WO1979000121A1

WO1979000121A1 - Process for obtaining food proteins of vegetable origin,with elimination of the toxic and non proteinaceous substances

Info

Publication number: WO1979000121A1
Application number: PCT/FR1978/000020
Authority: WO
Inventors: T Staron
Original assignee: Agronomique Inst Nat Rech; T Staron
Priority date: 1977-09-01
Filing date: 1978-08-31
Publication date: 1979-03-22
Also published as: BE869990A; GB2021120A; FR2401617B1; FR2401617A1; GB2021120B

Abstract

Production of food proteins of vegetable origin and detoxification of the toxic and non proteinaceous substances associated. The vegetable material is first treated at alkaline pH with hydrogen peroxide to prepare a solution of proteins, which is then acidified up to a pH ranging from 6 to 8.5. A clear solution of proteins is obtained to which catalase and then an anti-oxydant are added. The proteins are collected in the usual way. Extraction of proteinaceous fractions suitable for animal and human food.

Description

"Process for obtaining food proteins of plant origin, with elimination of toxic and non-protein substances"

The invention relates to the field of the treatment of plant materials, in particular for extracting the food proteins which they contain, while eliminating toxic and non-protein substances.

There is an increasing concern at the present time to obtain food proteins of plant origin. A great deal of work has already been done in this field and, in this regard, reference may be made to the article by T.STARON appeared in "LA RIVISTA ITALIANA DELLE SOSTANZE GRASSE -Vol.4 - Luglio 1974". This article constitutes the report of a conference given at the INTERNATIONAL CONGRESS ON VEGETABLE PROTEINS FOR HUMAN FOOD in MANTOUE, 3-4 October 1973. This document, as well as the bibliographical references which accompany it, summarize the state of the technique for the production of vegetable proteins capable of being used in human as well as animal nutrition. Currently known processes do not always meet the needs; for example, a lot of effort has been made in the treatment of soybeans, but there are other natural sotirces of vegetable proteins whose development has not yet been completed. in the case of soybeans, the proteins extracted are not perfectly suitable for human consumption, in particular because of their often undesirable flavor and even side effects. In addition, vegetable proteins are frequently associated with toxic products present in natural substrates, so the extraction processes lead to protein fractions which must undergo further purification and detoxification.

The subject of the invention is a general process for obtaining food proteins of plant origin. The invention particularly relates to a method applicable to a wide variety of plant materials which can be presented in the form of seeds, oil cakes, tubers or green plants.

The invention also makes it possible to develop plant materials containing proteins whose previous treatments were insufficient or ill-suited for the preparation and extraction of food proteins.

The subject of the invention is also a process making it possible to obtain, from plant materials such as soya, to which numerous researches have already been devoted, neutral protein products, that is to say devoid of flavor, digestible and without side effects.

Another subject of the invention is a method which ensures simultaneous detoxification of the proteins extracted when toxic products are present in the treated plant substrates.

In its most general form, the invention relates to a process for obtaining food proteins of plant origin, characterized by the following steps: a) the plant material containing the proteins is treated with hydrogen peroxide, in a reaction medium being at an alkaline pH of 8.5 to 11.5, thereby dissolving said proteins in the medium. b) separating the insoluble matter from the liquid medium of step a) thus constituting a protein solution, c) acidifying said protein solution to a pH of 6 to 8.5, thereby precipitating the insoluble fraction containing compounds other than the desired food proteins, d) separating the materials insoluble in the protein solution from step c), thereby obtaining a clarified protein solution, e) adding to said clarified solution at least one enzyme of the peroxidase type, capable destroy the residual hydrogen peroxide and any peroxides present in the pro solution clarified teic, f) at least one antioxidant is added to the protein solution obtained in step e), g) the solution from step f) is treated in a known manner in order to separate the proteins which it contains, which are recovered by the usual techniques.

As mentioned previously, the method of the invention is generally applicable to the treatment of any plant material containing food proteins. By way of example, the method was used for the treatment of the following substrates:

(l) seeds (soybeans, field beans, peas, lupine, sunflower, safflower, wheat, corn, oats),

(2) oil cakes (soy, sesame, peanut, sunflower, rapeseed, flax, cotton, safflower, coconut, palm kernel, jojoba), (3) tubers (potatoes), (4) green plants (alfalfa, spinach ,sorghum).

Of course, the mode of application of the method will vary somewhat depending on the nature of the substrate treated. The following description sets out in more detail the means used in the case of various substrates. (l) SEEDS

The seeds intended for food, or from which a fraction (oil) is withdrawn for food, must be of good quality and correspond to well defined criteria, which are generally regulated. These grade, class and variety criteria define: - the specific weight,

-the water, ash, protein, cellulose oil, adventitious and sclerotia seeds, antinutritional factors, mycotoxins, pesticide residues, broken grains, impurities (damaged grains, foreign seeds, plant debris , mineral elements, dead insects, animal debris - germ, wet, moldy, frozen batches, heated, acid, containing live insects and flavors are generally excluded.

The batches intended for obtaining the devro proteins meet the regulatory requirements applied to each production. (2) Crabs

The technologies applied to the seeds to extract the oil, destroy bitter toxic natural substances and evacuate residual solvents are numerous, varied and capable of altering the solubilities and the tritonational value of proteins. In addition, these cakes, intended for animal feed. are often insufficiently deoiled soiled with dust and reinjected with bleaching earths and lecithins from oil refining According to the invention, as regards the oil cakes intended to provide proteins for human consumption, the seeds from which they come will have to be cleaned, possible shelled, the oil will have to be extracted by cold pressio and by solvents of food grade, the temperature of cooking of the cakes should not exceed 105 ° C, they will not have to titrate more than 2% oil and 8% humidity. (3) TUBERS AND ROOTS

The tubers and roots must correspond to the standards required by the food industry (canneries, starch manufacturers, etc.). (4) GREEN PLANTS

Harvesting of green plants will be done when the protein content is highest (usually before flowering). Most of the proteins being located in the leaves, it is desirable to treat this part of the plant.

Avoid picking up too much dirt, dirt and other debris. Protein extraction must be carried out immediately after harvesting, storage favors the fixing of phenols on proteins, which results in insolubilization and a decrease in the nutritional value of these compounds. Of course, before being subjected to the process of the invention, the plant material to be treated must undergo mechanical preparation intended to facilitate contact with the reaction medium of step a). To this end, use will be made of means known in the art .cleaning, husking, dry grinding followed by sieving, or wet grinding, for example in a colloid mill. It is also clear that these means will have to be adapted to the particular form of presentation of the plant substrate to be treated. Examples will be given below. An essential step. of the process of the invention consists in treating the plant material with hydrogen peroxide in an alkaline medium, so as to dissolve the proteins which it contains. This step must be carried out under conditions ensuring intimate contact with the plant material and the liquid reaction medium. It is essential that the medium is maintained at an alkaline pH by the addition of any agent capable of producing such a pH. Such agents are known to those skilled in the art. the treatment of vegetable matter. They can be organic and / or inorganic compounds, for example sodium hydroxide, 'sodium carbonate, potassium hydroxide, ammonium hydroxide ,!' calcium hydroxide, magnesium hydroxide, or an organic base, such as alkanolamines, such as ethanolamine. The preferred alkaline agent is sodium hydroxide. In general, the compounds of divalent cations, such as calcium or magnesium hydroxide, are less favorable for the recovery of proteins, but this effect can be counterbalanced by the electrolytic effect of hydrogen peroxide used.

The precise pH value may vary somewhat depending on the nature of the plant substrate; in the case of seeds, the pH will be maintained between 8.5 and 11.5. In the case of tubers and roots, as well as for green plants, it is sufficient that the pH of the medium is maintained between 8 and 9 approximately.

Specific examples below will illustrate these modes of implementation. The amount of alkaline solution to be used depending on the nature of the substrate is generally of the order of 2 to 10 parts by weight of alkaline solution per part by weight of plant material. In the case of seeds, this quantity will be of the order of 5 to 10 parts, whereas, in the case of tubers and roots, one can be satisfied with a lower quantity ranging from 2 to 5 parts of alkaline solution.

The alkaline solution serves as a reaction medium. It can also be used as a grinding medium if grinding is carried out in the wet state of the substrate. In fact, the solubilization of proteins is obtained by the joint action of the alkaline medium and hydrogen peroxide. To the knowledge of the applicant, it has never been proposed until now to treat in an alkaline medium a plant material so as to extract the proteins which it contains by taking advantage of the reducing effect of hydrogen peroxide. Oxygenated water is a valuable reagent for the extraction of food proteins because it leaves no harmful residue in the reaction medium, since it decomposes simply into water and oxygen.

The amount of hydrogen peroxide to be used will vary depending on the particular substrate. When using oxygenated water at 110 volumes, which is commonly available in industry, the amount of H ₂ O ₂ will generally vary between 0.2 and 3% by volume, relative to the volume of the reaction medium. consisting of the alkaline solution.

The hydrogen peroxide can be supplied to the medium as such or else in the form of at least one precursor compound, preferably a food-grade precursor, such as sodium peroxide which supplies H ₂ O in situ to the medium.

Step a) is advantageously carried out at room temperature, but it could also be carried out under moderate heating conditions.

The contact time of the plant material and the alkaline medium in the presence of hydrogen peroxide must be sufficient to dissolve practically all the proteins contained in the plant material. Generally speaking, contact times of 5 to 20 minutes are suitable.

In the second step b) of the process, the insoluble materials are separated from the protein solution. This separation can be carried out by any known means, for example by centrifugation. The composition and nature of the insoluble fractions vary according to the substrate treated. However, they can be used in many cases for animal feed. Another important stage of the process of the invention is stage c), during which the protein solution is acidified until a pH which varies between 6 and 8.5 varies depending on the substrates, and which leads to an insoluble fraction don example, in the case of seeds, this fraction will contain heteroproteins, polysaccharides (mucilage, pectin) and other compounds. Acidification is carried out by adding water minus an acid-reacting substance, and preferably a acid known to those skilled in the art for the treatment of food materials, advantageously hydrochloric, sulfuric, phosphoric, carbonic acids, or organic acids, such as acetic, lactic or citric acids. Advantageously, strong hydrochloric and sulfuric acids of food grade are used. It should be noted that the reducing effect of H ₂ O ₂ continues during this step c). Thus, with regard to hydrogen peroxide, contact with the plant material takes place during steps a) and c).

In step d) of the process, the protein solution is clarified before being subjected to step e) during which residual hydrogen peroxide is destroyed, and all traces "of peroxide possibly present, by adding to said solution at least one enzyme of the peroxidase type. A preferred enzyme is cataiase, in particular extracted from beef liver. The illustrative examples below will provide quantitative information on the quantities of enzyme to be used. beef liver cataiasis, this amount will vary, for example, between 200 and 400g per 100 kg of protein dry matter in solution Step e) must be continued for a time sufficient for the destruction of hydrogen peroxide and peroxide In general, treatment times of 5-10 minutes are suitable.

Step f) of the process consists in adding to the protein solution originating from step e) at least one antioxidant agent known in this kind of technique, for example ditertio butylparacresol, also designated by the abbreviation BHT, or other compounds analogues.

It will be noted that, in the process of the invention, the antioxidant is used during an intermediate stage of the process, and it therefore simultaneously provides a protective effect on proteins. It should be noted in fact that, in known processes for extracting proteins from plant materials, it has already been proposed to protect proteins from oxidation by incorporating In the reaction medium of the reducing agents, it is only after the final protein fraction separated and dried that an antioxidant was added for protection. However, in the process of the invention, the reaction medium is already highly reducing. The antioxidant agent is therefore used in stage f) of the process and not after final separation of the protein fraction.

In step g), the desired proteins are recovered using known means for this purpose. It is possible, for example, to adjust the protein solution to the isoelectric pH, that is to say to acidify it to a pH of 4.7 to 5, by adding a food acid of the HCl or H _{2 type.} SO _{4. It} is also possible to effe kill a precipitation of proteins by coagulating these proteins by injecting water vapor into the solution. As a variant, it is also possible to acidify the medium by fermenting a microorganism therein, for example by carrying out lactic fermentation, in accordance with the process described in French patent 75 14 676 of May 12, 1975 in the name of the applicant and entitled "Process for processing of oil cakes and .grain seeds ". This process involves biological precipitation of the proteins extracted. Once the proteins have precipitated, the protein precipitate is recovered by centrifugation, and it is further treated, if necessary, by subjecting the protein pellet to a washing, after which a drying is carried out which provides food proteins in pulverulent form The effluents separated from the protein pellet in the last step of the process contain non-protein nitrogen, sugars, mineral salts, and various other elements. They can themselves be used to obtain food proteins by serving as a culture medium for microorganisms making it possible to prepare proteins from multicellular organisms. A suitable process for this purpose is described in French patent application 77 17 449 of June 7, 1977 in the name of the NATIONAL INSTITUTE FOR AGRONOMIC RESEARCH, having the title "Process for obtaining food proteins of fungal origin , or from multicellular organisms, device for its implementation and proteins thus obtained ". In summary, this process consists in cultivating at a temperature below 28 ° C the fungus Trichoderma Album on a nutritive medium. liquid, the pH thereof being maintained between about 3.7 and 4.8, with a dissolved oxygen content of about 6 to 10 mg / liter.

In the description which follows, the invention will be illustrated in more detail with reference to the appended drawings which are schematic representations of the main stages of the process applied respectively: for FIG. 1 with seeds, for FIG. 2 with tubers and roots, and for Figure 3 with green plants.

In addition, FIG. 4 shows, in detail, a variant of the process applied to soybean meal, making it possible to simultaneously obtain concentrates and protein isolates. Referring to Figure 1 of the accompanying drawings, which is an integral part of this description, there are specific indications on the methods of application of the process in the case of seeds. As previously mentioned, the process effluents can be rebalanced in nutrients and serve as a culture medium for filamentous microorganisms for the production of proteins from multicellular organisms (POP), grading 55 to 70%. of protein nitrogen, by the method of French patent 77 17,449.

Figure 2 is a schematic representation similar to Figure l, but in the case where the method is applied to the treatment of tubers and roots. In this case also, the process can be supplemented by an effluent treatment, for obtaining proteins from multicellular organisms, by the process of French patent 77 17 449 The same is true for FIG. 3 which illustrates the application of the process for the production of food proteins from green plants.

Same observation regarding Figure 4, which illustrates a process for the simultaneous preparation of protein concentrates and isolates from cooked soybean meal.

While for tubers, roots and green plants, the process can be effectively implemented in general according to the diagrams of Figures 2 and 3, the methods of application of the process illustrated in Figure 1 vary with the substrates and are described below: SOYBEANS

Applied to soybeans, the process provides isolates, or simultaneously a concentrate and an isolate. Isolates can be obtained from raw or cooked cake, concentrates from cooked cake. The quantities of H 0 _o to be used are from 0.3 to 1% (V / V). The cakes are finely ground and sieved on a sieve of 100 to 150 μm or else directly ground in a liquid medium in a colloid mill. Obtaining isolates

Depending on whether it is a raw or cooked soybean meal, the extraction pH will be from 10 to 11.5. The clarifying precipitation will be at pH = 7.3 - 7.7. Simultaneous obtaining of concentrates and isolates

In this case, the raw material will be sojacuit cake, from shelled seeds, grading 50% protein.

The extraction will be carried out with 5 to 10 parts of NaOH 0.03 to 0.05 N (pH = 8.5 to 10) comprising 0.3 to 1% of H ₂ O _2. The suitable contact time may be 20 mins.

Figure 4 shows the technology used. COLZA, SUNFLOWER, CARTHAME, EEVEROLES, PALMISTE COPRAH.

Applied to these cakes, the process makes it possible to obtain isolates of good quality, without flavors, of white or ocher color.

The proteins are extracted with 10 parts of 0.1 N sodium hydroxide (pH = 11.5), comprising 2% H ₂ O _{2, the} contact time is 5 to 10 minutes, The oil cakes are previously finely ground and tami ses on sieve from 150 to 300μ, or preferably ground in a liquid medium in a colloid mill, which limits oxidation. Clarification is carried out at pH = 7 for rapeseed and field beans, at pH = 8.5 for sunflower and safflower, at = 6.5 for palm kernel and copra. PEA SESAME

Proteins from pea flour and sesam cake are extracted with 10 parts of 0.05 N sodium hydroxide containing 1% of

H ₂ O _2. The contact time is 5 to 10 minutes.

Clarification is carried out at pH = 7 for peas and pH = 8 for sesame. PEANUT, COTTON, LUPINE, LINEN, JOJOBA

The seeds of oil cakes in this group are rich in toxic substances (aflatoxins, gossypol, alkaloids, glycosides, cyanogenics, derivatives of resorcinol) and, therefore, their residence times in the extraction solution must be prolonged.

The extraction is carried out with 10 parts of 0.1 N sodium hydroxide containing 2% of H ₂ O ₂ .

The extraction time varies from 20 min to 1 h for peanuts and cotton, and from 1 h 30 to 2 h 30 for lupine, flax, jojoba.

Clarification can be carried out at pH = 7 for peanuts and jojoba, at pH = 8 for cotton, lupine and flax. WHEAT, BUT, OATS and OTHER CEREALS

Cereal seeds are extracted with 5 to 7 parts of alkaline solution at pH = 9, comprising 0.3 to 0.5% H ₂ O _2. The contact time is 5 to 10 minutes.

The clarification is advantageously carried out at pH = 7. CONTROL METHODS

Organic nitrogen is dosed after mineralization according to the Berthelot method. The amino acid protein composition is determined after acid hydrolysis and resolution in a Technicon TSM _{1 device} .

The bacteriological purity of the fractions obtained is checked on selective media. Toxins (aflatoxins, thioglycosides, gossypol) and various metabolites (chlorogenic acid) are characterized, after extraction, by thin layer chromatography.

The nutritional value of the isolates and concentrates is determined on male Sprague Da-wley SPF rats of 50 g. The activity of bovine cataiasis is assessed by assaying H ₂ O ₂ with the oximeter or chemically according to the following method: Reagent: Sodium tungstate = 25g; phosphoric acid D = 1.71 =

10 ml; distilled water = 40 ml; boil 2 h; add ammonium metavanadate = 4g; distilled water = 50 ml, boil 2 h 30; add nitric acid D = 1.38 = 40 ml; distilled water 100 ml boil 2 h; add Reinecke salt = 4g; nitric acid D = 1.38 = 50 ml, boil for 1 hour. This reagent is stable.

Catalysis activity assay method

In a test tube, add while stirring:

0.1 ml of the solution containing the. cataiasis and H ₂ O ₂ 1.9 ml of phosphate buffer pH = 7 1.0 ml H ₂ O

Add 3 ml of 5 N sulfuric acid

Take 2 ml of this solution in a second test tube.

Add 0.1 ml of reagent Shake

Read with a spectrophotometer at λ = 490 nm

Make a blank with 2 ml 2.5 N sulfuric acid + 0.1 reagent.

PRODUCTS USED FOR EXTRACTION Soda and acids (H ₂ SO ₄ HCl) are of food quality. Antioxidants are incorporated in the amounts allowed. BHT was used at 2 to 7 mg per liter. The preparation of beef liver cataiase is carried out according to the following protocol: 100 g of healthy beef liver, freshly sampled or frozen, are ground with a "Turmix" in 600 to 800 ml of isotonic sucrose (25 g / l), then the solution is filtered through glass wool to remove the insoluble fraction. This preparation must be used extemporaneously, according to the methods described (200 to 400g of liver / 100 kg of product), or it can be frozen. THE OBTAINED RESULTS

The quantities of raw materials treated varied between substrates between 10 and 50 kg of dry matter. The average results obtained are recorded in the eight tables below, the analysis of which will be made separately. Table l

The solubilities of proteins in sodium hydroxide and their ability to precipitate at pH = 5 vary considerably depending on the substrates (the yields of isolates range between 27 and 77%).

Among the elements which alter the extractability, one can cite the quality of the seeds, the denaturation of proteins by the technologies applied to extract the oil, the high contents in ashes, in cellulose, in phenols, the fatty acids resulting from the rancidity of fats.

In most cases, while respecting the standards for substrates, the yields of isolates oscillate between 50 and 80%. TABLE II In this table are expressed the compositions of the amino acid fractions. It appears that the isolates are generally depleted in lysine, threonine, methionine-cystine, not because these. amino acids are destroyed, but because they remain in proteins insoluble in soda or in effluents.

The process of the invention does not reveal any loss of essential amino acids, nor synthesis of lysinoalanine.

Sodium-insoluble fractions can also be used in animal feed.

The effluents mainly include proteins, amino acids, sugars, ash and impurities (orthodiphenols, aromatic amines, etc.). After rebalancing, they can be used for growing filamentous mushrooms (Trichoderma album) with a view to obtaining proteins, by applying the process described in French patent n ° 77 17 449. TABLE III

This table shows the results of the simultaneous obtaining of soybean concentrates and isolates. The composition of the concentrate is excellent; few proteins are lost. The dry matter eliminated in the effluent consists of ash, organic acids, acid and indigestible sugars, pigments, saponins, phenols, bitter peρtides, substance conferring flavors and flatulence. The concentrates obtained are in the form of a white powder, odorless and tasteless, easily texturizable. The nutritional value of these concentrates is very high; they are easily incorporated into many human foods without giving them unpleasant flavors and side effects (flatulence).

The concentrates thus obtained have better physical and organoleptic properties than alcoholic and acid concentrates. TABLES IV and V

In Tables IV and V, a raw soybean meal is compared. to a cooked soybean meal. These tables illustrate the influence of technology on the behavior of proteins and their amino acid compositions. TABLE VI

This table shows the excellent results obtained on peanuts, cotton and rapeseed, thanks to the use of hydrogen peroxide in an alkaline medium. In fact, under the operating conditions, in 20 to 30 minutes, the aflatoxins are completely destroyed and the levels of gossypol, thioglycosides and isoflavones are very clearly reduced.

The process thus allows a considerable valorization of the cakes by destroying the contaminating and natural toxins. In addition, it eliminates and modifies a large number of organic molecules (phenols, flavones, saponins, complex sugars, pigments, etc.) which reduce the conservation, accessibility, nutritional value of food. This action has been confirmed by numerous nutritional experiences. TABLE VII The bacteriological checks carried out on the isolates show that the quality of these products is excellent.

TABLE VIII nutritional values.

The nutritional values of 16 proteins obtained according to the process were compared with lactic casein supplemented with methionine. The experiment was carried out on young male SPF weaned rats, breed S-prague Dawley; the duration of the experiment was 17 days and the protein level in food was 10%. Each diet was rebalanced in acid animals .

Analysis of Table VIII shows that the lactic casein and Trichoderma album batches are very clearly distinguished from all the vegetable proteins whose structures and compositions seem to limit the biological value for the rat.

The good behavior of all the regimes tested proves the improving action of the process of the invention.

Note, in the case of alfalfa, the large quantities of protein that are obtained per year per hectare (1800 to 3000 kg); In addition, obtaining dehydrated alfalfa is preceded by pressing which provides large quantities of juice. This rebalanced alfalfa juice is an excellent substrate for obtaining mushroom proteins (Trichoderma album) according to the method of French patent 77 17 449.

The above results show that the process of the invention makes it possible to exploit numerous sources of vegetable proteins which, at the present time, are not yet sufficiently exploited for this purpose in the world. Mention may be made, for example, of plant materials such as rapeseed, sunflower, peas, field beans, cereals, tubers and green plants. In the case of soybeans, the invention makes it possible to obtain proteins advantageously usable for human consumption.

According to a very advantageous additional characteristic of the invention, the method also allows a detoxification of the substrates, in particular peanuts and cotton, which will henceforth allow populations in disadvantaged regions to access a better balanced diet of proteins.

Moreover, the invention can be implemented with the essential aim of detoxifying plant substrates, without the proteins which they contain being extracted. In this case, the method of the invention can be limited to step a) described above of contacting substrates in an alkaline medium with hydrogen peroxide.

By way of example, the invention can be applied to eliminate the numerous mycotoxins which contaminate seeds and food.

In the process of the invention, the fact of starting the treatment at a strongly basic pH and to complete the reaction with H ₂ O ₂ at a low pH is of great importance, since the annoying molecules, associated with vegetable proteins, are thus transformed into irreversible structures, which can then be eliminated.

The invention is of great interest for the treatment of cooked soybean meal, in which case the reaction is carried out with hydrogen peroxide at a pH not exceeding 10. Until now, soy protein concentrates were obtained by a concentration in an acidic or alcoholic medium. The invention thus makes it possible to obtain soy protein concentrates which are perfectly suitable for human consumption, since they are free from substances which confer undesirable flavors and / or are insufficiently digestible.

Claims

1. Method for obtaining food proteins of plant origin, with elimination of toxic and non-protein substances, characterized by the following steps: a) the plant material containing the proteins is treated with hydrogen peroxide, in a medium reaction being at an alkaline pH of 8.5 to 11.5, thereby dissolving said proteins in the medium, b) separating the insoluble materials from the liquid medium of step a) thus constituting a protein solution, c) said protein solution is acidified to a pH of 6 to 8.5, thereby precipitating the insoluble fraction containing compounds other than the desired food proteins, d) separating the insoluble matters from the protein solution from step c), thereby obtaining a clarified protein solution e) adding to said clarified solution * at least one enzyme of the peroxidase type, capable of destroying the residual hydrogen peroxide and the peroxides, if necessary. sents in the protein solution clarified, f) is added to the protein solution obtained in step e) at least one antioxidant; g) the solution of step f) is treated in a known manner in order to separate the proteins which it contains, which are recovered by the usual techniques.

2. Method according to claim 1, characterized in that as plant material containing the proteins, one of the following substrates is used:

(1) seeds (soybeans, field beans, peas, lupine, sunflower, safflower wheat, corn, oats), (2) oil cakes (soy, sesame, peanut, sunflower, rapeseed, flax, cotton, safflower, copra, palm kernel, jojoba),

(3) tubers (potatoes)

(4) green plants (alfalfa, spinach, sorghum).

3. Method according to one of claims 1 or 2, charac-terized in that step a) is carried out under conditions ensuring intimate contact with the plant material and the liquid reaction medium, said material being, at this effect, previously submitted to. treatments known per se, adapted to the types of plant substrate used, such as: cleaning, husking, dry grinding followed by sieving, or else wet grinding, for example in a colloid mill.

4. Method according to any one of claims 1 to 3, characterized in that the pH of the reaction medium of step a) is maintained at an alkaline value by addition of a basic organic and / or inorganic agent, such as sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium hydroxide, calcium hydroxide, magnesium hydroxide or an organic base, such as alkanolamines, such as ethanolamine, the preferred alkaline agent being sodium hydroxide.

5. Method according to any one of claims 1 to 4, characterized in that the pH of the reaction medium of step a) is maintained, in the case of seeds, between 8.5 and 11.5 approximately, and, in the case of tubers and roots, as well as for green plants, between 8 and 9 approximately.

6. Method according to any one of claims 1 to 4, characterized in that a cooked soybean meal is treated, at an alkaline pH not exceeding 10, to obtain a soy protein concentrate.

7. Method according to any one of claims 1 to 5, characterized in that the amount of alkaline solution to be used during step a) is of the order of 2 to 10 parts by weight of alkaline solution per part by weight of vegetable matter, this quantity being, in the case of seeds of the order of 5 to 10 parts, whereas, for tubers and roots, it is 2 to 5 parts.

8. Process according to claim 2, characterized in that. that the alkaline solution serving as a reaction medium during step a) is also used as a medium for grinding the vegetable material when prior grinding is carried out in the wet state of the substrate.

9. Method according to any one of claims 1 to 8, characterized in that hydrogen peroxide is used as such or in the form of at least one precursor, preferably a food-grade precursor, such as sodium peroxide.

10. Process according to any one of claims 1 to 9, characterized in that the quantity of hydrogen peroxide, expressed in

H ₂ O ₂ at 110 volumes, vaxicenter 0.2 and 3% by volume, relative to the volume of the alkaline solution.

11. Process according to any one of claims 1 to 10, characterized in that step a) is carried out at room temperature, by making contact with the vegetable material and the alkaline medium in the presence of the hydrogen peroxide, for a sufficient time to dissolve practically all the proteins contained in the plant material.

12. Method according to any one of claims 1 to 11, characterized in that during step c), the protein solution from step b) is acidified until a varying pH is obtained. between 6 and 8.5 approximately, depending on the substrates, by adding at least one acid-reacting substance, preferably a food-grade acid such as hydrochloric, sulfuric or phosphoric acid, or an organic acid, such as acetic, lactic or citric acid, hydrochloric and sulfuric acids being preferred.

13. Method according to any one of claims 1 to 12, characterized in that, as an enzyme, during step e) an enzyme of the peroxidase type is used, preferably cataiase, in particular extracted from Liver of beef.

14. The method of claim 13, characterized in that the amount of cataiase used varies between 200 and 400g per 100 kg of protein dry matter of the clarified solution from step d).

15. Method according to any one of claims 1 to

14, characterized in that, as an antioxidant, ditertiobutylparacresol (BHT) or other antioxidants are used or mixtures of known antioxidants.

16. Method according to any one of claims 1 to 15, characterized in that, during step g), the proteins are recovered by treating the protein solution of step f) using a food acid such as HC1 or H ₂ SO ₄ , up to isoelectric pH (4.7 to 5) or by coagulating the proteins, injection of water vapor into the solution, or by operating a biological precipitation of the proteins by fermentation of a microorganism in the solution.

17. Proteins suitable for human and animal consumption obtained by the process according to any one of claims 1 to 16.

18. Soy protein concentrate obtained by the process according to claim 6.