Method for preparing high-purity yeast protein

Abstract

A high-purity yeast protein and a preparation method therefor, wherein the method comprises the following steps: inoculating an activated yeast strain into a liquid seed culture medium, culturing same in a shaker, then inoculating same into a fermentation culture medium for culturing, and centrifuging and washing same to obtain a yeast strain; preparing the yeast strain into a suspension solution, and performing a heat treatment to collect a precipitate; preparing the precipitate into a suspension, adding 5-50 U / mL of dextranase and 5-50 U / mL of cellulase at a pH of 5.0-7.0 and 30-60°C, and performing enzymatic hydrolysis to obtain a first enzymatic hydrolysate; adding a non-ionic solubilizer to the first enzymatic hydrolysate at a certain pH, and incubating the resulting mixure at a certain temperature to obtain a second enzymatic hydrolysate; and subjecting the second enzymatic hydrolysate to solid-liquid separation, washing and drying to obtain a high-purity yeast protein. The method reduces the possibility of protein denaturation. The final yeast protein product has a low dietary fiber content, a high branched-chain amino acid content and a high protein content, and exhibits good nutritional value and processing characteristics.

Description

A method for preparing high-purity yeast protein Technical Field

[0001] This invention relates to the field of yeast protein technology, and more particularly to a method for preparing high-purity yeast protein. Background Technology

[0002] Protein is one of the essential nutrients for the human body, participating in the body's structure and being indispensable for regulating various physiological functions. The FAO / WHO recommends a daily protein requirement of 0.75g per kilogram of body weight for healthy adults, with higher requirements for specific populations, such as 1.27g / (kg·d) for the elderly, and a recommended daily intake of 1.16g / (kg·d) for adults. As consumers' living standards continue to improve, the need for protein is increasing. Generally, sufficient protein can be obtained through food, but for certain groups, such as those with weak constitutions or fitness enthusiasts with high energy expenditure, relying solely on food may lead to digestive burden and excessive calorie intake. Therefore, they need to supplement with high-quality protein products, such as protein powder. However, the scarcity of high-quality protein resources remains a pressing issue.

[0003] Yeast is currently the most widely used and mature single-celled fungus by humans, and the extraction of yeast protein for use as edible functional protein or protein foods has gained increasing attention. Yeast protein is a high-quality protein, especially containing a certain proportion of branched-chain amino acids (leucine, isoleucine, and valine). Branched-chain amino acids can promote muscle anabolism and reduce catabolism, significantly increasing protein synthesis, promoting the release of related hormones, reducing fat synthesis, and improving athletic performance. However, due to the dense cell wall of yeast cells, protein extraction is relatively difficult, and it is not easy to remove the polysaccharide components of the cell wall. This results in a high dietary fiber content in the extracted yeast protein, leading to poor taste and low absorption and utilization.

[0004] Guo Long et al. published "Research on Extraction Technology of Waste Beer Yeast Protein," investigating four processes: ultrasonic extraction, freeze-thaw extraction, saline-thermal extraction, and hot-alkali extraction. The protein extraction rates were 3.47%, 4.15%, 5.66%, and 22.81%, respectively. The optimal extraction process for yeast protein was the alkaline-thermal extraction, with a sodium hydroxide addition of 1%. CN 102550795 A discloses a method for extracting high-purity selenium-containing protein from selenium-enriched yeast, using high-concentration hot-alkali extraction to obtain selenium-enriched yeast protein. CN201710518790.6 discloses a yeast protein, its preparation method, and its applications, with a protein content of over 75% and a sulfur-containing amino acid content of 30-35 mg / g. The preparation method of the yeast protein includes enzyme treatment followed by homogenization and cell disruption under 800-1500 bar pressure, solid-liquid separation, and drying. CN202110823547.1 discloses a low-yeast-flavor yeast protein, its preparation method, and its application, wherein the protein content reaches more than 78% and the nucleic acid content is less than 1.5%. CN202410148469.3 discloses a method for preparing yeast protein, wherein yeast and a hydrolyzing agent are extracted and separated by hot water hydrolysis, and then filtered to obtain the yeast protein, wherein the molecular weight of the yeast protein is ≥10kDa and ≤50kDa.

[0005] The methods described above often employ high-concentration strong alkali, high temperature, and high-pressure cell disruption for separation, extraction, and purification. Although some yeast proteins can achieve a final purity of around 75%, their branched-chain amino acid content is less than 20%, their dietary fiber content is high, usually above 15%, their taste is poor, and their dispersibility in water is extremely poor. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-purity yeast protein, which mainly includes yeast cell culture, yeast cell heat treatment, enzymatic cell disruption, solubilization, solid-liquid separation, and drying. This preparation method yields a high-purity yeast protein product with low dietary fiber and high branched-chain amino acid content. The yeast protein product has a protein content of over 75%, a branched-chain amino acid content of over 20%, and a dietary fiber content of less than 10%.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing high-purity yeast protein, wherein the high-purity yeast protein, by weight percentage, has a protein content ≥75%, a branched-chain amino acid content ≥20%, and a dietary fiber content ≤10%, and the preparation method includes the following steps:

[0009] S1. Yeast Cell Culture: After fermentation on slant agar, a loopful of activated yeast cells is inoculated into liquid seed culture medium and cultured on a shaker at 25-35℃ and 150-250 rpm for 12-24 hours. Then, a 5% (by weight) inoculum is added to the fermentation medium and cultured on a shaker at 25-35℃ and 150-250 rpm for another 12-24 hours. The mixture is then centrifuged, and the precipitate is collected to obtain the yeast cells. Fermentation of yeast in a medium rich in milk protein peptides promotes the synthesis of its cell protein.

[0010] S2. Heat treatment of yeast cells: Prepare a suspension of yeast cells obtained in step S1 with a weight percentage of 5%-15%. Adjust the pH to 7.0-9.0, incubate at 60-100℃ for 30-240 minutes, and centrifuge to obtain the precipitate. High-temperature treatment helps release water-soluble substances within the yeast cells, such as nucleic acids and trehalose, which is beneficial for subsequent extraction of high-purity protein components.

[0011] S3. Enzymatic cell disruption: Prepare a suspension of 5%-15% by weight of the precipitate obtained in step S2. After adjusting the pH to 5.0-7.0, add 5-50 U / mL of dextranase and 5-50 U / mL of cellulase at a temperature of 30-60℃ and hydrolyze for 4-24 hours to obtain the first enzymatic hydrolysate.

[0012] Yeast cell walls primarily contain yeast glucan and mannan. The combined action of glucanase and cellulase hydrolyzes high-molecular-weight polysaccharides in yeast cells, converting them into low-polymerization oligosaccharides, oligosaccharide esters, and polysaccharides, which are then washed away. This process also releases proteins encapsulated within the cells, facilitating yeast protein extraction. The enzyme dosage, hydrolysis temperature, and hydrolysis time must be carefully coordinated to achieve optimal results. For example, if the enzyme dosage is low, the hydrolysis temperature and time can be appropriately extended.

[0013] S4. Solubilization Treatment: Adjust the pH of the first enzymatic hydrolysate obtained in step S3 to 6.0-10.0, add a non-ionic solubilizer, and incubate at 50-70℃ for 30-120 min to obtain the second enzymatic hydrolysate. The weight of the non-ionic solubilizer added is 0.1%-5% (m / V) of the volume of the first enzymatic hydrolysate. Solubilization treatment improves cell wall permeability and the dissolution of non-protein substances such as fats, thereby removing impurities and increasing product purity. Solubilization treatment can remove lipids naturally present in yeast, increasing the protein content of the final product. Furthermore, lipid removal significantly improves the texture and dispersibility of the final product. The type and amount of solubilizer affect the lipid removal effect, thus affecting the protein content and texture of the final product.

[0014] S5. Separation and drying: The second enzymatic hydrolysate obtained in step S4 is subjected to solid-liquid separation. The precipitate is washed 2-3 times with the same volume of hot water at 40-60℃ as the second enzymatic hydrolysate. The precipitate is collected and dried to obtain high-purity yeast protein.

[0015] Furthermore, in step S1, yeast cells are obtained through fermentation culture, and the strains used can be selected from one or more of the genera Kluyveromyces, Saccharomyces, and Candida.

[0016] Furthermore, the preferred yeast is Kluyveromyces.

[0017] Further, in step S1, the slant culture medium comprises the following components by weight percentage: yeast extract 1%, peptone 2%, glucose 2%, and agar 2%; the seed culture medium is PD medium, which comprises the following components by weight percentage: yeast extract 1%, peptone 2%, and glucose 2%; the fermentation culture medium comprises the following components by weight percentage: cane molasses 6%, whey protein peptides 0.5-1.0%, (NH4)2SO4 0.4%, KH2PO4 0.6%, and K2SO4 0.1%; the slant culture medium, seed culture medium, and fermentation culture medium are all sterilized at 121°C under saturated steam for 15 min.

[0018] Furthermore, the lactoprotein peptides are selected from one or a combination of casein peptides and whey peptides. Using lactoprotein peptides as a partial nitrogen source in the fermentation medium can promote the synthesis of proteins and branched-chain amino acids within yeast cells. Lactoprotein peptides are bioactive substances obtained by chemically, fermenting, or enzymatically hydrolyzing milk proteins, and are mostly produced using enzymatic hydrolysis. Whey peptides and casein peptides are two such types. Casein peptides generally refer to casein polypeptides, which are hydrolysates of milk proteins. Whey peptides (also known as hydrolyzed whey protein or whey protein-hydrolyzed type) are products containing proteins, oligopeptides, and free amino acids, produced from whey through processes such as ultrafiltration concentration, laminar flow separation, enzymatic hydrolysis, and drying.

[0019] Furthermore, the pH of the fermentation medium is 5.5.

[0020] Furthermore, in step S2, the weight percentage of the prepared suspension is 6%-8%, the pH of the suspension is adjusted to 7.5-8.5, the holding temperature is 80-90℃, and the holding time is 60-120 min.

[0021] Furthermore, in step S3, the weight percentage of the suspension is 8%-12%, the enzymatic hydrolysis temperature is 40-55℃, and the enzymatic hydrolysis time is 8-12h.

[0022] Furthermore, in step S3, the pH of the first enzymatic hydrolysate is adjusted to 7.0-9.0, the HLB value of the nonionic solubilizer is 12-20, and the incubation time is 60-90 minutes. Using a highly hydrophilic nonionic solubilizer allows it to interact with hydrophilic substances in the system, improving the dissolution rate of these impurities.

[0023] Furthermore, in step S4, the drying method is freeze drying, drum drying, or spray drying.

[0024] The yeast protein preparation method of this invention does not involve high-concentration alkali treatment or protease treatment, reducing the possibility of protein denaturation during preparation. It also thoroughly removes non-protein components from yeast through fermentation, heat treatment, enzymatic hydrolysis of complex polysaccharides, and solubilization, thus reducing dietary fiber content. During yeast fermentation, milk-derived protein peptides are added as a partial nitrogen source, promoting the synthesis of intracellular proteins and branched-chain amino acids, increasing branched-chain amino acid content, and maintaining the original protein structure. The entire preparation process does not involve harsh steps such as high temperature and high pressure, making the method mild, easy to operate and implement. The final yeast protein product is low in dietary fiber, high in branched-chain amino acids, with a protein content of over 75%, a branched-chain amino acid content of over 20%, and a dietary fiber content of less than 10%, exhibiting good nutritional value and processing characteristics. For example, improved dispersibility allows the product to be combined with other additives to obtain various compound products. Detailed Implementation

[0025] A method for preparing high-purity yeast protein mainly includes the following steps: (1) yeast fermentation; (2) yeast cell heat treatment; (3) enzymatic cell disruption; (4) solubilization treatment; (5) solid-liquid separation; and (6) drying. The yeast protein product obtained by the above preparation method has a protein content of more than 75%, a branched-chain amino acid content of more than 20%, and a dietary fiber content of less than 10%.

[0026] Example 1

[0027] Culture medium:

[0028] Slant culture medium: YPD medium (1% yeast extract, 2% peptone, 2% glucose), 2% agar.

[0029] Seed culture medium: YPD medium (1% yeast extract, 2% peptone, 2% glucose).

[0030] Fermentation medium: 6% sugarcane molasses, 0.5% casein peptide, 0.4% (NH4)2SO4, 0.6% KH2PO4, 0.1% K2SO4, pH 5.5.

[0031] All culture media were sterilized at 121℃ under saturated steam for 15 minutes.

[0032] Yeast cell culture:

[0033] Commercially available Saccharomyces cerevisiae was fermented on YPD slant medium. One loop of activated Saccharomyces cerevisiae was then inoculated into 250 mL of liquid seed culture medium and cultured at 30°C and 180 rpm for 12 h on a shaker. Subsequently, a 5% inoculum was added to 2000 mL of fermentation medium and cultured under the same conditions (30°C, 180 rpm shaker) for 24 h. The cells were collected by centrifugation, and the protein content was determined to be 53.1%, with a branched-chain amino acid content of 21.4%.

[0034] Example 2

[0035] Culture medium:

[0036] Slant culture medium: YPD medium (1% yeast extract, 2% peptone, 2% glucose), 2% agar.

[0037] Seed culture medium: YPD medium (1% yeast extract, 2% peptone, 2% glucose).

[0038] Fermentation medium: 6% sugarcane molasses, 1% whey protein peptide, 0.4% (NH4)2SO4, 0.6% KH2PO4, 0.1% K2SO4, pH 5.5.

[0039] All culture media were sterilized at 121℃ under saturated steam for 15 minutes.

[0040] Yeast cell culture:

[0041] After fermenting *Kluyveromyces martensii* on an agar slant, a loopful of activated *Kluyveromyces martensii* was inoculated into 250 mL of liquid seed culture medium and cultured at 35°C and 250 rpm for 16 h on a shaker. Subsequently, a 5% inoculum was added to 2000 mL of fermentation medium and cultured under the same conditions (35°C and 250 rpm on a shaker) for 24 h. The cells were collected by centrifugation, and the protein content was determined to be 55.2%, with a branched-chain amino acid content of 22.5%.

[0042] Example 3

[0043] Yeast cell heat treatment: The *Kluyveromyces martensii* obtained in Example 2 was prepared into a 15% suspension with water, the pH was adjusted to 8.5 with NaOH, and the temperature was maintained at 80°C for 120 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0044] Enzymatic cell disruption: The precipitate was dissolved in water to form a 12% suspension, the temperature was adjusted to 55℃, the pH was adjusted to 5.0 with citric acid, and 50 U / mL glucanase and 50 U / mL cellulase were added. Enzymatic hydrolysis was carried out for 4 hours.

[0045] Solubilization treatment: After enzymatic hydrolysis, adjust the pH to 9.0 with NaOH, add 5% (m / V) food-grade Tween 80, and incubate at 50℃ for 90 min.

[0046] Separation: The liquid after the above solubilization treatment is centrifuged at 5000 rpm. The precipitate is redispersed with the same volume of 50℃ hot water, stirred and washed, and then centrifuged at 5000 rpm. The washing is repeated twice, and the centrifuged precipitate is collected.

[0047] Drying: Freeze-dry the precipitate to obtain yeast protein.

[0048] The prepared yeast protein product was tested and found to have a protein content of 81.3%, a branched-chain amino acid content of 23.3%, and a dietary fiber content of 8.4%.

[0049] Example 4

[0050] Yeast cell heat treatment: The brewer's yeast obtained in Example 1 was prepared into a 5% suspension by adding water, the pH was adjusted to 7.0 by adding NaOH, and the temperature was maintained at 60℃ for 240 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0051] Enzymatic cell disruption: Dissolve the precipitate in water to form an 8% suspension, adjust the temperature to 50℃, adjust the pH to 7.0 with HCl, add 5 U / mL glucanase and 5 U / mL cellulase, and enzymatically hydrolyze for 24 h.

[0052] Solubilization treatment: After enzymatic hydrolysis, adjust the pH to 6.0 with NaOH, add 0.5% (m / V) food-grade Tween 60, and incubate at 70℃ for 60 min.

[0053] Separation: The liquid after the above solubilization treatment is centrifuged at 5000 rpm. The precipitate is redispersed with the same volume of 50℃ hot water, stirred and washed, and then centrifuged at 5000 rpm. The washing is repeated twice, and the centrifuged precipitate is collected.

[0054] Drying: Dry the precipitate drum to obtain yeast protein.

[0055] The prepared yeast protein product was tested and found to have a protein content of 71%, a branched-chain amino acid content of 22.6%, and a dietary fiber content of 9.5%.

[0056] Example 5

[0057] Yeast cell heat treatment: The brewer's yeast obtained in Example 1 was prepared into a 10% suspension with water, the pH was adjusted to 7.5 with NaOH, and the temperature was maintained at 60℃ for 240 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0058] Enzymatic cell disruption: The precipitate was dissolved in water to form a 10% suspension. The temperature was adjusted to 55℃ and the pH to 5.0. 20 U / mL glucanase and 40 U / mL cellulase were added, and the mixture was enzymatically hydrolyzed for 8 hours.

[0059] Solubilization treatment: After enzymatic hydrolysis, adjust the pH to 8.0 with NaOH, add 2.0% (m / V) food-grade Tween 40, and incubate at 50℃ for 120 min.

[0060] Separation: The liquid after the above solubilization treatment is centrifuged at 5000 rpm. The precipitate is redispersed with the same volume of 50℃ hot water, stirred and washed, and then centrifuged at 5000 rpm. The washing is repeated twice, and the centrifuged precipitate is collected.

[0061] Drying: Freeze-dry the precipitate to obtain yeast protein.

[0062] The prepared yeast protein product, after testing, had a protein content of 82%, a branched-chain amino acid content of 22.9%, and a dietary fiber content of 7.8%.

[0063] Example 6

[0064] Yeast cell heat treatment: The *Kluyveromyces martensii* obtained in Example 2 was prepared into an 8% suspension by adding water, the pH was adjusted to 8.0 by adding NaOH, and the temperature was maintained at 80°C for 120 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0065] Enzymatic cell disruption: The precipitate was dissolved in water to form a 15% suspension. The temperature was adjusted to 50℃ and the pH to 6.0. 50 U / mL glucanase and 5 U / mL cellulase were added, and the mixture was enzymatically hydrolyzed for 8 hours.

[0066] Solubilization treatment: After enzymatic hydrolysis, adjust the pH to 6.0 with NaOH, add 5.0% (m / V) food-grade Tween 80, and incubate at 50℃ for 120 min.

[0067] Separation: Centrifuge the above liquid at 5000 rpm, take the precipitate and redisperse it with the same volume of 50℃ hot water, stir and wash, then centrifuge at 5000 rpm, repeat the washing twice, and collect the centrifuged precipitate.

[0068] Drying: The precipitate is spray-dried to obtain yeast protein.

[0069] The prepared yeast protein product, after testing, had a protein content of 82%, a branched-chain amino acid content of 22.9%, and a dietary fiber content of 7.8%.

[0070] Comparative Example 1

[0071] Yeast cell heat treatment: Commercially available brewing yeast was diluted with water to prepare a 10% suspension, the pH was adjusted to 8.0 with NaOH, and the temperature was maintained at 80℃ for 120 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0072] Enzymatic cell disruption: The precipitate was dissolved in water to form a 15% suspension. The temperature was adjusted to 55℃ and the pH to 5.0. 50 U / mL glucanase and 5 U / mL cellulase were added, and the mixture was enzymatically hydrolyzed for 8 hours.

[0073] Solubilization treatment: After enzymatic hydrolysis, adjust the pH to 6.0 with NaOH, add 5.0% (m / V) food-grade Tween 80, and incubate at 50℃ for 120 min.

[0074] Separation: Centrifuge the above liquid at 5000 rpm, take the precipitate and redisperse it with the same volume of 50℃ hot water, stir and wash, then centrifuge at 5000 rpm, repeat the washing twice, and collect the centrifuged precipitate.

[0075] Drying: The precipitate is spray-dried to obtain yeast protein.

[0076] The prepared yeast protein product, after testing, had a protein content of 81%, a branched-chain amino acid content of 17.4%, and a dietary fiber content of 12.8%.

[0077] Comparative Example 2

[0078] Yeast cell heat treatment: Commercially available brewing yeast was diluted with water to prepare a 10% suspension, the pH was adjusted to 8.0 with NaOH, and the temperature was maintained at 80℃ for 120 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0079] Enzymatic cell disruption: The precipitate was dissolved in water to form a 15% suspension. The temperature was adjusted to 50℃ and the pH to 7.0. 50 U / mL glucanase and 50 U / mL mannanase were added, and the mixture was enzymatically hydrolyzed for 8 hours.

[0080] Separation: Centrifuge the above liquid at 5000 rpm, take the precipitate and redisperse it with the same volume of 50℃ hot water, stir and wash, then centrifuge at 5000 rpm, repeat the washing twice, and collect the centrifuged precipitate.

[0081] Drying: The precipitate is spray-dried to obtain yeast protein.

[0082] The prepared yeast protein product, after testing, had a protein content of 73%, a branched-chain amino acid content of 18.4%, and a dietary fiber content of 17.5%.

[0083] Comparative Example 3

[0084] Yeast cell heat treatment: The *Kluyveromyces martensii* obtained in Example 2 was prepared into a 10% suspension with water, the pH was adjusted to 8.0 with NaOH, and the temperature was maintained at 80°C for 120 min. After the treatment, the precipitate was collected by centrifugation at 5000 rpm.

[0085] Enzymatic cell disruption: The precipitate was dissolved in water to form a 15% suspension. The temperature was adjusted to 50℃ and the pH to 6.0. 50 U / mL glucanase and 5 U / mL cellulase were added, and the mixture was enzymatically hydrolyzed for 8 hours.

[0086] Separation: Centrifuge the above liquid at 5000 rpm, take the precipitate and redisperse it with the same volume of 50℃ hot water, stir and wash, then centrifuge at 5000 rpm, repeat the washing twice, and collect the centrifuged precipitate.

[0087] Drying: The precipitate is spray-dried to obtain yeast protein.

[0088] The prepared yeast protein product, after testing, had a protein content of 78%, a branched-chain amino acid content of 21.3%, and a dietary fiber content of 8.3%.

[0089] In the above embodiments, the protein was determined using the Kjeldahl method, amino acids were determined using an amino acid analyzer, and dietary fiber was determined using the method specified in GB 5009.88 "Determination of Dietary Fiber in Food". The reagents used in the above embodiments are shown in Table 1.

[0090] Table 1. Reagents and Manufacturers

[0091] The above detailed description is a specific description of feasible embodiments of the present invention. These embodiments are not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included in the patent scope of this case.

Claims

1. A method for preparing high-purity yeast protein, characterized in that, The high-purity yeast protein, by weight percentage, has a protein content ≥75%, a branched-chain amino acid content ≥20%, and a dietary fiber content ≤10%. Its preparation method includes the following steps: S1. Yeast cell culture: After fermentation culture of yeast on slant medium, one loop of activated yeast cells is inoculated into liquid seed medium and cultured on a shaker at 25-35℃ and 150-250 r / min for 12-24 h. Then, 5% by weight is inoculated into fermentation medium and cultured on a shaker at 25-35℃ and 150-250 r / min for 12-24 h. After centrifugation, the precipitate is collected to obtain yeast cells. S2. Heat treatment of yeast cells: Prepare a suspension solution of yeast cells obtained in step S1 with a weight percentage of 5%-15%, adjust the pH to 7.0-9.0, keep it at 60-100℃ for 30-240 min, and obtain the precipitate after centrifugation. S3. Enzymatic cell disruption: The precipitate obtained in step S2 is prepared into a suspension with a weight percentage of 5%-15%. After adjusting the pH to 5.0-7.0, 5-50 U / mL of dextranase and 5-50 U / mL of cellulase are added at a temperature of 30-60℃. Enzymatic hydrolysis is carried out for 4-24 hours to obtain the first enzymatic hydrolysate. S4. Solubilizer treatment: After adjusting the pH of the first enzymatic hydrolysate obtained in step S3 to 6.0-10.0, add a non-ionic solubilizer and incubate at 50-70℃ for 30-120 min to obtain the second enzymatic hydrolysate. The weight of the non-ionic solubilizer added is 0.1%-5% of the volume of the first enzymatic hydrolysate in milliliters. S5. Separation and drying: The second enzymatic hydrolysate obtained in step S4 is subjected to solid-liquid separation. The precipitate is washed 2-3 times with the same volume of hot water at 40-60℃ as the second enzymatic hydrolysate. The precipitate is collected and dried to obtain high-purity yeast protein.

2. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S1, the yeast is selected from one or a combination of several genera including Kluyveromyces, Saccharomyces, and Candida.

3. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S1, the yeast is Kluyveromyces.

4. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S1, the slant culture medium comprises the following components by weight percentage: yeast extract 1%, peptone 2%, glucose 2%, and agar 2%. The seed culture medium is PD medium, which includes the following components by weight percentage: yeast extract 1%, peptone 2%, glucose 2%; The fermentation medium comprises the following components by weight percentage: 6% sugarcane molasses, 0.5-1.0% milk-based protein peptides, 0.4% (NH4)2SO4, 0.6% KH2PO4, and 0.1% K2SO4; The slant culture medium, seed culture medium and fermentation culture medium were all sterilized at 121℃ under saturated steam for 15 min.

5. The method for preparing high-purity yeast protein according to claim 4, characterized in that, The lactoprotein peptides are selected from one or a combination of two of casein peptides and whey peptides.

6. The method for preparing high-purity yeast protein according to claim 4, characterized in that, The pH of the fermentation medium is 5.

5.

7. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S2, the weight percentage of the prepared suspension is 6%-8%, the pH of the suspension is adjusted to 7.5-8.5, the holding temperature is 80-90℃, and the holding time is 60-120min.

8. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S3, the weight percentage of the suspension is 8%-12%, the enzymatic hydrolysis temperature is 40-55℃, and the enzymatic hydrolysis time is 8-12h.

9. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S4, the pH of the first enzymatic hydrolysate is adjusted to 7.0-9.0, the HLB value of the nonionic solubilizer is 12-20, and the incubation time is 60-90 min.

10. The method for preparing high-purity yeast protein according to claim 1, characterized in that, In step S4, the drying method is freeze drying, drum drying, or spray drying.

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