Probiotic fermented walnut yoghurt with stable antioxidant function and preparation method of probiotic fermented walnut yoghurt
By using the domesticated Lactobacillus plantarum JLAU103 starter culture, the problem of instability of the mixed system of walnut milk and cow's milk was solved, and a probiotic fermented walnut yogurt with stable antioxidant function was prepared, ensuring the stability of the fermentation process and the antioxidant effect.
Patent Information
- Application Number
- CN202511120982.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-12
- Publication Date
- 2025-10-10
AI Technical Summary
In the prior art, when walnut milk and cow's milk containing different nutritional ingredients are mixed, the system becomes unstable and the functional effects of the active substances cannot be maintained for a long time.
Domesticated Lactobacillus plantarum JLAU103 was used as the starter, and it was gradually domesticated to adapt to the walnut milk environment. Walnut pulp was mixed with cow's milk to prepare probiotic fermented walnut yogurt with stable antioxidant function.
The stability of the antioxidant effect of fermented walnut yogurt over a prolonged period of time is achieved, which is significantly better than traditional fermented yogurt without the need to add any stabilizers.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of functional food preparation, in particular to a probiotic fermented walnut yogurt with stable antioxidant function and a preparation method thereof. Background Art
[0002] Yogurt has become one of the most popular dairy products worldwide. Containing numerous probiotics, it can promote intestinal motility, lower cholesterol, prevent disease, and enhance immunity. It can also improve lactose intolerance in some people. In recent years, consumers have increasingly demanded more diverse and functional yogurts. Providing a yogurt that meets these diverse needs has become a hot topic in this research field.
[0003] Walnuts contain a wealth of nutrients, including protein, vitamins, fat, and minerals. Unsaturated fatty acids account for 86% of these nutrients, and the abundant lecithin can enhance brain function and prevent Alzheimer's disease. Walnut kernels are also rich in linoleic and linolenic acids, making walnut milk highly nutritious, with a smooth taste and rich aroma. However, walnut milk products primarily consist of walnut extract, and research on walnut yogurt is insufficient. Adding walnut milk to cow's milk not only retains the benefits of cow's milk but also enriches the final fermented milk's nutritional profile. However, mixing raw materials containing different nutrients creates an unstable system, preventing the active ingredients from maintaining their functions over time. Summary of the Invention
[0004] The invention aims to provide a probiotic fermented walnut yogurt with stable antioxidant function and a preparation method thereof. The fermented walnut yogurt is not only delicious and nutritious, but also has a stable antioxidant effect, and the antioxidant effect does not change significantly over time.
[0005] In order to achieve the above object, the present invention provides the following technical solutions:
[0006] In a first aspect, the present invention provides a probiotic fermented walnut yogurt with stable antioxidant function, which is obtained by sterilizing, fermenting, and refrigerating the raw materials in the following weight percentages: 60-80% fresh milk, 20-40% walnut pulp, 2-4% production starter, and 4-8% white sugar. The production starter uses domesticated Lactobacillus plantarum JLAU103, and the viable cell count is 9.2×10 9 CFU / ml.
[0007] Preferably, the domestication method of Lactobacillus plantarum JLAU103 comprises:
[0008] (1) Activation of the strain: 1 mL of Lactobacillus plantarum JLAU103 was spread on MRS solid medium using a spreader. After incubation at 37°C for 48 hours, a single colony was picked and transferred to MRS liquid medium. The culture was incubated at 37°C for 24 hours, and 2% (v / v) of the culture was subcultured. This process was repeated twice. The bacterial sludge was washed with sterile water, and the OD value of the bacterial solution was adjusted to 1 at 600 nm using a UV spectrophotometer for use in subsequent experiments.
[0009] (2) Domestication of the strain: The strain was gradually domesticated. Lactobacillus plantarum JLAU103 with a 5% OD value of 1 was inoculated into fresh milk and fermented at 37°C for 10 hours to obtain a first-level strain; the first-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 2:8, and fermented at 37°C for 6 hours to obtain a second-level strain; the second-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 3:7, and fermented at 37°C for 6 hours to obtain a third-level strain; the third-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 4:6, and fermented at 37°C for 6 hours to obtain a fourth-level strain; the fourth-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 5:5, and fermented at 37°C for 6 hours to obtain a production starter.
[0010] Preferably, the preparation method of the walnut paste includes: selecting full walnut kernels without mold, soaking the walnut kernels with skin in a 2% anhydrous sodium carbonate solution at 75°C for fifteen minutes, washing and peeling with high-pressure water, draining the water after washing, baking at 90°C for 1.5 hours, and then beating with water in a mass ratio of 1:4, and filtering with a 120-mesh sieve after beating.
[0011] Preferably, the raw material addition amounts are: 37.7% walnut pulp, 3.1% production starter, 6.4% white sugar, the fermentation temperature is 39.9° C., and the fermentation time is 8.1 h.
[0012] In a second aspect, the present invention further provides a method for preparing the above-mentioned probiotic fermented walnut yogurt with stable antioxidant function, comprising the following steps:
[0013] S1. Preparation of fermentation liquid
[0014] Fresh milk and walnut pulp were mixed evenly in a mass ratio of 8:2 to 6:4, 4-8% white sugar was added, and the mixture was preheated to 55°C and homogenized at 55°C with a homogenization pressure of 25 MPa for 5 minutes.
[0015] S2. Sterilization of liquid
[0016] The homogenized fermentation liquid was pasteurized at 90°C for 15 minutes and cooled to room temperature before use.
[0017] S3. Inoculation and Fermentation
[0018] The cooled fermentation liquid is inoculated with 2-4% domesticated Lactobacillus plantarum JLAU103, mixed evenly and fermented at 39-41° C. for 7-9 hours. The fermented walnut yogurt is refrigerated at 4° C. for 12 hours to obtain a probiotic fermented walnut yogurt with stable antioxidant function.
[0019] Preferably, the domestication method of Lactobacillus plantarum JLAU103 comprises:
[0020] (1) Activation of the strain: 1 mL of Lactobacillus plantarum JLAU103 was spread on MRS solid medium using a spreader. After incubation at 37°C for 48 hours, a single colony was picked and transferred to MRS liquid medium. The culture was incubated at 37°C for 24 hours, and 2% (v / v) of the culture was subcultured. This process was repeated twice. The bacterial sludge was washed with sterile water, and the OD value of the bacterial solution was adjusted to 1 at 600 nm using a UV spectrophotometer for use in subsequent experiments.
[0021] (2) Domestication of the strain: The strain was gradually domesticated. Lactobacillus plantarum JLAU103 with a 5% OD value of 1 was inoculated into fresh milk and fermented at 37°C for 10 hours to obtain a first-level strain; the first-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 2:8, and fermented at 37°C for 6 hours to obtain a second-level strain; the second-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 3:7, and fermented at 37°C for 6 hours to obtain a third-level strain; the third-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 4:6, and fermented at 37°C for 6 hours to obtain a fourth-level strain; the fourth-level strain was inoculated into a mixed system of walnut paste and fresh milk in a ratio of 5:5, and fermented at 37°C for 6 hours to obtain a production starter.
[0022] Preferably, the preparation method of the walnut paste includes: selecting full walnut kernels without mold, soaking the walnut kernels with skin in a 2% anhydrous sodium carbonate solution at 75°C for fifteen minutes, washing and peeling with high-pressure water, draining the water after washing, baking at 90°C for 1.5 hours, and then beating with water in a mass ratio of 1:4, and filtering with a 120-mesh sieve after beating.
[0023] Preferably, the raw material addition amounts are: 37.7% walnut pulp, 3.1% production starter, 6.4% white sugar, the fermentation temperature is 39.9° C., and the fermentation time is 8.1 h.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] The preparation method of the probiotic fermented walnut yogurt with stable antioxidant function provided by the present invention comprises the following steps: adding walnut pulp so that the yogurt itself has antioxidant capacity; using specially domesticated Lactobacillus plantarum JLAU103 instead of a traditional starter; allowing the bacterial flora to adapt to the walnut milk environment through domestication; making the fermentation system more stable without adding any stabilizer; thereby obtaining the probiotic fermented walnut yogurt with stable antioxidant function; and the antioxidant effect does not change significantly over time, and the functional effect is significantly better than that of traditional fermented yogurt. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.
[0027] Figure 1 These are the results of the effect of walnut pulp addition on the quality of walnut yogurt.
[0028] Figure 2 These are the results of the effect of sucrose addition on the quality of walnut yogurt.
[0029] Figure 3 This is the effect of inoculum size on the quality of walnut yogurt.
[0030] Figure 4 The results show the effect of fermentation temperature on the quality of walnut yogurt.
[0031] Figure 5 The results show the effect of fermentation time on the quality of walnut yogurt.
[0032] Figure 6 These are the response surface analysis results for the addition amount of walnut pulp and sugar.
[0033] Figure 7 These are the response surface analysis results for inoculum size and walnut pulp addition amount.
[0034] Figure 8 These are the response surface analysis results for fermentation temperature and walnut pulp addition amount.
[0035] Figure 9 These are the response surface analysis results for fermentation time and walnut pulp addition amount.
[0036] Figure 10 These are the response surface analysis results for sugar addition amount and inoculum amount.
[0037] Figure 11 Results of response surface analysis for sugar addition amount and fermentation temperature.
[0038] Figure 12 These are the response surface analysis results for sugar addition amount and inoculum amount.
[0039] Figure 13 These are the response surface analysis results for fermentation temperature and inoculum size.
[0040] Figure 14 These are the response surface analysis results for fermentation temperature and fermentation time.
[0041] Figure 15 This is a photo of walnut yogurt fermented with probiotics under optimal reaction conditions.
[0042] Figure 16 The scavenging rates of DPPH free radical, ABTS+ free radical, -OH free radical and Fe free radical of walnut yogurt fermented by Lactobacillus plantarum JLAU103 during 21 days of storage were analyzed. 2+ Chelating ability.
[0043] Figure 17 The scavenging rates of DPPH free radicals, ABTS+ free radicals, -OH free radicals and Fe content of walnut yogurt fermented with traditional starter instead of Lactobacillus plantarum JLAU103 during 21 days of storage were analyzed. 2+ Chelating ability. DETAILED DESCRIPTION
[0044] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0045] The present invention adopts Lactobacillus plantarum JLAU103 (classification name: Lactobacillus plantarum
[0046] Lactobacillus plantarum), deposited on November 22, 2021 in the General Microbiology Center of China Culture Collection Administration (CGMCC), address: No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, with the deposit number CGMCCNO.23952.
[0047] Example 1 Study on the acclimation conditions of bacterial strains
[0048] The strain was acclimated primarily through a stepwise acclimation process, allowing Lactobacillus plantarum JLAU103 to gradually adapt to the walnut and milk system. Optimal acclimation conditions were determined by measuring viable cell counts and the presence of stratification in the fermentation system. The fermentation time was determined by measuring the viable cell count and the presence of stratification in the acclimated system at a 2% inoculum. Fermentation times for fresh milk were set at 8, 9, 10, 11, and 12 hours. The results are shown in Table 1. Table 1 shows that when the inoculum was 2%, no stratification occurred in the pure milk. However, with increasing fermentation time, the viable cell count initially increased and then decreased, reaching a maximum at the 10th hour of fermentation. This condition was selected for subsequent acclimation. The mixed fermentation of walnuts and milk was performed at 5, 6, 7, 8, and 9 hours. The results are shown in Table 2. Table 2 shows that the viable cell count in the mixed milk reached its maximum at 6 hours, while stratification occurred after 8 hours. Therefore, the fermentation time for the mixed milk was determined to be 6 hours. Based on the optimal fermentation conditions, inoculation levels of 2%, 3%, 4%, 5%, and 6% were selected. The viable bacterial count and stratification of the final yogurt were measured, and the results are shown in Tables 3 and 4. Table 3 shows that the inoculation level for pure milk was 5%, and Table 4 shows that the inoculation level for mixed milk was 3%.
[0049] Tables 1 to 4 show the viable bacterial counts and stratification of the strains during acclimation. The optimal conditions were selected after comprehensive consideration. Walnut yogurt was inoculated with different strains to observe the fermentation process and determine the viable bacterial count. The results are shown in Table 5.
[0050] Table 1 Changes of bovine milk after inoculation with time
[0051]
[0052] Table 2 Changes over time after mixed milk inoculation
[0053]
[0054] Table 3 Changes in the amount of bacteria inoculated into milk
[0055]
[0056] Table 4 Changes in the amount of mixed milk inoculation
[0057]
[0058] Table 5 Changes in fermented walnut yogurt
[0059]
[0060] Example 2 Walnut Yogurt Formula and Key Process Parameters
[0061] The sensory evaluation method involved inviting 10 people (male:female = 1:1) to form a sensory evaluation panel. Evaluators were instructed not to consume alcohol or spicy foods within 12 hours prior to the evaluation and were strictly prohibited from discussing the evaluation process. Samples were placed in identical containers and randomly numbered. Each sample was rinsed with water and evaluated in turn, with a maximum score of 100. The sensory scores were used as indicators to evaluate the impact of various factors on walnut yogurt. The sensory evaluation criteria for set yogurt, as outlined in the "Sensory Evaluation Rules for Milk and Dairy Products" published by the China Dairy Industry Association, were used to evaluate the yogurt's flavor, aroma, texture, and color (Table 6).
[0062] Table 6 Sensory score table for coagulated yogurt
[0063]
[0064] (1) Effect of walnut pulp addition on the quality of walnut yogurt
[0065] The ratio of walnut pulp to milk was set to 1:9, 2:8, 3:7, 4:6 and 5:5. Under the condition of 2% inoculation, the yogurt was fermented at 37℃ for 6 hours and refrigerated at 4℃ for 12 hours. The sensory evaluation of the yogurt was carried out. The optimal addition amount of walnut pulp was determined to be a ratio of walnut pulp to milk of 3:7. The results are as follows Figure 1 shown.
[0066] (2) Effect of sucrose addition on the quality of walnut yogurt
[0067] Based on the optimal walnut pulp addition, sugar addition was 2%, 4%, 6%, and 8%. Under the condition of 2% inoculation, the yogurt was fermented at 37℃ for 6 hours and refrigerated at 4℃ for 12 hours. The sensory evaluation of the yogurt was carried out. The optimal sugar addition was determined to be 6% through sensory scoring. The results are as follows. Figure 2 shown.
[0068] (3) Effect of inoculation amount on the quality of walnut yogurt.
[0069] Based on the optimal walnut pulp and optimal sugar addition, the inoculum amount was set to 1%, 2%, 3%, 4%, and 5%. The yogurt was fermented at 37°C for 6 hours and refrigerated at 4°C for 12 hours before sensory evaluation. The optimal inoculum amount was determined to be 3% through sensory evaluation. Figure 3 shown.
[0070] (4) Effect of fermentation temperature on the quality of walnut yogurt.
[0071] Based on (1)(2)(3), the fermentation temperature was set at 37℃, 38℃, 39℃, 40℃, 41℃, and 42℃, and the fermentation was carried out for 6 hours. After refrigeration at 4℃ for 12 hours, the sensory evaluation of the yogurt was carried out. The optimal fermentation temperature was determined to be 40℃ through sensory scoring. The results are as follows Figure 4 shown.
[0072] (5) Effect of fermentation time on the quality of walnut yogurt.
[0073] Based on (1)(2)(3)(4), the fermentation time was set to 3h, 4h, 5h, 6h, 7h, 8h, 9h, and 10h, and the yogurt was refrigerated at 4℃ for 12h for sensory evaluation. The optimal fermentation time was determined to be 8h through sensory evaluation. The results are as follows Figure 5 shown.
[0074] The sensory score was selected as the response value, and the result data was fitted with a multivariate linear regression. The sensory score (R) was obtained, and the quadratic polynomial regression equation for the amount of walnut pulp added (A), sugar added (B), inoculation amount (C), fermentation temperature (D), and fermentation time (E) was:
[0075] R=-3824.61687+2.09494A-3.16125B+36.30937C+182.90167D+44.32292E+0.005125AB+0.009250AC-0.0107 50AD+0.047000AE+0.307500BC+0.277500BD+0.016250BE-0.670000CD+0.675000CE-0.047500DE-0.033281A 2 -0.716823B2-2.73146C 2 -2.27396D 2 -2.86229E 2
[0076] Based on the single factor experiment, a response surface experiment with five factors and three levels was conducted, and the sensory scores were used as the response values to determine the optimal yogurt formula. The factor level design of the response surface analysis experiment is shown in Table 7. The response surface experiment results are shown in Tables 8 and Figure 6-Figure 14 .
[0077] Table 7 Response surface analysis factors and levels
[0078]
[0079] Table 8 Response surface analysis experimental factor levels
[0080]
[0081]
[0082] *** indicates extremely significant (P < 0.01), ** indicates highly significant (0.001 <P<0.005)。
[0083] The optimal fermentation conditions and response data were obtained through optimization using Design-Expert13.0 software: 62.3% fresh milk, 37.7% walnut pulp, 3.1% production starter, 6.4% white sugar, fermentation temperature of 39.9°C, and fermentation time of 8.1h.
[0084] Example 3 Study on the Antioxidant Function of Walnut Yogurt
[0085] After evenly mixing 62.3% fresh milk and 37.7% walnut pulp, add 6.4% white sugar, preheat to 55℃, homogenize at 55℃ with a homogenization pressure of 25MPa for 5min; pasteurize the homogenized fermentation liquid at 90℃ for 15min, cool to room temperature and set aside; inoculate the cooled fermentation liquid with 3.1% domesticated Lactobacillus plantarum JLAU103, mix evenly and ferment at 39.9℃ for 8.1h, place the fermented walnut yogurt at 4℃ for 12h for refrigeration and ripening, and obtain probiotic fermented walnut yogurt with stable antioxidant function. Figure 15 shown.
[0086] 1. DPPH free radical scavenging ability determination
[0087] Add 2 ml of the above-mentioned probiotic fermented walnut yogurt sample solution and 2 ml of 60 μmol / L DPPH solution (dissolved in 95% anhydrous ethanol) to a test tube, mix well and react in the dark for 30 minutes, and measure the absorbance (A) at a wavelength of 517 nm. Replace the sample solution with an equal amount of distilled water and measure its absorbance A0. Replace the DPPH free radical solution with an equal amount of distilled water and measure the absorbance as B.
[0088] DPPH free radical scavenging rate (%) = [1-(AB) / A0] × 100%
[0089] 2. ABTS+ free radical scavenging ability determination
[0090] Weigh 0.0192g ABTS and 0.0034g K₂S₂O₄ in 5ml of distilled water, mix thoroughly, and store in a chromatography cabinet at 4°C, protected from light, for 12-16 hours. Before use, dilute the solution with 5mmol / L PBS buffer (pH 7.4) to an absorbance of 0.700±0.002 to prepare a working solution. Add 10µl of sample solution and 190µl of working solution to a 96-well plate, incubate for 6 minutes, and measure the absorbance (A) at 734nm using a microplate reader. Replace the sample solution with an equal amount of distilled water and measure its absorbance (A0). Replace the ABTS + free radical solution with an equal amount of distilled water, add 10µl of sample, and measure the absorbance (B).
[0091] ABTS+ free radical scavenging rate (%) = [1-(AB) / A0] × 100%
[0092] 3. Determination of -OH free radical scavenging ability
[0093] Add 2 ml of sample solution, 2 ml of 60 mmol / L FeSO4 solution and 3 mmol / L H2O2 solution to a test tube, mix and let it stand for 10 minutes, then add 2 ml of 6 mmol / L salicylic acid and mix evenly. Heat in a 37 ° C water bath in the dark for 30 minutes, and measure the absorbance (A) at a wavelength of 510 nm. Under the same operation, replace the sample solution with an equal amount of distilled water and measure its absorbance A0. Replace the FeSO4 solution with an equal amount of distilled water and measure the absorbance as B.
[0094] -OH radical scavenging rate (%) = [1-(AB) / A0] × 100%
[0095] 4. Fe 2+ Chelating ability
[0096] Add 0.5 ml of sample solution, 1 ml of 20 μmol / L FeCl2 solution, and 1 ml of 0.5 mmol / L Ferrozine solution to a test tube. Mix well and heat in a 25°C water bath in the dark for 20 minutes. Measure the absorbance (A) at a wavelength of 562 nm. Under the same operation, replace the sample solution with an equal amount of distilled water and measure its absorbance A0. Replace the Ferrozine solution with an equal amount of distilled water and measure the absorbance as B.
[0097] Fe 2+ Chelating ability (%) = [1-(AB) / A0] × 100%
[0098] The scavenging rates of DPPH free radical, ABTS+ free radical, -OH free radical and Fe free radical of walnut yogurt prepared under the optimal fermentation conditions of the present invention were investigated during the 21-day storage period. 2+ Chelating ability Figure 16 As shown in the table, different letters indicate significant differences between groups (p < 0.05), and the same letters indicate insignificant differences between groups (p > 0.05). The results showed that the antioxidant capacity of fermented walnut milk did not change significantly with the extension of storage time, indicating that fermented milk has good antioxidant capacity. On the 21st day, the DPPH free radical, ABTS+ free radical, -OH free radical scavenging rates and Fe2+ chelating capacity were still able to reach 65.85%, 43.15%, 72.67%, and 70.29%, respectively.
[0099] Under the same other conditions, the traditional starter (Lactobacillus bulgaricus and Streptococcus thermophilus 1:1) was used to replace Lactobacillus plantarum JLAU103 to ferment walnut yogurt. The DPPH free radical, ABTS+ free radical, -OH free radical scavenging rate and Fe 2+ Chelating ability, results such as Figure 17 As shown, different letters indicate significant differences between groups (p<0.05), and the same letters indicate no significant differences between groups (p>0.05). The results showed that with the extension of storage time, the antioxidant capacity of fermented walnut milk decreased significantly, and the scavenging rates of DPPH free radicals, ABTS+ free radicals, -OH free radicals and Fe 2+ The chelating capacity was consistently lower than that of walnut yogurt fermented with Lactobacillus plantarum.
[0100] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. Probiotic fermented walnut yogurt with stable antioxidant function, characterized in that: The following raw materials in weight percentage are used: 60-80% fresh milk, 20-40% walnut pulp, 2-4% production starter and 4-8% white sugar, which are sterilized, fermented and refrigerated to obtain the product. The production starter uses domesticated Lactobacillus plantarum JLAU103, whose viable cell count is 9.2×10 9 CFU / ml.
2. The probiotic fermented walnut yogurt with stable antioxidant function according to claim 1, characterized in that Described plant lactobacillus JLAU103 acclimation method comprises: (1) Activation of bacterial strains: Take 1 mL of Lactobacillus plantarum JLAU103 and spread it on MRS solid medium with a spreader. After 48 hours of incubation at 37°C, pick a single colony and place it in MRS liquid medium. Incubate it at 37°C for 24 hours, take 2% (v / v) of the culture medium, repeat twice, wash the bacterial sludge with sterile water, and adjust the bacterial solution OD value to 1 at 600 nm using a UV spectrophotometer for subsequent experiments. (2) Domestication of the strain: The strain was gradually domesticated. 5% plantarum Lactobacillus JLAU103 with an OD value of 1 was inoculated into fresh milk and fermented at 37°C for 10 hours to obtain the first-level strain; the first-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 2:8 and fermented at 37°C for 6 hours to obtain the second-level strain; the second-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 3:7 and fermented at 37°C for 6 hours to obtain the third-level strain; the third-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 4:6 and fermented at 37°C for 6 hours to obtain the fourth-level strain; the fourth-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 5:5 and fermented at 37°C for 6 hours to obtain the production starter.
3. The probiotic fermented walnut yogurt with stable antioxidant function according to claim 1, characterized in that The preparation method of the walnut pulp comprises: selecting full walnut kernels without mildew, soaking the walnut kernels with skin in a 2% anhydrous sodium carbonate solution at 75°C for 15 minutes, washing and peeling the walnut kernels with high pressure water, draining the water after washing, baking at 90°C for 1.5 hours, and then beating the walnut kernels with water in a mass ratio of 1:4, and filtering the walnut kernels with skin through a 120-mesh sieve after beating.
4. The probiotic fermented walnut yogurt with stable antioxidant function according to claim 1, characterized in that The raw material addition amounts are: 37.7% walnut pulp, 3.1% production starter, 6.4% white sugar, the fermentation temperature is 39.9° C., and the fermentation time is 8.1 h.
5. The method for preparing the probiotic fermented walnut yogurt with stable antioxidant function according to claim 1, characterized in that: The following steps are involved: S1. Preparation of fermentation liquid Mix fresh milk and walnut pulp in a mass ratio of 8:2-6:4, add 4-8% white sugar, preheat to 55°C, and homogenize at 55°C with a homogenization pressure of 25 MPa for 5 minutes. S2. Sterilization of liquid The homogenized fermentation liquid was pasteurized at 90°C for 15 minutes and cooled to room temperature before use. S3. Inoculation and Fermentation The cooled fermentation liquid was inoculated with 2-4% domesticated Lactobacillus plantarum JLAU103, mixed evenly and fermented at 39-41°C for 7-9 hours. The fermented walnut yogurt was placed at 4°C for 12 hours for refrigeration and ripening to obtain a probiotic fermented walnut yogurt with stable antioxidant function.
6. The method for preparing the probiotic fermented walnut yogurt with stable antioxidant function according to claim 5, characterized in that: The plant lactobacillus JLAU103 domestication method comprises: (1) Activation of bacterial strains: Take 1 mL of Lactobacillus plantarum JLAU103 and spread it on MRS solid medium with a spreader. After 48 hours of incubation at 37°C, pick a single colony and place it in MRS liquid medium. Incubate it at 37°C for 24 hours, take 2% (v / v) of the culture medium, repeat twice, wash the bacterial sludge with sterile water, and adjust the bacterial solution OD value to 1 at 600 nm using a UV spectrophotometer for subsequent experiments. (2) Domestication of the strain: The strain was gradually domesticated. 5% plantarum Lactobacillus JLAU103 with an OD value of 1 was inoculated into fresh milk and fermented at 37°C for 10 hours to obtain the first-level strain; the first-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 2:8 and fermented at 37°C for 6 hours to obtain the second-level strain; the second-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 3:7 and fermented at 37°C for 6 hours to obtain the third-level strain; the third-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 4:6 and fermented at 37°C for 6 hours to obtain the fourth-level strain; the fourth-level strain was inoculated into a mixture of walnut pulp and fresh milk in a ratio of 5:5 and fermented at 37°C for 6 hours to obtain the production starter.
7. The method for preparing the probiotic fermented walnut yogurt with stable antioxidant function according to claim 5, characterized in that: The preparation method of the walnut pulp comprises: selecting full walnut kernels without mildew, soaking the walnut kernels with skin in a 2% anhydrous sodium carbonate solution at 75°C for 15 minutes, washing and peeling the walnut kernels with high pressure water, draining the water after washing, baking at 90°C for 1.5 hours, and then beating the walnut kernels with water in a mass ratio of 1:4, and filtering the walnut kernels with skin through a 120-mesh sieve after beating.
8. The probiotic fermented walnut yogurt with stable antioxidant function according to claim 5, characterized in that The raw material addition amounts are: 37.7% walnut pulp, 3.1% production starter, 6.4% white sugar, the fermentation temperature is 39.9° C., and the fermentation time is 8.1 h.