Bifidobacterium longum SRU-1 with both bile salt hydrolase activity and alpha-glucosidase inhibitor activity and culture method thereof

Abstract

This invention discloses a strain of *Bifidobacterium longum* SRU-1, possessing both bile salt hydrolase activity and α-glucosidase inhibitory activity, with accession number CGMCC No. 36397. This strain was isolated from infant feces and identified as *Bifidobacterium longum* through morphological and molecular biological analysis. It exhibits excellent acid and bile salt tolerance, is non-hemolytic, and demonstrates superior self-aggregation and hydrophobicity. It can scavenge DPPH free radicals and possesses potential for lowering cholesterol and assisting in blood sugar control. This invention also provides its culture method; optimizing the culture medium can significantly increase the bacterial density, with the viable cell count reaching 1.34 × 10⁻⁶ when 20% prickly pear juice is added. 11 The concentration of CFU / mL is 5.8 times that of TPY medium. This strain can be used to ferment yogurt, producing a product with an acidity of 100°T-110°T and pH 4.4, excellent water retention, and combining the functions of probiotics with the nutritional advantages of prickly pear. It fills the technological gap in prickly pear multifunctional yogurt and is suitable for industrial food production.

Description

Technical Field

[0001] This invention belongs to the field of microbial technology, specifically relating to a strain of Bifidobacterium longum SRU-1 that possesses both bile salt hydrolase activity and α-glucosidase inhibitory activity, and its culture method. Background Technology

[0002] Bifidobacterium longum, as a classic strain in the field of probiotics, has clear safety qualifications and a solid foundation for application: it is not only included in the Qualified Presumption of Safety (QPS) list by the European Food Safety Authority (EFSA) and listed as a Generally Recognized As Safe (GRAS) substance by the U.S. Food and Drug Administration (FDA), but it also meets the requirements of my country's food industry standards and is included in the "List of Microbial Strains that Can Be Used in Food" and the "List of Microbial Strains that Can Be Used in Infant Food". It has the legal safety and compliance foundation for application in the food field, providing a core prerequisite for its industrial application in fermented foods.

[0003] From a functional perspective, the probiotic effects of *Bifidobacterium longum* are highly correlated with its intestinal colonization ability and metabolic activity. Among these, acid and bile salt tolerance are key indicators for the strain's ability to withstand extreme gastrointestinal environments and maintain its viability. Self-aggregation ability and cell hydrophobicity directly determine its efficiency in adhering to the host's intestinal epithelial tissue, forming an important basis for the interaction between the gut microbiota and the host. Furthermore, the bile salt hydrolase carried by this strain can catalyze the hydrolysis of bound bile salts into free bile salts, which then combine with cholesterol in the body to form soluble complexes and are excreted during metabolism, thus achieving a cholesterol-lowering effect. Its secreted α-glucosidase inhibitor can inhibit the activity of α-glucosidase on the intestinal mucosa, reducing the rate of glucose absorption in the intestine and effectively delaying postprandial blood glucose rise, demonstrating significant application potential in the field of metabolic health regulation.

[0004] Yogurt, as a core category of fermented dairy products, is made from cow's or goat's milk through lactic acid bacteria fermentation. It boasts both rich nutritional value and health benefits, and its quality and taste directly impact its market competitiveness. However, current yogurts fermented with a single strain of bacteria suffer from limited functional dimensions, failing to meet the diverse health needs of consumers. Furthermore, the homogenization of flavors in some products restricts innovation within the industry.

[0005] As a unique fruit and vegetable with both medicinal and edible properties, prickly pear is rich in vitamin C, phenolic compounds (flavonoids such as quercetin and rutin), polysaccharides, and superoxide dismutase (SOD), among other highly active ingredients. Its nutritional value and health potential highly align with the nutritional upgrade needs under the "Healthy China" strategy. However, prickly pear itself has a unique sour, astringent, and bitter flavor, making it less acceptable for direct consumption. Furthermore, existing processing methods struggle to fully preserve its active nutrients, resulting in its high added value not being fully realized and limiting its large-scale application in functional foods.

[0006] Currently, market development of prickly pear mainly focuses on primary products such as pulp and juice. The technology for combining prickly pear with Bifidobacterium longum to prepare compound fermented yogurt remains undeveloped. If the metabolic health-regulating function of Bifidobacterium longum can be combined with the highly active nutrients of prickly pear, and their synergistic effect can be achieved through optimized fermentation processes, it would not only improve the palatability of prickly pear but also enrich the nutritional dimensions and functional properties of yogurt. This would fill the market gap for compound fermented yogurt with cholesterol-lowering and blood sugar-controlling effects, while simultaneously promoting the high-value utilization of prickly pear resources, possessing significant industrial value and market prospects.

[0007] Therefore, there is an urgent need in this field for a novel Bifidobacterium longum that can be used in yogurt production. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention provides a Bifidobacterium longum SRU-1 with certain acid resistance, bile salt resistance, free radical scavenging ability (DPPH scavenging rate), bile salt hydrolase activity and α-glucosidase inhibitory activity.

[0009] On the one hand, the present invention provides a Bifidobacterium longum SRU-1, which was deposited on October 29, 2025 at the China General Microbiological Culture Collection Center (CGMCC, address: No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing), with accession number CGMCC No. 36397 and classified as Bifidobacterium longum.

[0010] On the one hand, the present invention provides the use of the aforementioned Bifidobacterium longum SRU-1 in the preparation of drugs that lower cholesterol, lower blood sugar and / or promote gastrointestinal digestion.

[0011] On the one hand, the present invention provides the application of the aforementioned Bifidobacterium longum SRU-1 in the preparation of fermented dairy products.

[0012] Specifically, the fermented dairy product is yogurt, with a fermentation endpoint pH of 4.0-4.5. Preferably, the yogurt has an acidity of 100°T-110°T and good water retention.

[0013] On one hand, the present invention provides a method for culturing Bifidobacterium longum SRU-1, wherein logarithmic phase Bifidobacterium longum is inoculated into a culture medium at a ratio of 1%-10%, wherein the culture medium is selected from any of the following:

[0014] (1) TPY basal medium containing any of the following components: soluble starch, glucose, mannitol, sucrose, FeSO4, MnSO4, CaCl2 or CuSO4;

[0015] (2) TPY liquid culture medium containing prickly pear juice;

[0016] Preferably, the inoculation rate is 2%-5%.

[0017] Specifically, the TPY basal culture medium includes hydrolyzed casein, soybean peptone, yeast extract, glucose, L-cysteine, dipotassium hydrogen phosphate, magnesium chloride, zinc sulfate, calcium chloride, ferric chloride, and Tween-80.

[0018] Specifically, the culture is carried out anaerobically at 37°C for 12-48 hours, preferably 24-36 hours.

[0019] Specifically, the prickly pear juice content in the TPY liquid culture medium is 0-100%, preferably 20%-60%.

[0020] Specifically, the prickly pear juice is added after being filtered through a 0.45μm filter membrane and then anaerobically cultured at 37℃ for 24-96 hours, preferably 48-72 hours.

[0021] On the other hand, the present invention also provides a method for preparing yogurt, comprising the following steps: first, sterilizing pure milk at high temperature, cooling it to 37-42°C, inoculating it with Bifidobacterium longum SRU-1, fermenting it at a constant temperature of 42°C until the pH reaches 4.0-4.5, stopping the fermentation, cooling it at 4°C, and allowing it to ripen for 12-24 hours. Preferably, the high-temperature sterilization is 95°C for 8-15 minutes. Preferably, the yogurt also contains prickly pear juice.

[0022] Specifically, the post-fermentation refers to the process of storing yogurt in a low-temperature environment (usually 2-6℃) for a period of time (generally 12-24 hours) after fermentation, so that the taste, texture, flavor and other aspects of the yogurt are further optimized and stabilized.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The Bifidobacterium longum SRU-1 obtained in this invention has good acid and bile salt resistance, DPPH removal ability, good self-aggregation and hydrophobicity, strong intestinal adhesion ability, stable probiotic effect, can pass through the gastrointestinal tract and colonize smoothly, has no hemolytic effect, is safe to eat, and at the same time has both bile salt hydrolase activity and α-glucosidase inhibitory activity, which can help reduce cholesterol and delay the rise of postprandial blood sugar.

[0025] (2) The strain Bifidobacterium longum SRU-1 obtained in this invention can be used to produce high-quality yogurt. The acidity of the yogurt produced is between 100°T and 110°T, pH 4.4, and the water holding capacity is close to that of yogurt products made with commercially available bacterial agents. It can also give yogurt the functions of lowering cholesterol and controlling blood sugar.

[0026] (3) The optimized culture medium raw materials of the present invention are readily available, low in cost, and simple to prepare. Combined with prickly pear juice, it can achieve high-density culture and greatly increase the number of viable bacteria, providing a new approach for food-grade large-scale culture.

[0027] (4) The *Bifidobacterium longum* SRU-1 strain obtained in this invention can survive in pure prickly pear juice, but the highest viable count (1.34) is achieved when the addition amount is 20%. 10 11 The CFU / mL concentration is 5.8 times that of TPY medium, which provides insights for expanding the culture medium for Bifidobacterium longum SRU-1 and applying prickly pear juice. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the colony morphology of Bifidobacterium longum SRU-1. The left side shows the colony morphology on TPY solid medium, and the right side shows the colony morphology on TPY solid medium containing X-Gal.

[0029] Figure 2 This is a microscopic image of Bifidobacterium longum SRU-1.

[0030] Figure 3 This is the PCR result of primer amplification of the target fragment.

[0031] Figure 4 This is a line graph showing the effect of bile salt concentration on colony growth, where a, b, c, and d represent the significance of the differences (P < 0.05).

[0032] Figure 5 The graph shows the effect of settling time on the self-aggregation ability of the strain, where b, c, and d represent the significance of the differences (P < 0.05).

[0033] Figure 6The images show the results of the SRU-1 hemolytic assay for Bifidobacterium longum. The left image shows the hemolytic assay results for Bifidobacterium longum, and the right image shows the hemolytic assay results for Staphylococcus aureus.

[0034] Figure 7 This is a plate graph showing the results of the bile salt hydrolase activity assay for Bifidobacterium longum SRU-1.

[0035] Figure 8 This is a schematic diagram of the growth curve and pH changes of Bifidobacterium longum SRU-1, with the growth curve on the left and the pH change on the right.

[0036] Figure 9 This is a schematic diagram showing the changes in the viable count of Bifidobacterium longum SRU-1 in liquid culture medium containing different proportions of prickly pear juice and TPY. The horizontal axis represents the ratio of TPY to prickly pear juice, and the horizontal axis represents the viable count.

[0037] Biological Preservation Information:

[0038] Bifidobacterium longum SRU-1 was deposited on October 29, 2025, at the China General Microbiological Culture Collection Center (CGMCC, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing), with accession number CGMCC No. 36397 and classified as Bifidobacterium longum. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result of the description. However, these embodiments are merely illustrative and do not constitute any limitation on the scope of protection defined by the claims of the present invention.

[0040] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that the upper and lower limits of the range and each intermediate value between them are specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0042] Example 1: Isolation and Identification of Bifidobacterium longum SRU-1

[0043] 1. Separation

[0044] Take infant fecal samples, serially dilute them, and spread 0.2 mL onto mupirocin lithium-modified MRS medium. Incubate anaerobically at 37°C for 48–72 h. Select smooth, intact, milky-white colonies and inoculate them onto TPY solid medium plates containing X-Gal. Incubate anaerobically at 37°C for 48 h. Incubate the plates aerobically at 37°C for about 30 min. Select colonies that turn blue, streak them, and select the largest single colony, which is the strain SRU-1 of this invention.

[0045] 2. Identification

[0046] (1) Colony morphology: Colonies were cultured anaerobically at 37℃ for 24 hours on TPY solid medium. The diameter was 1-2 mm. The colonies were round, smooth, moist, and milky white with neat, slightly raised edges. They appeared blue on TPY solid medium containing X-Gal (e.g., ...). Figure 1 As shown). Gram staining is positive (G+), and under a microscope, they appear as rod-shaped, chain-like structures (as shown). Figure 2 (As shown).

[0047] (2) Molecular biological identification: DNA was extracted from Bifidobacterium longum SRU-1 using the Ezup column-based bacterial genome extraction kit, and PCR amplification was performed using primers (27F: AGAGTTTGATCMTGGCTCAG 1492R: GGTTACCTTGTTACGACTTF) (see Figure 3 The gel electrophoresis conditions were 1.5% agarose gel, 1x TAE, 150 V, 100 mA, 20 min. The amplified products were then sequenced by Sangon Biotech (Shanghai) Co., Ltd. The 16S rDNA gene sequence was compared with known sequences in the NCBI database using BLAST software, and homology analysis was performed (see Table 1). The result identified it as *Bifidobacterium longum*, abbreviated as *Bifidobacterium longum* SRU-1, with its gene sequence shown in SEQ ID NO.1 and accession number CGMCC No. 36397.

[0048] Table 1. Homology of Bifidobacterium longum SRU-1

[0049]

[0050] Example 2: Detection of the probiotic capacity of Bifidobacterium longum SRU-1

[0051] 1. Acid resistance test

[0052] Preparation of simulated gastric juice (SGJ): 3 g / L pepsin was added to sterile saline (0.85%, w / v NaCl), and the pH was adjusted to 2 and 3 respectively using 1 mol HCl to obtain simulated gastric juice (SGJ).

[0053] Incubate at 37℃ for 18 hours until the viable cell count reaches 1. 10 9 CFU / mL of Bifidobacterium longum SRU-1 was inoculated into TPY medium containing SGJ (1:9V / V) and incubated at 37 ℃ for 1 and 2 h. The viable count was then calculated using the plate count method with gradient coefficients. TPY liquid medium served as the control group. In simulated gastric fluid at pH 2, the survival rate of Bifidobacterium longum SRU-1 was 76.91% after 1 h and 83.12% after 2 h. In simulated gastric fluid at pH 3, the survival rate was 78.21% after 1 h and 82.75% after 2 h. This indicates that Bifidobacterium longum SRU-1 has good acid resistance, as shown in Table 2.

[0054] Table 2. Effect of simulated gastric juice on the survival rate of Bifidobacterium longum SRU-1

[0055]

[0056] 2. Test for tolerance to bile salts

[0057] Incubate at 37℃ for 18 hours until the viable cell count reaches 1. 10 9 Bifidobacterium longum SRU-1 (CFU / mL) was inoculated into TPY liquid medium (1:9 V / V) containing 0.3%, 0.5%, and 0.7% (w / v) bile salts, and incubated at 37°C for 4 h. The medium was serially diluted, and viable counts were determined using the plate count method, with TPY liquid medium serving as the control group. The total colony count of Bifidobacterium longum SRU-1 in 0.3%, 0.5%, and 0.7% (w / v) bile salt-containing TPY liquid medium was 5.4–6.51 g (CFU / mL). Figure 4 As shown, bile salt tolerance is an important indicator of the survival ability of bacterial colonies in the gastrointestinal tract. Strong bile salt tolerance allows probiotics to function better in the gastrointestinal tract.

[0058] 3. Free radical clearance rate test

[0059] The fermentation broth of *Bifidobacterium longum* cultured at 37℃ for 18 h was centrifuged at 12000 rpm for 10 min at 4℃, and the supernatant was collected. 0.5 mL of the supernatant filtered through a 0.22 μm membrane was added to 1 mL of 0.1 mmol / L DPPH ethanol solution and 1.5 mL of 40% ethanol, shaken well, and allowed to stand in the dark for 30 min. The absorbance was measured at 517 nm. Anhydrous ethanol was used instead of DPPH solution, with all other parameters remaining the same, as a blank group. 40% ethanol was used instead of the sample solution, with all other parameters remaining the same, as a control group. The calculation showed that the fermentation supernatant of *Bifidobacterium longum* SRU-1 scavenged 56.39% ± 0.30% of DPPH free radicals.

[0060] 4. Self-cohesion test

[0061] Bifidobacterium longum SRU-1 was inoculated into the culture medium at a 5% inoculum size and cultured at 37℃ for 16 h. The cells were collected by centrifugation at 5000 r / min for 15 min, washed twice with sterile PBS buffer (pH=6.8), and the precipitate was resuspended in buffer. The buffer was used as a blank control. The cell concentration was adjusted with buffer to an initial absorbance of approximately 1 at 600 nm. A suitable amount of bacterial suspension was placed in test tubes and allowed to stand for 1 h, 24 h, and 48 h. The absorbance of the supernatant (1 mL) was measured. Using the initial absorbance as a reference, the self-aggregation capacity of the strain was calculated. Results are as follows: Figure 5 As shown, the self-cohesion of Bifidobacterium longum SRU-1 increased with time, especially at 24h, when the supernatant was clear and the self-cohesion reached 78.53%, and at 48h it reached 81.25%, indicating that the strain has good self-cohesion, which lays a good foundation for its interaction with intestinal epithelial cells.

[0062] 5. Hydrophobicity test

[0063] Bifidobacterium longum SRU-1 was inoculated into the culture medium at a 5% inoculum and cultured at 37℃ for 16 h. The cells were collected by centrifugation at 5000 r / min for 15 min, washed twice with sterile PBS buffer (pH=6.8), and the precipitate was resuspended in buffer. The buffer was used as a blank control. The cell concentration was adjusted with buffer to an initial absorbance of approximately 1 at 600 nm. 4 mL of the adjusted bacterial solution was taken, 0.8 mL of chloroform was added, and the mixture was vortexed at high speed for 2 min. After standing for 10 min, the layers separated, and the absorbance at 600 nm was measured. Using the initial absorbance as a reference, the hydrophobicity of the strain was calculated to be 66.03% ± 7.5%, which is relatively high, indicating good adhesion to the intestine.

[0064] 6. Hemolytic test

[0065] Bifidobacterium longum SRU-1 was inoculated onto Columbia blood agar plates, with Staphylococcus aureus as a positive control, and cultured at 37 ℃ for 48 h. The hemolytic activity and type of hemolysis were determined based on colony color and morphology. Results are as follows: Figure 6 As shown, the colonies of *Bifidobacterium longum* SRU-1 do not have a hemolytic zone, indicating that... - Hemolysis, i.e., no hemolysis, while the control group colonies have a transparent hemolytic ring around them.

[0066] 7. Detection of bile salt hydrolytic enzyme activity

[0067] Add 5 g / L taurine deoxycholic acid (TDCA), 2 g / L sodium thioglycolate, 0.37 g / L CaCl2, and 15 g / L agar to TPY liquid medium, sterilize at 121°C for 15 min, pour into sterile plates, and after solidification, evenly place sterile filter paper discs into the plates. Add 10 μL of fermented Bifidobacterium longum SRU-1 supernatant centrifuged at 8000 rpm for 10 min to each filter paper disc. Incubate anaerobically at 37°C for 72 h. A white precipitate appears around the filter paper disc (see...). Figure 7 This indicates that the strain possesses bile salt hydrolase activity and has the ability to lower cholesterol levels.

[0068] 8. Detection of inhibitory ability against α-glucosidase activity

[0069] Bifidobacterium longum SRU-1 was inoculated into TPY liquid medium at a 5% inoculum and cultured at 37 ℃ for 18 h. The fermentation broth was centrifuged at 6000 r / min and 4 ℃ for 10 min, and the supernatant was collected. 50 μL of the sample solution was added to a centrifuge tube, followed by 100 μL of 0.2 U / mL α-glucosidase solution. The mixture was incubated at 37 ℃ for 10 min, and then 50 μL of 5 mmol / L p-nitrophenol-α-D-pyranoside solution was added. The reaction was continued in a constant temperature water bath at 37 ℃ for 20 min. Finally, 50 μL of 0.2 mol / L Na2CO3 was added to terminate the reaction, and the absorbance was measured at 405 nm. The calculation showed that Bifidobacterium longum SRU-1 inhibited α-glucosidase activity by 59.59%, indicating that Bifidobacterium longum SRU-1 has a good inhibition rate of α-glucosidase activity, which means it has a good ability to lower blood sugar.

[0070] Example 3: Making yogurt using Bifidobacterium longum SRU-1

[0071] The production process and characteristics of the yogurt are as follows: First, pure milk is sterilized at 95℃ for 10 minutes, cooled to 42℃, and inoculated with a starter culture. Fermentation is stopped at a constant temperature of 42℃ until the pH is close to 4.5. The milk is then cooled to 4℃ for further ripening. Acidity is determined according to GB / T 12456-2021. Water retention is calculated by centrifuging at 8000 r / min for 15 minutes (4℃) and the ratio of the mass of the precipitate to the mass of the yogurt. The product characteristics are shown in Table 3. Yogurt made with *Bifidobacterium longum* SRU-1 is set-like, milky white, has a good taste, and exhibits good acidity and water retention.

[0072] Table 3. Characteristics of yogurt fermented with Bifidobacterium longum SRU-1

[0073]

[0074] Example 4: High-density culture method of Bifidobacterium longum SRU-1

[0075] The high-density culture method of Bifidobacterium longum SRU-1 in this invention is as follows:

[0076] (1) Activated Bifidobacterium longum SRU-1 was inoculated into TPY medium and cultured anaerobically at 37℃. OD600nm and pH were measured at 0h, 12h, 24h, 36h, and 48h. Plotting time on the x-axis and OD and pH values ​​on the y-axis, it was found that Bifidobacterium longum SRU-1 reached its maximum biomass and pH of 4.3 after 24h of culture. After 24h, the biomass decreased, and the pH change was not significant (see...). Figure 8 ).

[0077] (2) Logarithmic phase Bifidobacterium longum SRU-1 was inoculated at a ratio of 2% into TPY basal medium containing glucose, soluble starch, mannitol or sucrose respectively, and anaerobic cultured at 37℃ for 24h. Compared with TPY basal medium, the cell density was increased. As the preferred culture medium, the formula is as follows: per 1L of medium, there are 30g of soluble starch, 10.0g of hydrolyzed casein, 5.0g of soybean peptone, 2.0g of yeast powder, 5.0g of glucose, 0.5g of L-cysteine, 2.0g of dipotassium hydrogen phosphate, 0.5g of magnesium chloride, 0.25g of zinc sulfate, 0.15g of calcium chloride, 0.0001g of ferric chloride, 1.0g of Tween-80, and pH 6.5±0.1. The cell density was increased by 36% compared with TPY basal medium.

[0078] (3) Logarithmic phase Bifidobacterium longum SRU-1 was inoculated at a ratio of 2% into TPY basal medium containing FeSO4, MnSO4, CaCl2 or CuSO4, and anaerobic cultured at 37℃ for 24h. Compared with TPY basal medium, the cell density was increased. As the preferred culture medium, the formula is as follows: per 1L of medium, there are 0.3g FeSO4, 10.0g hydrolyzed casein, 5.0g soybean peptone, 2.0g yeast powder, 5.0g glucose, 0.5g L-cysteine, 2.0g dipotassium hydrogen phosphate, 0.5g magnesium chloride, 0.25g zinc sulfate, 0.15g calcium chloride, 0.0001g ferric chloride, 1.0g Tween-80, pH 6.5±0.1. Anaerobic culture at 37℃ for 24h increased the cell density by 60% compared with TPY basal medium.

[0079] (4) Logarithmic-phase Bifidobacterium longum SRU-1 was inoculated at a ratio of 5% into prickly pear juice and TPY liquid medium, and anaerobically cultured at 37℃ for 72 h. After serial dilution, it was plated on TPY medium and anaerobically cultured at 37℃ for 72 h, and then counted. During this process, the TPY liquid medium was sterilized at 120℃ for 15 min, and then prickly pear juice filtered through a 0.45 μm filter membrane was added proportionally. The viable count was as follows: Figure 9 As shown, using TPY medium as a reference, the addition of 20%, 40%, and 60% prickly pear juice increased the cell density of *Bifidobacterium longum* SRU-1 by 580.2%, 319.7%, and 192.9%, respectively. However, the cell density decreased by 82.23% and 84.77% when adding 80% and 100% juice, respectively, indicating that *Bifidobacterium longum* SRU-1 can survive in pure prickly pear juice. The 20% addition amount is the most suitable.

[0080] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A Bifidobacterium longum SRU-1 strain possessing both bile salt hydrolase activity and α-glucosidase inhibitory activity, characterized in that, Its accession number is CGMCC No.36397.

2. The use of the Bifidobacterium longum SRU-1 as described in claim 1 in the preparation of drugs that lower cholesterol, lower blood sugar and / or promote gastrointestinal digestion.

3. The application of Bifidobacterium longum SRU-1 as described in claim 1 in the preparation of fermented dairy products.

4. The application according to claim 3, characterized in that, The fermented dairy product is yogurt, with a fermentation endpoint pH of 4.0-4.

5. Preferably, the yogurt has an acidity of 100°T-110°T and good water retention.

5. The method for culturing Bifidobacterium longum SRU-1 according to claim 1, characterized in that, The logarithmic phase of Bifidobacterium longum was inoculated into a culture medium at a ratio of 1%-10%, wherein the culture medium was selected from any of the following: (1) TPY basal medium containing any of the following components: soluble starch, glucose, mannitol, sucrose, FeSO4, MnSO4, CaCl2 or CuSO4; (2) TPY liquid culture medium containing prickly pear juice; Preferably, the inoculation rate is 2%-5%.

6. The cultivation method according to claim 5, characterized in that, The TPY basal culture medium includes hydrolyzed casein, soybean peptone, yeast extract, glucose, L-cysteine, dipotassium hydrogen phosphate, magnesium chloride, zinc sulfate, calcium chloride, ferric chloride, and Tween-80.

7. The cultivation method according to claim 6, characterized in that, Anaerobic culture at 37℃ for 12-48 hours, preferably 24-36 hours.

8. The cultivation method according to claim 5, characterized in that, The prickly pear juice content in the TPY liquid culture medium is 0-100%, preferably 20%-60%.

9. The cultivation method according to claim 8, characterized in that, The prickly pear juice is added after being filtered through a 0.45μm filter membrane and then anaerobically cultured at 37℃ for 24-96h, preferably 48-72h.

10. A method for preparing yogurt, characterized in that, The process includes the following steps: first, sterilize pure milk at high temperature, cool it to 37-42℃, inoculate it with Bifidobacterium longum SRU-1 as described in claim 1, ferment it at a constant temperature of 42℃ until the pH reaches 4.0-4.5, then stop fermentation, cool it at 4℃ and allow it to ripen for 12-24 hours. Preferably, the high-temperature sterilization is performed at 95℃ for 8-15 minutes. Preferably, the yogurt also contains prickly pear juice.

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