Application of sodium alginate / lignin composite gel immobilized yeast carrier in improving ethanol fermentation efficiency under fermentation environmental stress conditions

Abstract

This invention discloses the application of sodium alginate / lignin composite gel immobilized yeast carrier in improving ethanol fermentation efficiency under fermentation environmental stress conditions. The sodium alginate / lignin composite gel immobilized yeast carrier can simultaneously resist multiple stresses, improve yeast survival rate and fermentation efficiency, resulting in increased product ethanol concentration and improved substrate consumption rate. Furthermore, the preparation process of the sodium alginate / lignin composite gel immobilized yeast carrier is simple and recyclable, maintaining a high synergistic effect even after multiple recycling cycles, thus showing broad application prospects in the industrial production of bioethanol.

Description

Technical Field

[0001] This invention relates to the field of bio-fermentation technology, specifically to the application of sodium alginate / lignin composite gel immobilized yeast carrier in improving the efficiency of ethanol fermentation under fermentation environmental stress conditions. Background Technology

[0002] Lignocellulose is the world's most abundant biomass resource, and its fermentation for fuel ethanol production has significant economic and social value. In lignocellulose feedstock, cellulose is encapsulated by hemicellulose and lignin, forming a complex structure that reduces cellulose accessibility and leads to lower conversion efficiency. Pretreatment is the primary step in utilizing lignocellulose biomass, but this process generates toxic byproducts that affect normal yeast growth and subsequent fermentation. These toxic byproducts include steroidal saponins (such as diosgenin) and heavy metal ions (such as Cd). 2+ Cu 2+ Fermented ethanol contains various compounds such as furanaldehydes. Meanwhile, pH fluctuations during fermentation (the pH of the fermentation system easily drops below 3.0 due to the accumulation of organic acids) and high-temperature stress can also severely inhibit yeast activity, leading to a decrease in ethanol yield.

[0003] Traditional free yeast fermentation exhibits poor stress resistance, while yeast immobilization is considered an effective method to improve the efficiency of ethanol fermentation, offering advantages such as cell reusability, high starch-sugar conversion rate, and good tolerance. However, single sodium alginate (SA) immobilization carriers suffer from drawbacks such as insufficient mechanical strength, weak adsorption capacity for hydrophobic inhibitors, and lack of microenvironment regulation functions. They are easily damaged in high-shear fermenters and struggle to cope with multiple stresses.

[0004] Currently, some researchers have attempted to improve carrier performance by optimizing immobilization processes, but these efforts mostly focus on mitigating single inhibitors and lack comprehensive strategies to address complex inhibitory environments. Therefore, there is an urgent need for a fermentation application method that can simultaneously resist multiple inhibitors and possesses both high stability and cyclicability, in order to reduce industrial production costs and improve ethanol fermentation efficiency. Summary of the Invention

[0005] To overcome the aforementioned defects and shortcomings in the existing technology, this invention provides the application of sodium alginate / lignin composite gel immobilized yeast carrier in improving the efficiency of ethanol fermentation under fermentation environmental stress conditions.

[0006] The first objective of this invention is to provide a sodium alginate / lignin composite gel immobilized yeast carrier.

[0007] The second objective of this invention is to provide the application of the above-mentioned sodium alginate / lignin composite gel immobilized yeast carrier in improving the efficiency of ethanol fermentation under fermentation environmental stress conditions.

[0008] The third objective of this invention is to provide a method for improving the efficiency of ethanol fermentation under fermentation environmental stress conditions.

[0009] This invention claims protection for the following:

[0010] A sodium alginate / lignin composite gel immobilized yeast carrier, wherein the sodium alginate / lignin composite gel immobilized yeast carrier is prepared by encapsulating yeast with sodium alginate and soluble lignin.

[0011] The method for preparing the soluble lignin includes the following steps: alkali dissolution and sonication of the lignin solution; separation of the liquid after sonication; dialyzing of the liquid; removal of the solvent after dialysis to obtain soluble lignin.

[0012] The lignin includes enzymatically hydrolyzed lignin, alkali lignin, sulfate lignin, lignin extracted by eutectic solvents, or ground wood lignin.

[0013] Preferably, the lignin is enzymatically hydrolyzed lignin.

[0014] Preferably, the encapsulation method is as follows: soluble lignin is mixed with sodium alginate solution, then yeast is added to obtain a mixed solution; the mixed solution is then added dropwise to a solution containing Ca. 2+ In solution, after cross-linking, a sodium alginate / lignin composite gel immobilized yeast carrier is obtained;

[0015] The sodium alginate / lignin composite gel immobilized yeast carrier utilizes hydrogen bonds between the phenolic hydroxyl groups of lignin and the carboxyl groups of sodium alginate, as well as the bonds between sodium alginate and Ca... 2+ Ionic bonds form a double cross-linked network.

[0016] Preferably, the ratio of sodium alginate to soluble lignin is (3-20):1.

[0017] More preferably, the ratio of sodium alginate to soluble lignin is 10:1.

[0018] Preferably, the crosslinking method is to stir, the stirring speed is 100-500 rpm, and the stirring time is 15-45 min.

[0019] Preferably, the Ca-containing 2+ The solution concentration is 0.1–0.4 M.

[0020] Preferably, the alkali dissolution involves adjusting the pH of the lignin solution to 10-13.

[0021] Preferably, the ultrasonic power is 200-400 W, the ultrasonic frequency is 30-50 kHz, and the ultrasonic duration is 0.5-2 h.

[0022] More preferably, the ultrasonic power is 300 W, the ultrasonic frequency is 40 kHz, and the ultrasonic duration is 1 h.

[0023] Preferably, the molecular weight cutoff of the dialysis bag used for dialysis is 500 to 5000 Da.

[0024] Preferably, the method for removing the solvent is rotary evaporation;

[0025] In the pretreatment process of lignocellulose, the lignin structure is inevitably degraded, generating a large amount of phenolic inhibitors. During the precipitation and recovery of lignin from the pretreatment liquid or fermentation broth, not only high-molecular-weight lignin precipitates, but many small-molecule phenolic compounds dissolved in the liquid are also carried down due to decreased solubility (pH changes, ionic strength changes) or co-precipitation / adsorption with the precipitated lignin. This results in the recovered lignin product containing a large amount of small-molecule phenolic impurities. These small-molecule phenolic compounds affect cell membrane permeability; therefore, lignin is generally considered to inhibit the activity of fermenting microorganisms, and no research has yet found applying lignin to ethanol fermentation systems. This invention creatively discovers that using soluble lignin treated with alkali dissolution, ultrasound, and dialysis can avoid penetrating the yeast cell membrane and causing toxicity.

[0026] More preferably, the temperature of the rotary evaporation is 45–60°C.

[0027] Application of any of the above-mentioned sodium alginate / lignin composite gel immobilized yeast carriers in improving the efficiency of ethanol fermentation under fermentation environmental stress conditions.

[0028] Preferably, the fermentation environmental stress conditions include low pH stress conditions, steroidal saponin stress conditions, and / or heavy metal stress conditions.

[0029] Preferably, the steroidal saponin stress condition in the fermentation environment is that the fermentation environment contains diosgenin.

[0030] Preferably, the heavy metal stress conditions in the fermentation environment are those containing cadmium and / or copper.

[0031] A method for improving the efficiency of ethanol fermentation under fermentation environmental stress conditions involves adding any of the above-mentioned sodium alginate / lignin composite gel immobilized yeast carriers to the fermentation system.

[0032] The added sodium alginate / lignin composite gel immobilized yeast carrier exerts its stress-resistance effect through a triple mechanism:

[0033] Mechanical barrier: The "hydrogen bond-ionic bond" double cross-linked network formed by lignin and sodium alginate (compressive strength 1.5-2.5 N, elastic modulus 150-200 kPa) can resist the shear force of stirring at 150 rpm (breakage rate <3%), preventing yeast leakage;

[0034] Inhibitor scavenging: The hydrophobic aromatic ring of lignin adsorbs steroidal saponins through π-π stacking (adsorption rate ≥95%), and the phenolic hydroxyl group chelates Cd through coordination. 2+ or Cu 2+ (Chlorination rate ≥70%), reducing the direct toxicity of inhibitors to yeast;

[0035] Microenvironment regulation: The weakly acidic groups of lignin buffer pH fluctuations, and the phenolic hydroxyl groups scavenge reactive oxygen free radicals (alleviating high-temperature oxidative stress), providing a stable metabolic environment for yeast.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This invention discloses the application of sodium alginate / lignin composite gel immobilized yeast carrier in improving ethanol fermentation efficiency under fermentation environmental stress conditions. The sodium alginate / lignin composite gel immobilized yeast carrier can simultaneously resist multiple stresses, improve yeast survival rate and fermentation efficiency, resulting in increased product ethanol concentration and improved substrate consumption rate. Furthermore, the preparation process of the sodium alginate / lignin composite gel immobilized yeast carrier is simple and recyclable, maintaining a high synergistic effect even after multiple recycling cycles, thus showing broad application prospects in the industrial production of bioethanol. Attached Figure Description

[0038] Figure 1 This is a diagram illustrating the mechanism of dual crosslinking via ionic and hydrogen bonds.

[0039] Figure 2 Infrared spectra of yeast carriers immobilized with soluble lignin, sodium alginate gel alone, and sodium alginate / lignin composite gel.

[0040] Figure 3 Low-temperature scanning electron microscope (SEM) images of yeast carriers immobilized in sodium alginate / lignin composite gel; (a): Low-temperature SEM image at a scale bar of 100 μm, (b): Low-temperature SEM image at a scale bar of 5 μm, (c): Low-temperature SEM image at a scale bar of 1 μm.

[0041] Figure 4 Low-temperature scanning electron microscope (SEM) images of yeast carriers immobilized on a single sodium alginate gel; (a): Low-temperature SEM image at a scale bar of 500 μm, (b): Low-temperature SEM image at a scale bar of 50 μm, (c): Low-temperature SEM image at a scale bar of 20 μm.

[0042] Figure 5 The glucose consumption rate of yeast carriers immobilized with sodium alginate / lignin composite gel, yeast carriers immobilized with sodium alginate alone, and activated yeast during fermentation was measured.

[0043] Figure 6 The adsorption rate of diosgenin on yeast carrier immobilized by sodium alginate / lignin composite gel was determined.

[0044] Figure 7 To immobilize yeast carriers with sodium alginate / lignin composite gels for Cu 2+ and Cd 2+ The adsorption rate.

[0045] Figure 8 The glucose consumption rate of the yeast carrier immobilized by sodium alginate / lignin composite gel during 1 to 10 recycling cycles was determined. Detailed Implementation

[0046] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0047] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0048] Example 1: Preparation of yeast carrier immobilized by sodium alginate / lignin composite gel

[0049] This embodiment provides a method for preparing a sodium alginate / lignin composite gel-immobilized yeast carrier, the specific steps of which are as follows:

[0050] S1. Preparation of soluble lignin: 16 g of enzymatically hydrolyzed lignin was added to 184 mL of ultrapure water, the pH was adjusted to 12 with NaOH, and the mixture was sonicated (300 W, 40 kHz) for 1 h. After filtration, the mixture was transferred to a 500 Da dialysis bag and dialyzed in ultrapure water at room temperature for 48 h (with water changed every 6 h). The soluble lignin powder was obtained by rotary evaporation (50 °C).

[0051] S2. Gel Crosslinking: Soluble lignin powder was added to 10 mL of 2% sodium alginate solution (w / v) to achieve a final concentration of 2 g / L. After mixing, 2.5 mL of activated yeast solution was added, followed by dropwise addition to 0.2 M CaCl2 solution. The mixture was stirred at 300 rpm for 30 min to form gel beads. The gel beads were washed three times with sterile water to obtain the sodium alginate / lignin composite gel immobilized yeast carrier.

[0052] Example 2: Preparation of yeast carrier immobilized by sodium alginate / lignin composite gel

[0053] This embodiment provides a method for preparing a sodium alginate / lignin composite gel-immobilized yeast carrier, the specific steps of which are as follows:

[0054] S1. Preparation of soluble lignin: 16 g of enzymatically hydrolyzed lignin was added to 184 mL of ultrapure water, the pH was adjusted to 12 with NaOH, and the mixture was sonicated (300 W, 40 kHz) for 1 h. After filtration, the mixture was transferred to a 500 Da dialysis bag and dialyzed in ultrapure water at room temperature for 48 h (with water changed every 6 h). The soluble lignin powder was obtained by rotary evaporation (50 °C).

[0055] S2. Gel Crosslinking: Soluble lignin powder was added to 10 mL of 1% sodium alginate solution (w / v) to achieve a final concentration of 0.5 g / L. After mixing, 2.5 mL of activated yeast solution was added, followed by dropwise addition to 0.1 M CaCl2 solution. The mixture was stirred at 100 rpm for 15 min to form gel beads. The gel beads were washed three times with sterile water to obtain the sodium alginate / lignin composite gel immobilized yeast carrier.

[0056] Example 3: Preparation of yeast carrier immobilized by sodium alginate / lignin composite gel

[0057] This embodiment provides a method for preparing a sodium alginate / lignin composite gel-immobilized yeast carrier, the specific steps of which are as follows:

[0058] S1. Preparation of soluble lignin: 16 g of enzymatically hydrolyzed lignin was added to 184 mL of ultrapure water, the pH was adjusted to 12 with NaOH, and the mixture was sonicated (300 W, 40 kHz) for 1 h. After filtration, the mixture was transferred to a 500 Da dialysis bag and dialyzed in ultrapure water at room temperature for 48 h (with water changed every 6 h). The soluble lignin powder was obtained by rotary evaporation (50 °C).

[0059] S2. Gel Crosslinking: Soluble lignin powder was added to 10 mL of 3% sodium alginate solution (w / v) to achieve a final concentration of 10 g / L. After mixing, 2.5 mL of activated yeast solution was added, followed by dropwise addition to 0.4 M CaCl2 solution. The mixture was stirred at 500 rpm for 45 min to form gel beads. The gel beads were washed three times with sterile water to obtain the sodium alginate / lignin composite gel immobilized yeast carrier.

[0060] Comparative Example 1: Preparation of yeast carrier immobilized on a single sodium alginate gel

[0061] Add 2.5 mL of activated yeast solution to 10 mL of 2% sodium alginate solution (w / v), then add dropwise to 0.2 M CaCl2 solution. Stir at 300 rpm for 30 min to crosslink and form gel beads. Wash the gel beads three times with sterile water to obtain a single sodium alginate gel-immobilized yeast carrier.

[0062] Example 4 Characterization of yeast carrier immobilized by sodium alginate / lignin composite gel

[0063] I. Experimental Methods

[0064] The yeast carrier immobilized with sodium alginate / lignin composite gel prepared in Example 1 and the yeast carrier immobilized with sodium alginate gel prepared in Comparative Example 1 were characterized by Fourier transform infrared spectroscopy and low-temperature scanning electron microscopy.

[0065] II. Experimental Results

[0066] In the sodium alginate / lignin composite gel immobilized yeast carrier prepared in Example 1, the hydrogen bonds between the phenolic hydroxyl groups of lignin and the carboxyl groups of sodium alginate, and the hydrogen bonds between sodium alginate and Ca... 2+ Ionic bonds form a double cross-linked network ( Figure 1 ), its infrared spectrum ( Figure 2 This shows that a single sodium alginate gel immobilized yeast vector at 1605 cm⁻¹ -1 A stretching vibration peak appears at this location, corresponding to Ca. 2+ Ionic cross-linking of ionic bonds. Lignin at 1597 cm⁻¹ -1 The phenolic hydroxyl stretching vibration peak at 1623 cm⁻¹ was observed in the yeast carrier immobilized in sodium alginate / lignin composite gel. -1 The offset indicates that hydrogen bonds have formed between the phenolic hydroxyl groups of lignin and the carboxyl or hydroxyl groups of sodium alginate. At 1025 cm⁻¹ -1 At this location, the intensity of the CO stretching vibration peak increases, further confirming the formation of a double cross-linked network of ionic and hydrogen bonds. This cross-linking method results in a three-dimensional network with refined and uniform pore size distribution. Figure 3 The control group's single sodium alginate gel-immobilized yeast carrier network had a wide pore size distribution and sparse cross-linking nodes. Figure 4 ).

[0067] Example 5: Effect of sodium alginate / lignin composite gel immobilized yeast carrier on ethanol fermentation

[0068] I. Experimental Methods

[0069] Prepare the basal culture medium: 100 g / L glucose, 1 g / L NH4Cl, 1 g / L KH2PO4, 0.3 g / L MgSO4·7H2O, pH 5.5.

[0070] Add the sodium alginate / lignin composite gel immobilized yeast carrier prepared in Example 1 to the basal culture medium, set up a control group (add 2.5 mL of activated yeast solution), and then ferment at 34℃ and 150 rpm for 24 h.

[0071] The concentrations of glucose and ethanol in the fermentation system were detected by instruments. The specific steps were as follows: the sample liquid was centrifuged at 10,000 rpm for 3 min, and the supernatant was taken. The concentrations of glucose and ethanol were then determined by liquid chromatography.

[0072] During fermentation, samples were taken every 5 hours to measure the remaining glucose concentration in the fermentation system until fermentation was completed, and the glucose consumption rate at different fermentation times was calculated. After fermentation, the ethanol concentration in the fermentation system was measured.

[0073] II. Experimental Results

[0074] The results are as follows Figure 5 As shown, the glucose consumption rate of the control group was 53%, and the ethanol concentration of the product was only 18.5 g / L; while after fermentation for 24 h with a yeast carrier immobilized by sodium alginate / lignin composite gel, the glucose consumption rate reached 87%, which was 64.2% higher than that of the control group, and the ethanol concentration of the product was 31.2 g / L, which was 68.6% higher than that of the control group.

[0075] Since the pH value of the fermentation system can easily drop below 3.0 due to the accumulation of organic acids, yeast activity is inhibited, ethanol yield and substrate consumption rate are reduced. The above results show that the sodium alginate / lignin composite gel immobilized yeast carrier can resist pH fluctuations and low pH stress during fermentation and improve fermentation efficiency.

[0076] Example 6: Effect of sodium alginate / lignin composite gel immobilized yeast carrier on ethanol fermentation under steroidal saponin stress.

[0077] I. Experimental Methods

[0078] Prepare the basal culture medium: 100 g / L glucose, 1 g / L NH4Cl, 1 g / L KH2PO4, 0.3 g / L MgSO4·7H2O, pH 5.5. Before fermentation, add 2 mg of diosgenin to the basal culture medium.

[0079] Add the sodium alginate / lignin composite gel immobilized yeast carrier prepared in Example 1 to the basal culture medium to a final concentration of 100 g / L, and set up a control group (adding the single sodium alginate gel immobilized yeast carrier prepared in Comparative Example 1). Then ferment at 34℃ and 150 rpm for 24 h.

[0080] After fermentation, the ethanol concentration in the fermentation system was measured according to Example 5, and the remaining diosgenin content was also measured to calculate the diosgenin adsorption rate. Specifically, the sample liquid was centrifuged at 10,000 rpm for 3 min, and the supernatant was collected. Since diosgenin has a characteristic absorption peak in the ultraviolet region (203 nm) and its absorbance is proportional to its concentration, the absorbance at this wavelength was measured using an ultraviolet-visible-infrared spectrometer, and the concentration of diosgenin after adsorption was calculated according to the standard curve. The diosgenin concentration before fermentation was recorded as A0, and the diosgenin concentration after fermentation was recorded as A1. The scavenging rate was... The calculation formula is:

[0081]

[0082] II. Experimental Results

[0083] The results are as follows Figure 6 As shown, the adsorption rate of diosgenin on the yeast carrier immobilized by sodium alginate / lignin composite gel reached 96.9%, while that of the control group was only 32.0%; the ethanol concentration of the product was 28.5 g / L, which was 131.7% higher than that of the control group (12.3 g / L).

[0084] The above results indicate that the sodium alginate / lignin composite gel immobilized yeast carrier still has high ethanol fermentation efficiency under diosgenin stress conditions, and can also adsorb and remove diosgenin in the fermentation system, thereby regulating the fermentation microenvironment.

[0085] Example 7: Effects of sodium alginate / lignin composite gel immobilized yeast carrier on ethanol fermentation under heavy metal stress.

[0086] I. Experimental Methods

[0087] Prepare the basal culture medium: 100 g / L glucose, 1 g / L NH4Cl, 1 g / L KH2PO4, 0.3 g / L MgSO4·7H2O, pH 5.5, and add Cu to the basal culture medium. 2+ and Cd 2+ The final concentration was 35 mg / L.

[0088] The sodium alginate / lignin composite gel immobilized yeast carrier prepared in Example 1 was added to the basal culture medium to a final concentration of 100 g / L. A control group (with 2.5 mL of activated yeast solution added) was set up, and then fermented at 34℃ and 150 rpm for 24 h.

[0089] After fermentation, the ethanol concentration and yeast survival rate in the fermentation system were measured according to Example 5, and the heavy metal ions (Cu) in the fermentation system were also measured. 2+ and Cd 2+The ion concentration was used to calculate the heavy metal chelation rate. Specifically, the sampled liquid was centrifuged at 10,000 rpm for 3 min, and the supernatant was collected. The ion concentration in the supernatant was measured using inductively coupled plasma atomic emission spectrometry (ICP). The ion concentration before fermentation was recorded as B0, and the ion concentration after fermentation was recorded as B1. The scavenging rate was... The calculation formula is:

[0090]

[0091] II. Experimental Results

[0092] Sodium alginate / lignin composite gel immobilized yeast carrier for Cd 2+ The chelation rate was 77.1% for Cu. 2+ The chelation rate was 94.3% ( Figure 7 The yeast survival rate reached 71.2%, while the yeast survival rate in the control group was only 22.5%. Fermentation using a yeast carrier immobilized with sodium alginate / lignin composite gel resulted in an ethanol concentration of 25.8 g / L, compared to 19.6 g / L in the control group.

[0093] The above results indicate that sodium alginate / lignin composite gel immobilized yeast carrier can effectively remove heavy metal ions, improve the survival rate of yeast under heavy metal stress conditions, and achieve efficient ethanol fermentation.

[0094] Example 8: Recycling of Sodium Alginate / Lignin Composite Gel Immobilized Yeast Carrier in Ethanol Fermentation

[0095] I. Experimental Methods

[0096] Prepare the basal culture medium: 100 g / L glucose, 1 g / L NH4Cl, 1 g / L KH2PO4, 0.3 g / L MgSO4·7H2O, pH 5.5.

[0097] Add the sodium alginate / lignin composite gel immobilized yeast carrier prepared in Example 1 to the basal culture medium to a final concentration of 100 g / L, and set up a control group (adding the single sodium alginate gel immobilized yeast carrier prepared in Comparative Example 1). Then ferment at 34℃ and 150 rpm for 24 h.

[0098] After fermentation, the sodium alginate / lignin composite gel immobilized yeast carrier was collected, washed three times with sterile water, and then the above fermentation process was repeated on the collected sodium alginate / lignin composite gel immobilized yeast carrier, and it was reused 10 times.

[0099] According to Example 5, the ethanol concentration in the fermentation system was measured and the glucose consumption rate after fermentation was calculated.

[0100] II. Experimental Results

[0101] In the group using sodium alginate / lignin composite gel to immobilize yeast carriers, the glucose consumption rate reached 73% in the 10th fermentation. Figure 8 The product ethanol concentration was 26.1 g / L, which was 83.9% of the first fermentation, significantly higher than the control group (the glucose consumption rate in the 10th fermentation was only 51%). This indicates that the sodium alginate / lignin composite gel immobilized yeast carrier can be recycled, thereby effectively reducing costs and making it suitable for the industrial production of ethanol from lignocellulose raw materials.

[0102] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. The application of sodium alginate / lignin composite gel immobilized yeast carrier in improving ethanol fermentation efficiency under fermentation environmental stress conditions, characterized in that, The sodium alginate / lignin composite gel immobilized yeast carrier was prepared by encapsulating yeast in sodium alginate and soluble lignin. The method for preparing the soluble lignin includes the following steps: alkali dissolution and sonication of the lignin solution, separation of the liquid after sonication, dialyzing of the liquid, removal of the solvent after dialysis, and thus obtaining the soluble lignin. The encapsulation method is as follows: soluble lignin is mixed with sodium alginate solution, then yeast is added to obtain a mixed solution; the mixed solution is then added dropwise to a solution containing Ca. 2+ In solution, after cross-linking, a sodium alginate / lignin composite gel immobilized yeast carrier is obtained; The ratio of sodium alginate to soluble lignin is (3-20):1; The fermentation environment stress conditions include low pH stress, steroidal saponin stress, and / or heavy metal stress.

2. The application according to claim 1, characterized in that, The alkaline dissolution involves adjusting the pH of the lignin solution to 10-13.

3. The application according to claim 1, characterized in that, The ultrasonic power is 200–400 W, the ultrasonic frequency is 30–50 kHz, and the ultrasonic duration is 0.5–2 h.

4. The application according to claim 1, characterized in that, The molecular weight cutoff of the dialysis bag used for dialysis is 500-5000 Da.

5. The application according to claim 1, characterized in that, The steroidal saponin stress condition in the fermentation environment is that the fermentation environment contains diosgenin.

6. A method for improving the efficiency of ethanol fermentation under fermentation environmental stress conditions, characterized in that, Add sodium alginate / lignin composite gel immobilized yeast carrier to the fermentation system. The sodium alginate / lignin composite gel immobilized yeast carrier is prepared by encapsulating yeast with sodium alginate and soluble lignin. The method for preparing the soluble lignin includes the following steps: alkali dissolution and sonication of the lignin solution, separation of the liquid after sonication, dialyzing of the liquid, removal of the solvent after dialysis, and thus obtaining the soluble lignin. The encapsulation method is as follows: soluble lignin is mixed with sodium alginate solution, then yeast is added to obtain a mixed solution; the mixed solution is then added dropwise to a solution containing Ca. 2+ In solution, after cross-linking, a sodium alginate / lignin composite gel immobilized yeast carrier is obtained; The ratio of sodium alginate to soluble lignin is (3-20):1; The fermentation environment stress conditions include low pH stress, steroidal saponin stress, and / or heavy metal stress.

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