Phytobacterium plantarum grx21 and application thereof in preparation of probiotic soybean milk custard sauce

Abstract

The invention discloses a plant lactobacillus grx21 and application thereof in preparation of probiotic soybean milk custard sauce, the plant lactobacillus grx21 is preserved in China General Microbiological Culture Collection Center (CGMCC), the preservation number is CGMCC No.36270, the preservation date is October 20, 2025, the suggested classification name is Lactiplantarum, the preservation number is CGMCC No.36270, the preservation number is CGMCC No.36270, the preservation number is CGMCC No.36270, the suggested classification name is Lactiplantarum, the preservation number is CGMCC No.36270, the preservation number is CGMCC No.36270, and the preservation number is CGMCC No.36270. The preservation address is Institute of Microbiology, Chinese Academy of Sciences, No.3, No.1 Yard, Beichen West Road, Chaoyang District, Beijing. The soybean milk and the fermented soybean milk are used for replacing traditional cow milk protein in the production process, and the obtained product is unique in flavor, rich in soybean flavor, soft and mellow, fine and smooth in taste, high in nutritive value, easy to absorb and more suitable for the eating habit of Asian people.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microorganisms and food fermentation, and particularly relates to Lactiplantibacillus plantarum grx21 and application thereof in preparation of probiotic soybean milk creme. BACKGROUND

[0002] Creme is called a universal sauce in the baking industry, which is a perfect combination of eggs, milk and sugar, and is widely used for decoration, filling and dipping sauce of cakes and breads. Traditional creme is mainly made of animal protein (whey protein, whole milk powder, etc.), which has a smooth taste and delicate body. However, the content of cholesterol and saturated fatty acids in animal protein is also high, and some people may have lactose intolerance after eating. In addition, the extensive use of animal protein also increases the impact of animal breeding on the environment, increases ecological pressure and causes environmental pollution.

[0003] Fermented soy milk is a fermented product with certain acidity, which is made of soy milk as the main raw material and added with lactic acid bacteria for fermentation. Lactic acid bacteria fermentation can also degrade anti-nutritional factors such as phytic acid, condensed tannin and trypsin inhibitor in soybeans, relieve the soybean odor, and decompose proteins to produce various amino acids and polypeptides, thereby improving the digestive absorption rate. SUMMARY

[0004] This section aims to summarize some aspects of the embodiments of the application and briefly introduce some preferred embodiments.

[0005] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0006] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a Lactiplantibacillus plantarum L.plantarum grx21, which is preserved in the China General Microbiological Culture Collection Center, with a preservation number of CGMCC No.36270, a preservation date of October 20, 2025, a recommended classification name of Lactiplantibacillus plantarum, and a preservation address of No.3, Institute of Microbiology, Chinese Academy of Sciences, Beijing City, Chaoyang District, Beichen West Road 1st Courtyard.

[0007] As a preferred scheme of the Lactobacillus plantarum provided in the application, the fermented soy milk has a pH of 4.51, a viable bacterial count of 9.25 log (CFU / ml), a survival rate of 43.36% at 65 DEG C, and a ꞵ-GC enzyme activity of 5.78 U / mL, and has good acid production characteristics, heat resistance and strong activity for inhibiting bacteria. In comparison, the commonly commercially available Lactobacillus plantarum has poor stability and low acid production efficiency when applied to soy milk caviar, while the L. plantarum grx21 has good acid production characteristics, heat resistance and strong activity for inhibiting bacteria.

[0008] A further object of the present application is to overcome the deficiencies in the prior art and provide an application of Lactobacillus plantarum in the preparation of probiotic soy milk caviar.

[0009] As a preferred scheme of the application, the application comprises,

[0010] Strain activation: L. plantarum grx21 preserved with glycerol is inoculated into a liquid culture medium, streaked and purified, and single colonies are picked and activated for 3 times in succession;

[0011] Preparation of fermented soy milk: the strain is inoculated into 12% soy milk at a mass ratio of 3%, and fermented at 37 DEG C until the pH is 4.5 to obtain lactic acid bacteria fermented soy milk;

[0012] Mixing and dissolving: egg, corn starch and white granulated sugar are mixed, beaten and sieved to obtain a prepared liquid;

[0013] Heating and gelatinization: the soy milk is boiled, cooled, and the prepared liquid is added in portions, heated and stirred until a viscous state is reached, butter is added and stirred until uniform, and placed in a refrigerator for cold storage and cooling for 1 h;

[0014] The probiotic fermented soy milk is added and stirred until uniform to obtain probiotic soy milk caviar.

[0015] As a preferred scheme of the application, the soy milk is 50 parts, the corn starch is 3-5 parts, the white granulated sugar is 5-10 parts, the egg is 5-10 parts, the butter is 3-5 parts, and the probiotic fermented soy milk is 20-25 parts by weight.

[0016] As a preferred scheme of the application, the temperature of the heating and stirring is 90-95 DEG C, and the stirring time is 10-15 minutes.

[0017] As a preferred scheme of the application, the temperature after cooling is 70-80 DEG C.

[0018] As a preferred scheme of the application, the temperature after cold storage and cooling in the refrigerator is 4-10 DEG C.

[0019] The present application has the following advantages:

[0020] (1) The L. plantarum grx21 provided by the present application is preserved in the China General Microbiological Culture Collection Center, with a preservation number of CGMCC No. 36270 and a preservation date of October 20, 2025. The recommended classification name is Lactiplantibacillus plantarum, and the preservation address is No. 3, Institute of Microbiology, Chinese Academy of Sciences, Beijing Chaoyang District, Beichen West Road 1st Courtyard. When applied to the preparation of soy milk caviar sauce process, the product has a unique flavor, rich soy flavor, dense and mellow taste, and smooth and delicate taste.

[0021] (2) The soy milk flavored caviar sauce and the preparation method thereof provided by the present application use soy milk and fermented soy milk to replace traditional milk protein in production, resulting in a product with a unique flavor, rich soy flavor, dense and mellow taste, and smooth and delicate taste. At the same time, it has high nutritional value, is easy to absorb, and is more suitable for the eating habits of Asians.

[0022] (3) The caviar sauce produced by the present application has a simple operation process, stable product quality, and is suitable for industrialized production.

[0023] (4) The plant protein content of the present application is high, which is more in line with the current global trend of popular and advocated healthy and natural ingredients. It can effectively reduce the dependence on animal protein and reduce the damage of animal husbandry to the ecological environment. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0025] Figure 1 The flow curve diagram of the probiotic soy milk caviar sauce in the embodiment of the present application.

[0026] Figure 2 The storage modulus diagram of the probiotic soy milk caviar sauce in the embodiment of the present application.

[0027] Figure 3 The loss modulus diagram of the probiotic soy milk caviar sauce in the embodiment of the present application.

[0028] Figure 4 The sensory evaluation diagram of the probiotic soy milk caviar sauce in the embodiment of the present application.

[0029] Figure 5 This is a graph showing the dehydration shrinkage value of probiotic soy milk custard sauce in an embodiment of the present invention. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Example 1

[0032] Preparation method of Lactobacillus plantarum:

[0033] This invention uses a plate coating separation method to screen lactic acid bacteria in naturally fermented sourdough samples collected in Yangzhou.

[0034] By measuring indicators such as acid production capacity, viable bacteria count, and antibacterial ability of lactic acid bacteria fermenting soy milk, strains of lactic acid bacteria with high acid production and strong activity were screened for fermenting soy milk.

[0035] 1. Isolation of lactic acid bacteria

[0036] The strain of this invention is a fermentable soy milk-producing Lactobacillus plantarum, which was screened by the inventors from a naturally fermented sourdough sample collected in Yangzhou. It was identified as belonging to Lactiplantibacillus plantarum and named grx21. This strain was deposited at the China General Microbiological Culture Collection Center (CGMCC) before the application date of this invention, with accession number CGMCC No. 36270, and the deposit date is October 20, 2025. The suggested classification name is Lactiplantibacillus plantarum. The deposit address is: Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing.

[0037] 2. Acid production characteristics, growth characteristics, heat resistance, antibacterial ability, and β-GC enzyme activity of lactic acid bacteria in soy milk.

[0038] 2.1 Acid-producing characteristics of lactic acid bacteria in soy milk

[0039] Different lactic acid bacteria have different fermentation times and acid-producing abilities in soy milk. Compared with cow's milk, soy milk lacks the carbon sources such as glucose and lactose required for the growth of lactic acid bacteria. Therefore, some lactic acid bacteria cannot grow well in soy milk, nor can they cause soy milk to curdle.

[0040] Experimental conditions for acid production characteristics test: pH value of fermented soybean milk was measured at different time periods (0-12 h) using a pH meter.

[0041] With pH 4.5 as the fermentation endpoint, the coagulation time of fermented soy milk ranged from 8 to 12 hours. Eight strains with poor acid-producing ability in soy milk (LP-17, LP-34, LP-51, LP-52, LP-61, LP-63, LP-68, LP-70) were screened out, and the growth ability of the remaining 21 lactic acid bacteria in soy milk was determined.

[0042] Table 1. pH changes of different lactic acid bacteria during soy milk fermentation.

[0043]

[0044] 2.2 Growth characteristics of lactic acid bacteria in soy milk

[0045] Tests on the growth characteristics of lactic acid bacteria in soy milk: The determination of viable bacteria count was based on GB4789.35-2016 "National Food Safety Standard - Microbiological Examination of Food - Lactic Acid Bacteria Examination".

[0046] As shown in Table 2, the viable bacterial count of all fermented soy milk samples reached above 8.0 Log CFU / mL, with 12 samples having viable bacterial counts between 9.0 and 10.0 Log CFU / mL. Among them, strain LP-23 had the highest viable bacterial count, at 10.08 Log CFU / mL.

[0047] Two strains (LP-20 and LP-32) with poor growth ability in soy milk were screened out by viable count, and the heat resistance of the remaining 19 lactic acid bacteria strains was determined.

[0048] Table 2. Changes in viable counts of different lactic acid bacteria during soy milk fermentation.

[0049]

[0050] 2.3 Heat resistance of different strains

[0051] Heat resistance test:

[0052] Water baths were set at 50℃, 55℃, 60℃, and 65℃. The second-generation stable fermentation broth was heated at each temperature for 30 minutes, then diluted to a suitable gradient. Viable cell counts were measured before and after heating. The survival rate (%) was calculated as follows: [Viable cell count before heating (CFU / mL) / Viable cell count after heating (CFU / mL)] * 100%

[0053] The optimal growth temperature for lactic acid bacteria is 30-37℃; temperatures above 50℃ can easily lead to the inactivation of the strains.

[0054] Furthermore, the higher the temperature, the faster the bacterial strain becomes inactive. Cell death caused by heat stress is generally considered to be caused by protein denaturation and aggregation at high temperatures. However, some lactic acid bacteria can enhance their survival ability under high-temperature environments by regulating the expression of their own genes to produce large amounts of heat shock proteins and by altering cellular physiological structures. Lactic acid bacteria with good heat resistance are more suitable for research related to heat stress, such as spray drying, and have greater application prospects.

[0055] Table 3 Survival rates of different strains at different temperatures

[0056]

[0057] Table 3 shows that the survival rate of all lactic acid bacteria decreased with increasing temperature. Strain LP-3 still maintained a relatively high survival rate of 43.36% at 65℃. Based on the survival rate, seven lactic acid bacteria strains with low survival rates (LP-7, LP-24, LP-36, LP-37, LP-40, LP-43, and LP-47) were removed, and the antibacterial activity of the remaining 12 strains was determined.

[0058] 2.4 Antibacterial ability of different strains

[0059] During fermentation, lactic acid bacteria can convert sugar into lactic acid and produce substances with antibacterial activity, such as hydrogen peroxide and bacteriocins, which can inhibit putrefactive bacteria and foodborne pathogens.

[0060] Testing the antibacterial ability of the strain:

[0061] The OD values ​​of second-generation cultures of Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Escherichia coli, and Salmonella were measured. 600 Adjust the pH to 0.5, then take 100 µL of pathogenic bacteria solution diluted 100 times and spread it evenly on LB solid medium. After punching wells on the plate, add 200 µL of second-generation strain culture medium to each well. Diffusion is carried out at 18℃ for 12 h until the fermentation broth is absorbed. Then, it is incubated at 37℃ for 24 h until inhibition zones appear. The antibacterial ability of the strain is compared by the diameter of the inhibition zones.

[0062] Table 4 shows that different strains exhibit varying inhibitory abilities against different pathogenic and putrefactive bacteria. Of the 12 strains, 5 strains showed inhibition zones greater than 20 mm against Staphylococcus aureus, 8 strains against Bacillus subtilis, 7 strains against Bacillus cereus, 11 strains against Escherichia coli, 12 strains against Salmonella, and 11 strains against Pseudomonas aeruginosa. Based on the size of the inhibition zones, 7 lactic acid bacteria strains with relatively poor overall inhibitory ability (LP-6, LP-9, LP-23, LP-27, LP-29, LP-30, and LP-46) were removed, and the enzyme activities of the remaining 5 strains were measured.

[0063] Table 4 Antibacterial properties of different strains

[0064]

[0065] 2.5 β-GC enzyme activity of different strains

[0066] β-GC can hydrolyze and utilize cellulose to synthesize functional oligosaccharides, that is, to convert poorly soluble cellulose into easily utilized small molecule oligosaccharides.

[0067] Test of β-GC enzyme activity of the strain: The test was performed using a β-GC activity assay kit. For specific steps, please refer to the kit instructions.

[0068] Table 5 shows that strain LP-3 had the highest β-GC enzyme activity, at 5.78 U / mL. Taking all factors into consideration, strain LP-3 was ultimately selected for subsequent experiments. LP-3 is *L. plantarum*, which was later renamed *L. plantarum grx21*. It is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36270, on October 20, 2025. The suggested classification name is *Lactiplantibacillus plantarum*, and the deposit address is: Institute of Microbiology, Chinese Academy of Sciences, No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing.

[0069] Table 5. β-GC enzyme activity assay of different strains

[0070]

[0071] Example 2

[0072] The custard sauce recipe table in this embodiment of the invention is shown in Table 6.

[0073] Table 6 Custard Sauce Recipe

[0074]

[0075] Preparation method of 15% probiotic soy milk custard:

[0076] (1) Preparation of lactic acid bacteria fermented soy milk:

[0077] Strain activation: L. plantarum grx21 preserved in glycerol tubes was inoculated into liquid culture medium, purified by streak plating, and single colonies were picked and activated three times consecutively.

[0078] Preparation of fermented soy milk: The strain was inoculated into 12% soy milk at a mass ratio of 3%, and fermented at 37℃ until the pH reached 4.5 to obtain lactic acid bacteria fermented soy milk.

[0079] (2) Preparation of probiotic soy milk custard sauce

[0080] Step 1, Mix and Dissolve: Mix eggs, cornstarch, and granulated sugar together, beat until smooth, and then sift.

[0081] Step 2, heating and gelatinization: After boiling the soy milk, cool it down and add the liquid prepared in Step 1 in several batches. Heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down.

[0082] Step 3: Take out the product from Step 2, add the above-mentioned weight of probiotic fermented soy milk, stir well, and you will get probiotic soy milk custard sauce.

[0083] Example 3

[0084] Preparation method of 25% probiotic soy milk custard:

[0085] (1) Preparation of lactic acid bacteria fermented soy milk:

[0086] Strain activation: L. plantarum grx21 preserved in glycerol tubes was inoculated into liquid culture medium, purified by streak plating, and single colonies were picked and activated three times consecutively.

[0087] Preparation of fermented soy milk: The strain was inoculated into 12% soy milk at a mass ratio of 3%, and fermented at 37℃ until the pH reached 4.5 to obtain lactic acid bacteria fermented soy milk.

[0088] (2) Preparation of probiotic soy milk custard sauce

[0089] Step 1, Mix and Dissolve: Mix eggs, cornstarch, and granulated sugar together, beat until smooth, and then sift.

[0090] Step 2, heating and gelatinization: After boiling the soy milk, cool it down and add the liquid prepared in Step 1 in several batches. Heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down.

[0091] Step 3: Take out the product from Step 2, add the above-mentioned weight of probiotic fermented soy milk, stir well, and you will get probiotic soy milk custard sauce.

[0092] Example 4

[0093] Preparation method of 35% probiotic soy milk custard:

[0094] (1) Preparation of lactic acid bacteria fermented soy milk:

[0095] Strain activation: L. plantarum grx21 preserved in glycerol tubes was inoculated into liquid culture medium, purified by streak plating, and single colonies were picked and activated three times consecutively.

[0096] Preparation of fermented soy milk: The strain was inoculated into 12% soy milk at a mass ratio of 3%, and fermented at 37℃ until the pH reached 4.5 to obtain lactic acid bacteria fermented soy milk.

[0097] (2) Preparation of probiotic soy milk custard sauce

[0098] Step 1, Mix and Dissolve: Mix eggs, cornstarch, and granulated sugar together, beat until smooth, and then sift.

[0099] Step 2, heating and gelatinization: After boiling the soy milk, cool it down and add the liquid prepared in Step 1 in several batches. Heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down.

[0100] Step 3: Take out the product from Step 2, add the above-mentioned weight of probiotic fermented soy milk, stir well, and you will get probiotic soy milk custard sauce.

[0101] Example 5

[0102] Preparation method of 45% probiotic soy milk custard:

[0103] (1) Preparation of lactic acid bacteria fermented soy milk:

[0104] Strain activation: L. plantarum grx21 preserved in glycerol tubes was inoculated into liquid culture medium, purified by streak plating, and single colonies were picked and activated three times consecutively.

[0105] Preparation of fermented soy milk: The strain was inoculated into 12% soy milk at a mass ratio of 3%, and fermented at 37℃ until the pH reached 4.5 to obtain lactic acid bacteria fermented soy milk.

[0106] (2) Preparation of probiotic soy milk custard sauce

[0107] Step 1, Mix and Dissolve: Mix eggs, cornstarch, and granulated sugar together, beat until smooth, and then sift.

[0108] Step 2, heating and gelatinization: After boiling the soy milk, cool it down and add the liquid prepared in Step 1 in several batches. Heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down.

[0109] Step 3: Take out the product from Step 2, add the above-mentioned weight of probiotic fermented soy milk, stir well, and you will get probiotic soy milk custard sauce.

[0110] Comparative Example 1

[0111] (1) Preparation of milk custard

[0112] Step 1, Mix and Dissolve: Mix eggs, cornstarch, and granulated sugar together, beat until smooth, and then sift.

[0113] Step 2, heating and gelatinization: Boil the milk and then cool it down. Quickly add the liquid prepared in Step 1 in several batches, heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down. Stir well to get the milk custard sauce.

[0114] Comparative Example 2

[0115] (1) Preparation of soy milk custard sauce

[0116] Step 1, Mix and Dissolve: Mix eggs, cornstarch, and granulated sugar together, beat until smooth, and then sift.

[0117] Step 2, heating and gelatinization: After boiling the soy milk, cool it down and add the liquid prepared in Step 1 in several batches. Heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down. Stir well to get soy milk custard sauce.

[0118] Experiment 1: Determination of Dynamic Rheological Properties

[0119] The static (apparent viscosity) and dynamic (frequency scanning) rheological properties of the custard sauce samples were measured using a rheometer. Apparent viscosity: The temperature was kept constant at 25℃, and the shear rate was set from 0 to 100 s⁻¹. -1 The rate change is 1 s -1 The change in the apparent viscosity of the sample is measured to determine the fluid type.

[0120] Frequency scanning: A 40 mm flat plate was selected as the fixture, the measurement gap was 2 mm, the temperature was fixed at 25℃, and the frequency range was 0.1~10Hz. The changes of energy storage modulus G' and loss modulus G” with the oscillation frequency were measured.

[0121] Experiment 2: Determination of textural properties:

[0122] Using a P 0.5 probe, the speed before the test was 1.00 mm / s, the speed during the test was 1.00 mm / s, the speed after the test was 10.00 mm / s, the distance was 10.00 mm, the trigger force was 3.0 g, and the test was repeated three times.

[0123] Experiment 3 Baking resistance test:

[0124] Take a round piece of baking parchment paper with a diameter of 29 mm, weigh out 6.2 g of custard sauce and fill the entire surface. Set the oven temperature to 180℃ for the bottom heat and 200℃ for the top heat, and bake for 20 minutes. Measure the bottom surface area of ​​the custard sauce after baking and calculate its baking resistance using the formula: Baking Resistance Formula:

[0125]

[0126] In the formula, W represents the baking resistance (%), S0 represents the bottom area of ​​the sauce before baking (mm²), and S1 represents the bottom area of ​​the sauce after baking (mm²).

[0127] Experiment 4: Measurement of colorimetric values:

[0128] Weigh 10 g of custard sauce sample, wrap it in transparent plastic wrap, and use a colorimeter to determine its color by measuring reflected light. Select a window size of 25 mm and measure the L*, a*, and b* values.

[0129] Experiment 5 Sensory evaluation measurement:

[0130] Ten students majoring in Food Science and Engineering were selected. All were non-smokers, aged 18-22, including five women and five men. Before scoring, they received standardized training and assessment on the descriptive aspects of custard sauce. A 9-point scale was used, with 1 representing the lowest score and 9 representing the highest. The scoring criteria are shown in Table 7.

[0131] Table 7 Sensory Scoring Criteria for Custard Sauce

[0132]

[0133] Experiment 6: Determination of the stability of custard sauce:

[0134] Place 25 g of sample in a centrifuge tube and store in a 4°C freezer for 7 days. Then centrifuge at 6300 × g for 30 min in a high-speed refrigerated centrifuge. Pour off the supernatant water and weigh the residue. Calculate the dehydration shrinkage value of the sample using the following formula:

[0135]

[0136] In the formula: M1 is the weight of the precipitated water, g; M2 is the total weight of the sample before centrifugation, g.

[0137] The probiotic soy milk custard sauces prepared in Examples 2-5 and Comparative Examples 1-2 of this invention were compared with pure milk, soy milk, and fermented soy milk custard sauces with different amounts of added probiotics in a series of tests, including sensory quality, texture, and stability. The results are as follows:

[0138] See the flow curve of probiotic soy milk custard sauce. Figure 1 ,like Figure 1 As shown, the apparent viscosity of probiotic-enriched soy milk custard sauce, compared to the control group (milk and soy milk), decreased significantly with increasing shear rate. When the shear rate exceeded 40 s⁻¹, the apparent viscosity stabilized. The soy milk group exhibited the highest apparent viscosity, while the apparent viscosity at 25% was similar to that of the milk group. Furthermore, the apparent viscosity decreased with increasing addition amount. In conclusion, the 25% group showed the best apparent viscosity.

[0139] For the energy storage modulus of probiotic soy milk custard sauce, please refer to [reference needed]. Figure 2 For the loss modulus of probiotic soy milk custard sauce, please refer to [reference needed]. Figure 3 ,like Figure 2 , Figure 3 As shown, throughout the entire testing frequency range, the storage modulus (G') and loss modulus (G") of all four groups of samples increased, with G' > G" being a typical characteristic of gels. Custard sauce exhibits a higher elasticity than viscous content, displaying solid-like properties. This is because high-protein ingredients such as eggs and milk were added during the production process. The proteins denatured upon heating, and when the temperature rose to a certain level, the expanded protein molecules re-aggregated, forming a gel. The custard sauce with added lactic acid bacteria-fermented soy milk showed significantly higher G' and G" values ​​than the milk group (p < 0.05), but lower than the soy milk group. Soluble polysaccharides, extracellular polysaccharides, and organic acids in fermented soy milk can reduce the G' and G" values ​​of the custard sauce. Furthermore, the soy milk-based custard sauce itself has a high soy protein content, leading to increased viscoelasticity and a poorer texture. The addition of lactic acid bacteria-fermented soy milk can improve the rheological properties of the custard sauce.

[0140] Table 8. Texture and baking resistance of probiotic soy milk custard sauce

[0141]

[0142] According to the results in Table 8, the addition of lactic acid bacteria to fermented soy milk significantly improved the viscosity and cohesiveness of custard sauce compared to the soy milk group (p<0.05). The increase in the amount of added soy milk began to dilute the custard sauce itself based on soy milk, and the 25% addition amount did not show a significant difference in texture characteristics compared to the milk group (p>0.05).

[0143] Among the 15%–45% lactic acid bacteria fermented soy milk additions, the baking tolerance is affected by the moisture content of the custard itself. The baking tolerance of the milk group is the same as that of the 25%–35% addition range. Because lactic acid bacteria fermented soy milk is acidic, the pH value of the custard decreases continuously with increasing dosage. Taking all factors into account, a 25% addition of lactic acid bacteria fermented soy milk is most suitable for making probiotic soy milk custard.

[0144] Table 9 Color difference values ​​of probiotic soy milk custard sauce

[0145]

[0146] Based on the color difference measurement results in Table 9, the soy milk custard sauce has the lowest L* (brightness) value. This is because soy milk has a high plant protein content, making it more prone to caramelization and Maillard reactions with white sugar during heating, producing dark brown substances that affect the product's color. Adding fermented soy milk significantly improves this. There is no significant difference in the a* value between the soy milk group and the custard sauce with added fermented soy milk, indicating that the soy milk group has little green bias. There is a significant difference in the b* value between the soy milk group and the custard sauce with added fermented soy milk; as the amount added increases, the b* value continuously decreases, indicating a less pronounced yellow hue.

[0147] See sensory evaluation results. Figure 4 The study found that the 25% probiotic soy milk custard had the best sensory quality, similar to the milk group. Besides similar color and spreadability, it also showed better firmness and texture. This is because adding fermented soy milk enriches the flavor and texture of the soy milk, reduces the beany taste, and the extracellular polysaccharides produced by lactic acid bacteria fermentation have water-retention properties, increasing moisture and improving the product's sensory quality. However, adding too much would lower the pH of the custard due to the acidity of the fermented soy milk, thus reducing the sensory score. Based on the comprehensive sensory quality analysis of the four aspects, the 25% group not only had good taste and color but also better firmness and texture, which is consistent with the test results in Table 8.

[0148] Dehydration shrinkage is a spontaneous release of moisture in refrigerated products like custard, and it's an important indicator of product storage stability; the lower the value, the better the sample's stability. Figure 5 It can be seen that in this experiment, there was no significant difference in the stability of custard sauce without fermented soy milk (p>0.05). However, there were significant differences in the dehydration shrinkage values ​​of the four groups of probiotic soy milk custard sauce (p<0.05), with 15-25% showing the best results. This is because the addition of lactic acid bacteria to fermented soy milk results in a certain water content and probiotic activity, thus leading to slightly lower refrigeration stability. Furthermore, custard sauce with high protein content is highly susceptible to denaturation during frozen storage. Denaturation causes its structure to expand, leading to increased water loss and a decline in quality. Therefore, its storage stability is somewhat lower compared to the milk and soy milk groups.

[0149] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. Lactiplantibacillus plantarum grx21, deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36270, deposited on October 20, 2025. The proposed classification name is Lactiplantibacillus plantarum. The deposit address is Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing.

2. The *Lactobacillus plantarum* as described in claim 1, characterized in that: The fermented soy milk had a pH of 4.51 and a viable count of 9.25 log (CFU / ml) at 10 h, a survival rate of 43.36% at 65℃, and a GC-enzyme activity of 5.78 U / mL.

3. The application of *Lactobacillus plantarum* as described in claim 1 or 2 in the preparation of probiotic soy milk custard.

4. The application as described in claim 3, characterized in that: include, Strain activation: L. plantarum grx21 preserved in glycerol tubes was inoculated into liquid culture medium, purified by streak plating, and single colonies were picked and activated three times consecutively. Preparation of fermented soy milk: The strain was inoculated into 12% soy milk at a mass ratio of 3%, and fermented at 37℃ until the pH reached 4.5 to obtain lactic acid bacteria fermented soy milk; Mix and dissolve: Mix eggs, cornstarch, and granulated sugar, beat until smooth, and sift to obtain the prepared liquid; Heat and gelatinize: Boil the soy milk and then cool it down. Quickly add it to the prepared liquid in batches, heat and stir until it becomes thick. Add the butter and stir well. Refrigerate for 1 hour to cool down. Add probiotic fermented soy milk and stir well to make probiotic soy milk custard.

5. The application as described in claim 4, characterized in that: By weight, the ingredients are: 50 parts soy milk, 3-5 parts corn starch, 5-10 parts white sugar, 5-10 parts eggs, 3-5 parts butter, and 20-25 parts probiotic fermented soy milk.

6. The application as described in claim 4, characterized in that: The heating and stirring temperature is 90-95℃, and the stirring time is 10-15 minutes.

7. The application as described in claim 4, characterized in that: The temperature after cooling is 70-80℃.

8. The application as described in claim 4, characterized in that: The temperature after the refrigerator is cooled down is 4~10℃.

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