Propionibacterium metabolite containing gamma-Glu-Abu and preparation method thereof

Abstract

The invention discloses a propionibacterium metabolite containing gamma-Glu-Abu and a preparation method of the propionibacterium metabolite, and belongs to the technical field of food seasonings, and the propionibacterium metabolite contains more than 0.1% of gamma-Glu-Abu per unit dry weight. The preparation method of the propionibacterium metabolite containing gamma-Glu-Abu comprises the following steps: culturing propionibacterium by using a culture medium added with two compounds of Abu and Glu, and preparing the propionibacterium metabolite containing gamma-Glu-Abu by using the obtained propionibacterium thallus. The bacteriostatic activity of the propionibacterium metabolite containing gamma-Glu-Abu is consistent with that of a conventional propionibacterium metabolite without Glu and Abu, that is, the bacteriostatic activity of the propionibacterium metabolite is not affected, and the propionibacterium metabolite containing gamma-Glu-Abu can be used for the same application as an existing propionibacterium metabolite, such as a preservative. Meanwhile, the obtained propionibacterium metabolite containing gamma-Glu-Abu has excellent strong taste, the flavor and taste of the propionibacterium metabolite can be improved, the taste is good, and the propionibacterium metabolite containing gamma-Glu-Abu can be applied to the industries of seasonings or food additives and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of food seasonings, and particularly relates to a propionibacterium metabolite containing gamma-Glu-Abu and a preparation method thereof. Background Art

[0002] Propionibacterium is an anaerobic, Gram-positive bacterium widely found in soil, cheese, milk, dairy products, and silage. In recent years, Propionibacterium has been discovered and used in food products, particularly as a secondary starter in Swiss cheese. In Swiss cheese, Propionibacterium contributes to its unique appearance, texture, and flavor. For example, during its growth, Propionibacterium releases a certain amount of CO2, which makes the cheese fluffy and porous. Furthermore, Propionibacterium metabolites, particularly organic acids, impart a unique flavor to the cheese. Furthermore, Propionibacterium fermentation produces vitamin B12, folic acid, propionic acid, and rutin.

[0003] Furthermore, propibactins have been discovered among Propionibacterium metabolites. Propionibactins are a class of antibacterial proteins or peptides produced by Propionibacterium. They are sensitive to proteases but insensitive to catalases, and primarily inhibit some Gram-negative bacteria and some molds and yeasts. Currently discovered propionibactins include PLG-1, Jensenins, Propionibactin T1, Propionibactin SM1, PAMP, and Microgard™. Propionibactins have great potential in food preservation. Nisin, currently a commonly used inhibitor, primarily inhibits Gram-positive bacteria. Combining these two agents can yield even greater antibacterial effects. Danisco currently combines Propionibacterium metabolites with other substances to develop and produce a series of products, such as MicroGARD™ 200.

[0004] Glutathione, formed by the combination of glutamic acid, cysteine, and glycine, is known to impart kokumi to food. Peptides represented by the general formula γ-Glu-Abu or γ-Glu-Abu-Gly have also been reported to impart kokumi to food and are more stable than glutathione. γ-Glutamyl transpeptidase is known to transfer glutamic acid from the γ position of glutathione to other amino-containing compounds. When the amino-containing compound is an amino acid, the reaction produces γ-Glu-Abu. However, there is currently no method for preparing Propionibacterium metabolites containing γ-Glu-Abu compounds. Summary of the Invention

[0005] To address the technical challenges of the prior art, the present invention proposes a propionibacterium metabolite containing γ-Glu-Abu and a method for preparing the same. Propionibacterium is cultured in a culture medium supplemented with two compounds, Abu and Glu, and the resulting propionibacterium cells are used to prepare the propionibacterium metabolite containing γ-Glu-Abu. This γ-Glu-Abu-containing propionibacterium metabolite imparts an excellent kokumi (rich flavor) to foods, improving the flavor and mouthfeel of the propionibacterium metabolite.

[0006] According to a first aspect of the technical solution of the present invention, a propionibacterium metabolite containing γ-Glu-Abu is provided, wherein the propionibacterium metabolite containing γ-Glu-Abu contains more than 0.1% of γ-Glu-Abu per unit dry weight.

[0007] Preferably, the propionibacterium in the propionibacterium metabolite is a propionibacterium that can take Glu and Abu into cells and accumulate γ-Glu-Abu in the cells.

[0008] Preferably, the propionibacterium in the propionibacterium metabolite is a mixture of Propionibacterium sieversii, Propionibacterium acidogenicum, Propionibacterium terrei and Propionibacterium janaschii.

[0009] Preferably, the propionibacterium metabolite containing γ-Glu-Abu is prepared by culturing propionibacterium in a culture medium supplemented with two compounds, Abu and Glu, and using the obtained propionibacterium cells.

[0010] Preferably, the propionibacterium metabolite containing γ-Glu-Abu is in the form of a paste, powder or solution.

[0011] According to a second aspect of the technical solution of the present invention, a method for preparing the above-mentioned Propionibacterium metabolite containing γ-Glu-Abu is provided, which comprises the following steps: Step S1: Preparation of Propionibacterium culture medium and activation of Propionibacterium strains; Step S2: fermenting and culturing Propionibacterium based on the activated Propionibacterium strain obtained in step S1; Step S3: preparing propionibacterium metabolites from the propionibacterium fermentation broth prepared under the fermentation conditions of step S2.

[0012] Preferably, the culture medium in step S1 is a culture medium capable of proliferating Propionibacterium.

[0013] Preferably, the carbon source of the culture medium is any one or more of glucose, sucrose, sodium lactate, molasses, lactose and whey powder; the nitrogen source is any one or more of ammonia, ammonium salt, yeast extract, corn steep liquor, peptone and beef extract; and the inorganic salt is any one or more of phosphate and sulfate.

[0014] Preferably, the amount of Abu added is 20 ppm or more, and the amount of γ-Glu added is 25 ppm or more.

[0015] Preferably, the amount of Abu added is 30 ppm or more, and the amount of γ-Glu added is 50 ppm or more.

[0016] Compared with the prior art, the propionibacterium metabolite containing γ-Glu-Abu and the preparation method of the present invention have the following beneficial technical effects: 1. The antibacterial activity of the Propionibacterium metabolite containing γ-Glu-Abu is consistent with that of the conventional Propionibacterium metabolite without the addition of Glu and Abu, that is, it does not affect the antibacterial activity of the Propionibacterium metabolite. The Propionibacterium metabolite containing γ-Glu-Abu can be used for the same purposes as the existing Propionibacterium metabolites, such as preservatives.

[0017] 2. Propionibacterial antimicrobial peptides, products of Propionibacteria, are known to inhibit the growth and proliferation of Gram-negative bacteria. However, these antimicrobial peptides have never been reported to impart a rich flavor to food. In particular, Propionibacterial metabolites have the ability to impart an excellent rich flavor to food. The Propionibacterial metabolites of the present invention can improve the flavor and mouthfeel of Propionibacterial metabolites, resulting in a favorable mouthfeel. The present method for preparing the Propionibacterial metabolite of γ-Glu-Abu is simple to operate and low-cost. DETAILED DESCRIPTION

[0018] In order to make the technical problems solved by the present invention, the technical solutions adopted, and the beneficial effects obtained more clearly understood, the present invention is further described in detail below with reference to specific embodiments. The specific embodiments described herein are only used to illustrate the present invention and are not intended to constitute any limitation of the present invention. Unless otherwise defined, all terms used in the present invention have the same meaning as commonly used in the field to which the present invention belongs.

[0019] The following specific examples are provided to help understand the present invention, but it should be understood that the embodiments and test examples listed in the present invention are only used to illustrate the present invention and do not constitute any limitation. The actual protection scope of the present invention is set forth in the claims.

[0020] The present invention discloses a propionibacterium metabolite containing γ-Glu-Abu and a preparation method thereof, belonging to the technical field of food seasonings. The propionibacterium metabolite containing γ-Glu-Abu contains more than 0.1% γ-Glu-Abu per unit dry weight. The preparation method of the propionibacterium metabolite containing γ-Glu-Abu is to culture propionibacterium with a culture medium supplemented with two compounds, Abu and Glu, and use the obtained propionibacterium cells to prepare the propionibacterium metabolite containing γ-Glu-Abu. The propionibacterium metabolite containing γ-Glu-Abu has the same antibacterial activity as conventional propionibacterium metabolites without Glu and Abu, that is, it does not affect the antibacterial activity of the propionibacterium metabolites. The propionibacterium metabolite containing γ-Glu-Abu can be used for the same purposes as existing propionibacterium metabolites, such as preservatives. At the same time, the propionibacterium metabolite containing γ-Glu-Abu obtained at this time has an excellent rich taste, can improve the flavor and taste of the propionibacterium metabolites, has a good taste, and can be used in industries such as seasonings or food additives.

[0021] In the present invention, when propionibacteria are inoculated into a propionibacterial culture medium, they can grow and secrete propionibacterial antimicrobial peptides. However, the resulting propionibacterial metabolites lack the kokumi flavor that imparts to food. When γ-Glu and Abu (Abu represents aspartic acid, and γ-Glu represents L-2-aminobutyric acid) are added to the culture medium under the same fermentation conditions and for the same fermentation time, a propionibacterial metabolite containing γ-Glu-Abu is obtained. Experimental verification has shown that the antibacterial activity of the propionibacterial metabolite containing γ-Glu-Abu is consistent with that of conventional propionibacterial metabolites without Glu and Abu, indicating that it does not affect the antibacterial activity of the propionibacterial metabolite. The propionibacterial metabolite containing γ-Glu-Abu can be used in the same applications as existing propionibacterial metabolites, such as as a preservative. Furthermore, the resulting propionibacterial metabolite containing γ-Glu-Abu exhibits an excellent kokumi flavor, improving the flavor and mouthfeel of propionibacterial metabolites and providing a favorable mouthfeel.

[0022] In one embodiment, a Propionibacterium metabolite containing γ-Glu-Abu can be in the form of a paste, a powder, or a solution, or there is no particular limitation.

[0023] In one embodiment, a Propionibacterium metabolite containing γ-Glu-Abu contains 0.1% or more of the Propionibacterium metabolite per dry weight. Preferably, a Propionibacterium metabolite containing γ-Glu-Abu contains 0.2% or more of γ-Glu-Abu per dry weight. More preferably, a Propionibacterium metabolite containing γ-Glu-Abu contains 0.5% or more of γ-Glu-Abu per dry weight.

[0024] In the present invention, there are no specific limitations on propionibacteria. Propionibacteria are defined as those capable of internalizing Glu and Abu and accumulating γ-Glu-Abu within their cells. Propionibacteria may be wild-type strains, mutants, or genetically recombinant strains. Mutants or genetically recombinant strains may be subjected to physical mutagenesis, such as ultraviolet light, or chemical mutagenesis, such as NTG, to enhance their ability to internalize Glu and Abu.

[0025] In one embodiment, there is no particular limitation on the propionibacterium. Propionibacterium is limited to propionibacteria that can take up Glu into cells and accumulate γ-Glu-Abu intracellularly, such as Propionibacterium schizophyllum, Propionibacterium acidogenum, Propionibacterium terrei, or Propionibacterium jannaschii. In a preferred embodiment, the propionibacteria are Propionibacterium schizophyllum and Propionibacterium acidogenum.

[0026] In another embodiment, a method of preparing a Propionibacterium metabolite containing γ-Glu-Abu of the present invention comprises the following steps: Step S1: Preparation of Propionibacterium culture medium and activation of Propionibacterium strains; further comprising the following steps: Step S11: preparing a Propionibacterium culture medium; selecting a culture medium in which Propionibacterium can proliferate. In a preferred embodiment, the carbon source of the culture medium is preferably glucose, sucrose, sodium lactate, molasses, lactose or whey powder; in a preferred embodiment, the nitrogen source of the culture medium is preferably ammonia, ammonium salt, yeast extract, corn steep liquor, peptone or beef extract; in a preferred embodiment, the inorganic salt of the culture medium is preferably phosphate or sulfate.

[0027] γ-Glu and Abu are added to the prepared culture medium, where γ-Glu represents glutamic acid and Abu represents 2-aminobutyric acid. In a preferred embodiment, γ-Glu and Abu may be present in the culture medium before the bacteria are cultured, or a mixture of γ-Glu and Abu may be added to the culture medium 48 hours before the cultivation of the propionibacterium. In a preferred embodiment, the mixture of γ-Glu and Abu is added to the culture medium 0-36 hours before the cultivation of the propionibacterium. In a preferred embodiment, the mixture of γ-Glu and Abu is added to the culture medium 0-12 hours before the cultivation of the propionibacterium. In a preferred embodiment, the mixture of γ-Glu and Abu is added to the culture medium 0-6 hours before the cultivation of the propionibacterium.

[0028] Step S12: Activate the Propionibacterium strain; remove the ampoule tube, open it, and use a sterile pipette to draw 0.3-0.5 mL of sterile culture medium into the ampoule tube in a clean bench to dissolve the Propionibacterium cells. Then, take a small amount and inject it into the culture medium. Incubate anaerobically at 37°C for 48 hours until visible colonies are formed.

[0029] Step S2: Ferment and culture the Propionibacterium based on the activated Propionibacterium strain obtained in Step S1. The culture conditions can be the same fermentation conditions used for the preparation of propionibacterium metabolites. The culture conditions can be appropriately modified depending on the propionibacterium used. Any method, such as batch culture or continuous culture, can also be used. In a preferred embodiment, the Propionibacterium is any one of Propionibacterium sieversii, Propionibacterium acidogenic, Propionibacterium terrei, and Propionibacterium janaschii. In a preferred embodiment, the Propionibacterium sieversii or Propionibacterium acidogenic is selected. In a preferred embodiment, the culture temperature of Propionibacterium sieversii or Propionibacterium acidogenic is set at 28°C-32°C and placed in an incubator for submerged liquid culture. In a preferred embodiment, the culture temperature of Propionibacterium sieversii or Propionibacterium acidogenic is set at 29°C-31°C and placed in an incubator for submerged liquid culture. In a preferred embodiment, the culture temperature of Propionibacterium sieversii or Propionibacterium acidogenic is set at 30°C and placed in an incubator for submerged liquid culture. The culture time of Propionibacterium sieversii or Propionibacterium acidogenic is set at 3-10 days. In a preferred embodiment, the culture time of Propionibacterium siegelii or Propionibacterium acidogens is set to 4-8 days. In a preferred embodiment, the culture time of Propionibacterium siegelii or Propionibacterium acidogens is set to 5-7 days.

[0030] Regarding the amounts of γ-Glu and Abu added to the culture medium, when the compounds are added before the start of culture (i.e., at 0 hours), the amount of Abu added is generally 20 ppm or greater, based on the final concentration in the culture medium at the time of addition. In a preferred embodiment, the amount of Abu added is 30 ppm or greater. In a preferred embodiment, the amount of Abu added is 75 ppm or greater. In a preferred embodiment, the amount of Abu added is 150 ppm or greater. In a preferred embodiment, the amount of γ-Glu added is 25 ppm or greater. In a preferred embodiment, the amount of γ-Glu added is 50 ppm or greater. In a preferred embodiment, the amount of γ-Glu added is 100 ppm or greater. In a preferred embodiment, the amount of γ-Glu added is 200 ppm. The amounts of γ-Glu and Abu added are not particularly limited in the present invention. However, considering comprehensive cost considerations such as cost and efficiency, the amounts of γ-Glu and Abu added can be set to 5000 ppm or less, and more preferably, the amounts of γ-Glu and Abu added are set to 500 ppm or less.

[0031] Step S3: Propionibacterium metabolites are prepared from the Propionibacterium fermentation broth prepared under the fermentation conditions of Step S2. The Propionibacterium metabolites can be obtained by rotary evaporating the Propionibacterium fermentation broth into a concentrated liquid, freeze-drying the Propionibacterium fermentation broth, or spray-drying the Propionibacterium fermentation broth into a powder. Glu and Abu added to the culture medium are taken up into the Propionibacterium cells and converted. More importantly, the resulting Propionibacterium metabolite containing γ-Glu-Abu exhibits an excellent rich flavor, improving the flavor and texture of the Propionibacterium metabolite, resulting in a favorable mouthfeel. Furthermore, the Propionibacterium metabolite can be prepared into a paste or spray-dried into a powder, depending on the intended use.

[0032] Among them, in a preferred embodiment, the propionibacterium fermentation liquid is concentrated by a rotary evaporation device at 40-60°C and 0.05-0.1MPa to obtain a propionibacterium metabolite concentrate. In another preferred embodiment, the propionibacterium fermentation liquid is pre-frozen at -40°C to -80°C and then freeze-dried in a freeze dryer at 0.1-10Pa and -50°C to 30°C to obtain a propionibacterium metabolite freeze-dried powder. In another preferred embodiment, the propionibacterium fermentation liquid is spray-dried in a spray drying tower at an inlet air temperature of 150-200°C and an outlet air temperature of 60-90°C to obtain a propionibacterium metabolite dry powder.

[0033] The above operation yields a Propionibacterium metabolite containing γ-Glu-Abu. In a preferred embodiment, the Propionibacterium metabolite contains 0.01% or more of γ-Glu-Abu per dry weight. In a further preferred embodiment, the Propionibacterium metabolite contains 0.05% or more of γ-Glu-Abu per dry weight. In a further preferred embodiment, the Propionibacterium metabolite contains 0.1% or more of γ-Glu-Abu per dry weight. In a further preferred embodiment, the Propionibacterium metabolite contains 0.15% or more of γ-Glu-Abu per dry weight.

[0034] The following further illustrates various details of the present invention in the form of embodiments.

[0035] Example 1: Preparation of Propionibacterium sieversii Metabolites Containing γ-Glu-Abu Step S1: preparing a culture medium for Propionibacterium sieversii and activating the Propionibacterium sieversii strain; which further comprises the following steps: Step S11: Prepare a culture medium for Propionibacterium sieversii. In this embodiment, the fermentation medium comprises the following components: 1.5% glucose, 0.6% sodium lactate, 1.5% yeast extract, 0.25% dipotassium hydrogen phosphate, and 0.05% manganese sulfate. The fermentation medium is prepared according to the above formula and dispensed into 150 mL screw-cap bottles. The culture medium is sterilized by autoclaving at 121°C for 15 minutes. After cooling to room temperature, the medium is placed on a sterile workbench and the initial pH of the culture medium is adjusted to 6.5 using 1M NaOH. Glu and Abu are added to prepare a fermentation medium containing a final concentration of 20 ppm Abu and 25 ppm Glu; and a fermentation medium containing a final concentration of 50 ppm Abu and 60 ppm Glu. These fermentation media contain two different concentrations of Glu and Abu.

[0036] Step S12: Activate the Propionibacterium sieversii strain. Remove the ampoule tube and use a sterile pipette to draw 0.3-0.5 mL of sterile culture medium into the ampoule tube after opening. Dissolve the freeze-dried Propionibacterium sieversii strain in the prepared liquid culture medium at an inoculum volume of 3%-10% (v / v). Then, take a small amount and inject it into the seed culture medium. Anaerobically culture the tube at 37°C for 48 hours until visible colonies are formed.

[0037] Step S2: fermentation culture of Propionibacterium sieversii; inoculate 7.5 mL of activated Propionibacterium sieversii bacterial solution into 150 mL of fermentation medium containing Glu and Abu compounds, and culture in a deep liquid incubator at 28° C.-32° C. for 5 h-7 h.

[0038] Step S3: Preparation of Propionibacterium sieversii metabolites: The P. sieversii fermentation broth prepared under the fermentation conditions of step S2 is centrifuged to obtain P. sieversii metabolites. Fermentation is terminated when the pH of the P. sieversii fermentation broth drops to approximately 4.5. The fermentation broth is rapidly cooled to below 4°C to prevent metabolite degradation. 100 mL of P. sieversii fermentation broth is diluted and mixed with an equal amount of distilled water. Two hoses are used to connect the water inlet and outlet of the high-pressure homogenizer chiller to the main unit's discharge cooler. The chiller is turned on to pre-cool the mixture until the preset temperature is reached. Ensure the pressure valve is relaxed and turn on the power switch. An appropriate amount of water is added to the feed port of the high-pressure homogenizer to remove air from the pipe. The mixed P. sieversii fermentation broth is poured into a sample cup and the pressure is adjusted to 800 Pa (80 MPa) for homogenization and fragmentation. After homogenization for 30 minutes, the homogenized and crushed Propionibacterium sieversii fermentation liquid was transferred into a clean container to obtain Propionibacterium sieversii metabolites.

[0039] Example 2 (Comparative Example): Preparation of Propionibacterium acidophilum metabolites without γ-Glu-Abu Step S1: Preparation of Propionibacterium sieversii culture medium and activation of Propionibacterium sieversii strains; further comprising the following steps: Step S11: Prepare the culture medium. In this embodiment, the fermentation culture medium comprises the following components: 1.5% glucose, 0.6% sodium lactate, 1.5% yeast extract, 0.25% dipotassium hydrogen phosphate, and 0.05% manganese sulfate. The fermentation culture medium is prepared according to the above recipe and dispensed into 150 mL screw-cap bottles. The bottles are sterilized by autoclaving at 121°C for 15 minutes, cooled to room temperature, and placed on a sterile workbench. The initial pH of the culture medium is adjusted to 6.5 using 1 M NaOH.

[0040] Step S12: Activate the strain. Remove the ampoule tube and use a sterile pipette to draw 0.3 mL-0.5 mL of sterile culture medium into the ampoule tube after opening. Dissolve the freeze-dried Propionibacterium sieversii strain in the prepared liquid culture medium at an inoculum volume of 3%-10% (v / v). Then, take a small amount and inject it into the seed culture medium. Anaerobically culture at 37°C for 48 hours until visible colonies are formed.

[0041] Step S2: fermenting and culturing Propionibacterium sieversii; inoculating 7.5 mL of activated Propionibacterium sieversii bacterial liquid into 150 mL of fermentation medium, and placing the culture medium in a deep liquid incubator at 28° C.-32° C. for 5 h-7 h.

[0042] Step S3: Preparation of Propionibacterium sieversii metabolites: The P. sieversii fermentation broth prepared under the fermentation conditions of Step S2 is centrifuged to obtain P. sieversii metabolites. Fermentation is terminated when the pH of the P. sieversii fermentation broth drops to approximately 4.5. The fermentation broth is rapidly cooled to below 4°C to prevent metabolite degradation. 100 mL of P. sieversii fermentation broth is diluted and mixed with an equal amount of distilled water. Two hoses are used to connect the water inlet and outlet of the high-pressure homogenizer's chiller to the main unit's discharge cooler. The chiller is turned on to pre-cool the broth until the preset temperature is reached. Ensure the pressure valve is relaxed and turn on the power switch. An appropriate amount of water is added to the feed port of the high-pressure homogenizer to remove air from the pipe. The mixed P. sieversii fermentation broth is poured into a sample cup and the pressure is adjusted to 800 Pa (80 MPa) for homogenization and fragmentation. After homogenization for 30 minutes, the homogenized and crushed Propionibacterium sieversii fermentation liquid was transferred into a clean container to obtain Propionibacterium sieversii metabolites.

[0043] Test Example 1: Testing the effect of adding a mixture of Abu and Glu to Propionibacterium schizophyllum As shown in Example 1 for preparing the metabolites of Propionibacterium shieldii containing γ-Glu-Abu, Propionibacterium shieldii was first activated: the ampoule tube was removed and opened, and 0.3-0.5 mL of sterile culture medium was drawn into the ampoule tube with a sterile pipette. The freeze-dried strain of Propionibacterium shieldii was dissolved in the prepared liquid culture medium at an inoculum volume of 3%-10% (v / v), and then a small amount was injected into the seed culture medium, and anaerobically cultured at 37°C for 48 hours until visible colonies were formed.

[0044] Fermentation of Propionibacterium sieversii: The seed culture was removed and inoculated into a control fermentation medium, a fermentation medium containing a mixture of Abu and Glu (final Abu concentration of 20 ppm, final Glu concentration of 25 ppm) (marked as a), and a fermentation medium containing a mixture of Abu and Glu (final Abu concentration of 50 ppm, final Glu concentration of 60 ppm) (marked as b). The inoculation amount was 3%-10% (v / v), the fermentation temperature was 28°C-32°C, and the submerged liquid culture was carried out for 5-7 days.

[0045] After the fermentation of Propionibacterium shiehii is complete, a control Propionibacterium fermentation broth, a Propionibacterium fermentation broth, and b Propionibacterium fermentation broth are obtained. 100 mL of each of the control Propionibacterium fermentation broth, a Propionibacterium fermentation broth, and b Propionibacterium fermentation broth are diluted and mixed evenly with equal amounts of distilled water. Two hoses are used to connect the water inlet and outlet of the high-pressure homogenizer to the main unit's discharge cooler. The chiller is turned on to pre-cool the broth until it reaches the preset temperature. Ensure the pressure valve is relaxed and turn on the power switch. Add an appropriate amount of water to the inlet of the high-pressure homogenizer to remove air from the pipe. Pour the mixed Propionibacterium shiehii fermentation broth into a sample cup and adjust the pressure to 800 Pa (80 MPa) for homogenization and disruption. After 30 minutes of homogenization, the homogenized Propionibacterium shiehii fermentation broth is transferred to a clean container to obtain Propionibacterium shiehii metabolites. The obtained Propionibacterium sieversii metabolites were ultrafiltered, and the Abu, Glu, and γ-Glu-Abu contents in the Propionibacterium metabolites were measured. Furthermore, the Propionibacterium metabolites containing the bacteria were dried at 100°C to a constant weight, thereby calculating the Abu, Glu, and γ-Glu-Abu contents in a given amount of Propionibacterium fermentation broth. The results are shown in Table 1.

[0046] Table 1 Contents of Abu, Glu and γ-Glu-Abu in Propionibacterium fermentation broth

[0047] As shown in Table 1, when a mixture containing Abu and Glu was added to the culture medium of Propionibacterium, the contents of Abu, Glu and γ-Abu-Glu in the fermentation broth of Propionibacterium increased.

[0048] The three Propionibacterium fermentation broths (Propionibacterium fermentation broth, Propionibacterium fermentation broth a, and Propionibacterium fermentation broth b), control fermentation medium-fermentation broth, fermentation medium-fermentation broth, and fermentation medium-fermentation broth were each concentrated under reduced pressure using a rotary evaporator to 1 / 5-1 / 10 of their original volumes, yielding concentrated control fermentation medium-fermentation broth, concentrated fermentation medium-fermentation broth, and concentrated fermentation medium-fermentation broth. The concentrated control fermentation medium-fermentation broth, concentrated fermentation medium-fermentation broth, and concentrated fermentation medium-fermentation broth were then placed in a freeze dryer and freeze-dried at -40°C to -50°C for 24-48 hours to yield concentrated control fermentation medium-dried powder, concentrated fermentation medium-dried powder, and concentrated fermentation medium-dried powder. The concentrated control fermentation medium-dried powder, concentrated fermentation medium-dried powder, and concentrated fermentation medium-dried powder were then placed in a constant temperature drying oven, dried at 40-60°C to a constant weight, and sealed and stored at 4°C.

[0049] 1.0 g each of the three concentrated control fermentation medium powders, concentrated fermentation medium a powder, and concentrated fermentation medium b powders were weighed and dissolved in 10 mL of sterile deionized water to prepare 10% (w / v) control, fermentation medium a powder, and fermentation medium b powder solutions. The control, fermentation medium a powder, and fermentation medium b powder solutions were centrifuged at 3000-5000 rpm for 10-15 minutes. The supernatants were ultrafiltered through a 0.22 μm ultrafiltration membrane to obtain clear filtrates. The Abu, Glu, and γ-Glu-Abu contents of these three powder solutions were assayed. The antibacterial activity of these three powder solutions was also tested using the critical dilution method using Pseudomonas putida as an indicator bacterium. Furthermore, a series of gradient dilutions were performed on the control fermentation medium-dry powder solution, fermentation medium a-dry powder solution, and fermentation medium b-dry powder solution. Equal amounts of indicator bacteria suspension were inoculated. After incubation, the minimum inhibitory concentration (MIC) was observed and recorded. The results are shown in Table 2.

[0050] Table 2 Contents and antibacterial activities of Abu, Glu, and γ-Glu-Abu in dry powder solutions of Propionibacterium metabolites

[0051] According to Table 2, the following conclusion can be drawn: when a mixture containing Abu and Glu is added to the Propionibacterium culture medium, the Propionibacterium metabolites prepared after fermentation will also contain a certain amount of Abu, Glu, and γ-Glu-Abu, and the antibacterial properties of the Propionibacterium metabolites will not be affected.

[0052] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple variations of the technical solution of the present invention can be made. These simple variations all fall within the scope of protection of the present invention.

[0053] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any manner unless there is any contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations. In addition, the various different embodiments of the present invention can also be combined in any manner, as long as they do not violate the concept of the present invention, and they should also be regarded as the contents disclosed by the present invention.

Claims

1. A propionibacterium metabolite containing γ-Glu-Abu, characterized in that The γ-Glu-Abu-containing Propionibacterium metabolite contains 0.1% or more of γ-Glu-Abu per unit dry weight.

2. The propionibacterium metabolite containing γ-Glu-Abu according to claim 1, characterized in that The propionibacterium in the propionibacterium metabolite is a propionibacterium that can take Glu and Abu into cells and accumulate γ-Glu-Abu in the cells.

3. The propionibacterium metabolite containing γ-Glu-Abu according to claim 2, characterized in that The propionibacterium in the propionibacterium metabolite is a mixture of Propionibacterium sieversii, Propionibacterium acidogenicum, Propionibacterium terrei and Propionibacterium janaschii.

4. The propionibacterium metabolite containing γ-Glu-Abu according to claim 1, characterized in that The propionibacterium metabolite containing γ-Glu-Abu is prepared by culturing propionibacterium in a culture medium supplemented with two compounds, Abu and Glu, and using the obtained propionibacterium cells.

5. The propionibacterium metabolite containing γ-Glu-Abu according to claim 1, characterized in that The propionibacterium metabolite containing γ-Glu-Abu is in the form of a paste, powder or solution.

6. A method for preparing the propionibacterium metabolite containing γ-Glu-Abu according to any one of claims 1 to 5, characterized in that: It includes the following steps: Step S1: Preparation of Propionibacterium culture medium and activation of Propionibacterium strains; Step S2: fermenting and culturing Propionibacterium based on the activated Propionibacterium strain obtained in step S1; Step S3: preparing propionibacterium metabolites from the propionibacterium fermentation broth prepared under the fermentation conditions of step S2.

7. The method for preparing a propionibacterium metabolite containing γ-Glu-Abu according to claim 6, characterized in that: The culture medium in step S1 is a culture medium capable of proliferating Propionibacterium.

8. The method for preparing a propionibacterium metabolite containing γ-Glu-Abu according to claim 7, characterized in that: The carbon source of the culture medium is any one or more of glucose, sucrose, sodium lactate, molasses, lactose and whey powder; the nitrogen source of the culture medium is any one or more of ammonia, ammonium salt, yeast extract, corn steep liquor, peptone and beef extract; and the inorganic salt of the culture medium is any one or more of phosphate and sulfate.

9. The method for preparing a propionibacterium metabolite containing γ-Glu-Abu according to claim 6, characterized in that: The amount of Abu added is 20 ppm or more, and the amount of γ-Glu added is 25 ppm or more.

10. The method for preparing a propionibacterium metabolite containing γ-Glu-Abu according to claim 6, characterized in that: The amount of Abu added is 30 ppm or more, and the amount of γ-Glu added is 50 ppm or more.

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