Candida utilis with high yield of protein and application thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-02
- Publication Date
- 2026-07-03
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Figure CN122326410A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microbial technology, specifically a high-protein-producing Candida utilis strain and its applications. Background Technology
[0002] With the rapid development of animal husbandry, my country's demand for protein feed is increasing day by day. On the other hand, the main protein raw materials in my country's feed come from imported plant proteins such as soybeans. Under the current increasingly tense international environment, the shortage of protein feed has seriously affected the development of my country's animal husbandry.
[0003] Single-cell protein, also known as bacterial protein or microbial protein, has been proven in numerous animal studies to partially replace dietary protein. *Candida utilis* (…) Cyberlindnera jadinii Also known as gluten-producing yeast or edible yeast. C. jadinii It can utilize a wide range of carbon sources, including pentose sugars such as xylose and hexose sugars such as glucose, fructose and sucrose, as well as glycerol, starch, fruit residues, etc. C. jadinii It has the advantages of rapid growth and reproduction, high single-cell protein content, and rich in various nutrients such as nucleotides, enzymes, B vitamins and oligosaccharides, and occupies an important position in the production of single-cell protein.
[0004] However, in applications requiring higher protein ratios and quality, the protein content and composition of existing strains still fall short of production needs. Furthermore, while agricultural and forestry wastes (straw, mushroom compost, etc.) are abundant and inexpensive, they are rich in recalcitrant structures such as cellulose, hemicellulose, and lignin. Under these substrate conditions, *Candida utilis* exhibits low sugar conversion and slow growth rates, resulting in insufficient single-cell protein yield and limiting its promotion in low-cost and resource-based utilization areas. Summary of the Invention
[0005] The purpose of this invention is to provide a high-protein-producing Candida utilis strain and its applications.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: A high-protein Candida utilis strain, Candida utilis ( Cyberlindnera jadinii )24-3 was deposited on November 27, 2025 at the Guangdong Provincial Center for Microbial Culture Collection, accession number GDMCC No:67370, located at 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou.
[0007] An application of the aforementioned high-protein-producing Candida utilis, specifically its application in the production of single-cell proteins.
[0008] The application of the high-protein-producing Candida utilis in the fermentation of yeast bran as a substrate for the production of single-cell protein.
[0009] The high-protein-producing Candida utilis is subjected to aerobic fermentation at 28-32°C and pH 5-7 using fermentation culture containing bacterial bran or industrial waste gas as substrate to produce single-cell protein.
[0010] When the substrate contains bacterial bran, the composition is as follows: 10-20 g / L ammonium sulfate, 0.15-0.35 g / L magnesium sulfate, and 1-3 g / L potassium dihydrogen phosphate are added to each liter of pretreated bacterial bran enzymatic hydrolysate.
[0011] The pretreated bacterial bran hydrolysate is prepared by mixing the pretreated bacterial bran with 0.05 M citrate buffer at a pH of 4.4 to 4.8 at a solid-liquid mass ratio of 1:(4-10), adjusting the pH of the system to 4.8 to 5.0, preheating at 45°C to 55°C for 10 to 30 minutes, then adding 0.5% to 4.0% of cellulase by dry weight of the bacterial bran, and enzymatically hydrolyzing at 45°C to 55°C and shaking at 150 to 250 rpm for 24 to 72 hours to obtain the bacterial bran hydrolysate. The pretreated mushroom residue is prepared by mixing mushroom residue with an aqueous solution containing sulfite and alkali, cooking at 120°C to 160°C for 60 to 180 minutes, followed by solid-liquid separation. The resulting solid residue is washed and dried to obtain the pretreated mushroom residue. The mass-to-volume ratio of the mushroom residue to the aqueous solution containing sulfite and alkali is 1-3:6-8. The final concentration of sulfite in the aqueous solution containing sulfite and alkali is 2.5-5 wt%, and the final concentration of alkali is 0.01-0.05 wt%. The alkali is sodium hydroxide or potassium hydroxide. or, The mushroom residue is soaked in a dilute acid solution with a mass fraction of 0.5% to 2% for 0.5 to 2 hours, then maintained at a steam pressure of 1.0 to 1.5 MPa for 10 to 20 minutes, followed by instantaneous depressurization to complete the explosion. The exploded material is then dried to obtain pretreated mushroom residue.
[0012] The mushroom residue is a lignocellulose byproduct left after harvesting edible fungi. It mainly contains residual fungal mycelium and incompletely degraded lignocellulose biomass. The edible fungi may include enoki mushrooms, oyster mushrooms, shiitake mushrooms, etc.
[0013] A bacterial agent that produces single-cell proteins, the bacterial agent containing the bacterial strain.
[0014] The bacterial agent contains a culture of the bacterial strain, a culture suspension, or a fermentation broth.
[0015] Advantages of this invention This invention utilizes *Candida utilis* C. jadinii2.615 strain was mutagenized to obtain the mutant strain Candida utilis 24-3. The mutant strain was used to rapidly and cost-effectively produce single-cell protein by using yeast bran hydrolysate as a substrate, thereby reducing waste treatment costs.
[0016] 1. Strain performance: After ARTP mutagenesis, the mutant strain has a faster growth rate, a shorter lag phase, and a higher protein content than the original strain, making it suitable for producing single-cell protein.
[0017] 2. Resource utilization of dual waste materials reduces processing costs: This invention constructs Candida utilis C. jadinii The highly efficient mutant Candida utilis 24-3, 2.615, enables it to directly utilize the enzymatic hydrolysate of fungal bran and / or the carbon source products obtained after treatment of industrial waste gas as culture substrates. This effectively realizes the synergistic resource utilization of agricultural waste (such as edible fungi cultivation waste) and industrial waste gas (such as exhaust gas containing components such as CO, CO2, and H2), which is conducive to reducing the disposal costs and environmental burden of the two types of waste.
[0018] 3. It has a high protein content and good application prospects: The resulting single-cell protein has a high protein content, accounting for more than 58% of the dry weight. It has a balanced amino acid composition and is rich in B vitamins and nucleotides, making it a high-quality protein source that can be widely used in livestock and aquatic feed, functional food additives, or organic fertilizers. Attached Figure Description
[0019] Figure 1 The starting strain provided for the embodiments of the present invention C. jadinii 2.615 lethal curve.
[0020] Figure 2 The image shows the mutation effect of the mutant strain provided in the embodiment of the present invention.
[0021] Figure 3 The image shows the genetic stability results of the mutant strain provided in the embodiments of the present invention.
[0022] Figure 4 The graph shows the effect of different amounts of enzyme on the yield of fermentable sugars in the substrate, as provided in the embodiments of the present invention.
[0023] Figure 5 The diagram shows the effect of nitrogen source optimization in the culture medium of the strain provided in the embodiment of the present invention; where A is the number of viable bacteria after fermentation with different nitrogen sources after adding sulfonated lignin, B is the dry weight after fermentation with different nitrogen sources after adding sulfonated lignin, and C is the protein content after fermentation with different nitrogen sources after adding sulfonated lignin.
[0024] Figure 6The graph shows the effect of adding different concentrations of Mg and Ca ions to the culture medium for the strains provided in the embodiments of the present invention, and the resulting viable cell counts.
[0025] Figure 7 The graph shows the effect of adding different concentrations of Cu, Zn, and Mn ions to the culture medium for the strains provided in the embodiments of the present invention, and the resulting viable cell counts.
[0026] Figure 8 The graph shows the effect of adding different concentrations and types of phosphates to the culture medium for the strains provided in the embodiments of the present invention, resulting in different viable cell counts.
[0027] Figure 9 The image shows the fermentation effect of the culture medium containing the bacterial bran enzymatic hydrolysis product provided in the embodiment of the present invention. Detailed Implementation
[0028] The following examples further illustrate specific embodiments of the present invention. It should be noted that the specific embodiments described herein are merely for illustration and explanation and are not intended to limit the scope of the present invention.
[0029] This invention uses agricultural and forestry waste as a culture medium to produce single-cell protein. By enhancing the degradation capacity of cellulose and / or hemicellulose and / or improving substrate availability, it improves the conversion efficiency of agricultural and forestry waste, thereby shortening the fermentation cycle, increasing sugar conversion rate, and increasing single-cell protein yield.
[0030] Candida utilis 24-3 was fermented in a culture medium under aerobic conditions. The selected control temperature was 25-30℃, preferably 28℃; the selected control pH was 5.0-7.0, preferably 5.8-5.9; the selected acid for pH adjustment was hydrochloric acid, and the selected base for pH adjustment was sodium hydroxide.
[0031] Single-cell protein was recovered from the fermentation broth obtained above, and the cells were separated by low-speed centrifugation to obtain crude single-cell protein.
[0032] Alternatively, syngas fermentation products can be used as substrates to produce single-cell proteins, with industrial waste gas as the carbon source. The products are converted by microorganisms and / or biocatalytic reactions to produce acetate, thus realizing the production of acetate from industrial waste gas.
[0033] Candida utilis 24-3 was fermented in a culture medium under aerobic conditions. The selected control temperature was 25-30℃, preferably 28℃; the selected control pH was 5.0-7.0, preferably 5.8-5.9; and the selected acid for adjusting the pH was the clear liquid of syngas fermentation broth.
[0034] Single-cell protein was recovered from the fermentation broth obtained above, and the cells were separated by low-speed centrifugation to obtain crude single-cell protein.
[0035] Example 1: Screening of mutant strains (1) ARTP mutagenesis: The starting strain of Candida utilis was cultured overnight in YPD medium at 30°C and 200 rpm. C. jadinii 2.615 (purchased in May 2021 from China General Microbiological Culture Collection Center (CGMCC)), awaiting growth to OD. 600 Mutagenesis was initiated at a value around 5 (early logarithmic phase). The OD values of the bacterial culture, which had been cultured to the logarithmic growth phase, were increased using sterile water. 600 Dilute to approximately 1, take 10 μL of the diluted solution and transfer it to the surface of a metal slide. Place the slide in the operating chamber of the ARTP mutagenesis instrument. Set the ARTP mutagenesis instrument to a working gas (helium) flow rate of 10 SLM and an irradiation spacing of 2 mm. Based on the lethality curve of the starting strain (see...),... Figure 1 Set the optimal mutagenesis time (54 s). After mutagenesis, quickly place the slide into an EP tube containing 500 μL of sterile water and vortex for 1 min to resuspend all the bacteria in the sterile water. Spread 50 μL of the bacterial suspension onto a YPD plate and incubate statically at 28°C for 48 h.
[0036] (2) Screening: Colonies with the largest diameter were selected and transferred to 48-well plates containing YPD liquid medium. The plates were then incubated in an automated growth apparatus for 24 h. One well contained a single clone of the starting strain as a control. Absorbance was measured every 60 min using the automated growth apparatus during the incubation process. A growth curve was plotted with incubation time on the x-axis and absorbance on the y-axis. The maximum specific growth rate and delay time were extracted based on the Gompertz model. The model function is Equation (2): (2) In the formula, t represents time; y = ln(OD) t / OD0), where OD0 represents the initial OD value; OD t D represents the OD value at time t; D = ln(OD) ∞ / OD0); μmax represents the maximum specific growth rate (h-1); λ represents the delay time (h).
[0037] The relative maximum specific growth rate and relative delay time are calculated according to formulas (3) and (4): (3) (4) In the formula, μ rel μmax represents the relative maximum specific growth rate of the mutant strain. mutμmax represents the maximum specific growth rate of the mutant strain. WT Δλ represents the maximum specific growth rate of the wild type; Δλ represents the relative lag time; λ mut Indicates the delay time of the mutant strain; λ WT This indicates the delay time for the wild type.
[0038] Then, a scatter plot was drawn with the relative maximum specific growth rate (μrel) as the ordinate and the relative delay time (Δλ) as the abscissa (see [reference]). Figure 2 To aid in screening for superior mutants, a horizontal auxiliary line of μrel>1.3 and a vertical auxiliary line of Δλ<0 were constructed, resulting in 17 mutants with growth advantages (Table 1), which were preserved for further screening.
[0039] Table 1 Initial Screening Results
[0040] (3) Secondary screening: The strains screened in the primary screening were inoculated into shake flasks containing 30 mL of YPD medium and cultured at 28℃ and 200 rpm for 24 h. The bacterial biomass and bacterial protein content were measured, and the protein content was used as the basis for secondary screening. The strains obtained after secondary screening are strains numbered 24-3 in Table 2.
[0041] Biomass determination: 20 mL of culture medium was added to a pre-dried and weighed 50 mL centrifuge tube. The tube was centrifuged at 8000 rpm for 5 min. The cells were resuspended in pure water and centrifuged again at 8000 rpm for 5 min. This process was repeated three times to remove residual culture medium. After the final washing, the supernatant was discarded. The tube was then placed at room temperature until all cells had settled to the bottom, and then pre-cooled overnight at -80℃. The cells were then freeze-dried to constant weight to obtain bacterial powder. The weight of the bacterial powder after drying was measured, which represents the bacterial biomass.
[0042] Protein content determination: The crude protein content of the bacterial powder obtained during the above biomass determination process was determined using a fully automated Kjeldahl nitrogen analyzer according to the GB / T 6432-2018 method. The protein content of 17 mutant strains was obtained (Table 2).
[0043] Table 2 Results of Rescreening
[0044] (4) Genetic stability test: The strains obtained from the secondary screening were cultured continuously for 8 generations using YPD medium under the same conditions as the secondary screening. The protein content of each single cell was measured every 2 generations according to the protein content determination method described above (see Figure 3 ).
[0045] Depend on Figure 3It is evident that after eight generations of passage, the protein content and dry weight of the mutant strain 24-3 obtained from the secondary screening did not change significantly, indicating that the mutant strain has good genetic stability.
[0046] The obtained strain is Candida utilis ( C. jadinii Synthetic strain 24-3 was deposited at the Guangdong Provincial Microbial Culture Collection Center on November 27, 2025, with accession number GDMCC No:67370. The resulting *Candida utilis* mutant strain showed a 49.3% increase in growth rate and a 14.1% increase in protein content in YPD medium compared to the original strain.
[0047] Example 2 Pretreatment of mushroom residue can be categorized into two methods: lignin extraction combined with enzymatic hydrolysis, or steam explosion combined with enzymatic hydrolysis. Specifically: 1) Lignin extraction combined with enzymatic hydrolysis (1) Lignin extraction treatment: Weigh 200 g of anhydrous sodium sulfite and 10 g of sodium hydroxide, dissolve them in 7 kg of pure water to obtain a mixed solution, weigh 2 kg of uncrushed enoki mushroom substrate, mix the mixed solution and enoki mushroom substrate and add them to a rotary cooker, keep warm at 140℃ for 120 min. After the treatment, use a filter bag to separate the solid and liquid, wash the collected solid residue with pure water until the pure water is colorless and neutral after washing, put it in an oven to dry to constant weight, weigh it and seal it for storage.
[0048] (2) Enzymatic hydrolysis: Weigh five portions of the above-treated bacterial residue with the same dry weight, and mix each portion with 0.05 M citrate-sodium citrate buffer at pH 4.6 at a solid-liquid mass ratio of 1:5 (g / g). After mixing, adjust the pH to 4.9±0.05 with 10% HCl or 10 M NaOH, preheat in a 50℃ water bath for 20 min, add different amounts of cellulase C.Tec3 (cellulase purchased from Novozymes, its usage is as described in the product instructions, the cellulase amounts are 0.66 wt%, 1.32 wt%, 2 wt%, 2.66 wt%, 3.33 wt%), mix well, and place in a constant temperature shaker at 50℃ and 200 rpm for 48 h. After enzymatic hydrolysis, detect the fermentable sugars in the product using high performance liquid chromatography (see Figure 4 ).
[0049] 2) Steam explosion treatment combined with enzymatic hydrolysis (1) Steam explosion treatment: After soaking the mushroom substrate in an excess of 1% dilute sulfuric acid solution for 1 hour, conventional steam explosion technology was used to maintain the pressure at 1.3 MPa for 15 minutes, and then the pressure was released instantaneously to complete the steam explosion. The pretreated substrate was dried and weighed.
[0050] (2) Enzymatic hydrolysis: Five portions of the above-treated bacterial residue with the same dry weight were weighed and mixed with each portion of bacterial residue using 0.05 M citrate-sodium citrate buffer at pH 4.6 at a solid-liquid mass ratio of 1:5 (g / g). After mixing, the pH was adjusted to 4.9±0.05 with 10% HCl or 10 M NaOH. The mixture was preheated in a 50℃ water bath for 20 min. Different amounts of cellulase C.Tec3 were added (the cellulase was purchased from Novozymes, and its usage was as described in the product instructions, with cellulase amounts of 0.66 wt%, 1.32 wt%, 2 wt%, 2.66 wt%, and 3.33 wt%). After mixing, the mixture was placed in a constant temperature shaker and enzymatically hydrolyzed at 50℃ and 200 rpm for 48 h. After enzymatic hydrolysis, the fermentable sugars in the product were detected according to the high performance liquid chromatography (see [reference]). Figure 4 ).
[0051] Depend on Figure 4 It can be seen that the sugar concentrations produced by the two methods are almost the same when the amount of cellulase is 2.66 wt% and 3.33 wt%. Considering all factors, the optimal enzymatic hydrolysis conditions should be 2.66 wt% of cellulase. The fermentable sugar concentration after enzymatic hydrolysis of the bran pretreated by steam explosion is 27.56 g / L, and the fermentable sugar concentration after enzymatic hydrolysis of the bran extracted by lignin is 33.14 g / L.
[0052] In summary, the optimal pretreatment method is lignin extraction combined with 2.66 wt% enzyme treatment; That is, (1) Lignin extraction treatment: Weigh 200 g of anhydrous sodium sulfite and 10 g of sodium hydroxide, dissolve them in 7 kg of pure water to obtain a mixed solution, weigh 2 kg of uncrushed enoki mushroom substrate, mix the mixed solution and enoki mushroom substrate and add them to a rotary cooker, keep warm at 140℃ for 120 min. After the treatment, use a filter bag to separate the solid and liquid, wash the collected solid residue with pure water until the pure water is colorless and neutral after washing, put it in an oven to dry to constant weight, weigh it and seal it for storage.
[0053] (2) Enzymatic hydrolysis: Weigh five portions of the above-treated bacterial residue with the same dry weight, and mix each portion of bacterial residue with 0.05 M, pH 4.6 citrate-sodium citrate buffer at a solid-liquid mass ratio of 1:5 (g / g). After mixing, adjust the pH to 4.9±0.05 with 10% HCl or 10M NaOH, preheat in a 50℃ water bath for 20 min, add different amounts of cellulase C.Tec3 (cellulase purchased from Novozymes, its usage is as described in the product instructions, the amount of cellulase is 2.66 wt%), mix well, and place in a constant temperature shaker at 50℃ and 200 rpm for 48 h.
[0054] Example 3: Optimization of Fermentation Medium (1) Centrifuge the lignin extraction fungal digest at 10,000 rpm for 10 min and collect the supernatant as the culture medium for the enzymatic digestion supernatant. The supernatant of the subsequent lignin extraction enzymatic digest is referred to as the lignin extraction supernatant; (2) Single-factor optimization of nitrogen source: Ammonium sulfate, ammonium chloride, corn steep liquor, and ammonium acetate were selected as nitrogen sources and added to the bacterial bran enzymatic hydrolysate, with the same nitrogen content as YPD medium, i.e., 4.14 g / L nitrogen, as a control. The calculated addition amounts were: ammonium sulfate 19.7 g / L, ammonium chloride 15.8 g / L, corn steep liquor 29.5 g / L, and ammonium acetate 22.7 g / L. C. jadinii The optimal nitrogen source was determined using viable cell count, dry weight, and protein content as indicators. The optimization results are as follows: Figure 5 As shown.
[0055] Depend on Figure 5 It is evident that the culture medium using ammonium sulfate as the nitrogen source has significantly higher viable cell count, dry weight, and protein content than ammonium chloride, corn steep liquor, and ammonium acetate. Therefore, ammonium sulfate is identified as the optimal nitrogen source.
[0056] (3) Optimization of single-factor metal ions: Mg was selected 2+ Ca 2+ Cu 2+ Zn 2+ Mn 2+ Five metal ions were added to the bacterial bran enzymatic hydrolysate at four different concentration gradients, with no metal ions added as a control. The optimal metal ion and concentration range were determined using the viable cell count as the indicator. The optimization results are as follows: Figure 6 , Figure 7 As shown.
[0057] Depend on Figure 6 and Figure 7 It can be seen that adding 0.2 g / L of Mg 2+ Ions significantly promoted yeast growth, increasing the number of viable cells by 39.73% compared to the control group. 2+ Ions have no significant effect; the addition of Cu 2+ Zn 2+ and Mn 2+ After ionization, the number of colonies was significantly reduced compared to the control group, indicating that yeast growth was inhibited.
[0058] (4) Different types of phosphates (KH2PO4, K2HPO4, NaHPO4·12H2O) were selected and four gradient concentrations of 5 mM, 7.5 mM, 10 mM, and 12.5 mM were set and added to the bacterial bran enzymatic hydrolysate, with no phosphate added as a control. The optimal phosphate and concentration range were determined based on the viable cell count. The optimization results are as follows: Figure 8 As shown.
[0059] Depend on Figure 8 It can be seen that the optimal phosphate is potassium dihydrogen phosphate, and the optimal addition concentration is 7.5 mM. Compared with the control group, the colony count increased by 100.01%.
[0060] In summary, the optimal culture medium for the enzymatic hydrolysis product of bacterial bran is to add 15 g of ammonium sulfate, 0.2 g of magnesium sulfate, and 1 g of potassium dihydrogen phosphate to each liter of the above-mentioned optimal pretreated bacterial bran enzymatic hydrolysate.
[0061] Example 4 Strain: Candida utilis C. jadinii 24-3; Reactor: 2 L shake flask; Culture medium for bacterial bran enzymatic hydrolysis product was prepared by adding 15 g / L ammonium sulfate, 0.2 g / L magnesium sulfate, and 1 g / L potassium dihydrogen phosphate to each liter of the optimally pretreated bacterial bran enzymatic hydrolysate. The culture medium was autoclaved at 115℃ for 30 min.
[0062] Fermentation conditions: 28℃, 250 rpm, inoculum size 10 wt%. Figure 9 It can be seen that after 18 hours of fermentation, OD 600 It reaches 36, with a short lag period and fast growth rate. It enters the plateau phase at 18 hours, with a protein content of 7.21 g / L and a yield of 0.4 g / (L·h) at 18 hours, a protein content of 7.63 g / L and a yield of 0.25 g / (L·h) at 30 hours, and a protein yield of up to 0.56 g / (L·h) during the logarithmic phase.
Claims
1. A high-protein-producing Candida utilis strain, characterized by: Candida utilis ( Cyberlindnera jadinii )24-3 was deposited at the Guangdong Provincial Center for Microbial Culture Collection on November 27, 2025, with accession number GDMCCNo:67370.
2. The application of the high-protein-producing Candida utilis according to claim 1, characterized in that: The application of the high-protein-producing Candida utilis in the production of single-cell proteins.
3. The application of the high-protein-producing Candida utilis according to claim 2, characterized in that: The application of the high-protein-producing Candida utilis in the fermentation of yeast bran as a substrate for the production of single-cell protein.
4. The application of the high-protein-producing Candida utilis according to claim 3, characterized in that: The high-protein-producing Candida utilis is subjected to aerobic fermentation at 28-32°C and pH 5-7 using fermentation culture containing bacterial bran or industrial waste gas as substrate to produce single-cell protein.
5. The application of the high-protein-producing Candida utilis according to claim 3, characterized in that: When the substrate contains bacterial bran, the composition is as follows: 10-20 g / L ammonium sulfate, 0.15-0.35 g / L magnesium sulfate, and 1-3 g / L potassium dihydrogen phosphate are added to each liter of pretreated bacterial bran enzymatic hydrolysate.
6. The application of the high-protein-producing Candida utilis according to claim 5, characterized in that: The pretreated bacterial bran enzymatic hydrolysate is prepared by mixing pretreated bacterial bran with a buffer solution with a pH of 4.4 to 4.8 at a solid-liquid mass ratio of 1:(4-10), adjusting the pH of the system to 4.8 to 5.0, preheating at 45°C to 55°C for 10 to 30 minutes, then adding 0.5% to 4.0% of cellulase by dry weight of the bacterial bran, and enzymatically hydrolyzing at 45°C to 55°C and shaking at 150 to 250 rpm for 24 to 72 hours to obtain the bacterial bran enzymatic hydrolysate. The pretreated mushroom residue is prepared by mixing mushroom residue with an aqueous solution containing sulfite and alkali, cooking at 120°C to 160°C for 60 to 180 minutes, followed by solid-liquid separation, and washing and drying the resulting solid residue to obtain the pretreated mushroom residue. Or, The mushroom residue is soaked in a dilute acid solution with a mass fraction of 0.5% to 2% for 0.5 to 2 hours, then maintained at a steam pressure of 1.0 to 1.5 MPa for 10 to 20 minutes, followed by instantaneous depressurization to complete the explosion. The exploded material is then dried to obtain pretreated mushroom residue.
7. A bacterial agent producing single-cell protein, characterized in that: The inoculum contains the high-protein-producing Candida utilis as described in claim 1.
8. The bacterial agent for producing single-cell protein according to claim 7, characterized in that: The inoculum contains a culture, culture suspension, or fermentation broth of Candida utilis, a high-protein-producing yeast.