A method for preparing duck liver protein with reduced fishy smell and improved functional properties

Abstract

The invention discloses a method for preparing duck liver protein with reduced fishy smell and improved functional properties. The method is characterized in that the method comprises the steps of cutting the duck liver into small pieces, removing fascia and fat, soaking the pieces in a 1wt% composite deodorant solution for 30 to 90 minutes, and then pickling the pieces in a 0.05 to 2 M salt water for 30 to 60 minutes; defatting the duck liver, adding propylene glycol and trehalose, adding pure water and fully mixing the pieces, and then placing the pieces in an ultra-high hydrostatic pressure device for treatment at 320 to 380 MPa for 10 minutes; mixing the defatted precipitate after the ultra-high hydrostatic pressure treatment with pure water at a mass ratio of 1:2, and then adjusting the pH value by an alkali extraction and acid precipitation method, so as to obtain the duck liver protein with reduced fishy smell and improved protein functional properties. The method has the advantages of being able to efficiently remove the fishy smell of the duck liver and simultaneously improving the oil holding capacity, water holding capacity, emulsification activity and emulsification stability of the duck liver protein.

Description

Technical Field

[0001] The invention belongs to the technical field of meat product food processing, and in particular relates to a method for preparing duck liver protein with reduced fishy smell and improved functional characteristics. Background Art

[0002] As an important by-product of livestock and poultry meat processing, livestock and poultry liver has attracted much attention in the meat processing industry in recent years due to its high protein content and rich nutrients. Among them, duck liver has become one of the most popular categories of livestock and poultry liver due to its unique flavor and high nutritional value. However, the strong fishy smell of duck liver not only affects its processing adaptability and interferes with its edible quality, but also significantly affects the functional properties and nutritional stability of liver-derived animal protein. This greatly limits its application in food and reduces consumer acceptance. The fishy smell of duck liver mainly comes from volatile compounds such as trimethylamine, dimethylamine, amino acid degradation products and various aldehydes. These fishy substances usually come from liver metabolites, as well as lipid oxidation decomposition, protein degradation or microbial metabolic activity products during processing and storage. Fishy compounds interact with liver proteins in non-covalent ways such as hydrophobic and electrostatic interactions to form protein-fishy substance complexes. At the same time, the binding sites of the two usually occur inside the protein folding structure. Since the contact frequency and elution force of the complex formed inside the protein folding structure with the extraction solvent are significantly reduced, it is difficult to completely remove the fishy substances of liver protein under conventional processing conditions during the extraction process. Therefore, developing efficient deodorization technology that not only stabilizes or improves the functional properties of the protein but also reduces or eliminates the interference of fishy substances, thereby enhancing the flavor and application potential of duck liver protein is a technical problem that needs to be solved urgently in the current livestock and poultry processing industry.

[0003] Existing deodorization technologies mainly include chemical methods and biological methods. Chemical methods usually use oxidants, reductants or cross-linking agents to directly react with fishy substances to achieve the purpose of deodorization. However, these methods often cause irreversible changes in the protein products to be extracted, such as denaturation, degradation or the introduction of other odors, affecting the functional properties and quality of the protein. Biological methods mainly use enzymatic hydrolysis, fermentation and other means to degrade fishy substances through microorganisms or enzyme systems, but the process is complicated, the conditions are strict, it is difficult to control its progress, and it is easy to cause protein degradation, which is not suitable for liver protein deodorization. Since stable complexes may be formed between fishy substances and proteins, traditional chemical and biological methods are difficult to effectively remove fishy smells. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing duck liver protein which can effectively remove the fishy smell of duck liver and improve the oil holding capacity, water holding capacity, emulsification activity and emulsification stability of duck liver protein, thereby reducing the fishy smell and improving the functional characteristics.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing duck liver protein with reduced fishy smell and improved functional properties, comprising the following steps:

[0006] (1) Pretreatment: Cut the duck liver into small pieces, remove the fascia and fat, and soak it in a 1 wt% composite deodorizing agent solution for 30 to 90 min to obtain a preliminarily deodorized duck liver;

[0007] (2) Pickling: Wash the duck liver obtained in step (1) with pure water and pickle it in 0.05-2 M salt water for 30-60 min;

[0008] (3) defatting: after the pickled duck liver in step (2) is taken out and washed, the duck liver and pure water are mixed in a mass ratio of 1:2, and the mixture is homogenized in a blender for 3 to 5 minutes to obtain a duck liver solution. Ethanol is added to the duck liver solution at a mass volume ratio of 1 g:2 mL at 30 to 40° C. to extract the duck liver solution. After sufficient stirring, the mixture is allowed to stand for 4 to 8 hours, and then the supernatant is discarded by centrifugation. The precipitate is placed in an oven and baked at 30 to 40° C. to remove the ethanol, thereby obtaining a brown block-like defatted precipitate.

[0009] (4) Extracting duck liver protein: Add 0.3% of the mass of propylene glycol and 0.5% of trehalose to the defatted precipitate obtained in step (3), and add 50% of the mass of pure water to mix thoroughly, then put it into an ultra-high hydrostatic pressure device and treat it at 320-380 MPa for 10 min; mix the defatted precipitate after ultra-high hydrostatic pressure treatment with pure water in a mass ratio of 1:2, and then adjust the pH value by alkali extraction and acid precipitation method to obtain duck liver protein with reduced fishy smell and improved protein functional properties.

[0010] Furthermore, the composite deodorizing agent in step (1) is composed of the following raw materials and their mass percentages: 25% propylene glycol, 40% trehalose, 5% KCl, 20% corn starch and 10% pineapple fiber.

[0011] Furthermore, the alkali extraction and acid precipitation method described in step (4) is as follows: the pH is adjusted to 11-11.4 with a sodium hydroxide solution, and the mixture is continuously stirred with a vibrator at 45-55°C for 5 hours, and then centrifuged to obtain the supernatant, and the pH is adjusted to 4.1-4.5 with a hydrochloric acid solution. After standing at 4°C overnight, the supernatant is discarded by centrifugation, and the precipitate is dissolved with a small amount of deionized water, and freeze-dried to obtain duck liver protein with reduced fishy smell and improved protein functional properties.

[0012] Compared with the prior art, the advantages of the present invention are: the preparation method of duck liver protein with reduced fishy smell and improved white functional properties of the present invention comprises a deodorizing agent soaking pretreatment, ultra-high hydrostatic pressure treatment, and a deodorizing method of propylene glycol and trehalose treatment. By soaking the duck liver in a deodorizing agent, the fishy substances can be initially removed, reducing the difficulty of subsequent treatment; the ultra-high hydrostatic pressure treatment can induce the appearance of molten globule-like proteins, preventing the combination of fishy substances and proteins; and trehalose and propylene glycol, as a protein conformation stabilizer and chemical bond blocker, stabilize the molten globule-like protein conformation induced by ultra-high hydrostatic pressure, further block and reduce the combination of fishy compounds and proteins, and improve the functional properties of duck liver protein; finally, the pH value is adjusted by an alkali extraction and acid precipitation method, the duck liver protein is effectively separated and extracted, and the residue of fishy substances is further reduced. These steps work synergistically, not only can duck liver be efficiently deodorized, but also can improve the functional properties of duck liver protein such as oil retention, water retention, emulsification activity and emulsification stability.

[0013] In summary, the present invention provides a method for preparing duck liver protein with reduced fishy smell and improved functional properties, which not only realizes the extraction of low-fishy smell protein, but also improves the functional properties of duck liver protein. The extraction method can efficiently remove fishy smell, improve its flavor and texture, and provide a new technical path for the high-value-added development and utilization of duck liver protein and other visceral meat products. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the TMA effect diagram of duck liver protein samples under 5 different extraction methods;

[0015] Figure 2 This is the DMA effect diagram of duck liver protein samples under 5 different extraction methods;

[0016] Figure 3 This is the HA effect diagram of duck liver protein samples under 5 different extraction methods;

[0017] Figure 4 This is the FA effect diagram of duck liver protein samples under 5 different extraction methods;

[0018] Figure 5 is the total concentration of volatile flavor compounds in duck liver protein samples extracted by five different methods;

[0019] Figure 6 The water and oil holding capacity of duck liver protein samples under five different extraction methods;

[0020] Figure 7 The emulsifying activity and emulsifying stability of duck liver protein samples extracted by five different methods;

[0021] Figure 8 The carbonyl content of duck liver protein samples under five different extraction methods;

[0022] Fig. 9 The electron microscope scanning images of duck liver protein samples extracted by five different methods;

[0023] Fig.10 The electrophoresis patterns of duck liver protein samples extracted by five different extraction methods are shown below;

[0024] Fig.11 The different secondary structures of duck liver protein samples extracted by five different methods;

[0025] Fig.12 The intrinsic fluorescence spectra of duck liver protein samples extracted by five different methods;

[0026] Fig.13 The UV absorption spectra of duck liver protein samples extracted by five different methods are shown below;

[0027] Fig.14 The second derivative UV-visible spectra of duck liver protein samples extracted by five different methods;

[0028] Fig.15 Fourier transform infrared spectra of duck liver protein samples extracted by five different methods;

[0029] Fig.16 The surface hydrophobicity of duck liver protein samples under five different extraction methods;

[0030] Fig.17 The contents of active thiol groups and total thiol groups in duck liver protein samples extracted by five different extraction methods. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings.

[0032] 1. Experimental methods

[0033] 1. Determination of fishy substances: Take 5 mL of duck liver protein solution with a concentration of 5 mg / mL, add 10 mL of 7.5wt% trichloroacetic acid solution, and use a high-speed homogenizer to break it at 12000 rpm for 1 min. After standing, use a centrifuge to centrifuge at 4 ℃ and 8000× g for 10 min, transfer the supernatant into a volumetric flask, and make up to volume with 7.5wt% trichloroacetic acid solution.

[0034] Determination of trimethylamine (TMA): Take 200 uL of the above supernatant, add 50 μL of 10wt% formaldehyde solution, 500 μL of toluene and 150 μL of 25wt% NaOH solution, and shake for 15 min to mix thoroughly. Transfer the toluene layer to a test tube containing 125 μL of 0.02wt% picric acid solution, and finally transfer it to a test tube containing an appropriate amount of anhydrous Na2SO4, and measure its absorbance at 410 nm.

[0035] Determination of dimethylamine (DMA): Take 1 mL of the above supernatant and mix it with 100 uL of cuprammonium reagent, vortex for 2 minutes, add 1 mL of 5wt% CS2-benzene solution, incubate in a 50℃ water bath for 2 minutes, vortex again for 2 minutes, then add 100 μL of 30wt% acetic acid solution and let stand for 3 minutes. Transfer the toluene layer to a test tube containing an appropriate amount of anhydrous Na2SO4 and measure its absorbance at 440 nm.

[0036] Determination of formaldehyde (abbreviated as FA): adjust the pH of the above supernatant to about 6, take 1 mL of the supernatant into a test tube, add 1 mL of acetylacetone solution, react in a boiling water bath for 15 min, cool to room temperature, and measure the absorbance at 412 nm.

[0037] Determination of histamine (abbreviated as HA): 5 mL of duck liver protein solution with a concentration of 5 mg / mL was added to 10 mL of 10wt% trichloroacetic acid solution and soaked for 2-3 h. After shaking for 2 min, centrifuged at 4°C and 8000 g for 5 min, and filtered to obtain the supernatant. Take 2 mL of the filtrate and adjust the pH to 10-12 with NaOH, add 3 mL of n-pentanol, shake and extract for 5 min, and centrifuge at 4°C and 8000 g for 5 min. Take 2 mL of n-pentanol and transfer it to a 10 mL centrifuge tube, add 3 mL of 1 mol / L HCl solution, shake for 2 min, and discard the n-pentanol layer. Take 2 mL of HCl extract, add 3 mL of Na2SO4 and 3 mL of azo reagent, add water to the scale, mix well, let stand for 10 min, and measure its absorbance at 480 nm.

[0038] 2. Detection of volatile flavor substances in the headspace: Take 5 mL of duck liver protein solution with a concentration of 5 mg / mL and add it to the headspace sample bottle. Insert the 50 / 30 μm DVB / CAR / PDMS extraction head into the headspace bottle to extract the volatile flavor compounds of duck liver (extraction at 50°C for 30 min), and then insert the extraction needle into the gas chromatograph (abbreviated as GC) injection port (250°C) for desorption for 5 min. GC conditions: injection port temperature 250°C, splitless mode, carrier gas He, flow rate 0.8 mL / min, VLCOL column (60 m × 0.32 mm × 1.8 μm). Heating program: start column temperature 40°C for 5 min, increase to 200°C at 5°C / min, increase to 250°C at 15°C / min and maintain for 8 min. Mass spectrometry (MS) conditions: ion source temperature 230°C, 70 eV electron bombardment EI mode (0.9 kV), Scan mode for qualitative and quantitative detection of volatile flavor compounds, detection range m / z 45-600. Unknown volatile flavor compounds in duck liver protein were identified by comparing the mass spectra with known compounds in the NIST17 mass spectrometry database.

[0039] 3. Determination of the functional properties of duck liver protein.

[0040] (1) Water-holding capacity and oil-holding capacity test: The water-holding capacity test method is to weigh 0.5 g of duck liver protein sample and place it in a centrifuge tube. Gradually add water and stir until the sample is precipitated in a slurry. Then shake the centrifuge tube by hand and centrifuge it at 8000 g for 10 min. Discard the supernatant and weigh it. The oil-holding capacity test method is to weigh 0.5 g of duck liver protein sample and place it in a 10 mL centrifuge tube. Add 3 mL of soybean oil with a disposable syringe needle. After stirring for 1 min, place it in a water bath at 25°C for 30 min, centrifuge it at 8000 g for 10 min, remove the unabsorbed soybean oil in the upper layer, and weigh it.

[0041] (2) Emulsification performance test: 1 mL of soybean oil and 4 mL of duck liver protein solution with a concentration of 2 mg / mL were homogenized using a high-speed homogenizer to form a crude emulsion. After homogenization, 50 μL of the emulsion was taken from the bottom of the test tube at 0 min and 10 min, respectively, and diluted 100 times with 0.1% (w / v) sodium dodecyl sulfate solution. Using sodium dodecyl sulfate solution as a blank, the absorbance values ​​at 500 nm were measured using a UV-visible spectrophotometer, and the emulsification activity (abbreviated as EAI) and emulsification stability (abbreviated as ESI) were calculated using the following formula.

[0042] Emulsifying activity = [(2 × 2.303) × A0 × dilution] / [c (1-Φ) × 1000], unit is m 2 / g; emulsion stability = 10 × A0 / (A0−A10 ), unit min, where: c is the protein concentration before emulsification, Φ represents the oil volume fraction of the emulsion (v / v), Φ=0.2; A0 and A 10 The absorbance values ​​are at 0 min and 10 min, respectively.

[0043] (3) Detection of total carbonyl content: 0.1 mL of 5 mg / mL duck liver protein solution was placed in a centrifuge tube, and 0.4 mL of 10 mmol / L 2,4-dinitrophenylhydrazine (DNPH) hydrochloric acid solution was added and mixed by vortexing for 1 min. The mixture was reacted at 37°C in the dark for 30 min. Then 0.5 mL of 1 mol / L trichloroacetic acid was added and mixed by vortexing for 1 min. The mixture was centrifuged at 12,000 rpm for 10 min at 4°C. The supernatant was discarded and the precipitate was retained. The precipitate was washed four times with 1 mL of anhydrous ethanol-ethyl acetate mixed solution (the volume ratio of anhydrous ethanol to ethyl acetate was 1:1). Each wash was mixed by vortexing for 1 min. The mixture was centrifuged at 12,000 rpm for 10 min at 4°C. The supernatant was discarded and the precipitate was retained. Then 1.25 mL of 6 mol / L guanidine hydrochloride was added to dissolve the mixture. The mixture was centrifuged at 12,000 rpm for 15 min at 4°C. The supernatant was taken and the precipitate was heated at 370°C for 15 min. The carbonyl content was determined by measuring the absorbance at nm. The control group was added with 0.4 mL of 2 mol / L DNPH-free hydrochloric acid solution, and the others were the same as the experimental group.

[0044] Carbonyl content (μmol / g) = (A 370 -A0) / (22×d×ρ)×1.25×105, where: A 370 is the absorbance of the experimental group at 370 nm; A0 is the absorbance of the control group at 370 nm; d is the optical diameter of the quartz dish, in cm; ρ is the protein sample concentration, in mg / L.

[0045] 4. Determination of the structure and function of duck liver protein.

[0046] (1) Scanning electron microscope: The accelerating voltage of the scanning electron microscope (S-3400N, Hitachi) was 10 kV. Before scanning, the duck liver protein sample was evenly fixed on the gelatinized electron microscope sample stage, placed in the gold spraying machine, and gold was sprayed under vacuum conditions for 120 s. The scanning electron microscope was recorded at 3.0 K and 5.0 K magnifications.

[0047] (2) Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE): 5 μL of non-reducing protein loading buffer (J2310373, Shanghai Aladdin Biochemical Technology Co., Ltd.) was added to 20 μL of 5 mg / mL duck liver protein solution. After heating at 100°C for 8 min in a digital dry bath, 10 μL of the sample was separated using 12 wt% separation gel and 5 wt% stacking gel. Molecular weight markers (11-245 kDa) were run as references, and the gel images were recorded using the Gel Doc XR+ imaging system.

[0048] (3) Circular dichroism spectroscopy: A duck liver protein solution was prepared in phosphate buffer and dialyzed in a dialysis bag for 24 h. The dialyzed solution was diluted to 0.5 mg / mL in phosphate buffer and analyzed. The absorption difference between left and right circularly polarized light at 193 nm and 260 nm was recorded at 20°C using a JASCO Chriascan spectropolarimeter with a bandwidth of 2 nm, a scanning speed of 100 nm / min, and a quartz cell with an optical path length of 0.1 cm. The far-UV spectrum of the diluted duck liver protein solution was obtained.

[0049] (4) Intrinsic fluorescence spectroscopy: Duck liver protein was mixed with 20 mM phosphate buffer to obtain a 0.5 mg / mL duck liver protein solution. The solution was analyzed by a fluorescence photometer (F-4600, Hitachi, Japan) at 25 °C. A quartz cuvette with a pathlength of 1 cm was used. The excitation wavelength was 290 nm and the emission spectrum range was 300-460 nm. The excitation and emission slit widths were 2.5 nm, and a scanning speed of 1200 nm / min was used.

[0050] (5) UV-visible spectrum and second-order derivative UV-visible spectrum: Duck liver protein was dissolved in 20 mM phosphate buffer to obtain a duck liver protein solution with a concentration of 0.5 mg / mL, and then the UV-visible absorption spectrum was measured using a UV-visible spectrophotometer (UV-330, Unicam UV-Vis, Shanghai, China). The absorbance of the duck liver protein sample was scanned from 190 to 320 nm. Subsequently, the second-order derivative spectrum of the UV-visible absorbance (d 2 A / dλ 2 ).

[0051] (6) Fourier transform infrared (FTIR) spectroscopy: The FTIR spectrum of duck liver protein was obtained using an FTIR spectrometer (FT / IR-4700, Jasco Corp., Tokyo, Japan). 1 mg of duck liver protein freeze-dried powder was mixed with 100 mg of potassium bromide crystals and then ground using an agate pestle and mortar under an infrared lamp and then pressed into a 13 mm diameter disk with a pressure of 15 tons for 2 min. The FTIR spectrum was obtained at 400–4000 cm −1 Obtained within range.

[0052] (7) Surface hydrophobicity detection: Duck liver protein was mixed with 20 mM phosphate buffer to obtain a 0.5 mg / mL duck liver protein solution. 8-aniline-1-naphthalenesulfonic acid fluorescent probe (ANS) was mixed with 20 mM phosphate buffer to obtain an 8 mmol / L ANS solution. 10 μL of ANS solution was taken and thoroughly mixed with 2 mL duck liver protein solution. The sample was kept in the dark for 30 min to ensure complete equilibrium, then vortexed for 5 s, and then the fluorescence intensity was recorded at 470 nm under 390 nm excitation, recorded as FI. FI was plotted against duck liver protein concentration (mg / mL), and the slope of the linear regression analysis was used as an indicator of the surface hydrophobicity, recorded as H0 value.

[0053] (8) Reactive thiol (abbreviated as R-SH) and total thiol (abbreviated as T-SH) detection: duck liver protein was mixed with 20 mM phosphate buffer to obtain a 5 mg / mL duck liver protein solution. T-SH detection: 500 μL duck liver protein solution was mixed with 2.5 mL Tris-glycine-8M urea buffer and 20 μL 4 mg / mL 5, 5-dithiobis(2-nitrobenzoic acid) reagent. The mixture was reacted at 25°C in the dark for 30 min, and the absorbance of the solution was measured at 412 nm using an enzyme reader. R-SH detection: 500 μL duck liver protein solution was mixed with 2.5 mL Tris-glycine-8M urea buffer. The mixture was reacted at 25°C in the dark for 30 min, and the absorbance of the solution was measured at 412 nm using an enzyme reader. 2. Specific embodiments:

[0055] Example 1: A method for preparing duck liver protein with reduced fishy smell and improved functional properties, comprising the following steps:

[0056] Step 1, pretreatment: cut the duck liver into small pieces, remove the fascia and fat, and soak in a 1.0wt% composite deodorant solution for 90 min to obtain a preliminarily deodorized duck liver, wherein the composite deodorant is composed of the following raw materials and their mass percentages: 25% propylene glycol, 40% trehalose, 5% KCl, 20% corn starch and 10% pineapple fiber;

[0057] Step 2, pickling: wash the duck liver obtained in step 1 with pure water, and pickle it in 0.1 M salt water for 30 min;

[0058] Step 3, defatting: take out the duck liver obtained in step 2, wash it, mix the duck liver and pure water in a mass ratio of 1:2, homogenize it in a high-speed blender for 3 minutes to obtain a duck liver solution, add ethanol to the duck liver solution at a mass volume ratio of 1g:2mL at 40°C for extraction, stir it thoroughly for 40 minutes, let it stand for 6 hours, centrifuge it at 8000g for 15 minutes, discard the supernatant, spread the precipitate, put it in an oven and bake it at 40°C to fully remove the ethanol, and obtain a blocky brown defatted precipitate;

[0059] Step 4, extracting duck liver protein: add 0.3% propylene glycol and 0.5% trehalose by weight of the defatted precipitate to the defatted precipitate obtained in step 3, add 50% pure water by weight of the defatted precipitate and mix thoroughly, then put it into an ultra-high hydrostatic pressure device and treat it at 350 MPa for 10 min; mix the defatted precipitate after ultra-high hydrostatic pressure treatment with pure water in a mass ratio of 1:2, adjust the pH to 11.2 with 12 M sodium hydroxide solution, stir continuously with a vibrator at 50°C for 5 h, and then centrifuge at 5000 g for 15 min; take the supernatant and adjust the pH to 4.3 with 3.6wt% hydrochloric acid solution, place it at 4°C overnight, centrifuge it at 13400 g for 30 min, discard the supernatant, dissolve the precipitate with a small amount of deionized water, and freeze-dry to obtain duck liver protein with reduced fishy smell and improved functional properties, which is sealed and stored at -40°C and recorded as UHP + NaCl + PG + ALG, referred to as UNPA group.

[0060] Comparative Example 1 is the same as Example 1, except that step 2 is omitted; step 4 is adjusted to mix the defatted precipitate obtained in step 3 with pure water in a mass ratio of 1:2, and then adjust the pH value by alkali extraction and acid precipitation to obtain duck liver protein, that is, the addition of propylene glycol and trehalose to the defatted precipitate is omitted during step 4, and the ultra-high hydrostatic pressure treatment process is omitted, which is recorded as RE group.

[0061] Comparative Example 2 is the same as Example 1, except that: Step 4 is adjusted to add 50% of the mass of pure water to the defatted precipitate obtained in Step 3 and mix thoroughly, then put it into an ultrahigh hydrostatic pressure device and treat it at 350 MPa for 10 min; the defatted precipitate after ultrahigh hydrostatic pressure treatment is mixed with pure water in a mass ratio of 1:2, and then the pH value is adjusted by alkali extraction and acid precipitation method to obtain duck liver protein, that is, the addition of propylene glycol and trehalose to the defatted precipitate is omitted when performing Step 4, which is recorded as UHP + NaCl, referred to as UN group.

[0062] Comparative Example 3 is the same as Example 1, except that: 0.5% of the mass of trehalose was added to the defatted precipitate obtained in step 3, and 50% of the mass of pure water was added to the defatted precipitate and mixed thoroughly, and then placed in an ultrahigh hydrostatic pressure device and treated at 350 MPa for 10 min; the defatted precipitate after ultrahigh hydrostatic pressure treatment was mixed with pure water in a mass ratio of 1:2, and then the pH value was adjusted by alkali extraction and acid precipitation method to obtain duck liver protein, that is, the addition of propylene glycol to the defatted precipitate was omitted during step 4, recorded as UHP + NaCl + ALG, referred to as UNA group.

[0063] Comparative Example 4 is the same as Example 1, except that: 0.3% of the mass of propylene glycol was added to the defatted precipitate obtained in step 3, and 50% of the mass of pure water was added to the defatted precipitate to be fully mixed, and then placed in an ultrahigh hydrostatic pressure device and treated at 350 MPa for 10 min; the defatted precipitate after ultrahigh hydrostatic pressure treatment was mixed with pure water in a mass ratio of 1:2, and then the pH value was adjusted by alkali extraction and acid precipitation method to obtain duck liver protein, that is, the addition of trehalose to the defatted precipitate was omitted during step 4, recorded as UHP + NaCl + PG, referred to as UNP group.

[0064] 3. Analysis of experimental results.

[0065] 1. Analysis of duck liver pretreatment and deodorization: Slowly thaw the duck liver at room temperature, wash the blood on the surface of the duck liver with running water, remove the fascia and fat on the surface of the duck liver, and cut the duck liver into small pieces of uniform weight. The small pieces of duck liver were respectively placed in a solution of 1wt% NaCl, 1wt% β-cyclodextrin, and 1.0wt% composite deodorant (the composite deodorant is composed of the following raw materials and their mass percentages: 25% propylene glycol, 40% trehalose, 5% KCl, 20% corn starch, and 10% pineapple fiber) for deodorization. The deodorization time was 0, 30, 60, and 90 min. After deodorization, rinse the duck liver and use absorbent paper to dry the surface water of the duck liver for fishy substance detection. The results are shown in Tables 1 and 2.

[0066] Table 1 Determination results of TMA and DMA in different treatment groups

[0067]

[0068] Table 2 Determination results of HA and FA in different treatment groups

[0069]

[0070] It can be seen from Tables 1 and 2 that 1.0 wt % NaCl, 1.0 wt % β-cyclodextrin and 1.0 wt % composite deodorant had different immersion times (0, 30, 60, 90 min) in removing the fishy substances (TMA, DMA, HA and FA) in duck liver, and the differences in the effects of each group at each time period were evaluated.

[0071] The removal rates of the experimental groups were calculated with 0 min in each group as the benchmark group. As the immersion time reached 30 min, the removal rates of TMA, DMA, HA and FA in the 1.0wt% NaCl group were 56.10%, 12.32%, 53.91% and 8.02%, respectively; those in the 1.0wt% β-cyclodextrin group were 46.91%, 23.23%, 62.61% and 4.28%, respectively; and the removal rates of TMA, DMA, HA and FA in the 1.0wt% composite deodorant group were 62.11%, 20.96%, 56.77% and 24.33%, respectively. By comparing the removal rates of fishy substances in each group, it was found that at 30 min, the 1wt% β-cyclodextrin group had the highest removal rates for DMA and HA, and the 1.0wt% composite deodorant group had the highest removal rates for TMA and FA, indicating that the deodorization effects of 1.0wt% composite deodorant and 1wt% β-cyclodextrin were better than those of 1.0% NaCl at 30 min, which also verified the advantages of composite deodorants over conventional deodorants.

[0072] When the time reached 60 min, for the 1.0wt% NaCl group, the removal rates of TMA, DMA, HA, and FA increased by 1.20%, 7.41%, 6.21%, and 1.87%, respectively, and the removal rates of the 1.0wt% β-cyclodextrin group increased by 12.18%, 6.88%, 1.86%, and 9.36%, respectively. The removal rates of the 1.0wt% composite deodorant group increased by 13.10%, 13.61%, 6.71%, and 13.37%, respectively, indicating that the removal rates of the fishy substances in each group increased with the increase of time. Comparing the removal rates of fishy substances in each group, it was found that the 1.0wt% composite deodorant group had the highest removal rates for TMA, DMA, HA and FA, which were 75.20%, 34.57%, 63.48% and 37.70% respectively, while the 1.0wt% β-cyclodextrin group had slightly lower removal rates for TMA and DMA, which were 59.09% and 30.11% respectively, while the removal rate of HA was 64.47%. At 60 minutes, the 1.0wt% composite deodorant group had the best overall removal effect on fishy substances, followed by the 1.0wt% β-cyclodextrin group and the 1.0wt% NaCl group, indicating that the composite deodorant selected in the experiment has a better deodorizing effect than the traditional single deodorant.

[0073] At 90 min, the removal rates of the fishy substances in each group were: the removal rates of TMA, DMA, HA and FA in the 1.0wt% NaCl group were 57.52%, 19.36%, 61.37% and 17.11%, respectively, among which the removal rates of TMA, HA and FA increased by 0.22%, 1.25% and 7.22%, respectively, while the removal rate of DMA decreased by 0.37%; the removal rates of 1wt% β-cyclodextrin group were 70.05%, 30.88%, 65.71% and 13.97%, respectively. .96% and 7.49%, the removal rate of TMA increased by 12.11%, DMA and HA increased by 2.25% and 1.49% respectively, but the removal rate of FA decreased by 6.15%; the 1.0wt% composite deodorant group reached 87.31%, 36.32%, 69.32% and 29.68% respectively, among which the removal rates of TMA and HA increased significantly by 14.57% and 5.84%, DMA increased by 0.52%, and the removal rate of FA decreased by 8.02%. Comparison of the removal rates of the three groups of fishy substances showed that the 1.0wt% composite deodorant was significantly better than 1.0wt% NaCl and 1.0wt% β-cyclodextrin in the removal effect of the four fishy substances, indicating that the 1.0wt% composite deodorant had the best removal effect on the four fishy substances. Comparing the changes in removal rates, the increases in removal rates of the 1.0wt% NaCl group, 1.0wt% β-cyclodextrin group and 1.0wt% composite deodorant group all decreased significantly, or even showed a downward trend, indicating that continuing to increase the soaking time would not significantly increase the deodorization effects of each group. The removal rates of TMA, DMA, HA and FA by the 1.0wt% composite deodorant group were stronger than those of other conventional deodorants, indicating that the composite deodorant was more capable than the traditional deodorant.

[0074] However, despite the use of composite deodorizers to pre-treat duck livers by repeated elution and long-term soaking, the residual fishy amine substances in the samples were still as high as 12.69% to 63.68%, and the samples still showed obvious fishy odor characteristics after pre-treatment. The main reason is that some fishy substances interacted with duck liver proteins and were difficult to completely remove through the adsorption-desorption behavior of composite deodorizers; at the same time, composite deodorizers mainly acted on compounds with high polarity such as TMA, DMA, HA and FA, and had low removal efficiency for alcohols, ketones and ester compounds with low polarity and stronger interaction with proteins. Therefore, in view of the above two factors, a targeted deodorization process and the introduction of new deodorization factors were used for secondary deodorization in the subsequent protein extraction process of pre-treated duck liver samples.

[0075] 2. Analysis of changes in duck liver protein odor substances: The results of determination of TMA, DMA, FA and HA contents of duck liver protein samples prepared by different extraction methods in the specific examples are shown in Tables 3 and 4.

[0076] Table 3 Determination results of TMA and DMA of duck liver protein samples under different extraction methods

[0077]

[0078] Table 4 Determination results of HA and FA of duck liver protein samples under different extraction methods

[0079]

[0080] According to Table 3, Table 4 and Figure 1-Figure 4 , and the removal rates of different fishy substances in 5 groups were compared. Compared with the RE group, the removal effects of TMA, DMA and HA in each group were significantly improved, indicating that ultra-high hydrostatic pressure treatment has a significant removal effect on fishy substances. The reason is that ultra-high hydrostatic pressure induces the unfolding of duck liver protein structure during the extraction process, and the formed molten globule-like protein transfers the fishy substances to the protein surface for easy elution by the extraction solvent.

[0081] Furthermore, the removal rates of TMA and FA in the UNA and UNP groups were compared with those in the UN group. The removal rates of TMA and FA in the UN group were lower than those in the UNA group (6.84% and 6.04% lower) and the UNP group (0.80% and 13.65% lower), indicating that the addition of trehalose and propylene glycol during the extraction process was more conducive to the removal of TMA and FA. The removal rates of TMA, DMA and FA in the UNPA group were better than those in the UNA group (1.84%, 2.64% and 3.19% higher, respectively) and the UNP group (9.98%, 31.25% and 16.80% higher, respectively), indicating that the synergistic treatment of trehalose and propylene glycol had a better deodorizing effect than single treatment.

[0082] In general, the UNPA group performed well in the removal of all four fishy substances, especially in the removal rate of TMA, DMA, and FA. The effect of the UNPA group was significantly enhanced, indicating that the ultra-high hydrostatic pressure induced the unfolding of the duck liver protein structure during the extraction process, and the formed molten globule-like protein transferred the fishy substances to the protein surface for easy elution by the extraction solvent. At the same time, combined with structural stabilizing factors such as trehalose and propylene glycol, the deodorizing effect of the liver protein molten globule-like protein was further enhanced, proving the significant advantages of the UNPA group in optimizing the duck liver protein processing process.

[0083] 3. Analysis of headspace volatile components of duck liver protein: The total concentration of volatile flavor substances of duck liver protein prepared by different extraction methods in the specific examples is as follows: Figure 5 As shown. Figure 5It can be seen that the relative abundance of the GC-MS peak area of ​​duck liver protein obtained by different treatments has obvious changes. Compared with the UN group, the content of the UNA group increased significantly, indicating that after trehalose combined with protein, the components in the protein that were originally difficult to detect were detected, thereby increasing the peak area; compared with the UN group, the UNP content decreased, indicating that propylene glycol made the volatile flavor substances in duck liver protein more smoothly released during the extraction process of duck liver protein; compared with the UNA and UNP groups, the changes in the UNPA group also verified that the synergistic treatment of trehalose and propylene glycol was more conducive to the release of volatile flavor substances in duck liver protein.

[0084] 4. Analysis of the functional properties of duck liver protein.

[0085] (1) Analysis of the water-holding capacity and oil-holding capacity of duck liver protein samples prepared by different extraction methods in the specific examples.

[0086] like Figure 6 As shown in the figure, in terms of water holding capacity, the water holding capacity of the UN group was lower than that of the RE group, but better than that of the UNA group and the UNP group, indicating that the ultra-high hydrostatic pressure treatment had a certain effect on reducing water holding capacity. The UNPA group was significantly better than the other groups, with a water holding capacity that was 13.3% higher than that of the RE group, 71.7% higher than that of the UNA group, and 1.11 times higher than that of the UNP group, indicating that the synergistic treatment of propylene glycol and trehalose had a significant effect in improving water holding capacity.

[0087] In terms of oil holding capacity, compared with the RE group, the oil holding capacity of other groups showed certain differences in values, but the differences were not significant. Among them, the UN group and UNP group were slightly higher than other groups, indicating that ultra-high hydrostatic pressure treatment induced protein unfolding, which helped to improve oil holding capacity. The UNP group was slightly lower than the UN group, indicating that propylene glycol, as a polar molecule, had a certain offsetting effect on the oil holding capacity of the extracted protein, which was similar to the result of the polar molecule treatment of trehalose. The oil holding capacity of the UNPA group was lower than that of the UNP group, confirming that the addition of trehalose reduced the oil holding capacity to a certain extent. Overall, the UNPA group performed best in terms of water holding capacity, showing the significant advantage of the synergistic treatment of propylene glycol and trehalose in improving water holding capacity. Although oil holding capacity and water holding capacity cannot be taken into account at the same time, the UNPA group still has a certain guarantee of oil holding capacity while improving water holding capacity, and its value is still significantly higher than that of the RE group.

[0088] (2) Analysis of the emulsification properties of duck liver protein samples prepared by different extraction methods in specific examples.

[0089] like Figure 7As described above, compared with the emulsifying activity (abbreviated as EAI) of the RE group, the emulsifying activity of the UNA, UN, UNP, and UNPA groups increased significantly, indicating that ultra-high hydrostatic pressure treatment may cause changes in the protein structure and expose some hydrophobic groups. These changes can enhance the adsorption capacity of the protein at the oil-water interface, thereby improving the emulsification; the emulsification of the UNPA group is 60.2% higher than that of the RE group, 53.4% ​​higher than that of the UNA group, 26.2% higher than that of the UN group, and 6.6% higher than that of the UNP group, indicating that the synergistic treatment of propylene glycol and trehalose can improve the emulsification of duck liver protein; compared with the RE group, the emulsification stability (abbreviated as ESI) of the UN, UNP, and UNPA groups decreased significantly, indicating that ultra-high hydrostatic pressure causes changes in the protein conformation, affecting its interfacial film formation in the emulsion, thereby reducing the emulsification stability. Overall, the UNPA group performed best in terms of emulsification, and was better than the UN and UNP groups in terms of emulsification stability.

[0090] (3) Total carbonyl content of duck liver protein samples prepared by different extraction methods in specific examples.

[0091] A significant change in protein after oxidation is the formation of carbonyl groups. The carbonyl content is widely used to measure the degree of protein oxidation. Generally speaking, the higher the carbonyl content, the greater the degree of protein oxidation. Figure 8 As shown in the figure, compared with the RE group, the total carbonyl contents of the UNA, UN, UNP and UNPA groups increased, indicating that the oxidation degree of duck liver protein was aggravated after ultra-high hydrostatic pressure treatment; compared with the UN group, the total carbonyl contents of the UNA and UNP groups decreased, indicating that trehalose can stabilize the protein structure, and propylene glycol has good antioxidant properties and can react with free radicals, which can prevent the oxidation of protein to a certain extent; and compared with the UN group, the total carbonyl content of the UNPA group was slightly increased, indicating that the antioxidant effect of trehalose and propylene glycol when used in combination is not a simple addition, because trehalose and propylene glycol induce significant polarity changes in the extracted protein, causing the carbon groups inside the molecule to rearrange, further confirming the difference in the regulatory effect of the synergistic effect of the two on protein structure, and providing more tools for regulating the ultrastructural characteristics of proteins during the extraction process.

[0092] 5. Structural analysis of duck liver protein.

[0093] (1) Electron microscopic analysis of duck liver protein prepared by different extraction methods in the specific examples: Fig. 9As shown in the figure, under 3K and 5K magnifications, the surface of the RE group was convex and the structure was loose. The protein structure of the UN group after ultrasound was even looser. The UNA, UNP and UNPA groups after trehalose, propylene glycol and the combined treatment of the two had certain improvements, the most obvious of which was the UNPA group, which had the smoothest surface and a relatively compact structure. This shows that the structural stability of duck liver protein was significantly improved under the combined treatment of trehalose and propylene glycol, which is helpful to maintain the unfolded conformation and loose structure of the protein during the extraction process and promote the elution of fishy substances.

[0094] (2) Gel electrophoresis analysis of duck liver protein prepared by different extraction methods in the specific examples: Fig.10 As shown, the band of RE group was the lightest. Compared with RE group, UNP and UNA groups were similar to RE group, while the optical density of samples of UN and UNPA groups increased significantly, and the band intensity of subunits increased, indicating that ultra-high hydrostatic pressure and the addition of trehalose and propylene glycol may make subunits easier to separate or increase in number, thereby improving the conformational elasticity of duck liver protein molecules. This shows that on the basis of composite deodorant pretreatment and ultra-high hydrostatic pressure treatment, the combination of propylene glycol and trehalose can maximize the spatial stretchability and stability of protein.

[0095] (3) Circular dichroism analysis of duck liver protein prepared by different extraction methods in the specific examples: Fig.11As shown in the figure, by comparing the differences in protein secondary structure between the groups, it was found that different treatment groups had different effects on protein secondary structure. Compared with the RE group, the α-helix content of the UNPA group increased by 17.83%, indicating that it was more able to maintain or form an α-helix structure under the synergistic treatment of ultra-high hydrostatic pressure, trehalose and propylene glycol, which was helpful for the stability and functional properties of the protein. The β-fold content also increased significantly in the UNPA group, increasing by 16.97% compared with the RE group, indicating that the synergistic treatment of ultra-high hydrostatic pressure, trehalose and propylene glycol had a significant effect on promoting the formation of β-folds, which may help to enhance the mechanical strength and stability of the protein. The reduction of β-turn was more significant in the UN and UNP groups, decreasing by 15.73% and 15.60% respectively, while the random coil increased in the UNP group compared with the RE group, indicating that under the synergistic effect of ultra-high hydrostatic pressure and propylene glycol, the hydrophobic area on the protein surface was exposed, resulting in the reduction and rupture of intramolecular hydrogen bonds, thereby reducing the proportion of β-turns, and the proportion of random coils showed a decreasing trend; the secondary structure of the protein did not change significantly, while the tertiary structure was modified to varying degrees, indicating that the synergistic treatment of ultra-high hydrostatic pressure and trehalose and propylene glycol successfully induced the unfolding structure of the molten globule-like protein. Overall, the UNPA group performed outstandingly in all aspects, indicating that the addition of trehalose and propylene glycol, the factors stabilizing the unfolding structure, made the molten globule-like protein structure induced by ultra-high hydrostatic pressure more stable, and further helped the fishy substances transferred to the protein surface to be continuously eluted during the extraction process.

[0096] (4) Measurement of endogenous fluorescence spectra of duck liver protein prepared by different extraction methods in specific embodiments: Fig.12 The changes in the endogenous fluorescence intensity of duck liver protein in different treatment groups are shown. The fluorescence intensity of the RE group was the highest, and the fluorescence intensity of the UN group was the lowest, indicating that the composite deodorant pretreatment and ultra-high hydrostatic pressure treatment exposed more fluorescent groups of the protein to the polar environment or enhanced the polar environment, increasing the chance of solvent quenching. The fluorescence intensity of other treatment groups such as the UNA group and the UN group was between the RE group and the UNPA group, showing a certain degree of conformational change, indicating that propylene glycol and trehalose can enhance the stability of the protein structure to a certain extent and avoid the exposure of more fluorescent groups.

[0097] (5) UV-visible spectra and second-order derivative UV-visible spectra analysis of duck liver proteins prepared by different extraction methods in specific embodiments: Fig.13 and Fig.14 The changes in UV-visible spectra and second-order UV spectra are shown. Fig.13It can be seen that the absorption peaks of each group have changed, indicating that the treatment of each group has caused changes in the protein structure and environment. Among them, the absorption peak and spectrum of the UNPA group at a specific wavelength have changed the least, indicating that the composite deodorant pretreatment and ultra-high hydrostatic pressure treatment may destroy the hydrogen bonds and hydrophobic interactions of the protein, causing changes in the protein structure, while the synergistic effect of trehalose and propylene glycol has stabilized the protein structure, resulting in only slight changes in the tertiary structure of the protein. Fig.14 It can be seen that the characterization of the second-order derivative of the UV spectrum shows two peaks and troughs between 282 nm and 290 nm. The characteristic peak of tyrosine (abbreviated as Tyr) at 282 nm shows a weak red shift, and the peak value shows an increase, indicating that the structure of the protein is folded or unfolded, affecting the environment of tyrosine, so that the tyrosine residue may be exposed to a more polar environment. The corresponding characteristic peak of tryptophan (abbreviated as Trp) at 290 nm also shows a certain red shift, but its amplitude is lower than that of Tyr, indicating that ultra-high hydrostatic pressure treatment helps the duck liver protein to unfold and expose the Tyr residue. The UNPA group has the lowest peak, which further illustrates that the synergistic effect of trehalose and propylene glycol has a stabilizing effect on the structure of the protein and weakens the changes in the tertiary structure of the protein.

[0098] (6) Fourier transform infrared (FTIR) spectral analysis of duck liver protein prepared by different extraction methods in the specific examples: Fig.15 As shown in the figure, the absorption spectrum of the amide I band (1600-1700 cm -1 ) is related to the secondary structure of proteins, 1646-1664 cm -1 、1615-1637 / 1682-1700 cm -1 、1664-1681 cm -1 and 1637-1645 cm -1 The regions were designated as α-helix, β-sheet, β-turn, and random coil, respectively. Based on the FTIR spectrum, the amide I region (1600–1700 cm -1 ) The secondary structure of the protein in the 4 groups was slightly changed compared with the RE group, indicating that these treatments induced changes in the secondary structure of the protein. The intensity change of the UNPA group was the smallest when the UNA, UN, UNP and UNPA groups were compared, which also showed that the pretreatment with the composite deodorant and ultra-high hydrostatic pressure induced changes in the protein conformation, while the synergistic effect of trehalose and propylene glycol played a certain role in stabilizing the protein conformation.

[0099] (7) Determination of surface hydrophobicity: Fig.16 The surface hydrophobicity of duck liver protein in each treatment group is shown. Fig.16It can be seen that compared with the RE group, the surface hydrophobicity of the UNA group was weakened, the surface hydrophobicity of the UNP group was slightly enhanced, and the surface hydrophobicity of the UN and UNPA groups was significantly enhanced, among which the surface hydrophobicity of the UNPA group was the strongest. The enhanced hydrophobicity of the UN group indicated that the structure of the protein was changed after the pretreatment with the composite deodorant and the ultra-high hydrostatic pressure treatment, so that the internal hydrophobic groups were exposed, thereby improving the surface hydrophobicity. The UNPA group had the strongest hydrophobicity, indicating that the combined action of trehalose and propylene glycol can better expose the hydrophobic area of ​​the protein, thereby improving the surface hydrophobicity. The higher surface hydrophobicity helps the protein to adsorb on the oil-water interface and reduce the interfacial tension, and has better emulsification.

[0100] (8) Determination of reactive thiol groups (abbreviated as R-SH) and total thiol groups (abbreviated as T-SH) of duck liver protein samples prepared by different extraction methods in the specific examples: Fig.17 As shown in the figure, the contents of total thiol and active thiol in RE group were 16.55 and 35.38 μmol / g, respectively. Compared with RE group, the total thiol content in UNA and UN groups did not change significantly after treatment, and it decreased significantly in UNP and UNPA groups; while the active thiol content in UN group decreased significantly, and it changed slightly in UNA, UNP and UNPA groups. The reduction of total thiol in UNP and UNPA groups usually indicates the formation of disulfide bonds in proteins, which is an important stabilizing factor for the secondary and tertiary structures of proteins, indicating that the synergistic treatment of trehalose and propylene glycol may stabilize the structure of proteins. Active thiol groups can usually be used as an important indicator to characterize the tertiary structure or folding state of proteins. The active thiol region has not been damaged or chemically modified by external factors, and the R-SH value in UNPA group is closer to that in RE group, which further indicates that trehalose and propylene glycol effectively protect the thiol groups in proteins from oxidative damage and retain the activity and characteristics of proteins to the greatest extent.

[0101] The above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by a person skilled in the art within the spirit and scope of the present invention shall also fall within the protection scope of the present invention.

Claims

1. A method for preparing duck liver protein with reduced fishy smell and improved functional properties, characterized in that The following steps are involved: (1) Pretreatment: Cut the duck liver into small pieces, remove the fascia and fat, and soak the duck liver in a 1 wt% composite deodorizing agent solution for 30 to 90 min to obtain a preliminarily deodorized duck liver, wherein the composite deodorizing agent is composed of the following raw materials and their mass percentages: 25% propylene glycol, 40% trehalose, 5% KCl, 20% corn starch and 10% pineapple fiber; (2) Pickling: Wash the duck liver obtained in step (1) with pure water and pickle it in 0.05-2 M salt water for 30-60 min; (3) defatting: after the pickled duck liver in step (2) is taken out and washed, the duck liver and pure water are mixed in a mass ratio of 1:2, and the mixture is homogenized in a blender for 3 to 5 minutes to obtain a duck liver solution. Ethanol is added to the duck liver solution at a mass volume ratio of 1 g:2 mL at 30 to 40° C. to extract the duck liver solution. After sufficient stirring, the mixture is allowed to stand for 4 to 8 hours, and then the supernatant is discarded by centrifugation. The precipitate is placed in an oven and baked at 30 to 40° C. to remove the ethanol, thereby obtaining a brown block-like defatted precipitate. (4) Extracting duck liver protein: Add 0.3% of the mass of propylene glycol and 0.5% of trehalose to the defatted precipitate obtained in step (3), and add 50% of the mass of pure water to mix thoroughly, then put it into an ultra-high hydrostatic pressure device and treat it at 320-380 MPa for 10 min; mix the defatted precipitate after ultra-high hydrostatic pressure treatment with pure water in a mass ratio of 1:2, and then adjust the pH value by alkali extraction and acid precipitation method to obtain duck liver protein with reduced fishy smell and improved protein functional properties.

2. The method for preparing duck liver protein with reduced fishy smell and improved functional properties according to claim 1, characterized in that The alkali extraction and acid precipitation method described in step (4) is as follows: the pH is adjusted to 11-11.4 with a sodium hydroxide solution, and the mixture is continuously stirred with a vibrator at 45-55°C for 5 hours, and then the supernatant is centrifuged and the pH is adjusted to 4.1-4.5 with a hydrochloric acid solution. After standing at 4°C overnight, the supernatant is discarded by centrifugation, and the precipitate is dissolved with a small amount of deionized water and freeze-dried to obtain duck liver protein with reduced fishy smell and improved protein functional properties.

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