阅读说明：本技术 一种鼠李糖乳杆菌胞外多糖及其制备方法与应用 (Lactobacillus rhamnosus exopolysaccharide and preparation method and application thereof ) 是由 王家彬 潘力 王斌 于 2021-01-28 设计创作，主要内容包括：本发明公开一种鼠李糖乳杆菌胞外多糖及其制备方法与应用,属于微生物技术领域。本发明采用分离自香满楼牌酸牛奶的鼠李糖乳酸菌菌株为出发菌株,生产胞外多糖,该胞外多糖为均一组分,其分子量为88650Da；且包含甘露糖、葡萄糖醛酸、葡萄糖、木糖、半乳糖和阿拉伯糖。该胞外多糖具有良好的体外降糖作用,检测到其具有良好的体外抑制α-葡萄糖苷酶的能力,且工艺简单,市场前景广阔,热力学性能稳定,适合规模化生产。因此,该多糖是一种有潜力的用于预防和治疗糖尿病的活性成分。此外,作为益生菌的发酵产物,与降血糖领域内常见的化学类药物相比,其具有活性成分简单易得、价格低廉、无副作用等优势,具有很大的应用价值。(The invention discloses lactobacillus rhamnosus exopolysaccharide and a preparation method and application thereof, belonging to the technical field of microorganisms. The invention adopts the lactobacillus rhamnosus strain separated from the Manchu brand yoghurt as a starting strain to produce extracellular polysaccharide, wherein the extracellular polysaccharide is a uniform component and has the molecular weight of 88650 Da; and comprises mannose, glucuronic acid, glucose, xylose, galactose and arabinose. The extracellular polysaccharide has a good in-vitro hypoglycemic effect, has a good in-vitro alpha-glucosidase inhibition capacity when detected, and is simple in process, wide in market prospect, stable in thermodynamic performance and suitable for large-scale production. Therefore, the polysaccharide is a potential active ingredient for the prevention and treatment of diabetes. In addition, as a fermentation product of probiotics, compared with common chemical drugs in the field of blood sugar reduction, the probiotic bacteria have the advantages of simple and easily obtained active ingredients, low price, no side effect and the like, and have great application value.)

1. A preparation method of lactobacillus rhamnosus exopolysaccharide is characterized by comprising the following steps:

carrying out anaerobic fermentation by using lactobacillus rhamnosus, extracting fermentation liquor by an alcohol precipitation method to obtain crude exopolysaccharide, and separating and purifying the crude exopolysaccharide by molecular sieve chromatography to finally obtain the exopolysaccharide of the lactobacillus rhamnosus;

the lactobacillus rhamnosus is obtained by separating and purifying the coumarone brand yoghurt.

2. The preparation method of extracellular polysaccharide of lactobacillus rhamnosus according to claim 1, which is characterized by comprising the following steps:

(1) carrying out anaerobic fermentation culture on lactobacillus rhamnosus to obtain a fermentation culture solution;

(2) centrifuging the fermentation culture solution to remove thallus, taking supernatant, performing high-temperature inactivation treatment, and adding trichloroacetic acid to remove protein to obtain supernatant;

(3) extracting polysaccharide from the supernatant by an alcohol precipitation method, and carrying out vacuum freeze drying on the obtained product to obtain crude extracellular polysaccharide, which is marked as EPS-1;

(4) and further purifying the crude exopolysaccharide on a Sephacryl TM-S-200HR column, and performing vacuum freeze drying to obtain the exopolysaccharide of the lactobacillus rhamnosus, which is marked as EPS 1-1.

3. The method for preparing the exopolysaccharide of lactobacillus rhamnosus according to claim 2, characterized in that:

in the step (1), lactobacillus rhamnosus is inoculated in an MRS broth culture medium according to the inoculation amount of 3% by volume, and fermentation culture is carried out at 37 +/-0.5 ℃ for 12-24 h to obtain a fermentation culture solution.

4. The method for preparing the exopolysaccharide of lactobacillus rhamnosus according to claim 2, characterized in that:

in the step (2), the high-temperature inactivation treatment method comprises the following steps: boiling for 15-20 minutes at a high temperature of 100 ℃;

in the step (2), the method for removing protein by adding trichloroacetic acid comprises the following steps: adding trichloroacetic acid into the supernatant subjected to high-temperature inactivation treatment until the final concentration is 4.5-5.5% m/v, then stirring to enable the trichloroacetic acid to fully react, centrifuging, and removing residual cells and precipitated protein to obtain the supernatant.

5. The method for preparing the exopolysaccharide of lactobacillus rhamnosus according to claim 2, characterized in that:

in the step (3), the alcohol precipitation method comprises the following steps: adding 2-4 times volume of absolute ethyl alcohol into the supernatant, standing at 3-5 ℃ for 8-12 h, centrifuging, taking the precipitate, and carrying out vacuum freeze drying to obtain crude extracellular polysaccharide, which is marked as EPS-1.

6. The method for preparing the exopolysaccharide of lactobacillus rhamnosus according to claim 2, characterized in that:

in the step (4), the crude extracellular polysaccharide is dissolved in ultrapure water, and further purified on a Sephacryl TM-S-200HR column, the ultrapure water is used as an eluent, the sample loading amount is 4.8mL, and the flow rate is set to be 0.6-0.8 mL/min.

7. The lactobacillus rhamnosus exopolysaccharide is characterized in that:

the lactobacillus rhamnosus exopolysaccharide is a uniform component, and the molecular weight of the lactobacillus rhamnosus exopolysaccharide is 88650 Da;

the lactobacillus rhamnosus exopolysaccharide comprises mannose, glucuronic acid, glucose, xylose, galactose and arabinose, wherein the molar ratio is as follows: mannose: glucuronic acid: glucose: xylose: galactose: arabinose 31.19: 23.01: 36.62: 2.03: 3.57: 3.58.

8. lactobacillus rhamnosus exopolysaccharide according to claim 7 characterized by: prepared by the preparation method of any one of claims 1 to 6.

9. Use of lactobacillus rhamnosus exopolysaccharide according to claim 7 or 8 for the preparation of a product for lowering blood sugar.

10. Use according to claim 9, characterized in that: the lactobacillus rhamnosus exopolysaccharide is used as an alpha-glucosidase inhibitor.

Technical Field

The invention belongs to the technical field of microorganisms, and particularly relates to lactobacillus rhamnosus exopolysaccharide and a preparation method and application thereof.

Background

With the improvement of living standard of people, the incidence rate of diabetes mellitus is higher and higher due to excessive nutrient intake. While type two diabetes (T2 DM) is one of the most common chronic diseases in patients with abnormally high blood glucose levels. Because the pathogenesis of the disease is complex and the influence factors are many, no effective prevention and treatment measures exist at present.

The drugs clinically used for diabetes mainly include acarbose, voglibose and miglitol. Among these diabetes drugs, acarbose is an α -glucosidase inhibitor that can compete with oligosaccharides on the small intestine epithelial cell side and bind reversibly to α -glucosidase. The activity of the compound can inhibit the hydrolysis of 1, 4-glycosidic bond, thereby achieving the effect of reducing blood sugar. However, these drugs, such as acarbose, have significant side effects, such as abdominal distension and diarrhea. Therefore, some researchers have been working on finding natural products to alleviate the frequent side effects associated with the use of synthetic drugs. Although natural products are not as common and effective as synthetic drugs, they have moderate biological activity and are a natural functional food that can be easily incorporated into the basic diet. Therefore, the search for high-efficiency natural hypoglycemic products is of great significance.

Probiotics have been increasingly used to develop functional foods, which have also proven effective in improving gastrointestinal health and certain metabolic syndromes, including cancer, obesity, and even psychiatric disorders. The important role of probiotics in the treatment of diabetes has also been recognized. However, most of the data of the probiotics for controlling diabetes are directly obtained from animal experiments, the research on the specific mechanism of the probiotics for regulating blood sugar is few, and the application prospect of the probiotics in type 2 diabetes is not widely explored. Inhibition of alpha-glucosidase is an important pathway for T2D management. Screening potential probiotics with effective alpha-glucosidase inhibitory activity can be used for regulating blood sugar concentration, so that the potential probiotics can be used as an auxiliary medicine for treating diabetes. The alpha-glucosidase inhibitory activity in yoghurts containing exopolysaccharides was previously reported to be significant (RAMCHANDRAN et al.2009). The lactic acid bacteria fermentation supernatant has the potential ability of reducing blood sugar, and the content of Exopolysaccharide (EPS) in the fermentation supernatant is in positive correlation with the blood sugar reducing activity (Li et al.2016). The hypoglycemic effect of the probiotic may be due to EPS produced by the probiotic.

In summary, the research of screening probiotic strains with potential hypoglycemic ability and the hypoglycemic active ingredients produced by the strains is a hot issue of the present society. However, no report is available that extracellular polysaccharides extracted from probiotics with significant α -glucosidase inhibitory activity also have similar in vitro glucose-lowering ability.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a preparation method of lactobacillus rhamnosus exopolysaccharide.

The invention also aims to provide the exopolysaccharide prepared by the preparation method.

The invention further aims to provide application of the exopolysaccharide.

The invention takes yoghourt in south China as a source, and utilizes a conventional strain separation method (such as a gradient dilution method, a coating culture method and the like) to collect and screen probiotic strains. Then screening a strain with potential blood sugar reducing capability by adopting a method for inhibiting alpha-glucosidase in vitro, and selecting a dominant strain, namely Lactobacillus rhamnosus LB1lac10 with the highest in vitro blood sugar reducing activity. The strain has a very similar inhibition rate to the positive control acarbose, and is isolated from the Manchu brand yoghurt. On the basis, the extracellular polysaccharide of the fermentation product of the strain is extracted by an alcohol precipitation method. And further purifying the collected crude exopolysaccharide. And then the hypoglycemic capacity of the polysaccharide is verified by adopting a method for inhibiting alpha-glucosidase in vitro, and the extracellular polysaccharide produced by the polysaccharide has potential hypoglycemic capacity. And the structure composition of the purified extracellular polysaccharide is preliminarily explored. By comparison with the known literature and patents, the polysaccharide is considered to be a novel extracellular polysaccharide which is not discovered yet, has the potential capability of regulating blood sugar and has great application value.

The lactobacillus rhamnosus is derived from the Manchu brand yoghurt, can produce extracellular polysaccharide with high yield, has the function of reducing blood sugar, provides a new idea for developing medicaments for preventing and treating diabetes, is a very potential strain, and has wide application prospect. The exopolysaccharide has good hypoglycemic activity, so the polysaccharide is a potential active ingredient for preventing and treating diabetes.

The purpose of the invention is realized by the following technical scheme:

a preparation method of lactobacillus rhamnosus exopolysaccharide comprises the following steps: carrying out anaerobic fermentation by using lactobacillus rhamnosus, extracting fermentation liquor by an alcohol precipitation method to obtain crude exopolysaccharide, and separating and purifying the crude exopolysaccharide by molecular sieve chromatography to finally obtain the exopolysaccharide of the lactobacillus rhamnosus;

the method specifically comprises the following steps:

(1) carrying out anaerobic fermentation culture on lactobacillus rhamnosus LB1lac10 to obtain a fermentation culture solution;

(2) centrifuging the fermentation culture solution to remove thallus, taking supernatant, performing high-temperature inactivation treatment, and adding trichloroacetic acid to remove protein to obtain supernatant;

(3) extracting polysaccharide from the supernatant by an alcohol precipitation method, and carrying out vacuum freeze drying on the obtained product to obtain crude extracellular polysaccharide, which is marked as EPS-1;

(4) and further purifying the crude exopolysaccharide on a Sephacryl TM-S-200HR column, and performing vacuum freeze drying to obtain the exopolysaccharide of the lactobacillus rhamnosus, which is marked as EPS 1-1.

The lactobacillus rhamnosus LB1lac10 is obtained by separating and purifying domethan sour milk; the conventional strain separation method comprises a gradient dilution method, a coating culture method and the like;

the lactobacillus rhamnosus strain for producing exopolysaccharide has the following characteristics:

the single bacterial colony of the strain on the MRS solid culture medium is round, has smooth surface and is milk white,

the edge is neat, the color has a wiredrawing phenotype, and the gram stain is purple blue.

The MRS culture medium comprises (g.L)^-1): glucose (20), Tween 80(1.08), MnSO₄·4H₂O(0.05)、MgSO₄·7H₂O (0.2), anhydrous sodium acetate (5), ammonium citrate tribasic (2), casein (10), beef extract (10), yeast extract (4), K₂HPO₄(2) (pH 5.7. + -. 0.2). The solid medium contained 1.5% agar. All materials were sterilized at 121 ℃ for 20 minutes prior to use.

Preferably, in the step (1), lactobacillus rhamnosus is inoculated into the MRS broth according to the inoculation amount of 3% by volume, and fermentation culture is carried out at 37 +/-0.5 ℃ for 12-24 h (preferably 18h), so as to obtain the fermentation culture solution.

In the step (2),

preferably, the centrifugation conditions are 4 ℃, 11000rpm, 15 min.

Preferably, the method for high-temperature inactivation treatment comprises the following steps: boiling at 100 deg.C for 15-20 min (preferably 15min) to inactivate enzymes which may degrade polysaccharide.

Preferably, the method for removing protein by adding trichloroacetic acid comprises the following steps: adding trichloroacetic acid into the supernatant after the high-temperature inactivation treatment until the final concentration is 4.5-5.5% (m/v) (preferably 5%), stirring to enable the trichloroacetic acid to fully react, centrifuging (4 ℃, 8000rpm, 20min), and removing residual cells and precipitated protein to obtain the supernatant.

The stirring time is 20-40 minutes, and further 30 minutes.

In the step (3), the step (c),

preferably, the alcohol precipitation method is as follows: adding 2-4 times volume of absolute ethyl alcohol (preferably 3 times volume of absolute ethyl alcohol) into the supernatant, standing at 3-5 ℃ for 8-12 h (preferably 4 ℃ for 8h), centrifuging, taking the precipitate, and performing vacuum freeze drying to obtain crude extracellular polysaccharide, which is marked as EPS-1;

in the step (4), the step (c),

dissolving the crude exopolysaccharide in ultrapure water, and further purifying on a Sephacryl TM-S-200HR column, wherein the sample loading amount is 4.8mL by taking the ultrapure water as an eluent, and the flow rate is set to be 0.6-0.8 mL/min (preferably 0.7 mL/min).

An extracellular polysaccharide of lactobacillus rhamnosus is prepared by the preparation method.

The extracellular polysaccharide of Lactobacillus rhamnosus is a homogeneous component, and has molecular weight of 88650 Da.

The lactobacillus rhamnosus exopolysaccharide comprises mannose (Man), glucuronic acid (GlcUA), glucose (Glc), xylose (Xyl), galactose (Gal) and arabinose (Ara), wherein the molar ratio is as follows: mannose: glucuronic acid: glucose: xylose: galactose: arabinose 31.19: 23.01: 36.62: 2.03: 3.57: 3.58.

the application of the lactobacillus rhamnosus exopolysaccharide in preparing a product for reducing blood sugar;

further, the lactobacillus rhamnosus exopolysaccharide is applied as an alpha-glucosidase inhibitor.

Diabetes is a common disease and frequently-occurring disease which endangers human health at present, the prevention and treatment of diabetes is one of targets which are overcome by human beings, all countries in the world search for new effective active ingredients for preventing and treating diabetes, alpha-glucosidase inhibitors are medicines for treating diabetes at present, and screening and searching for effective and safe alpha-glucosidase inhibitors are hot spots which are concerned by scientists in all countries at present.

The exopolysaccharide produced by the lactobacillus rhamnosus of the invention shows good hypoglycemic activity in an in vitro hypoglycemic test, and compared with a hypoglycemic effect agent, the hypoglycemic effect agent has stronger hypoglycemic activity. When the concentration of the alpha-glucosidase is 0.01, 0.1, 0.15 and 0.2U/mL, the inhibition rate of the purified polysaccharide EPS1-1(0.5mg/mL) on the alpha-glucosidase reaches 95.89 percent, 37.51 percent, 25.97 percent and 15.33 percent respectively. Shows good in vitro hypoglycemic activity.

Compared with the prior art, the invention has the following advantages and effects

(1) The lactobacillus rhamnosus strain has wide sources and the capability of high yield of exopolysaccharides. The exopolysaccharide has potential blood sugar regulation and control effects, provides a new idea for developing diabetes prevention and treatment medicines, and is a very potential strain.

(2) The rhamnose lactobacillus strain which produces the exopolysaccharide and is separated from the Manchu brand yoghurt is used as a starting strain to produce the exopolysaccharide, and the exopolysaccharide has good in-vitro hypoglycemic effect, simple process, wide market prospect and stable thermodynamic property, and is suitable for large-scale production. In addition, as a fermentation product of probiotics, compared with common chemical drugs in the field of blood sugar reduction, the probiotic bacteria have the advantages of simple and easily obtained active ingredients, low price, no side effect and the like.

(3) The exopolysaccharide disclosed by the invention is detected to have good capability of inhibiting alpha-glucosidase in vitro.

(4) After the composition and the structure of the exopolysaccharide EPS1-1 are analyzed, the exopolysaccharide EPS1-1 is different from the known exopolysaccharide, shows stronger hypoglycemic activity in an in vitro hypoglycemic test, and is possibly a new member of a lactobacillus exopolysaccharide family.

Drawings

FIG. 1 shows the plate culture characteristics of LB1lac10 strain of the present invention.

FIG. 2 shows the gram-stained microscopic form of LB1lac10 strain of the present invention.

FIG. 3 is the elution profile of extracellular polysaccharide purified by the strain LB1lac10 of the present invention.

FIG. 4 is an infrared spectrum detection spectrogram of extracellular polysaccharide EPS1-1 of the strain LB1lac10 of the invention.

FIG. 5 is a detection spectrogram of a monosaccharide component of extracellular polysaccharide EPS1-1 of the strain LB1lac10 of the invention; wherein a is different monosaccharide standards; b is EPS 1-1.

FIG. 6 shows the ultraviolet full-wavelength detection results of crude exopolysaccharide EPS-1 produced by the strain LB1lac10 and purified exopolysaccharide EPS 1-1.

FIG. 7 shows the variation of maximum absorption wavelength of Congo red (Congo red) and Congo red and EPS1-1 complex solution (Congo red + EPS 1-1).

FIG. 8 shows the Nuclear Magnetic Resonance (NMR) detection results of the strain LB1lac10 exopolysaccharide EPS1-1 of the present invention; wherein A is¹H NMR spectrum results; b is¹³C NMR spectrum results.

FIG. 9 is a diagram showing the results of the thermostability analysis of exopolysaccharide EPS1-1 of strain LB1lac10 according to the present invention; wherein, A is thermogravimetric analysis (TGA); b is Differential Scanning Calorimetry (DSC).

FIG. 10 shows the effect of extracellular polysaccharide EPS1-1 produced by LB1lac10 of the present invention on the inhibition of alpha-glucosidase.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

The test methods in the following examples, in which specific experimental conditions are not specified, are generally performed according to conventional experimental conditions or according to the experimental conditions recommended by the manufacturer. The materials, reagents and the like used are, unless otherwise specified, reagents and materials obtained from commercial sources.

Example 1: screening method of rhamnose lactic acid bacteria strain for producing exopolysaccharides

The exopolysaccharide-producing Lactobacillus rhamnosus strain in this study was obtained from the Hematoda yoghurt of south China, by a conventional separation technique, by gradient dilution of the culture with 0.85% physiological saline (10)^-1-10^-7) And then uniformly plating on an MRS solid culture medium plate by using a disposable spreader. The MRS broth culture medium comprises the following components (g.L)^-1): glucose (20), Tween 80(1.08), MnSO₄·4H₂O(0.05)、MgSO₄·7H₂O (0.2), anhydrous sodium acetate (5), ammonium citrate tribasic (2), casein (10), beef extract (10), yeast extract (4), K₂HPO₄(2) (pH 5.7. + -. 0.2). The solid medium contained 1.5% agar. All materials were sterilized at 121 ℃ for 20 minutes prior to use.

After 2 days of culture at 37 ℃ under anaerobic conditions, strains with typical colony morphology were selected for gram stain observation.

Example 2: identification of the above exopolysaccharide-producing Lactobacillus rhamnosus strains

The lactobacillus rhamnosus strain for producing exopolysaccharide has the following characteristics:

the single colony of the strain on an MRS solid culture medium is round, has a smooth surface, is milky white, has a neat edge, has a wiredrawing phenotype, and is violet blue in gram stain (as shown in figures 1 and 2).

The rhamnose lactobacillus strain which produces the exopolysaccharide and is obtained by screening is temporarily named as LB1lac 10. In order to further determine the species of the strain, the genome of the strain was extracted by an enzymatic method, the total DNA of the strain was extracted according to the procedure of a Czochralski organism bacterial genome DNA extraction kit (general Biotech bacteriological DNA extraction kit), gene amplification was performed using the sample as a template, the 16S rDNA gene of the strain was amplified using the universal primers 27F and 1492R, the amplified product was recovered and sent to Tianyihui (Guangzhou) Genscience and technology Limited for sequencing, and the species identification was performed by determining the sequence of the 16S rDNA. The sequence results obtained were Blast aligned at NCBI, putative standard sequence data homologous to the 16S rDNA of this strain were obtained from the database in Gen Bank, sequence similarity was calculated using MEGA6.6.5 and phylogenetic analysis was performed using leader-Joining algorithm.

The results showed that the sequence homology with Lactobacillus rhamnosus and the like was more than 99%. Thus, the strain LB1lac10 belongs to lactobacillus rhamnosus on a phylogenetic taxonomic classification. The result is consistent with the physiological and biochemical identification result, so that a strain is finally determined to be Lactobacillus rhamnosus named as Lactobacillus rhamnosus LB1lac10, which is abbreviated as LB1lac10 by integrating the results of colony morphology, thallus morphology feature observation and molecular biology sequencing.

The Lactobacillus rhamnosus can be obtained by repeatedly separating and purifying Colophonium brandy yoghurt in south China.

Example 3: the lactobacillus rhamnosus strain for producing exopolysaccharides has the capability of reducing blood sugar in vitro

The in vitro sugar-reducing capacity of the lactobacillus rhamnosus strain for producing the exopolysaccharide comprises the following steps:

step 1: LB1lac10 frozen at-80 ℃ was inoculated into liquid MRS broth and incubated under anaerobic conditions at 37 ℃ for 18 hours. The second generation was then activated for subsequent experiments and cultured LB1lac10 was centrifuged at 6000rpm for 10 minutes at 4 ℃.

Viable bacteria suspension: after centrifugation, the LB1lac10 broth was washed twice with phosphate buffered saline (PBS, 0.1M, pH 6.8) to adjust the strain concentration to 1X 10⁹CFU/mL。

Suspension of inactivated bacteria: live bacteria (1X 10)⁹CFU/mL) was boiled at 100 ℃ for 20 minutes.

Step 2: mu.L of 20mmol/L PNPG (4-nitrophenyl-D-glucopyranoside) and 25. mu.L of the sample were first added to a 96-well plate and incubated at 37 ℃ for 10 minutes. Then, 50. mu.L of 20U/mL α -glucosidase was added and reacted at 37 ℃ for 20 minutes. Finally, 100. mu.L of 0.1mol/L Na was added₂CO₃The reaction was terminated. The reaction solution having a wavelength of 405nm was detected by a microplate reader (TECAN, infinite M200). Percent inhibition was calculated using Acarbose (Acarbose) as a positive control using the following formula:

inhibition ratio (%) [1- (C-D)/(A-B) ]

Wherein A is the absorbance of the sample containing no alpha-glucosidase, B is the absorbance of the sample containing no alpha-glucosidase, C is the absorbance of the sample containing alpha-glucosidase, and D is the absorbance of the sample containing no alpha-glucosidase.

The lactobacillus rhamnosus strain LB1lac10 for producing exopolysaccharides has the ability of reducing blood sugar in vitro: 12.75% + -0.007% of viable bacteria suspension and 6.19% + -0.0048% of inactivated bacteria suspension. From the experimental results, it can be seen that the activity of the live bacterial suspension of LB1lac10 on alpha glucosidase inhibition was 12.75% + -0.007. As a positive control, the activity of the acarbose on the alpha-glucosidase can reach 15.06% + -0.011. The Lactobacillus rhamnosus LB1lac10 strain has high inhibitory activity, is relatively close to positive control acarbose, and has great potential and application market. We also targeted this strain for subsequent studies.

In addition, the suspension of the inactivated LB1lac10 bacteria also has a certain inhibitory activity on alpha-glucosidase, which is 6.19% +/-0.0048. This may be a competitive inhibition of certain substances present inside and outside the cell, inhibiting alpha-glucosidase. Several studies have shown that the inhibitory activity of alpha glucosidase may be due to exopolysaccharides produced by lactic acid bacteria. Therefore, we will mainly study exopolysaccharides of Lactobacillus rhamnosus LB1lac10 in which alpha-glucosidase inhibitory ability is high.

Example 4: extraction, purification and content determination of exopolysaccharide produced by lactobacillus rhamnosus LB1lac10

An appropriate amount of the strain is picked from an MRS solid culture medium and inoculated into an MRS broth culture medium. Culturing at 37 deg.C under anaerobic condition for 48h to obtain fermentation broth. FIG. 1 shows the plate culture characteristics of LB1lac10 strain of the present invention.

A highly potent strain having α -glucosidase inhibitory activity (LB1lac10) was cultured in 380mL of MRS broth at 37 ℃ for 18 hours in an anaerobic environment with an inoculum size of 3% (v: v). The cells were separated by centrifugation (4 ℃, 11000rpm, 15min) and boiled at high temperature of 100 ℃ for 15min to inactivate enzymes that might degrade the polysaccharide. After cooling, 100% (v: v) trichloroacetic acid (TCA, alatin) was added to achieve a TCA concentration of 5%. The solution was then stirred for 30 minutes to allow sufficient contact of the trichloroacetic acid, and then centrifuged (4 ℃, 8000rpm, 20min) to remove residual cells and precipitated proteins. Taking the supernatant for later use. Adding three times of anhydrous ethanol into the supernatant, standing at 4 deg.C for 8 hr, centrifuging (4 deg.C, 11000rpm, 20min), and precipitating to obtain crude exopolysaccharide EPS-1. Then, the same amount of distilled water was added thereto to re-suspend the reaction mixture, and the sugar content of EPS-1 was measured by the phenol-sulfuric acid method. Weighing, and calculating the yield of EPS-1 to be 8.24 g/L.

The crude exopolysaccharide EPS-1 was freeze dried in vacuo and further purified on Sephacryl TM-S-200HR column. The crude exopolysaccharide EPS-1 is dissolved in 20mL of ultrapure water, and the eluent is ultrapure water. The amount of the sample was 4.8mL, and the flow rate was set to 0.7 mL/min. Each tube was collected for 8 minutes for a total of 40 tubes. Then, the sugar content of each tube was measured by the phenol-sulfuric acid method, and an elution curve was plotted (as shown in FIG. 3). The collection tube number is the abscissa and the absorbance value is the ordinate. It can be seen from the figure that EPS-1 can obtain two peaks, the major component of the first large peak (8-11 tubes) is collected. We then examined the purity of each tube in turn to determine individual components. After combining the solutions identified as single components, we dried the single samples in a vacuum freeze dryer for 24 hours to give the purified exopolysaccharide, designated EPS 1-1.

Example 5: infrared spectroscopic analysis of Lactobacillus rhamnosus LB1lac10 extracellular polysaccharide EPS1-1

The purified exopolysaccharide EPS1-1 obtained in example 4 was subjected to infrared spectroscopic measurements. The specific method comprises the following steps: about 1mg of the dried EPS1-1 sample was mixed with 100mg of dried KBr powder and then pressed into pellets of 1mm thickness for measurement. At 4000-^-1FT-IR spectra were recorded on an FT-IR spectrometer (N ICOLETI S50, FT-IR). The results are shown in FIG. 4. As can be seen from FIG. 4, at 3448cm^-1(3200-3600cm^-1) The broad and strong characteristic absorption peak at (a) is caused by tensile vibration of the O-H bonds of the polysaccharide. Indicating that a plurality of hydroxyl groups exist in EPS1-1 molecule; at 2966cm^-1Is a C-H stretching vibration peak; the two groups of absorption peaks are characteristic peaks of sugar. At 1606cm^-1And 1384cm^-1The absorption peak at (a) can be attributed to asymmetric and symmetric C ═ O tensile vibration of the carboxyl group, indicating the presence of aldehyde acids; other characteristic peaks of the polysaccharide are 1200cm^-1To 1000cm^-1Insofar, this is caused by tensile vibration of the C-O-C or C-O-H bond, indicating the presence of pyranose. Therefore, specific polysaccharides can be judged by observing the intensity and position of specific peaks in this region. At 572cm^-1The peak at (a) is caused by symmetric stretching vibration of the pyranose ring. The infrared spectrum shows that the extracted exopolysaccharide sample EPS1-1 from Lactobacillus rhamnosus LB1lac10 contains most of characteristic absorption peaks related to polysaccharide, and can be identified as polysaccharide.

Example 6: detection of extracellular polysaccharide molecular weight and monosaccharide components of lactobacillus rhamnosus LB1lac10

The molecular weight of the polysaccharide fraction was determined by Gel Permeation Chromatography (GPC) (Kook et al, 2019). Sample preparation: weighing a proper amount of the sample in a volumetric flask (about 5mg/mL), dissolving the sample by using a mobile phase, and fixing the volume. The method comprises the following steps: waters 1525 high performance liquid chromatograph (with 2410 refractive index detector and Empower workstation)

Chromatographic conditions are as follows:

a chromatographic column: ultrahydrogel^TMLinear 300mm×7.8mmid×2；

The mobile phase is 0.1mol/LNaNO₃；

The flow rate is 0.8 mL/min;

the column temperature is 30 ℃;

the loading was 20. mu.L.

Dextran standards for molecular weight calibration curves (all purchased from sigma): dextran T-20000(MW2000000), Dextran T-150(MW133800), Dextran T-40(MW36800), Dextran T-10(MW9700, Dextran T-5(MW2700), Log molecular weight of 19.690min for retention time of 13.2-0.434T. EPS1-1, molecular weight of 88650Da calculated as standard curve.

5mg of purified polysaccharide EPS1-1 was dissolved in 2mL of 2mol/L trifluoroacetic acid (TFA, Macklin). Then hydrolyzed in an oven at 120 ℃ for 4 hours. After hydrolysis, TFA was removed by rotary evaporation with cooling. Then 1mL of methanol was added for rotary evaporation, which was repeated 3-5 times to completely remove TFA. EPS1-1 was dissolved in 1mL of ultrapure water to prepare a 5mg/mL polysaccharide solution. Then, 500. mu.L of a 0.3mol/L NaOH solution and 500. mu.L of a 0.5mol/L PMP (1-phenyl-3-methyl-5-pyrazolone) solution were directly added thereto and mixed, followed by reaction at 70 ℃ for 1 hour. After cooling to room temperature, 500. mu.L of 0.3mol/L HCl was added and 1mL of CH was added repeatedly₂CL₂Three times to remove PMP. The supernatant was passed through a 0.22 μm filter for subsequent experiments. HPLC detection is carried out, and the detection conditions are as follows:

a chromatographic column: CNW Technologies, Athena C18-WP,250 mm. times.4.6 mm,5 μm

The instrument comprises the following steps: agilent Technologies,1220Infinity LC

Mobile phase: PBS (0.1M) acetonitrile (v: v) ═ 83:17

Sample loading amount: 10 μ L

Flow rate: 1mL/min

Detection wavelength: 245nm

And determining the composition of the monosaccharide according to the HPLC detection result.

The same PMP derivatization method was performed on equimolar monosaccharide standards, and HPLC was performed under the same conditions as the control. Takes D-mannose, L-rhamnose, D-glucose, D-galactose, D-xylose and L-arabinose (Solarbio, Beijing) as raw materials.

The monosaccharide composition results are shown in FIG. 5. The results showed that EPS1-1 was mainly composed of mannose (Man), glucuronic acid (GlcUA), glucose (Glc), xylose (Xyl), galactose (Gal) and arabinose (Ara) in molar ratios of 31.19: 23.01: 36.62: 2.03: 3.57: 3.58. unlike the compositions of other exopolysaccharides described in the known literature and patents, EPS1-1 may be a new member of the exopolysaccharide family of lactic acid bacteria.

Example 7: ultraviolet full-wavelength detection of crude exopolysaccharide EPS-1 produced by strain LB1lac10 and purified exopolysaccharide EPS1-1

Respectively dissolving EPS-1 and EPS1-1 in ultrapure water (1mg/mL), and recording the ultraviolet-visible absorption spectrum in the wavelength range of 190-350 nm by using a U-3010 spectrophotometer (HITACHI).

The results of the experiment are shown in FIG. 6. The results show that crude exopolysaccharide EPS-1 produces two peaks at about 260nm and 200nm, respectively, indicating that the sample is impure. In addition to polysaccharides, there are nucleic acids, proteins or other impurities. After purification by Sephacryl TM-S-200HR column, EPS1-1 produced only one peak of polysaccharide at around 200nm, and no significant absorption was observed at 260nm, demonstrating the absence of nucleic acid in EPS 1-1. Furthermore, there was no or weak absorption at the 280nm spectrum, indicating that there was no protein in EPS 1-1.

Example 8: the change of the maximum absorption wavelength of Congo red and EPS1-1 composite solution with the concentration of NaOH

And performing conformational analysis on the purified extracellular polysaccharide component by adopting a Congo red method. 1mL of polysaccharide sample (0.5mg/mL) and Congo red solution (50. mu. mol/L) with the same volume, then NaOH solutions with different volumes and concentrations of 1mol/L were added to make the final concentrations 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4mol/L, and the mixture was stored at room temperature for 5min, and the same NaOH concentration and Congo red mixed solution was used as a control. Scanning at the wavelength of 400-600 nm by using an ultraviolet-visible spectrometer, and determining the maximum absorption wavelength (lambda max) of the mixture.

The maximum absorption wavelength of the extracellular polysaccharide EPS1-1 produced by the strain LB1lac10 of the invention in NaOH solutions with different concentrations after being combined with Congo red solution is shown in figure 7. As can be seen from the figure, when the concentration of NaOH is in the range of 0-0.1 mol/L, the EPS1-1 has a red shift phenomenon, and the maximum absorption wavelength of the composite solution and the maximum absorption wavelength of the pure Congo red solution show the same rising trend along with the increase of the concentration of NaOH. When the concentration of NaOH is within the range of 0.1-0.4 mol/L, the maximum absorption wavelength of the pure Congo red solution shows a stable trend. However, when the concentration of NaOH is in the range of 0.15-0.25 mol/L, the maximum absorption wavelength of the composite solution of EPS1-1 and Congo red is gradually reduced, which indicates that three-strand helix exists in EPS1-1, the structure of which is changed in the alkaline environment with higher concentration, and the three-strand helix may be untied. Until the NaOH concentration increased to 0.3mol/L, the dissociation was essentially complete. It has been reported that exopolysaccharides produced by Lactobacillus helveticus MB2-1 have triple helix structure, possibly contributing to their anticancer activity (Li et al 2015d).

Example 9: the detection result of the purified exopolysaccharide in nuclear magnetic resonance

EPS1-1 was subjected to NMR structural analysis. About 35mg of EPS1-1 dissolved in 0.5mL of D₂And (4) in O. The purified EPS1-1 was recorded on a 400M Hz NMR spectrometer at 25 deg.C¹H and¹³c NMR spectra (Bruker AVANCEIII, Germany). Chemical shifts are automatically recorded and expressed in ppm. The results are shown in FIG. 8.

Wherein¹The H NMR spectrum region mainly comprises an anomeric proton region (delta 4.5-5.5ppm) and a H2-H6 connection proton signal region (delta 3.1-4.5 ppm). However, signal overlap in the range of delta 3.1-4.5ppm is severe and the glycosidic bond configuration of EPS is mainly obtained by analysis of the signals of the anomeric proton region. As can be seen from FIG. 8A, there are three absorption peaks in the anomeric proton region, and the absorption peak at 4.69ppm is marked by D₂Caused by O. The other two chemical shifts (δ) were 5.31, 4.95ppm, respectively, indicating that EPS1-1 may contain two different glycosidic linkages, and 2 glycosidic linkages are pyranoses in the α configuration. The signal peak appearing at 5.31ppm is the characteristic absorption peak of alpha-D-glucose isomeric hydrogen, and the result is compared with that of a sample in an FT-IR spectrum at 1200-^-1The characteristic absorption peaks at (a) are relatively consistent. Furthermore, the chemical shift at δ 540ppm showed no significant proton signal, indicating that the EPS1-1 component is pyranose, which is consistent with FT-IR spectroscopy.

Polysaccharides¹³The C NMR spectrum mainly includes anomeric carbon region (. delta.95-110 ppm) and non-anomeric carbon regionAnomeric carbon region (. delta.50-85 ppm). As can be seen in FIG. 8B, there are two intensity signals at the anomeric carbon region of 99.73 and 98.21ppm, indicating that there are two types of glycosidic linkages, corresponding to¹Isomeric proton signals at 5.31 and 4.95ppm in H NMR. The main signal is generated at 99.73ppm, and the signal peak corresponds to → 4) - α -D-Glcp- (1 →. The weak signal in the region delta 160-delta 180ppm (174.98ppm) indicates that it contains trace amounts of aldehyde acids, consistent with analysis of monosaccharide composition. There was no signal peak in the region of 101 to 105ppm, indicating that EPS1-1 contains only glycosidic linkages in the alpha configuration. There was no significant signal near δ 90ppm, indicating the absence of furan ring structures in the polysaccharide. 60.49ppm and 61.10ppm correspond to C-6, no substitution occurred.

In general, the α and β configurations occur in the heteropolysaccharide of lactic acid bacteria. However, some EPS only contain exopolysaccharides produced by the alpha configuration, such as lactobacillus acidophilus DSM20079, lactobacillus plantarum 70810, consistent with our results. In summary, EPS1-1 contains two different sugar residues, has an α configuration of pyranose, with the main glycosidic bond → 4) - α -D-Glcp- (1 →). Considering that acarbose also contains α -D-glucosyl- (1 → 4), we speculate that this is an important reason that EPS1-1 also has the ability to inhibit α -glucosidase activity.

Example 10: thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) results of the purified exopolysaccharide

The thermal stability of the extracellular polysaccharide is an important factor influencing the potential industrial application of the extracellular polysaccharide, and has important significance for researching the biological activity of EPS. 3.806mg of EPS1-1 purified polysaccharide was weighed out and placed in Al₂O₃In the crucible, the flow rate of Ar gas was set to 50mL/min, and the EPS1-1 sample was heated from 30 ℃ to 800 ℃ at a linear heating rate of 10 ℃/min, during which the weight of the polysaccharide sample and the change in melting point were recorded using a TGA-DSC thermogram (Mettler 1600HT), to obtain TGA and DSC plots.

The TGA-DSC curve of the purified polysaccharide EPS1-1 of L.rhamnosus LB1lac10 is shown in FIG. 9. It can be seen from the figure that the EPS1-1 degradation process is mainly as follows: when the temperature is increased from 30 ℃ to 135 ℃, the EPS1-1 has total weight loss of 11.62% (0.44mg), which is mainly caused by moisture or other volatile substances, and the EPS1-1 has a large amount of carboxyl groups. The weight of the polysaccharide is basically kept unchanged between 135 ℃ and 220 ℃; as the temperature continued to increase, the EPS1-1 exhibited a maximum mass loss of 70.74% (2.69mg), during which it was found that the degradation temperature (Td) of the polysaccharide sample was 310.70 ℃, with the partial weight loss being due primarily to degradation of the sample itself; finally, the weight of the EPS1-1 sample was gradually reduced until a constant weight of 0.52mg (13.58%).

In addition, the melting point of EPS1-1 was 246.86 ℃ as determined by Differential Scanning Calorimetry (DSC). The difference in thermal stability of EPS1-1 may be related to molecular structure and monosaccharide composition. For example, KR780676EPS is a galactan composed of galactose units only, and has a melting point of 274.65 ℃; and YW11 EPS is prepared by mixing the following components in a ratio of 2.71: 1, and the melting point of the heteroglycan consisting of glucose and galactose is 143.6 ℃. The temperature does not exceed 150 ℃ in the conventional sterilization and processing process of common industrial products, and the degradation temperature (310.70 ℃) and the melting point (246.86 ℃) of EPS1-1 produced by L.rhamnosus LB1lac10 are far more than 150 ℃, which shows that the heat stability is good, and the method can be applied to the fields of industry and food.

Example 11: application of purified exopolysaccharide EPS1-1 as alpha-glucosidase inhibitor

mu.L of 20mmol/L PNPG and 25. mu.L of sample (0.5mg/mL EPS1-1) were first added to a 96-well plate and incubated at 37 ℃ for 10 min. Then, 50. mu.L of 0.2U/mL of α -glucosidase was added thereto, and the reaction was carried out at 37 ℃ for 20 minutes. Finally, 100. mu.L of 0.1mol/LNa was added₂CO₃The reaction was terminated. The reaction solution having a wavelength of 405nm was detected by a microplate reader (TECAN, infinite M200). Percent inhibition was calculated using acarbose as the positive control using the following formula:

inhibition ratio (%) [1- (C-D)/(A-B) ]

Wherein A is the absorbance of the sample containing no alpha-glucosidase, B is the absorbance of the sample containing no alpha-glucosidase, C is the absorbance of the sample containing alpha-glucosidase, and D is the absorbance of the sample containing no alpha-glucosidase.

The effect of the purified polysaccharide as an α -glucosidase inhibitor is shown in fig. 10.

Compared with the inhibition capability of the alpha-glucosidase under different concentrations (0.2U/mL, 0.15U/mL, 0.1 and 0.01U/mL), the alpha-glucosidase inhibitor has obvious alpha-glucosidase inhibition capability which respectively reaches 15.33%, 25.97%, 37.51% and 95.89%. The results show that EPS1-1 shows strong hypoglycemic activity in vitro tests, is a very potential hypoglycemic active ingredient, can play the potential role of inhibiting the activity of alpha-glucosidase, has great potential of reducing blood sugar, and is expected to provide new active ingredients and sources for the prevention of diabetes and the development of drugs.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.