilised 15 minutes at 15 psigSolution 3Vitamins and or amino acid as described belowsterilised by filtration.______________________________________
All solutions were added as necessary, aseptically. In 8.5 liter chemostat the conditions of growth were as follows:
Temperature 30.degree. C.; aeration 1 VVM; agitation 800 rpm single 6 bladed disc turbine 0.5 D in fully baffled vessel. Organism, our strain of Fusarium graminearum Schwabe IMI 145425. The pH maintained at 5.0 by automatic addition of sterile ammonia.
Samples were taken, filtered, washed with water and dried.
__________________________________________________________________________ .mu. Max. Yield Mycelium NPU based NPU based hr..sup.-1 factor TN % AN % on TN on AN__________________________________________________________________________(i) Solution 3 such that the final 0.17-0.19 0.5 7.2 to 7.9 6.3 to 6.8 54 65 concentrate of Biotin in the culture medium was 20 .mu.g/l(ii) Solution 3, such that the 0.20-0.21 0.5 7.7 to 8.6 6.1 to 6.5 59 78 final concentration of Biotin in the culture medium was 20 .mu.g/l and of methionine was 600 mg/l__________________________________________________________________________
EXAMPLE 6
Culture medium of the following composition was prepared:
______________________________________ %______________________________________Bean starch (.alpha.-amylase treated) 3.0 carbohydrateCorn steep liquor 1.33Ammonium sulphate 0.25Potassium di-hydrogen phosphate 0.15Magnesium sulphate 0.025Antifoam polypropylene 0.025glycol 2000 (v/w)Sterilised pH 4.0 for 30 minutes at 15 p.s.i.g.______________________________________
The medium was fed to the 8.5 liter chemostat under the same conditions as in Example 5 except that the pH was varied between 3.5 and 6.0 and growth rate throughout 0.1 hr.sup.-1. Samples were taken, filtered, washed with water and dried. The following result was obtained:
______________________________________ TN AN NPU based NPU based % % on TN on AN______________________________________Product grown at pH 4.0 7.8 6.6 54 67Product grown at pH 5.0 8.6 7.1 57 71Product grown at pH 6.0 7.7 5.9 61 80______________________________________
EXAMPLE 6(b)
The culture medium and conditions were as in Example 6 except that the pH was held at 5.0 throughout the run and the temperature was varied between 26.degree. and 34.degree. C. The optimum temperature was found to be 30.degree.-32.degree. C.
Examples 7 to 11 describe the fermentation of five variants or isolates of Fusarium graminearum Schwabe IMI 145425.
EXAMPLE 7
Duplicate shake flasks of 1-liter capacity were prepared containing 200 mls. of the following medium:
______________________________________ Final con- centration %______________________________________Solution 1 Glucose (sterilised 3.0 separately pH 3.0, 10 p.s.i./10 min.)Solution 2 Ammonium sulphate 0.565 Potassium Dihydrogen 1.0 Phosphate MgSO.sub.4 :7H.sub.2 O 0.025 FeSO.sub.4 :(NH.sub.2).sub.2 SO.sub.4 :6H.sub.2 O 0.0005 MnSO.sub.4 :4H.sub.2 O 0.0005 CuSO.sub.4 :5H.sub.2 O 0.0001 CoCl.sub.2 :6H.sub.2 O 0.0001 CaCl.sub.2 :2H.sub.2 O 0.0015 Na.sub.2 MoO.sub.4 2H.sub.2 O 0.00001 NaOH 0.2 Salts sterilised at 15 p.s.i.g./15 min. Final pH 6.0Solution 3 Vitamins as described below were sterilised by filtration______________________________________
The solutions were added aseptically to give a final volume of 200 ml. then the flasks were inoculated with washed spores of our strain of Fusarium graminearum I-7 IMI 154209 to give a concentration of 8.times.10.sup.3 /ml.
The conditions of growth were temperature 30.degree. C., 140 r.p.m. on orbital shaker with 2" throw.
At hourly intervals the growth was measured by measuring the Optical Density of a sample at 600 m.mu.. From the results obtained the following growth rates were established.
______________________________________ Growth rate h.sup.-1______________________________________(i) Solution 3 omitted (minimal very slow medium)(ii) Solution 3 such that the final 0.22 concentration of Biotin in the culture medium was 50.mu.g/l(iii) Solution 3 such that the final 0.27 concentration of Biotin in the culture medium was 50.mu.g/l and Choline chloride 50 mg/l.______________________________________
EXAMPLE 8
The procedure of Example 7 was repeated but the strain I-7 was replaced by our strain of Fusarium graminearum Schwabe I-8. The following growth rates were established
______________________________________ Growth rate h.sup.-1______________________________________(i) As 7 (i) very slow(ii) As 7 (ii) 0.22(iii) As 7 (iii) 0.27______________________________________
EXAMPLE 9
The procedure of Example 7 was repeated but the strain I-7 was replaced by our strain of Fusarium graminearum Schwabe I-9. The following growth rates were established:
______________________________________ Growth rate h.sup.-1______________________________________(i) As 7 (i) very slow(ii) As 7 (ii) 0.21(iii) As 7 (iii) 0.27______________________________________
EXAMPLE 10
The procedure of Example 7 was repeated but the strain I-7 was replaced by our strain of Fusarium graminearum Schwabe I-15. The following growth rates were established:
______________________________________ Growth rate h.sup.-1______________________________________(i) As 7 (i) very slow(ii) As 7 (ii) 0.21(iii) As 7 (iii) 0.27______________________________________
EXAMPLE 11
The procedure of Example 7 was repeated but the strain I-7 was replaced by our strain of Fusarium graminearum Schwabe I-16. The following growth rates were established:
______________________________________ Growth rate h.sup.-1______________________________________(i) As 7 (i) very slow(ii) As 7 (ii) 0.21(iii) As 7 (iii) 0.27______________________________________
EXAMPLE 12
The procedure of Example 7 was repeated but the strain I-7 was replaced by the parent strain Fusarium graminearum Schwabe IMI 145425. The following growth rates were established:
______________________________________ Growth rate h.sup.-1______________________________________(i) As 7 (i) very slow(ii) As 7 (ii) 0.22(iii) As 7 (iii) 0.27______________________________________
Examples 13 and 14 describe fermentation using strains of Fusaria other than Fusarium graminearum.
EXAMPLE 13
A spore suspension of Fusarium solani strain A7-16 (IMI 154217) was inoculated into a seed fermenter of 80 liter volume containing a glucose, corn steep liquor medium. After growing up the seed fermenter to 10-20 gms per liter, it was split in two, 40 liters to each 400 liter vessel. The seed was inoculated into a medium of the following composition:
______________________________________ %______________________________________Starch 6.0KH.sub.2 PO.sub.4 0.20(NH.sub.4).sub.2 SO.sub.4 0.25Corn Steep Liquor 0.50(50% Total Solids)______________________________________
pH was 5.5 maintained by addition of sterile ammonia; Temperature 30.degree. C. Pressure 30 p.s.i.g. Air rate 1.0 v.v.m. The revolutions of the stirrer were increased steadily from 92 to 184 r.p.m. to maintain dissolved oxygen in the vessel. The agitator consisted of two turbines 0.4D. When the carbohydrate had been utilised the grown mycelium was removed from the fermenter, filtered, washed with water, centrifuged, and dried in a warm air band drier at 75.degree. C. The dried product had the following composition:
______________________________________Total nitrogen 9.1%Ash 8.3%______________________________________
When fed to rats this material gave an NPUop of 41 based on Total Nitrogen.
EXAMPLE 14
Fusarium oxysporum strain A9-23 (IMI 154214) was grown exactly as in the previous example except the starch was replaced by cane molasses at a concentration that produced 6.0% sugars.
The dried product had the following composition:
______________________________________Total Nitrogen 9.9%Ash 10.8%NPUop 47.0 based on Total Nitrogen______________________________________
Methods of analysis for Total Nitrogen (TN) Automatic Kjeldahl digestor (Technicon). A Ferrari, Ann. N.Y. Sci. 87, 792 (1960).
Amino nitrogen (AN) 2:4:6-Tri-nitro benzene sulphuric acid (modified). M. A. Pinnegar, Technicon Symposium 1965, p. 80.
Our Application No. 23452/70 (Ser. No. 1,346,061) describes and claims our specific novel strain of Fusarium graminearum Schwabe IMI 145425 and variants and mutants thereof.
The separated proliferated organism comprising the edible protein-containing substance obtained by the fermentation processes of our Applications Nos. 8977/70 (Ser. No. 1,331,471) and 30584/70 and Cognate No. 10466/71 (Ser. No. 1,346,062) may be incorporated into a foodstuff for human or animal consumption.
The processes of our Applications Nos. 8977/70 (Ser. No. 1,331,471) and 30584/70 and Cognate No. 10466/71 (Ser. No. 1,346,062) are capable of producing an edible protein-containing substance comprising fungal mycelium which possesses a high net protein utilisation value on rat assays of at least 70 based on the .alpha.-amino nitrogen.
If single-cell protein is to be used as a primary protein source for human consumption the Protein Advisory Group of the Food and Agricultural Organization (FAO) World Health Organisation (who) has advised that the nucleic acid content should be reduced to a level which would allow a maximum intake in the range of 2 grams of nucleic acid per day.
For a processing method to be acceptable, it must not only decrease the nucleic acid level to the required degree, but it also must be inexpensive and must not contaminate the food product with undesirable chemicals.
It is an object of the present invention to provide a process for the reduction of levels of nucleic acid in particular ribonucleic acid (RNA) in proliferated microorganisms combined with the minimum loss of protein to render them more acceptable as human food.
We have developed a process for treating cells of grown non-toxic microfungus of the class Fungi Imperfecti which can meet the above requirements of the World Health Organisation.
The invention provides fungal mycelium possessing a reduced level of RNA of below 4%.
Thus the invention provides fungal mycelium containing Fusarium graminearum Schwabe IMI 145425 possessing a reduced level of RNA of below 3% by weight, preferably below 2% by weight.
The invention also provides fungal mycelium containing Penicillium notatum-chrysogenum IMI 138291 possessing a reduced level of RNA of below 4%.
According to the present invention there is provided a process for reducing the nucleic acid content in the production of an edible protein-containing substance comprising contacting a grown non-toxic microfungus of the class Fungi Imperfecti with a solvent comprising between 40% and 100% (by volume) of a lower alkanol containing up to three carbon atoms and thereafter incubating at a pH between 5 and 9.5 and at a temperature between 30.degree. C. and 80.degree. C. for a time of at least 90 seconds.
The process may be applied to a grown non-toxic strain of Fusarium, Penicillium notatum or Penicillium chrysogenum, Penicillium funiculosum or Aspergillus niger.
The strain of Fusarium may be a strain of Fusarium graminearum Schwabe in particular IMI 145425, Fusarium oxysporum or Fusarium solani as described and claimed in our Applications Nos. 23452/70 (Ser. No. 1,346,061) and 30584/70 and Cognate No. 10466/71 (Ser. No. 1,346,062).
The strain of Penicillium notatum or Pencillium chrysogenum may be a strain of Penicillium notatumchrysogenum, for example IMI 138291, as described and claimed in our Applications Nos. 8977/70 (Ser. No. 1,331,471) and 8978/70 (Ser. No. 1,331,472).
The lower alkanol containing up to three carbon atoms may be methyl alcohol, ethyl alcohol, propyl alcohol or isopropyl alcohol. Ethyl alcohol and isopropyl alcohol are solvents permitted by the Solvents in Food Regulations, 1967. The preferred solvent in the process of the present invention is isopropyl alcohol (IPA). Instead of pure isopropyl alcohol aqueous solutions containing between 40 or 50% by volume and up to 100% I.P.A. may be employed.
The incubation may conveniently be carried out at a temperature between 45.degree. C. and 60.degree. C. for a time of between 1.5 minutes and 40 minutes.
The incubation step may conveniently be carried out in the presence of a buffer solution for example NH.sub.4 Cl/NH.sub.4 OH or NH.sub.4 Cl/HCl.
The post fermentation process of the present invention for reducing the nucleic acid content of microorganisms is essentially a two stage process.
Stage 1
The grown microbial protein or fungal mycelium obtained for example by the fermentation process described and claimed in our Applications Nos. 8977/70 (Ser. No. 1,331,471) and 30584/70 and Cognate No. 10466/71 (Ser. No. 1,346,062) may be harvested, filtered to remove growth medium and washed, if desired. It may then be suspended in the alkanol solvent for example for 1 minute at 20.degree. C. or contacted with an alkanol solvent water mixture. The majority or all of the alkanol solvent may be removed by such methods as vacuum filtration, filter pressing or centrifugation. The duration of contact with the alkanol solvent may be varied but is generally in the range between 15 seconds and 15 minutes. The temperature may vary between 0.degree. C. and 60.degree. C.
Stage 2
The cells may then be brought into intimate contact with aqueous buffer solutions in the pH range 5 to 9.5. Thus the solvent treated cells may then be resuspended and incubated in aqueous buffer solution at pH 8.6 and temperature 45.degree. C. An example of a suitable buffer solution is 0.1M ammonium chloride solution with ammonium hydroxide added to adjust the pH to 8.6.
The resulting treated cells may then be harvested again for example by filtration and washing with water and thereafter formulated into foods or dried by various methods.
When the process is carried out in the pilotplant the pH is adjusted to 5 after RNA removal. The purpose of this acidification is twofold (a) the material becomes "whiter" and (b) the texture changes and this enables harvesting by vacuum filtration to be carried out easier.
The resulting solvent treated microbial protein or fungal mycelium may have a RNA content of 1-4% compared to 7 to 10% of the untreated proliferated organism.
The cells may be analysed to determine their chemical composition and to evaluate the efficiency of the nucleic acid reduction process.
Following is a description by way of example of methods of carrying the invention into effect.
References to "Biomass Loss" denote weight lost during processing.
Ribonucleic acid (RNA) content was determined by a modification of the method of Schmidt G. and Thannhauser, S. J., J. Biol.Chem., 1945, 161, 83.
Method of analysis for Total Nitrogen (TN) Automatic Kjeldahl digestor (Technicon). A Ferrari, Ann. N.Y. Sci. 87, 792 (1960).
Amino nitrogen (AN) TNBS (modified). M. A. Pinnegar, Technicon Symposium 1965, p.80.
EXAMPLE A
Reduction of the Nucleic Acid Levels in Various Micro-Organisms
Fusarium graminearum IMI 145425 was cultivated by the following procedure:
Medium in distilled water:
______________________________________K.sub.2 HPO.sub.4 15.05 gL.sup.-1(NH.sub.4).sub.2 HPO.sub.4 6.64 gL.sup.-1tri Sodium Citrate 15.7 gL.sup.-1Citric Acid 5.48 gL.sup.-1K.sub.2 SO.sub.4 1.0 gL.sup.-1Choline chloride 50 mgL.sup.-1Biotin 50 .mu.gL.sup.-1Glucose 30 gL.sup.-1______________________________________
Minimal Salts
______________________________________MgCl.sub.2.6H.sub.2 O 0.2 gL.sup.-1ZnSO.sub.4 0.003 gL.sup.-1MnCl.sub.2 4H.sub.2 O 0.005 gL.sup.-1FeCl.sub.3.6H.sub.2 O 0.01 gL.sup.-1CuCl.sub.2.6H.sub.2 O 0.001 gL.sup.-1NaMoO.sub.4.2H.sub.2 O 0.001 gL.sup.-1CoCl.sub.2.6H.sub.2 O 0.001 gL.sup.-1CaCl.sub.2.2H.sub.2 O 0.015 gL.sup.-1______________________________________
Sterilisation
All components with the exception of glucose are sterilised together, and the amounts of these materials required for 1 liter of medium are dissolved, made up to 850 ml. and distributed into 5 1 liter conical flasks, each containing 170 ml. A 30% w/v solution of glucose is prepared and sterilised in 20 ml. portions in universal bottles. Sterilisation is effected in an autoclave at 15 p.s.i. for 15 minutes.
Growth conditions
Before inoculation with 10 ml. of a growing culture, the contents of one bottle of sterile glucose solution is added to each flask. Culture of A3/5 then proceeds on an Orbital Shaker, with 2 inch throw, at 160 r.p.m. and a temperature of 30.degree. C. The culture is harvested after 18 hours.
Cells were collected and washed on a Buchner filtration system and treated as follows:
(i) Suspended in 66% v/v isopropyl alcohol for 1 minute at 20.degree. C.
(ii) Isopropyl alcohol was removed by filtration.
(iii) The treated cells were incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer at pH 8.6 and 45.degree. C. for various times. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________ Time of Incuba-Micro- tion % RNA % Amino % Totalfungi Treatment Minutes Content Nitrogen Nitrogen______________________________________F. None None 10.86 7.57 9.80gramine-arum Nucleic Zero 9.86 8.23 10.98 acid Reduction Nucleic 20 2.29 8.84 10.45 acid Reduction Nucleic 40 1.88 8.68 9.91 acid Reduction Nucleic 60 1.69 8.73 10.56 acid Reduction______________________________________
Conclusion
The level of nucleic acid was effectively reduced by the treatment described.
Penicillium notatum chrysogenum IMI 138291 was cultivated by the following procedure:
Medium
______________________________________2% Soluble starch0.2% Spray dried corn steep liquor0.2% Mycological peptone0.4% (NH.sub.4).sub.2 SO.sub.40.2% KH.sub.2 PO.sub.41% Sucrose______________________________________
The medium is made up with hot tap water, and dispensed in 200 ml. aliquots into conical shake flasks.
0.1 ml. of liquid amylase was added to each shake flask and incubated at 70.degree. C. for 15 minutes so that the starch was broken down and the viscosity reduced.
Sterilisation
The flasks were sterilised in an autoclave at 15 p.s.i. for 20 minutes.
Growth conditions
A spore inoculum was added to each flask and the culture grown at 30.degree. C. on an orbital shaker with a 2 inch throw at 160 r.p.m. After growth for 24 hours, 10 ml. of the growing culture was used as growing inoculum which was added to more flasks containing the starch medium. Cells produced after a further 24 hours growth were harvested, washed and used as follows:
(i) Suspended in 66% (v/v) isopropyl alcohol for one minute at 20.degree. C.
(ii) Isopropyl alcohol was removed by filtration.
(iii) The treated cells were incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer at pH 8.6 and 40.degree. C. for various times. The incubations were carried out at a slurry concentration of approximately 10 gm/l with stirring.
Results
__________________________________________________________________________ Time ofMicro- Incubation % RNA % Amino % Total % Biomassfungi Treatment Minutes content Nitrogen Nitrogen Loss__________________________________________________________________________P. notatum- None None 7.19 5.78 7.58 0chrysogenumP. notatum- Nucleic 15 3.60 6.64 8.47 30chrysogenum Acid ReductionP. notatum- Nucleic 40 3.25 6.47 8.52 32chrysogenum Acid ReductionP. notatum- Nucleic 60 3.32 6.34 8.04 32chrysogenum Acid Reduction__________________________________________________________________________
Conclusion
The level of nucleic acid was reduced by the treatment described.
Penicillium funiculosum IMI 79195 was cultivated by the following procedure:
Medium
______________________________________KH.sub.2 PO.sub.4 15 g/lNaOH 1 g/lDextran 1 g/lCaster Oil 10 g/lSolution A.sup.+ 5 ml/lSolution B.sup.+ 5 ml/lSolution C.sup.+ 5 ml/lYeast extract 10 g/l______________________________________
Minimal salts
______________________________________A.sup.+ B.sup.+ C.sup.+______________________________________MgSO.sub.4 50 g/l CaCl.sub.2 3 g/l FeSO.sub.4 1 g/lZnSO.sub.4 1 g/lMnSO.sub.4 1 g/l CoCl.sub.2 0.2 g/lCuSO.sub.4 0.2 g/l______________________________________
All in distilled water.
Sterilisation
Adjust pH of medium to 5.5 before sterilisation. Autoclave all components together. (50 minutes 15 p.s.i.)
Growth conditions
______________________________________(Batch culture) Volume 101. (Fermenter) Temperature 28.degree. C. Stirrer 400 r.p.m. Air flow 101/minutes Harvest time 80 hours Inoculum size 5% by volume (shake flask culture)______________________________________
Cells were collected and washed on a Buchner filtration system and treated as follows:
(i) Suspended in 80% isopropyl alcohol for 1 minute at 20.degree. C.
(ii) Isopropyl alcohol was removed by filtration.
(iii) The treated cells were incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer at pH 8.6 and 37.degree. C. for 60 minutes. The incubation was carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________Micro- % RNA % Amineorganism Treatment content N % Total N______________________________________P. None 4.23 3.74 5.81funiculosumP. Nucleic 2.80 4.46 7.34funiculosum Acid Reduction______________________________________
Conclusion
The level of nucleic acid was reduced by the treatment described.
Aspergillus niger NRRL 330 was cultivated by the following procedure:
The medium and sterilisation procedure were identical to that described for P. notatum-chrysogenum.
Growth conditions were also identical except that cells grown directly from spores were used instead of cells cultivated from growing inoculum.
Cells were collected and washed on a Buchner filtration system and treated as follows:
(i) Suspended in 66% (v/v) isopropyl alcohol for 1 minute at 20.degree. C.
(ii) Isopropyl alcohol was removed by filtration.
(iii) The treated cells were incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer at pH 8.6 and 40.degree. C. for various times. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
__________________________________________________________________________ Time ofMicro- Incubation % RNA % Amino % Total % Biomassfungi Treatment Minutes Content Nitrogen Nitrogen loss__________________________________________________________________________A. niger None None 6.36 4.03 5.70 noneA. niger Nucleic zero acid ReductionA. niger Nucleic 15 1.88 4.40 6.30 27 acid ReductionA. niger Nucleic 30 1.86 4.35 5.77 28 acid ReductionA. niger Nucleic 60 1.82 4.25 5.62 32 acid Reduction__________________________________________________________________________
Conclusion
The level of nucleic acid was effectively reduced by the treatment described.
EXAMPLE B
Effect of the % Iso-propyl Alcohol on the Efficiency of the Nucleic Acid Reduction Process
F. graminearum IMI 145425, cultivated as described in Example A, was contacted with various isopropyl alcohol/water mixtures at 20.degree. C. for 2 minutes. The treated cells were then incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer pH 8.5 at 37.degree. C. for 20 minutes. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________% IPA % Biomass(by volume) Treatment loss % RNA remaining______________________________________ 0 None 0.0 9.33 0 Nucleic 1.8 9.33 acid reduction10 Nucleic 1.1 10.68 acid reduction20 Nucleic 11.3 9.74 acid reduction30 Nucleic 19.4 8.87 acid reduction40 Nucleic 25.6 4.58 acid reduction50 Nucleic 26.5 3.03 acid reduction60 Nucleic 28.0 3.25 acid reduction70 Nucleic 27.6 2.86 acid reduction80 Nucleic 26.3 3.35 acid reduction90 Nucleic 23.8 3.69 acid reduction100 Nucleic 25.1 4.58 acid reduction______________________________________
Conclusion
The nucleic acid removal process is most effective in the range of 40-100% isopropyl alcohol.
In the case of the treatment with 10 & 20% IPA the final RNA content is greater than the starting material; this is because RNA is removed to a lesser extent than biomass lost.
EXAMPLE C
Effect of Contact With IPA at Various Temperatures on the Subsequent Nucleic Acid Reduction Process
F. graminearum IMI 145425, cultivated as described in Example A, was contacted with 100% IPA at 0.degree., 20.degree., 40.degree., and 60.degree. C. for 2 minutes, then incubated with 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer pH 8.5 for 20 minutes at 39.degree. C. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________Temperature ofIPA treatment % RNA remaining______________________________________No treatment 9.04 0.degree. C. 3.4220.degree. C. 3.4740.degree. C. 2.5260.degree. C. 2.33______________________________________
Conclusion
The nucleic acid reduction process is effective over the temperature range studied.
EXAMPLE D
Effectiveness of Various Alcohols on the Nucleic Acid Reduction Process
F. graminearum IMI 145425, cultivated as described in Example A, was contacted with 100% iso-propyl alcohol, 70% iso-propyl alcohol, 70% propyl alcohol, 100% ethyl alcohol or 100% methyl alcohol at 20.degree. C. for two minutes, then incubated with 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer pH 8.5 at 37.degree. C. or 40.degree. C. for various time periods. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________ Time and temperature % RNAAlcohol used of second incubation remaining______________________________________None None 9.16100% iso-propyl 30 mins. at 37.degree. C. 2.53alcohol100% iso-propyl 120 mins. at 37.degree. C. 0.70alcoholiso-propyl 20 mins. at 40.degree. C. 1.81alcoholpropyl alcohol 20 mins. at 40.degree. C. 1.93100% ethyl alcohol 30 mins. at 37.degree. C. 2.17100% ethyl alcohol 120 mins. at 37.degree. C. 0.64100% methyl alcohol 30 mins. at 37.degree. C. 5.50100% methyl alcohol 120 mins. at 37.degree. C. 1.17______________________________________
Conclusion
The RNA reduction process is successfully activated by a lower alkanol containing up to three carbon atoms.
EXAMPLE E
Duration of Contact With Iso-propyl Alcohol
F. graminearum IMI 145425, cultivated as described in Example A, was contacted with 66% (v/v) IPA at 20.degree. C. for various times then incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer pH 8.5 at 37.degree. C. for 60 minutes. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________Contact time % RNA % Biomasswith 66% IPA remaining lost______________________________________0 9.25 015 seconds 1.12 361 minute 1.14 382 minutes 0.98 405 minutes 1.23 --15 minutes 1.27 41______________________________________
Conclusion
Over the contact times studied nucleic acid removal was efficient. In practice the contact time for best RNA reduction is around 2 minutes, at longer contact times the % biomass lost tends to rise to unacceptably high values.
EXAMPLE F
Efficiency of Nucleic Acid Reduction With Buffers Over a pH Range of 4-10
F. graminearum IMI 145425, cultivated as described in Example A, was contacted with 100% iso-propyl alcohol at 20.degree. C. and incubated with the following series of buffers at 30.degree. C. for 3 hours. The incubations were carried out at a slurry concentration of approximately 10 g/l with stirring.
Results
______________________________________ %Buffer in second stage RNA Remaining______________________________________0.1 M NH.sub.4 Cl + HCl to bring to pH 4.0 11.490.1 M NH.sub.4 Cl + HCl to bring to pH 4.5 9.070.1 M NH.sub.4 Cl + HCl to bring to pH 5.0 5.850.1 M NH.sub.4 Cl + HCl to bring to pH 5.5 3.520.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 6.0 2.630.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 6.5 1.600.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 7.0 0.960.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 7.5 0.970.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 8.0 0.590.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 8.5 0.910.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 9.0 1.690.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 9.5 3.840.1 M NH.sub.4 + NH.sub.4 OH to bring to pH 10.0 7.00______________________________________
Conclusion
The nucleic acid removal is effective with this buffer system over the pH range 5-9.5.
EXAMPLE G
Efficiency of Nucleic Acid Reduction Carried Out in Buffers of Varying Ionic Strengths
F. graminearum IMI 145425 cultivated as described in Example A, was contacted with 66% (v/v) IPA at 20.degree. C. for 1 minute, and incubated in buffers or non-buffered solutions of varying ionic strengths at 45.degree. C. The incubations were carried out at approximately 10 g/l with stirring.
Results
__________________________________________________________________________ Time of incubationBuffer at 45.degree. C. % Amino % Totalsystem Treatment (Minutes) % RNA Nitrogen Nitrogen__________________________________________________________________________None None None 10.89 7.57 9.80Distilled Nucleic acid reduced 0 11.21 7.82 10.53water " 20 7.38 8.07 10.22pH 5.7 " 40 4.79 7.97 10.12 " 60 2.57 8.40 9.84Non-buffered " 0 11.17 8.35 10.81ammonia " 20 4.54 8.85 10.07solutionsufficient " 40 3.14 8.85 10.68to bringto pH 8.5 " 60 2.55 8.79 10.300.02M " 0 9.96 8.46 10.89NH.sub.4 Cl/NH.sub.4 OH " 20 3.21 8.62 10.38buffer " 40 2.39 8.73 10.36pH 8.5 " 60 1.82 8.90 10.120.1M " 0 9.86 8.23 10.98NH.sub.4 Cl/NH.sub.4 OH " 20 2.29 8.84 10.45buffer " 40 1.88 8.68 9.91pH 8.5 " 60 1.69 8.73 10.560.5M " 0 10.02 8.21 10.58NH.sub.4 Cl/NH.sub.4 OH " 20 5.85 8.35 10.13buffer " 40 5.63 8.42 10.01pH 8.5 " 60 5.58 8.54 10.121.0M " 0 10.19 7.56 10.89NH.sub.4 Cl/NH.sub.4 OH " 20 10.45 7.72 10.48buffer " 40 9.96 7.99 10.81pH 8.5 " 60 9.89 8.15 10.58__________________________________________________________________________
Conclusion
Nucleic acid is most effectively reduced at lower ionic strengths. The optimum conditions for rapid reduction being 0.1M buffer.
EXAMPLE H
The Nucleic Acid Reduction Process Studied at Various Temperatures
F. graminearum IMI 145425, cultivated as described in Example A, was contacted with 66% (v/v) IPA at 20.degree. C. for 2 minutes, and incubated in 0.1M NH.sub.4 Cl/NH.sub.4 OH buffer pH 8.5 for various durations at various temperatures. The incubations were carried out at approximately 10 g/l with stirring.
Results
______________________________________Temperature Time of incubationof buffer minutes % RNA remaining______________________________________Control -- 9.4430.degree. C. 0 10.8330.degree. C. 20 8.4030.degree. C. 40 7.0630.degree. C. 60 7.4530.degree. C. 90 4.7630.degree. C. 120 4.1137.degree. C. 0 10.1237.degree. C. 20 5.0237.degree. C. 40 3.5537.degree. C. 60 3.5537.degree. C. 90 1.8037.degree. C. 120 1.0245.degree. C. 0 10.0945.degree. C. 20 2.5845.degree. C. 40 0.9945.degree. C. 60 0.6945.degree. C. 90 0.6945.degree. C. 120 0.6155.degree. C. 1.5 2.1655.degree. C. 3.0 1.1055.degree. C. 4.5 0.7660.degree. C. 1.5 1.9660.degree. C. 3.0 1.7860.degree. C. 4.5 1.1170.degree. C. 2.0 4.1970.degree. C. 3.5 3.3070.degree. C. 5.0 3.5680.degree. C. 1.5 5.6580.degree. C. 3.0 5.4080.degree. C. 4.5 5.31______________________________________
Conclusion
Nucleic acid reduction takes place over the temperature range 30.degree. C.-80.degree. C. The most efficient conditions are at a temperature of 60.degree. C., where satisfactory reduction of RNA was achieved within 90 seconds.
According to the present invention there is provided a process for reducing the nucleic acid content in the production of an edible protein-containing substance which comprises maintaining a grown non-toxic microfungus of the class Fungi Imperfecti in a suspension at a pH between 4.7 and 7.0 and at a temperature between 55.degree. and 72.degree. C. for a time of at least 60 seconds.
The process may be applied to a grown non-toxic strain of Fusarium.
The strain of Fusarium may be a strain of Fusarium graminearum Schwabe in particular IMI 145425, Fusarium oxysporum or Fusarium solani as described and claimed in our Applications Nos. 23452/70 (Ser. No. 1,346,061) and 30584/70 and cognate 10466/71 (Ser. No. 1,346,062).
The grown non-toxic microfungus of the class Fungi Imperfecti may conveniently be maintained in a suspension at a pH between 4.7 and 7.0 and at a temperature between 55.degree. and 68.degree. C. for a time of at least 200 seconds.
The post fermentation process of the present invention for reducing the nucleic acid content of micro-organisms is essentially a single-stage process.
The grown microbial protein or fungal mycelium obtained for example by the fermentation process described and claimed in our Application No. 30584/70 and cognate No. 10466/71 (Ser. No. 1,346,062), may be harvested, filtered to remove growth medium and washed, if desired. The cells may then be brought into intimate contact with aqueous buffer solutions in the pH range 4.7 to 7.0. Thus the cells may then be resuspended and incubated in tap water at pH 6.3 and temperature 63.degree. C. for a period of 20 minutes.
The resulting treated cells may then be harvested again for example by filtration and washing with water and thereafter formulated into foods or dried by various methods.
In order to confine the loss of protein to a minimum it is desirable to raise the temperature of the cell suspension to a given temperature within the range of 55.degree. and 72.degree. C. as rapidly as possible; substantially the same temperature may subsequently be maintained for a period of 5 to 60 minutes.
An optional prior step designed to inhibit or destroy the proteolytic activity comprises maintaining a grown non-toxic microfungus of the class Fungi Imperfecti at the selected isothermal temperature of between 55.degree. and 72.degree. C. at a pH where there is no proteolytic activity for a time sufficient to destroy the protease but not the ribonuclease.
Thus with a view to improving the protein economy of the present isothermal process the cells may be held at a pH of 8.5 at the selected isothermal temperature, preferably 65.degree. C., for a duration of between 1/2 minute and 5 minutes, preferably 1 minute before the isothermal process is commmenced (i.e. with an adjustment of the pH to between 4.7 and 7).
The resulting fungal mycelium may have an RNA content of 1 to 4% compared to 7 to 12% of the untreated proliferated organism. In certain instances the RNA content may be less than 1%.
The cells may be analysed to determine their chemical composition and to evaluate the efficiency of the nucleic acid reduction process.
Following is a description of methods of determining the chemical composition.
References to "Biomass Loss" denote weight loss during processing.
Ribonucleic acid (RNA) content is determined by a modification of the method of Schneider, W. C. Analyst, 1945, 161, 293.
Method of analysis for Total Nitrogen (TN) Automatic Kjeldahl digester (Technicon), A. Ferrari, Ann. N.Y. Sci 87, 792.
Amino nitrogen (AN) TNBS (modified). M. A. Pinnegar, Technicon Symposium 1965, p. 80.
Following is a description by way of example of methods of carrying the invention into effect.
Fusarium graminearum IMI 145425 was cultivated continuously by the following procedure:
______________________________________Medium in tap water.Potato Starch 60 g/l(treated with .alpha.-amylaseand glucamylase)MgSO.sub.4 7H.sub.2 O 0.75 g/lZnSO.sub.4 7H.sub.2 O 10.0 mg/lCuSO.sub.4 5H.sub.2 O 2.0 mg/lNaMoO.sub.4 2H.sub.2 O 2.0 mg/lCoCl 6H.sub.2 O 2.0 mg/lMnSO.sub.4 4H.sub.2 O 10.0 mg/lFeSO.sub.4 7H.sub.2 O 20.0 mg/lNH.sub.4 H.sub.2 PO.sub.4 3.0 g/lK.sub.2 SO.sub.4 2.4 g/lNaCl 0.125 g/lBoric acid 0.5 mg/lBiotin 0.005 mg/lPPG 2000 0.04 mg/lFermenter operation conditionsTemperature 30.degree. C.pH 6.0Pressure 15.5 psigStirrer speed 230 rpmAir flow 800 1/minuteDissolved oxygen 6.5 (arbitary units where air saturation is 80)Sterilisation Temperature 135.degree. C. by continuous sterilisation (90 secs holding time)Dilution rate 0.14 hr.sup.-1Fermenter Volume 1300 1Inoculum: Prior to continuous growth the fermenter wasoperated in a batch fashion from a 20 1 inoculum of agrowing culture. When batch growth was complete thefermenter was put on stream under the above conditions.______________________________________NoteIn some of the examples which follow the % RNA content isnot corrected for "Biomass Loss". ##STR1## The % RNA content not corrected for Biomass Loss is 2%(ie 2 g from the original 100 g of cells ##STR2## 100 = 2.86% (ie 2 g in a final 70 g of product)The Isothermal Process like other RNA reduction processesgenerally results in approximately 30% Biomass loss. Howeverbecause the biomass loss is not generally determined oneach sample it becomes necessary to quote RNA content ofthe product as a function of the starting material.Results EXAMPLE A The Nucleic Acid Reduction Process Studied at Various
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were suspended at a slurry concentration of approximately 10 g/l in tap water at various temperatures for various durations.
Results
______________________________________ % RNA Content Duration (Not % of the Temperature of corrected original of Incubation Incubation for Biomass RNATreatment .degree.C. minutes Loss) remaining______________________________________Control 55 -- 8.09 100Nucleic Acid 55 5 8.09 100reductionNucleic Acid 55 10 6.58 81reductionNucleic Acid 55 20 3.40 42reductionNucleic Acid 55 40 1.16 14reductionNucleic Acid 55 60 0.80 10reductionControl 58 -- 7.56 100Nucleic Acid 58 5 6.26 83reductionNucleic Acid 58 10 3.55 47reductionNucleic Acid 58 20 1.79 24reductionNucleic Acid 58 30 1.21 16reductionNucleic Acid 58 45 0.88 12reductionControl 60 -- 10.84 100Nucleic Acid 60 5 8.15 75reductionNucleic Acid 60 10 4.92 45reductionNucleic Acid 60 20 2.39 22reductionNucleic Acid 60 30 1.68 15reductionNucleic Acid 60 45 1.29 12reductionControl 62 -- 9.85 100Nucleic Acid 62 1 11.25 --ReductionNucleic Acid 62 5 6.37 65ReductionNucleic Acid 62 10 4.19 43ReductionNucleic Acid 62 20 2.30 23ReductionNucleic Acid 62 30 1.83 19ReductionControl 64 -- 11.34 100Nucleic Acid 64 1 11.96 --ReductionNucleic Acid 64 5 6.12 54ReductionNucleic Acid 64 10 4.10 36ReductionNucleic Acid 64 20 2.70 24ReductionNucleic Acid 64 30 2.39 21ReductionControl 66 -- 8.22 100Nucleic Acid 66 1 7.03 86ReductionNucleic Acid 66 5 3.13 38ReductionNucleic Acid 66 10 2.29 28ReductionNucleic Acid 66 20 1.99 24ReductionNucleic Acid 66 30 2.18 27ReductionControl 68 -- 8.47 100Nucleic Acid 68 1 6.78 80ReductionNucleic Acid 68 5 3.03 36ReductionNucleic Acid 68 10 2.56 30ReductionNucleic Acid 68 20 2.44 29ReductionNucleic Acid 68 30 2.36 28ReductionControl 70 -- 7.51 100Nucleic Acid 70 1 3.29 44ReductionNucleic Acid 70 5 2.65 35ReductionNucleic Acid 70 10 2.40 32ReductionNucleic Acid 70 20 2.33 31ReductionNucleic Acid 70 30 2.22 30ReductionControl 72 -- 7.62 100Nucleic Acid 72 1 5.35 70ReductionNucleic Acid 72 5 2.74 36ReductionNucleic Acid 72 10 2.43 32ReductionNucleic Acid 72 20 2.33 31ReductionNucleic Acid 72 30 2.33 31ReductionControl 75 -- 9.16 100Nucleic Acid 75 1 6.02 66ReductionNucleic Acid 75 5 5.10 57ReductionNucleic Acid 75 10 5.04 55ReductionNucleic Acid 75 20 4.73 52ReductionNucleic Acid 75 30 4.49 49ReductionControl 80 -- 8.72 100Nucleic Acid 80 1 5.69 65ReductionNucleic Acid 80 5 5.26 60ReductionNucleic Acid 8O 10 5.11 59ReductionNucleic Acid 80 20 4.57 52ReductionNucleic Acid 80 30 4.51 52Reduction______________________________________
Conclusions
With mould cultivated in the manner described it is possible to reduce the nucleic acid level to acceptably low values within the temperature range 55.degree.-72.degree. C.
The ideal isothermal temperature depends on the extent of RNA removal desired and the duration which can be tolerated on economic grounds.
The preferred conditions for our purposes are pH 6, 62.5.degree. C. for 18 minutes (see also Example B).
EXAMPLE B
Efficiency of Nucleic Acid Reduction Over a pH Range of 4-9.5 at 62.5
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were suspended in tap water at 62.5.degree. C. and a slurry concentration of approximately 10 g/l. The pH was controlled at the desired value by automatic addition of either HCl or NH.sub.4 OH. Samples were incubated for 18 minutes.
Results
__________________________________________________________________________ % of the % of original Duration % of % the AN re- pH of of incub- RNA Bio original maining incub- ation in % % mass RNA in theTreatment ation minutes product AN TN Loss remaining product__________________________________________________________________________Control -- -- 8.24 5.9 7.68 -- 100 100Isothermal 9.5 18 7.31 6.27 8.60 23.9 67.5 81at 62.5.degree. C.Isothermal 9.0 18 8.36 6.36 8.77 21.4 79.7 84.7at 62.5.degree. C.Isothermal 8.5 18 8.29 6.31 8.52 20.8 79.7 84.7at 62.5.degree. C.Isothermal 8.0 18 8.28 6.19 8.41 21.4 79.0 82.5at 62.5.degree. C.Isothermal 7.0 18 2.06 6.34 7.74 28.3 17.9 77.0at 62.5.degree. C.Isothermal 6.0 18 1.01 6.46 7.80 31.4 8.4 75.1at 62.5.degree. C.Isothermal 5.0 18 1.39 6.48 7.95 32.1 11.4 74.6at 62.5.degree. C.Isothermal 4.0 18 7.26 6.48 8.49 27.7 63.7 79.4at 62.5.degree. C.__________________________________________________________________________
Conclusions
(1) The pH optimum for the process carried out at 62.5.degree. C. is in the range pH 4.7-7.0. Maximum reduction was at pH 6.0.
(2) Unfortunately, optimum pH for protein retention is not pH 6.0 but pH 8.5-9.0.
(3) Observations on colours: The dried solids, moist filter cakes and slurries at pH's of 6.0 and above were dark grey. Those at pH 5.0 were fawn, and at pH 4.0 the material was white. After the RNA reduction has been accomplished it may therefore be desirable to adjust the pH to 4.0 to obtain a white product.
EXAMPLE C
Efficiency of Nucleic Acid Reduction Carried Out in Solutions of Varying Logic Ionic Strengths
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were suspended at a slurry concentration of approximately 10 g/l in solutions of varying ionic strengths. The pH was automatically maintained at pH 6 and the incubation was carried out at 62.5.degree. C. for a duration of 20 minutes.
Results
______________________________________ Incubation Solution % RNA (maintained in % Amino % TotalTreatment at pH 6) product Nitrogen Nitrogen______________________________________Control -- 8.58 6.63 8.85Nucleic Acid Distilled water 1.50 7.12 8.69ReductionNucleic Acid 0.01 M NaCl 1.18 6.98 8.81ReductionNucleic Acid 0.05 M NaCl 1.05 6.99 9.04ReductionNucleic Acid 0.10 M NaCl 1.04 7.06 8.96ReductionNucleic Acid 0.20 M NaCl 0.87 6.69 8.64ReductionNucleic Acid 0.50 M NaCl 0.91 6.77 8.50ReductionNucleic Acid 0.50 M NH.sub.4 Cl 0.62 7.02 8.64Reduction______________________________________
Conclusions
In the range studied NaCl and NH.sub.4 Cl had little effect on the nucleic acid reduction process.
EXAMPLE D
Efficiency of Nucleic Acid Reduction at Various Slurry Concentrations
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were suspended at various slurry concentrations in tap water at 63.degree. C. for various durations.
Results
______________________________________ Time of Slurry Incubation % RNA Content Concentration (minutes- (Not correctedTreatment g/l seconds) for biomass loss)______________________________________None (Control) None None 8.85Nucleic Acid 1 g/liter 1.00 7.46ReductionNucleic Acid 1 g/liter 7.20 3.27ReductionNucleic Acid 1 g/liter 15.30 2.37ReductionNucleic Acid 1 g/liter 30.30 1.85ReductionNucleic Acid 2 g/liter 1.00 6.87ReductionNucleic Acid 2 g/liter 7.20 2.34ReductionNucleic Acid 2 g/liter 16.30 1.41ReductionNucleic Acid 2 g/liter 31.00 1.31ReductionNucleic Acid 4 g/liter 1.00 7.17ReductionNucleic Acid 4 g/liter 8.00 2.50ReductionNucleic Acid 4 g/liter 16.20 1.34ReductionNucleic Acid 4 g/liter 30.10 0.91ReductionNucleic Acid 10 g/liter 2.00 7.35ReductionNucleic Acid 10 g/liter 9.40 2.02ReductionNucleic Acid 10 g/liter 18.00 1.10ReductionNucleic Acid 10 g/liter 30.20 0.76ReductionNucleic Acid 20 g/liter 2.20 6.05ReductionNucleic Acid 20 g/liter 6.40 3.13ReductionNucleic Acid 20 g/liter 16.20 1.59ReductionNucleic Acid 20 g/liter 30.00 0.88ReductionNucleic Acid 40 g/liter 1.20 5.31ReductionNucleic Acid 40 g/liter 5.10 5.25ReductionNucleic Acid 40 g/liter 15.00 1.68ReductionNucleic Acid 40 g/liter 30.50 1.02Reduction______________________________________
Conclusion
The results show that broadly speaking slurry concentration only affects RNA reduction in as much as heat transfer is affected (i.e. high slurry concentrations may require stirring to ensure rapid temperature equilibration).
EXAMPLE E
Efficiency of Nucleic Acid Reduction Under Various Agitation Conditions
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were suspended at approximately 10 g/liter in tap water at 63.degree. C. under various agitation conditions.
Results
______________________________________ Agitation in Grant % RNA Content Water Bath Duration of (Not corrected strokes/ incubation for BiomassTreatment minute minutes Loss)______________________________________None (Control) None None 8.30Nucleic Acid Zero 1 7.31ReductionNucleic Acid Zero 5 2.33ReductionNucleic Acid Zero 10 1.04ReductionNucleic Acid Zero 20 0.67ReductionNucleic Acid Zero 30 0.59ReductionNucleic Acid 50 1 7.44ReductionNucleic Acid 50 5 2.59ReductionNucleic Acid 50 10 1.23ReductionNucleic Acid 50 20 0.84ReductionNucleic Acid 50 30 0.74ReductionNucleic Acid 250 1 6.26ReductionNucleic Acid 250 5 2.10ReductionNucleic Acid 250 10 1.37ReductionNucleic Acid 250 20 1.13ReductionNucleic Acid 250 30 1.13Reduction______________________________________
Conclusion
The results show that it is not necessary to stir the slurry during the Isothermal process. The effect of shaking at this slurry concentration is negligible. This has tremendous implications from the chemical engineering point of view when scale-up to larger plant is carried out.
EXAMPLE F
Typical Nucleic Acid Reduction Experiment
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were resuspended at a slurry concentration of approximately 10 g/l in a solution of 0.1M NaCl. The pH was automatically maintained at pH 6 and the incubation was carried out at 62.5 C. for a duration of 20 minutes.
Results
______________________________________ 31.9 g Biomass100 g of fungus containing 68.1 g product Lost______________________________________37.30 g protein 30.00 g protein + ##STR3## -- 8.58 g RNA 0.71 g RNA______________________________________
Conclusion
The product contains 44% protein and 0.8% ribonucleic acid i.e. a protein to nucleic acid ratio of 55:1. The starting material contains 37.3% protein and 8.58% ribonucleic acid i.e. a protein to nucleic acid ratio of 4.35:1.
EXAMPLE G
An Optional Prior Process Designed to Destroy the Protease Activity Without Substantially Destroying the Ribonuclease Activity
F. graminearum IMI 145425, cultivated as described earlier was harvested and washed on a Buchner filtration system. The cells were suspended in distilled water at 65.degree. C. and a slurry concentration of approximately 10 g/l. The pH was controlled at 8.5 for various times.
After this prior treatment the cells were subjected to RNA removal by the isothermal process at 65.degree. C., pH 6 for 20 minutes.
Results
______________________________________ % of % AN % TN RNA in in in % BiomassTreatment product product product Loss______________________________________Control 8.37 6.26 8.31 Zero1/2 minutes at pH 1.09 7.03 9.12 43.48.5 + 20 min pH 61 minute at pH 1.31 7.23 9.49 35.08.5 + 20 min pH 62 minutes at pH 1.52 7.21 9.38 35.48.5 + 20 min pH 65 minutes at pH 2.52 7.24 9.38 31.48.5 + 20 min pH 6______________________________________
Conclusions
The optimal example which removes the maximum quantity of RNA but at the same time retains maximal Biomass and amino nitrogen is fulfilled by conditions of 1 minutes at 65.degree. C. and pH 8.5 followed by the isothermal process at 65.degree. C. pH 8.5 for 20 minutes.
Examples of Successful Reduction of the Nucleic Acid Levels in Various Micro-organisms Other Than A3/5
EXAMPLE H
Fusarium solani IMI 154217 was cultivated by the following procedure:
Medium in distilled water:
______________________________________ MgSO.sub.4.7H.sub.2 O 0.25 g/literKH.sub.2 PO.sub.4 15.0 g/liter(NH.sub.4).sub.2 SO.sub.4 2.83 g/literBiotin 0.05 ml/liter (of stock solution 1 mg/ml)Choline 50 mg/literTrace elements 5 ml/liter (STOCK SOLUTION)NaOH 1 g/liter.fwdarw. pH 6.0Glucose 10% solution (20 mls added after sterilization)______________________________________
Minimal Salts or Trace element stock solution
______________________________________ZnCl.sub.2 1 g/literMnCl.sub.2 4H.sub.2 O 1 g/literFeCl.sub.3 6H.sub.2 O 2 g/literCuCl.sub.2 2H.sub.2 O 0.2 g/literNaMnO.sub. 4 2H.sub.2 O 0.2 g/literCoCl.sub.2 6H.sub.2 O 0.2 g/literCaCl.sub.2 2H.sub.2 O 2 g/liter______________________________________
Sterilisation
All components with the exception of glucose were sterilised together, and the quantity of these materials required for 1 liter of medium were dissolved, made up to 850 ml and distributed in 5 1 liter conical flasks, each containing 170 ml. A 0.10% w/v solution of glucose was prepared and sterilized in 20 ml portions in universal bottles. Sterilisation was effected in an autoclave at 15 p.s.i. for 15 minutes.
Growth Conditions
Before inoculation with 10 ml of a spore suspension, the contents of one bottle of sterile glucose solution were added to each flask. Culture of the organism then proceeded on an Orbital Shaker, with 2 inch throw, at 160 r.p.m and a temperature of 30.degree. C. The culture was harvested after 48 hours.
Nucleic Acid Reduction Process
Cells were collected and washed on a Buchner filtration system and suspended at a slurry concentration of approximately 10 g/liter in tap water at 64.degree. C. and the pH adjusted to 6 with NaOH and H.sub.2 SO.sub.4.
Results
______________________________________ Time of % RNA % aminoMicrofungi Treatment incubation content nitrogen______________________________________F. solani None None 5.15 5.4 Nucleic 10 2.95 5.92 Acid Reduction Nucleic 20 0.67 6.11 Acid Reduction Nucleic 30 0.55 6.00 Acid Reduction______________________________________
Conclusion
The level of Nucleic acid was effectively reduced by the treatment described.
EXAMPLE I
Fusarium oxysporum IMI 154214 was cultivated in a similar manner to that described for F. solani except that the growth medium contained 0.5 g/liter oxoid yeast extract and 0.5 g/liter mycological peptone in addition to the chemicals listed in Example H.
The cells were harvested after 72 hours and the nucleic acid reduction process conducted as in the previous example.
Results
______________________________________ Time of incubation % RNA % aminoMicrofungi Treatment minutes content nitrogen______________________________________F. oxysporum None None 6.57 6.28 Nucleic 10 1.00 7.47 Acid Reduction Nucleic 20 0.65 7.45 Acid Reduction Nucleic 30 0.54 7.53 Acid Reduction______________________________________
Conclusion
The level of Nucleic acid was effectively reduced by the treatment described.
EXAMPLE J
The Nucleic Acid Reduction Process as Carried Out in Pilot Plant
F. graminearum IMI 145425, cultivated as described earlier was processed without separation from the growth medium as follows:
1. Mycelium slurry at a concentration of 20 grams per liter exists from the fermenter at a temperature of 30.degree. C. and a pH of 6 and enters a mono-pump.
2. The mycelial slurry is pumped to a steam injector and the temperature of the material raised from 30.degree. C. to 64.degree. C. rapidly, the duration of the temperature rise, preferably being instantaneous (in practice being less than 5 seconds).
3. The material now at 64.degree. C. and pH 6 is moved through a pipe and its temperature maintained for a duration of 45 minutes.
4. The material is passed through a heat exchanger to cool to approximately 20.degree. C. (to reduce the possibility of later microbial infection).
5. The slurry is passed into the trough of a rotary vacuum filter.
6. Liquid is drawn through a filter belt and the mycelium accumulates on the filter. The filter drum rotates above the liquid level carrying the mycelial cake.
7. The filter cake is washed with about 2 bed volumes of water. The filter drum continues to rotate and a vacuum pulls the cake to about 70% moisture by weight.
8. The mycelial cake is scraped off the drum.
9. The cake is reslurried in water and spray dried.
Results
______________________________________ % Amino % RNA Nitrogen % Total NitrogenTreatment Content Content Content______________________________________Dry untreated 8.22 6.45 8.74materialDry nucleic 0.43 6.86 8.30acid reducedmaterial______________________________________
Conclusion
The nucleic acid content is effectively reduced by the process described.
In the fermentation operation conditions it is possible to employ a higher dilution rate of up to 0.20 hrs.sup.-1, for example 0.17 hrs.sup.-1.

Number	Date	Country	Kind
44708/73	Sep 1973	GBX
7087/75	Oct 1975	GBX

Number	Name	Date
3139385	Ogata et al.	Jun 1964
3243354	Nakao et al.	Mar 1966
3634194	Frankenfeld et al.	Jan 1972
3686144	Tamura et al.	Aug 1972
3775393	Akin et al.	Nov 1973
3809776	Chao	May 1974
4061781	Solomons et al.	Dec 1977

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