Litchi polysaccharide, preparation method and application thereof, and preparation method of yogurt containing same

Abstract

The present invention discloses a litchi polysaccharide composed of 42.87% galactose, 30.43% arabinose, and 26.70% glucose by mass. A preparation method comprises using litchi juice as a raw material, and obtaining a litchi polysaccharide with a specific structure through yeast fermentation, centrifugation, nanofiltration, ultrafiltration, and ion adsorption column chromatography purification. A preparation method for yogurt containing the litchi polysaccharide comprises adding the litchi polysaccharide to a yogurt fermentation medium, inoculating Weissella fusion to carry out fermentation, and obtaining the yogurt. The method for preparing the litchi polysaccharide of the present invention is simple, and the obtained litchi polysaccharide has a significant effect of promoting the production of extracellular polysaccharides by fermenting yogurt with Weissella fusion, and significantly improving the texture and flavor of the yogurt.

Description

Technical Field

[0001] The present invention relates to the technical field of food-derived polysaccharides, and more particularly to a litchi polysaccharide, a preparation method and application thereof, and a preparation method of yogurt containing the same. Background Art

[0002] With the improvement of living standards and growing health awareness among Chinese residents, the role of dairy products in their diets has significantly increased. Yogurt, as a food with health benefits, has become increasingly popular among consumers. With the growing awareness of yogurt consumption in the Chinese market, consumers not only demand a variety of yogurt flavors, but also its quality has become a major factor influencing their purchases. However, during the production and storage of yogurt, problems such as whey precipitation, thin texture, sandy texture, and small particles are common. Currently, most factories use chemical thickeners such as hydroxypropyl distarch phosphate to alleviate these problems. While this improves the texture and mouthfeel of the yogurt, it also somewhat obscures the original flavor, thus affecting its quality. Furthermore, countries such as Europe and the United States have already explicitly banned the addition of thickeners and stabilizers to yogurt products. Although relevant policies have not yet been implemented in my country, this may be a future trend in the development of yogurt products. Therefore, the search for natural and safe alternatives to thickeners has become a hot topic of research.

[0003] Extracellular polysaccharides (EPS), a natural viscous fermentation agent, are mucus or capsular polysaccharides secreted by microorganisms outside their cell walls during their growth and metabolism. They possess high viscosity and excellent rheological properties, making them natural and safe thickeners, emulsifiers, and stabilizers. They replace or reduce the use of traditional thickeners and stabilizers, improving food texture and taste, and are widely used in the food industry. Among EPS-producing microorganisms, Weissella fusilis is a recognized safe food microorganism. The EPS produced by its metabolism is non-toxic to humans, comes from a safe and reliable source, and has important health benefits, such as enhancing immunity, fighting tumors, combating ulcers, and lowering cholesterol.

[0004] However, the current yield of EPS synthesized by Weissella fusion is generally low, which limits its application in industrial production.

[0005] Therefore, how to promote the production of EPS by Weissella fusion is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a litchi polysaccharide, a preparation method and application thereof, and a preparation method of yogurt containing the same. By preparing litchi polysaccharides with a specific structure, it is possible to significantly promote the production of extracellular polysaccharides with a specific structure by Weissella fusion, and improve the flavor and texture of yogurt.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The invention discloses a litchi polysaccharide, which consists of 42.87% of galactose, 30.43% of arabinose and 26.70% of glucose in percentage by mass.

[0009] Furthermore, the above-mentioned litchi polysaccharide is connected by α-1,6, α-1,3 and α-1,5.

[0010] Furthermore, the structure of the above-mentioned litchi polysaccharide is that the main chain is formed by →3-β-D-Galp-(1→6)-β-D-Galp-(1→3)-β-D-Galp-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→), and α-L-Araf-(1→5)-α-L-Araf-(1→) is connected to the O-3 position of →6)-β-D-Galp-(1→) to form a branch, or β-D-Glcp or α-L-Araf is connected to the O-6 position of →3)-β-D-Galp-(1→) to form a branch, and the degree of polymerization is 32-56.

[0011] Furthermore, the structural formula of the above litchi polysaccharide is:

[0012]

[0013] A method for preparing the above-mentioned litchi polysaccharide specifically comprises the following steps:

[0014] (1) fermenting the litchi juice with yeast, centrifuging, nanofiltering, and ultrafiltering to obtain a litchi polysaccharide solution;

[0015] (2) adding the litchi polysaccharide solution to a DEAE-52 chromatography column, eluting with a NaCl-Tris-HCl solution as an eluent, collecting the eluate, and concentrating to obtain a litchi polysaccharide concentrate;

[0016] (3) Adding the litchi polysaccharide concentrate to a Sephadex G-100 chromatography column, eluting with phosphate buffer as an eluent, collecting the eluate, concentrating, and drying to obtain litchi polysaccharide.

[0017] Furthermore, in the above step (1), the concentration of litchi juice is 400-600 mg / mL; the yeast is Saccharomyces cerevisiae at a concentration of 200-500 mg / L; the fermentation temperature is 25-37°C and the fermentation time is 48-96 hours; the centrifugal force is 5000×g and the time is 10 minutes; the molecular weight cutoff of the membrane used for nanofiltration is 5000 Da; the molecular weight cutoff of the membrane used for ultrafiltration is 300 Da; and the purity of the litchi polysaccharide solution is 40%-50%.

[0018] The beneficial effects of adopting the above-mentioned further technical solution are that yeast fermentation first utilizes the monosaccharides or oligosaccharides in the litchi juice liquid, which can remove most of the monosaccharides or oligosaccharides; the yeast can be removed by centrifugation, thereby greatly facilitating the removal of monosaccharides; polysaccharides with larger molecular weight can be separated by a 5000 Da filter membrane; and litchi polysaccharides can be further enriched by a 300 Da filter membrane while removing small molecular impurities (such as salt ions and monosaccharides).

[0019] Furthermore, in the above step (2), the sample volume of the litchi polysaccharide solution is 10-20 mL, and the mass concentration is 2%-4% (w / v); the inner diameter of the DEAE-52 chromatography column is 3.5-5.0 cm, and the length is 60-100 cm; the concentration of the NaCl-Tris-HCl solution is 0.2-1.0 mol / L, and the pH is 7.0-9.0; the elution flow rate is 0.5-1.0 mL / min; the eluate is collected for 300-900 min; and the purity is 75%-85%.

[0020] Furthermore, in the above step (3), the loading amount of litchi polysaccharide concentrate is 2-5 mL, and the mass concentration is 0.2%-0.5% (w / v); the inner diameter of the Sephadex G-100 chromatography column is 1.6-3.5 cm, and the length is 50-100 cm; the concentration of the phosphate buffer is 0.05-0.15 mol / L, and the pH is 7.0-9.0; the elution flow rate is 0.5-1.0 mL / min; the eluate is collected for 50-400 min; and the purity of the litchi polysaccharide is 95%-99%.

[0021] The beneficial effect of adopting the above-mentioned further technical solution is that high volume and high concentration sugar solution, too short chromatography column and too fast elution flow rate will lead to poor separation effect, while low volume and low concentration sugar solution, too high chromatography column and too slow elution flow rate will greatly reduce the separation efficiency; the concentration and pH of the eluent will affect the separation effect, and the collection time affects the concentration and structure of the target polysaccharide.

[0022] A use of the litchi polysaccharide or the litchi polysaccharide prepared by the above preparation method in the production of extracellular polysaccharides by fusogenic Weissella.

[0023] A method for preparing yogurt containing the above litchi polysaccharide or the litchi polysaccharide prepared by the above preparation method specifically comprises the following steps: adding litchi polysaccharide to yogurt fermentation medium, inoculating fusion Weissella for fermentation, and obtaining yogurt.

[0024] Furthermore, the addition amount of the above-mentioned litchi polysaccharide is 5%-15% (w / v); the yogurt fermentation medium includes 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose, and the pH is 6.3; the inoculation amount of fusion Weissella is 2%-4% (v / v); the fermentation temperature is 30-40°C, the rotation speed is 50-100 r / min, and the time is 36-72h.

[0025] The beneficial effect of adopting the above further technical solution is that if the concentration of litchi polysaccharide in the yogurt fermentation medium is too low, it will affect the production of exopolysaccharides that promote fusion of Weissella; while if the concentration is too high, it will cause the plasmolysis of fusion of Weissella and inhibit the growth of significant bacteria.

[0026] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The present invention uses litchi juice as raw material, removes monosaccharides and disaccharides through yeast, and removes solids by centrifugation to obtain clear juice. Nanofiltration and ultrafiltration technologies are combined to greatly simplify the purification steps of litchi polysaccharides. In addition, ion exchange chromatography and dextran gel chromatography are combined to prepare litchi polysaccharides with a purity of more than 95% and a specific structure. The litchi polysaccharide is composed of 42.87% galactose, 30.43% arabinose and 26.70% glucose by mass, and is connected by α-1,6, α-1,3 and α-1,5.

[0028] 2. The litchi polysaccharide of the present invention can significantly promote the fusion of Weissella to produce a homotypic exopolysaccharide with a specific structure (the main chain is mainly →6-α-Glcp-1→, with a small amount of side chain α-T-Glcp connected to the O-3 of →6)-α-D-Glcp-(1→), with a molecular weight of 1.0-2.0×10 5 Da; and can significantly improve the viscosity, hardness, chewiness and elasticity of yogurt, while increasing the contents of 2-methylpropyl butyrate, 2-acetylfuran, hexanal and ethyl butyrate, and reducing the contents of 2-hexanone-M, 2-ethylfuran, toluene, propionic acid and 2-methylbutanol to improve the flavor of yogurt.

[0029] 3. The method for preparing litchi polysaccharide of the present invention is simple, and the prepared litchi polysaccharide has a significant effect of promoting the production of extracellular polysaccharides by yogurt fermented by Weissella fusion, and significantly improves the texture and flavor of yogurt.

[0030] 4. The present invention adds litchi polysaccharide as a prebiotic to the yogurt fermentation system to promote lactic acid bacteria (Weissella fusion) to produce EPS as a natural thickener, thereby achieving the purpose of increasing the viscosity of the fermented product (yogurt) without introducing chemical additives. It has no toxic side effects on the human body and is environmentally friendly. It is an important means to replace additives and can significantly improve the flavor, texture and nutritional quality of yogurt. It has broad application prospects in the dairy industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the NMR spectrum of litchi polysaccharide in Example 1 of the present invention;

[0032] Figure 2 This is the NMR spectrum of the extracellular polysaccharide of Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] Litchi polysaccharide is composed of 42.87% galactose, 30.43% arabinose and 26.70% glucose by mass, and is connected by α-1,6, α-1,3 and α-1,5. The main chain is formed by →3-β-D-Galp-(1→6)-β-D-Galp-(1→3)-β-D-Galp-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→), and α-L-Araf-(1→5)-α-L-Araf-(1→ is connected to the O-3 position of →6)-β-D-Galp-(1→) to form a branch, or β-D-Glcp or α-L-Araf is connected to the O-6 position of →3)-β-D-Galp-(1→) to form a branch. The degree of polymerization is 40.

[0036] The preparation method of the above-mentioned litchi polysaccharide specifically comprises the following steps:

[0037] (1) Saccharomyces cerevisiae at a concentration of 500 mg / L was added to 500 mg / mL litchi juice, and the juice was fermented at 25°C for 72 h until the reducing sugar content decreased and remained stable. The juice was then centrifuged at 5000 × g for 10 min, the supernatant was nanofiltered through a membrane with a molecular weight cutoff of 5000 Da, and the filtrate was ultrafiltered through a membrane with a molecular weight cutoff of 300 Da. The retentate was collected to obtain a litchi polysaccharide solution.

[0038] (2) 15 mL of a 3% litchi polysaccharide solution was added to a DEAE-52 chromatography column with an inner diameter of 3.5 cm and a length of 100 cm, and eluted with a 0.2 mol / L NaCl-Tris-HCl solution with a pH of 8.0 at a flow rate of 1.0 mL / min. The eluate was collected for 300-900 min and concentrated to obtain a litchi polysaccharide concentrate;

[0039] (3) 3 mL of 0.3% litchi polysaccharide concentrate was added to a Sephadex G-100 chromatography column with an inner diameter of 1.6 cm and a length of 100 cm, and eluted with 0.1 mol / L phosphate buffer at a pH of 8.0 as the eluent at a flow rate of 1.0 mL / min. The eluate was collected for 50-400 min, concentrated, and dried to obtain litchi polysaccharide.

[0040] The preparation method of yogurt containing the above-mentioned litchi polysaccharide specifically comprises the following steps: adding 10% litchi polysaccharide to a yogurt fermentation medium containing 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose and having a pH of 6.3, sealing the medium with a cover, boiling it in a boiling water bath for 15 minutes, cooling it to 37°C, inoculating it with 3% fused Weissella bacteria, and fermenting it at a temperature of 30°C and a rotation speed of 100 r / min for 72 hours to obtain yogurt.

[0041] Example 2

[0042] Litchi polysaccharide is composed of 42.87% galactose, 30.43% arabinose and 26.70% glucose by mass, and is connected by α-1,6, α-1,3 and α-1,5. The main chain is formed by →3-β-D-Galp-(1→6)-β-D-Galp-(1→3)-β-D-Galp-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→), and α-L-Araf-(1→5)-α-L-Araf-(1→ is connected to the O-3 position of →6)-β-D-Galp-(1→), or β-D-Glcp or α-L-Araf is connected to the O-6 position of →3)-β-D-Galp-(1→). The degree of polymerization is 32.

[0043] The preparation method of the above-mentioned litchi polysaccharide specifically comprises the following steps:

[0044] (1) Saccharomyces cerevisiae at a concentration of 350 mg / L was added to 600 mg / mL litchi juice, and the mixture was fermented at 30°C for 48 h until the reducing sugar content decreased and remained stable. The juice was then centrifuged at 5000 × g for 10 min, the supernatant was nanofiltered through a membrane with a molecular weight cutoff of 5000 Da, and the filtrate was ultrafiltered through a membrane with a molecular weight cutoff of 300 Da. The retentate was collected to obtain a litchi polysaccharide solution.

[0045] (2) 20 mL of a 4% litchi polysaccharide solution was added to a DEAE-52 chromatography column with an inner diameter of 5.0 cm and a length of 60 cm, and eluted with a 1.0 mol / L NaCl-Tris-HCl solution with a pH of 7.0 as an eluent at a flow rate of 1.0 mL / min. The eluate was collected for 300-900 min and concentrated to obtain a litchi polysaccharide concentrate;

[0046] (3) 5 mL of 0.5% litchi polysaccharide concentrate was added to a Sephadex G-100 chromatography column with an inner diameter of 3.5 cm and a length of 50 cm, and eluted with 0.15 mol / L phosphate buffer at a pH of 7.0 as an eluent at a flow rate of 1.0 mL / min. The eluate was collected for 50-400 min, concentrated, and dried to obtain litchi polysaccharide.

[0047] The preparation method of yogurt containing the above-mentioned litchi polysaccharide specifically comprises the following steps: adding 15% litchi polysaccharide to a yogurt fermentation medium containing 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose and having a pH of 6.3, sealing the medium with a cover, boiling it in a boiling water bath for 15 minutes, cooling it to 37°C, inoculating it with 2%-4% fused Weissella bacteria, and fermenting it at a temperature of 40°C and a rotation speed of 50 r / min for 36 hours to obtain yogurt.

[0048] Example 3

[0049] Litchi polysaccharide is composed of 42.87% galactose, 30.43% arabinose and 26.70% glucose by mass, and is connected by α-1,6, α-1,3 and α-1,5. The main chain is formed by →3-β-D-Galp-(1→6)-β-D-Galp-(1→3)-β-D-Galp-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→), and α-L-Araf-(1→5)-α-L-Araf-(1→ is connected to the O-3 position of →6)-β-D-Galp-(1→) to form a branch, or β-D-Glcp or α-L-Araf is connected to the O-6 position of →3)-β-D-Galp-(1→) to form a branch. The degree of polymerization is 48.

[0050] The preparation method of the above-mentioned litchi polysaccharide specifically comprises the following steps:

[0051] (1) Saccharomyces cerevisiae at a concentration of 200 mg / L was added to 500 mg / mL litchi juice, and the juice was fermented at 37°C for 48 h until the reducing sugar content decreased and remained stable. The juice was then centrifuged at 5000 × g for 10 min, the supernatant was nanofiltered through a membrane with a molecular weight cutoff of 5000 Da, and the filtrate was ultrafiltered through a membrane with a molecular weight cutoff of 300 Da. The retentate was collected to obtain a litchi polysaccharide solution.

[0052] (2) 10 mL of a 2% litchi polysaccharide solution was added to a DEAE-52 chromatography column with an inner diameter of 3.5 cm and a length of 80 cm, and eluted with a 0.5 mol / L NaCl-Tris-HCl solution with a pH of 9.0 as the eluent at a flow rate of 0.5 mL / min. The eluate was collected for 300-900 min and concentrated to obtain a litchi polysaccharide concentrate;

[0053] (3) 2 mL of 0.2% litchi polysaccharide concentrate was added to a Sephadex G-100 chromatography column with an inner diameter of 1.6 cm and a length of 80 cm, and eluted with 0.05 mol / L phosphate buffer at a pH of 7.0 as the eluent at a flow rate of 1.0 mL / min. The eluate was collected for 50-400 min, concentrated, and dried to obtain litchi polysaccharide.

[0054] The preparation method of yogurt containing the above-mentioned litchi polysaccharide specifically comprises the following steps: adding 5% litchi polysaccharide to a yogurt fermentation medium containing 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose and having a pH of 6.3, sealing the medium with a cover, boiling it in a boiling water bath for 15 minutes, cooling it to 37°C, inoculating it with 2%-4% fused Weissella bacteria, and fermenting it at a temperature of 35°C and a rotation speed of 75 r / min for 48 hours to obtain yogurt.

[0055] Comparative Example 1

[0056] The preparation method of litchi polysaccharide solution specifically comprises the following steps: adding 500 mg / L of brewer's yeast to 500 mg / mL of litchi juice, fermenting at 25°C for 72 hours until the reducing sugar content decreases and remains stable, then centrifuging at 5000×g for 10 minutes, nanofiltration of the supernatant through a membrane with a molecular weight cutoff of 5000 Da, ultrafiltration of the filtrate through a membrane with a molecular weight cutoff of 300 Da, and collecting the retentate to obtain a litchi polysaccharide solution with a purity of 40%-50%.

[0057] The preparation method of yogurt containing the above-mentioned litchi polysaccharide solution specifically comprises the following steps: adding 10% litchi polysaccharide solution to a yogurt fermentation medium containing 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose and having a pH of 6.3, sealing the medium with a cover, boiling it in a boiling water bath for 15 minutes, cooling it to 37°C, inoculating it with 3% fused Weissella bacteria, and fermenting it at a temperature of 30°C and a rotation speed of 100 r / min for 72 hours to obtain yogurt.

[0058] Comparative Example 2

[0059] The preparation method of litchi polysaccharide concentrate specifically comprises the following steps:

[0060] (1) adding 500 mg / L of saccharomyces cerevisiae to 500 mg / mL of litchi juice, fermenting at 25°C for 72 h until the reducing sugar content decreased and remained stable, then centrifuging at 5000 × g for 10 min, nanofiltration of the supernatant through a membrane with a molecular weight cutoff of 5000 Da, ultrafiltration of the filtrate through a membrane with a molecular weight cutoff of 300 Da, and collecting the retentate to obtain a litchi polysaccharide solution with a purity of 40%-50%;

[0061] (2) 15 mL of a 3% mass concentration litchi polysaccharide solution was added to a DEAE-52 chromatography column with an inner diameter of 3.5 cm and a length of 100 cm, and eluted with a NaCl-Tris-HCl solution with a concentration of 0.2 mol / L and a pH of 8.0 at a flow rate of 1.0 mL / min. The eluate was collected for 300-900 min and concentrated to obtain a litchi polysaccharide concentrate with a purity of 75%-85%.

[0062] The preparation method of yogurt containing the above-mentioned litchi polysaccharide concentrated liquid specifically comprises the following steps: adding 10% litchi polysaccharide concentrated liquid to a yogurt fermentation medium containing 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose and having a pH of 6.3, sealing the medium with a cover, boiling it in a boiling water bath for 15 minutes, cooling it to 37°C, inoculating it with 3% fused Weissella bacteria, and fermenting it at a temperature of 30°C and a rotation speed of 100 r / min for 72 hours to obtain yogurt.

[0063] Comparative Example 3

[0064] The preparation method of yogurt containing sucrose specifically comprises the following steps: adding 10% sucrose to a yogurt fermentation medium containing 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose and having a pH of 6.3; sealing the medium with a cover, boiling it in a boiling water bath for 15 minutes; cooling it to 37°C, inoculating it with 3% fused Weissella bacteria, and fermenting it at a temperature of 30°C and a rotation speed of 100 r / min for 72 hours to obtain yogurt.

[0065] Performance Testing

[0066] 1. Nuclear magnetic resonance analysis of litchi polysaccharides and extracellular polysaccharides

[0067] 100 mg each of the litchi polysaccharide and extracellular polysaccharide prepared in Examples 1-3 were completely dissolved in 95% D2O and freeze-dried three times. The litchi polysaccharide was dissolved in D2O, filtered through a 0.22 μm aqueous filter membrane, and then loaded into a nuclear magnetic resonance tube.

[0068] Detection conditions: Bruker 600M superconducting nuclear magnetic resonance spectrometer, TXI inverted triple resonance probe (5mm), 1 H. 13 C. 1 H- 1 HCOSY, HSQC, NOSEY, and HMBC spectra were all detected at 298 K; 1 H spectrum and 13 The C spectra were scanned at 600 and 150 MHz using a standard Bruker pulse sequence. 1 H- 1 HCOSY, HSQC, NOSEY and HMBC analyses were performed, and the spectra were analyzed using MestReNova 6.1.1 software.

[0069] Example 1 The NMR spectrum of litchi polysaccharide is as follows Figure 1 As shown, the nuclear magnetic spectrum of the extracellular polysaccharide in Example 1 is as follows Figure 2 shown.

[0070] Depend on Figure 1 It can be seen that through one-dimensional and two-dimensional nuclear magnetic ( 1 H. 13 C. 1 H- 1 HCOSY, HSQC, HMBC) analysis and identification showed that the litchi polysaccharide prepared in Example 1 had a specific structure, and the structural formula was:

[0071]

[0072] In addition, one-dimensional and two-dimensional nuclear magnetic resonance ( 1 H. 13 C. 1 H- 1 HCOSY, HSQC, HMBC) analysis and identification showed that the litchi polysaccharide prepared in Example 2 had a specific structure, and the structural formula was:

[0073]

[0074] Through one-dimensional and two-dimensional nuclear magnetic 1 H. 13 C. 1 H-1 HCOSY, HSQC, HMBC) analysis and identification showed that the litchi polysaccharide prepared in Example 3 had a specific structure, and the structural formula was:

[0075]

[0076] Depend on Figure 2 It can be seen that the litchi polysaccharide prepared in Example 1 can significantly promote the production of homotypic exopolysaccharides of a specific structure by the fusion of Weissella. The structural formula of the exopolysaccharide is:

[0077]

[0078] In addition, the litchi polysaccharide prepared in Example 2 can significantly promote the production of homotypic exopolysaccharides of a specific structure by the fusion of Weissella. The structural formula of the exopolysaccharide is:

[0079] The litchi polysaccharide prepared in Example 3 can significantly promote the production of homotypic exopolysaccharides of a specific structure by the fusion of Weissella. The structural formula of the exopolysaccharide is:

[0080] 2. Yogurt texture analysis

[0081] The yogurts prepared in Examples 1-3 and Comparative Examples 1-3 were respectively analyzed for hardness, viscosity, elasticity, cohesion, stickiness and chewiness using a texture analyzer.

[0082] The results are shown in Table 1.

[0083] Table 1 Texture analysis results of yogurts of Examples 1-3

[0084]

[0085]

[0086] As shown in Table 1, compared with Comparative Examples 1-3, the litchi polysaccharides prepared in Examples 1-3 can significantly improve the hardness, viscosity, elasticity, cohesion, stickiness and chewiness of yogurt, thereby improving the texture of yogurt.

[0087] 3. Yogurt flavor analysis

[0088] 2 g of each of the yogurts prepared in Examples 1-3 and Comparative Examples 1-3 were placed in a 20 mL headspace bottle and incubated at 60° C. for 15 min before GC-IMS analysis. The chromatographic column type was MXT-5 (0.53 mm×15 m), the column temperature was 60° C., the carrier gas was N2, the IMS temperature was 45° C., the injection volume was 500 μL, the injection temperature was 85° C., and the analysis time was 20 min.

[0089] The results are shown in Table 2.

[0090] Table 2 Flavor analysis results of yogurt of Examples 1-3

[0091]

[0092]

[0093] As shown in Table 2, compared with Comparative Examples 1-3, the litchi polysaccharides prepared in Examples 1-3 can simultaneously increase 2-methylpropyl butyrate, 2-acetylfuran, hexanal and ethyl butyrate, and reduce 2-hexanone-M, 2-ethylfuran, toluene, propionic acid and 2-methylbutanol, thereby improving the yogurt flavor.

[0094] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing litchi polysaccharide, comprising the following steps: (1) fermenting the litchi juice with yeast, centrifuging, nanofiltering, and ultrafiltering to obtain a litchi polysaccharide solution; The yeast is Saccharomyces cerevisiae at a concentration of 200-500 mg / L; the fermentation temperature is 25-37° C. and the fermentation time is 48-72 hours; (2) adding the litchi polysaccharide solution to a DEAE-52 chromatography column, eluting with a NaCl-Tris-HCl solution as an eluent, collecting the eluate, and concentrating to obtain a litchi polysaccharide concentrate; The concentration of the NaCl-Tris-HCl solution is 0.2-1.0 mol / L, and the pH is 7.0-9.0; the flow rate of the elution is 0.5-1.0 mL / min; and the eluate is collected for 300-900 min; (3) adding the litchi polysaccharide concentrate to a Sephadex G-100 chromatography column, eluting with phosphate buffer as an eluent, collecting the eluate, concentrating, and drying to obtain the litchi polysaccharide; The concentration of the phosphate buffer is 0.05-0.15 mol / L, and the pH is 7.0-8.0; the flow rate of the elution is 1.0 mL / min; and the eluate is collected for 50-400 minutes.

2. The method for preparing litchi polysaccharide according to claim 1, wherein In step (1), the concentration of the litchi juice is 400-600 mg / mL; the centrifugal force of the centrifugation is 5000×g, and the time is 10 min; the molecular weight cutoff of the membrane used in the nanofiltration is 5000 Da; the molecular weight cutoff of the membrane used in the ultrafiltration is 300 Da; and the purity of the litchi polysaccharide solution is 40%-50%.

3. The method for preparing litchi polysaccharide according to claim 1, wherein: In step (2), the loading amount of the litchi polysaccharide solution is 10-20 mL, and the mass concentration is 2%-4%; the inner diameter of the DEAE-52 chromatography column is 3.5-5.0 cm, and the length is 60-100 cm; and the purity is 75%-85%.

4. The method for preparing litchi polysaccharide according to claim 1, wherein In step (3), the loading amount of the litchi polysaccharide concentrate is 2-5 mL, and the mass concentration is 0.2%-0.5%; the inner diameter of the Sephadex G-100 chromatography column is 1.6-3.5 cm, and the length is 50-100 cm; the purity of the litchi polysaccharide is 95%-99%.

5. Use of litchi polysaccharide prepared by the preparation method according to claim 1 in the production of exopolysaccharides by Weissella fusogenum.

6. A method for preparing yogurt containing litchi polysaccharide obtained by the preparation method according to claim 1, characterized in that: The specific steps include: The yogurt is obtained by adding litchi polysaccharide to a yogurt fermentation medium and inoculating the culture medium with fused Weissella for fermentation.

7. The method for preparing yogurt according to claim 6, wherein: The addition amount of the litchi polysaccharide is 5%-15%; the yogurt fermentation medium includes 0.12 mg / mL skim milk powder and 0.6 mg / mL sucrose, and the pH is 6.3; the inoculation amount of the fusion Weissella is 2%-4%; the fermentation temperature is 30-40°C, the rotation speed is 50-100 r / min, and the time is 36-72 hours.

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