Serratia marcescens G3, fermentation inoculant thereof and application of serratia marcescens G3 in preparation of browning inhibitor

Abstract

The invention provides serratia marcescens G3, a fermentation inoculant thereof and an application of the serratia marcescens G3 in preparation of a browning inhibitor. The strain G3 is preserved in China General Microbiological Culture Collection Center on November 15, 2023, and the preservation number is CGMCC No.29042. The invention further provides a preparation method of the serratia marcescens G3. Experiments prove that the strain fermentation liquor, the strain thallus, the strain crushing liquid and the thallus crude protein have a relatively strong inhibition effect on PPO. The invention provides an application of the strain in the aspect of inhibiting browning. Experiments prove that protein substances in the strain crushing liquid can significantly reduce the browning degree of potato slurry and the activity of PPO, so that browning is delayed. The serratia marcescens G3 has a strong inhibition effect on the potato PPO, can be prepared into a microbial preparation for inhibiting browning, and has an important market application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of microorganisms, and particularly relates to a strain of Serratia marcescens G3 and a fermentation agent thereof, and application thereof in preparing a browning inhibitor. Background Art

[0002] Potato (Solanum tuberosum L.), also known as potato, sweet potato, etc., is the fourth most important food crop in the world. my country is the world's largest potato producer. Its potato consumption pattern is mainly fresh food, accounting for more than 50% of my country's potato consumption. Potato tubers contain a lot of starch, and are rich in protein and amino acids. They have the most complete vitamins among all food crops, and have a delicate taste, which is deeply favored by consumers. With the continuous modernization of my country's society, people are increasingly adapting to the fast-paced life. Fresh-cut fruits and vegetables have flooded into the market with strong advantages, and fresh-cut potatoes have become the most common type of fresh-cut fruits and vegetables. At the same time, problems in the processing of fresh-cut potatoes are gradually emerging. When cutting potatoes, the metabolic activity is enhanced due to external mechanical injuries, and the internal tissue is in contact with external oxygen, resulting in browning. The browning of potatoes has a series of problems such as poor appearance, loss of freshness, and weight loss, which reduces its sensory quality, thereby affecting the processing and sales of the fresh-cut potato industry.

[0003] The currently widely used browning control technology has unstable browning inhibition effect and safety issues, and cannot effectively meet the industrial production of the potato industry. In recent years, some plant proteases have been used to alleviate the browning of fresh-cut fruits and vegetables, and some proteases can degrade PPO. Although these plant proteases in the prior art are safe and reliable, they are difficult to produce on a large scale due to limited sources and difficult extraction. Finding microbial proteases that can degrade or highly inhibit the activity of PPO is of great significance to the research on inhibiting browning. Summary of the invention

[0004] In view of the problems in the above-mentioned prior art, the purpose of the present invention is to provide a strain of Serratia marcescens G3 and its fermentation agent and its application in the preparation of browning inhibitors. The present invention screened and obtained a strain of Serratia marcescens G3, fermented the strain, and applied the fermentation liquid, bacterial cells and bacterial cell crushing liquid of the strain G3 to fresh-cut potatoes. Experiments have shown that the fermentation liquid, bacterial cells and bacterial cell crushing liquid of the strain G3 can reduce the activity of polyphenoloxidase (PPO) and have a good inhibitory effect on the browning of fresh-cut potatoes. The experimental results show that the strain has broad application prospects for the preparation of browning inhibitors.

[0005] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0006] The invention provides a strain of Serratia marcescens G3, which is classified and named as Serratia marcescens and is deposited in the General Microbiological Center of China Microbiological Culture Collection Committee with a deposit number of CGMCC No.29042.

[0007] Further: the strain G3 is a Gram-negative bacterium, its colonies are oval, the bacteria are milky white, opaque, smooth and moist, sticky, with irregular edges and flagella around them.

[0008] Furthermore: the suitable growth temperature of the strain G3 is 28-37°C and the pH is 5-12.

[0009] The present invention also provides the fermentation agent of the Serratia marcescens G3, which comprises fermentation liquid, bacterial strain bodies, bacterial body crushing liquid and crude protein of the strain.

[0010] Further: the bacterial content of Serratia marcescens G3 in the fermentation broth is 8×10 9 / mL-6×10 10 Pieces / mL.

[0011] Furthermore: the disruption conditions of the bacterial cell disruption liquid are: power 300-400 W, time 15-45 min.

[0012] Furthermore: the optimal formula ratio of the strain G3 LB medium (growth medium) is: 1% tryptone, 0.5% yeast extract, 1% sodium chloride, by mass ratio, natural pH, and high-pressure sterilization at 121°C for 20 min.

[0013] Furthermore: the optimal formula ratio of the fermentation medium of the strain G3 is: 1.7% tryptone, 0.5% yeast extract, 0.25% dipotassium hydrogen phosphate, 0.25% glucose, 0.3% soy peptone, by mass ratio, pH 7.6, and high-pressure sterilization at 115°C for 15 min.

[0014] Furthermore: the fermentation conditions of the G3 bacteria are: the optimum pH is 7, the culture temperature is 37°C, and the culture time is 24 h.

[0015] Further: the fermented bacterial solution was centrifuged at 4°C and 10,000 r / min for 10 min, rinsed with sterile deionized water, and re-dissolved to obtain the strain cells.

[0016] Furthermore: the preparation conditions of the G3 fermentation bacterial cell disruption liquid are: ultrasonic disruption treatment, temperature 0°C, disruption power 400W, time 45min (working 3s, resting 8s).

[0017] Further: the protein substances in the G3 fermentation cell disrupted liquid are obtained by ammonium sulfate precipitation and dialysis desalination at a temperature of 4°C, and the dialysis end point is that the pH of the dialysate does not change much before and after.

[0018] The present invention also provides the use of the Serratia marcescens strain G3 and / or the fermentation bacterial agent in inhibiting browning.

[0019] Furthermore: the G3 fermentation agent has a strong inhibitory effect on the browning degree and PPO activity of potato slurry, thereby delaying the browning of potato slurry.

[0020] The present invention also provides the use of the Serratia marcescens G3 or the fermentation agent in preparing a browning inhibitor.

[0021] Furthermore: the browning inhibitor can inhibit the browning of potatoes.

[0022] The advantages and beneficial effects of the present invention are as follows: a strain of Serratia marcescens G3 is isolated and screened by the present invention, and the Serratia marcescens G3 can grow in LB solid / liquid medium, the growth temperature is 28-37°C, the pH is 5-12, the salt concentration is 171 mmol / L, the optimum growth temperature is 37°C, the optimum pH is 7, the culture end point is OD value equal to 2.0±0.2, and the growth medium components are 1% tryptone, 0.5% yeast extract, and 1% sodium chloride. The fermentation uses TSB medium, the fermentation temperature is 37°C, the pH is 7, the fermentation time is 24 h, and the fermentation medium components are 1.7% tryptone, 0.5% yeast extract, 0.25% dipotassium hydrogen phosphate, 0.25% glucose, and 0.3% soy peptone. The concentration of the bacteria under the optimal conditions is 8×10 9 / mL-6×10 10 Pieces / mL.

[0023] The present invention proves through experiments that the Serratia marcescens G3 and its fermentation agent can inhibit the browning degree of potato slurry and the activity of PPO, has the advantages of stable properties, simple cultivation, obvious effect, wide applicable conditions and no environmental pollution, etc., can be prepared into a biocontrol agent for controlling potato browning, significantly improves the commodity value of potatoes, and does not change potato properties and genes, has high efficiency and obvious effect. The fermentation agent of the present invention has the advantages of high viable count, strong adaptability of strains in bacterial suspension, stable strain performance, simple preparation method, low cost, etc., and has good market application prospects.

[0024] The present invention provides a safe, reliable and low-cost biological enzyme preparation capable of degrading or highly inhibiting PPO. By screening microorganisms with high protease production, proteases capable of degrading or highly inhibiting PPO are screened, which provides a new direction for solving the problems faced by the potato industry and also provides new ideas for the research field of browning of fresh-cut fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is to screen the Serratia marcescens G3 strain;

[0026] Figure 2 The invention relates to the identification of the Serratia marcescens G3 strain;

[0027] Figure 3 This is a colony photo of Serratia marcescens G3 isolated and purified by the present invention on an enzyme solid culture medium;

[0028] Figure 4 The effect of the fermentation liquid of Serratia marcescens G3 on the browning of potato pulp;

[0029] Figure 5 The effect of the Serratia marcescens G3 bacteria of the present invention on potato slurry, browning degree, PPO activity and protease activity;

[0030] Figure 6 The effect of the Serratia marcescens G3 bacterial cell disrupting liquid on the browning of potato slurry described in the present invention;

[0031] Figure 7 The effect of different ultrasonic treatments of the Serratia marcescens G3 bacterial cell disrupted liquid on the browning of potato slurry;

[0032] Figure 8 The present invention is a SDS-PAGE electrophoresis analysis of the Serratia marcescens G3 before and after fermentation, the cell fragmentation liquid and the purified crude protein;

[0033] Fig. 9 The invention discloses the influence of crude protein in the Serratia marcescens G3 bacterial cell crushing liquid on the browning degree and PPO activity of potato slurry. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below in conjunction with specific implementation modes, but the examples cited are only used to illustrate the present invention, and the protection scope of the present invention is not limited thereto.

[0035] Example 1: Screening of Serratia marcescens G3 strain

[0036] After sampling from soil, rotten fruits (cherry tomatoes, broccoli, pitaya, etc.) and soy products, incubate in sterile water at 28°C and 200 r / min for 30 min. Take 250 μL and inoculate in LB medium, incubate at 28°C and 200 r / min for 24 h to obtain enriched bacterial liquid.

[0037] Take 100 μL of enriched bacterial solution and perform gradient dilution. -5 100 μL of bacterial solution was evenly spread on the screening medium, and inverted and cultured at 28 ℃ for 48 h. According to the presence and size of the transparent circle, bacteria and fungi strains with different morphologies were initially screened out, and the initially screened strains were placed in a 2 mL centrifuge tube with 1 mL LB, shaken and cultured at 200 r / min for 6 h, and then stored in a 30% sterile glycerol tube and stored in a -80 ℃ refrigerator.

[0038] Take out a small amount of the corresponding strain from the -80 ℃ refrigerator and place it in a 2 mL centrifuge tube with 1 mL LB, and shake and culture at 200 r / min until it becomes turbid. Take 1 mL of the turbid bacterial solution and place it in a 50 mL conical flask with 30 mL LB, and shake and culture at 200 r / min for 5 h.

[0039] 2 μL of activated bacterial solution was taken and inverted on casein medium (casein (casein) 0.5%, yeast extract 0.1%, potassium dihydrogen phosphate 0.1%, potassium dihydrogen phosphate 0.05%, glucose 0.1%, magnesium sulfate 0.01%, agar 1%, by mass, pH 6.5, 115 ℃ autoclave for 15 min.) for 24 h, bacterial temperature 37 ℃, mold temperature 28 ℃. After the culture, the colony diameter (d) and proteolysis circle diameter (D) were measured with a vernier caliper, D / d was calculated, and the protease activity was measured. The results are shown in Table 1. The proteolysis circle diameter, colony diameter, D / d ratio, and protease activity of G3 bacteria were all high, indicating that G3 is a high-yield protease strain with good biological activity.

[0040] Table 1 Decomposition zone to colony diameter ratio (D / d) and protease activity of the selected strains

[0041]

[0042] Note: The letter S represents the strain screened from the soil near the canteen of Shandong Agricultural University; the letter FQ represents the strain screened from rotten tomatoes; the letter G represents the strain screened from the soil near the State Key Laboratory of Wheat of Shandong Agricultural University; the letter DZ represents the strain screened from rotten bean dregs.

[0043] The 15 high-yield protease strains were fermented at 200 r / min, 37 ℃ for bacteria and 28 ℃ for fungi for 24 h, and the OD values ​​were kept basically the same each time. The fermentation products were applied to potato slurry. Figure 1 As shown, the browning degree of the FQ23 and DZ4 strain treatment groups was not much different from that of the control group. Although the browning degree of the other strain treatment groups decreased to varying degrees, the browning degree of the G1, G2, and G3 strain fermentation liquid treatment was the lowest, and the difference with the control group was the largest.

[0044] Example 2: Identification of Serratia marcescens G3 strain

[0045] (1) Morphological, physiological and biochemical characteristics of the strain:

[0046] The colony morphology of strain G3 on enzyme medium is as follows Figure 2 The strain G3 shown in (A) is a Gram-negative short rod, whose colony is oval, milky white, opaque, smooth and moist, sticky, with irregular edges and flagella around it. The suitable growth temperature of strain G3 is 28~37℃ and pH is 5~12.

[0047] (2) 16S rDNA identification of strains:

[0048] The genome of strain G3 was extracted using a genome extraction kit and used as a template to amplify the genome using 16S rDNA universal primers 27F (5'-GAG AGT TTG ATC CTG GCT CAG-3') and 1492R (5'-ACG GAT ACC TTG TTA CGA CTT -3') and sequence the genome. The 16S rDNA sequence is shown in SEQ ID No. 1. The strain was identified by NCBI BLAST comparison, and the results showed that the homology between strain G3 and Serratia marcescens reached 99%. Sequence comparison was performed using DNAMAN, and the results were as follows: Figure 2 As shown in (B).

[0049] The present invention deposits the screened Serratia marcescens G3, and the depositing unit is the General Microbiology Center (CGMCC) of China Microbiological Culture Collection Administration; the address is Institute of Microbiology, Chinese Academy of Sciences, No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing; the deposit number of Serratia marcescens is CGMCC No.29042; the deposit date is November 15, 2023.

[0050] Example 3: Isolation and purification of Serratia marcescens G3 strain

[0051] The strain G3 was transferred to LB solid medium and separated by streaking until a single colony of the purified strain was obtained. The results are as follows: Figure 3 shown.

[0052] Example 4: Effect of Serratia marcescens G3 fermentation broth on potato slurry browning

[0053] Activation of strains: Take out the G3 strain from the -80 ℃ refrigerator, pick a small amount and inoculate it into a 2 mL centrifuge tube containing 1 mL LB, and culture it at 200 r / min until it becomes turbid.

[0054] Bacterial proliferation: inoculate 1 mL of turbid bacterial solution into a 50 mL conical flask containing 30 mL of LB, shake and culture at 200 r / min for 5 h, and measure the bacterial solution concentration (OD value) with a nucleic acid analyzer to keep it at around 2.0.

[0055] Bacterial fermentation: 3% of the above concentration of bacterial solution was inoculated into a 50 mL conical flask containing 10 mL TSB, and cultured at 200 r / min for 24 h. The fermented bacterial solution was centrifuged at 4 °C and 10,000 r / min for 10 min, and the supernatant was taken and filtered through a 0.22 μm filter membrane to obtain the microbial fermentation solution. The precipitate was the fermented bacteria. TSB was used as the control group, and the fermentation solutions of G1, G2, and G3 were used as the treatment groups. The inhibitory effects of the fermentation solutions on potato browning were shown in Figure 2. Figure 4 As shown in (A), the browning degree of the group treated with the fermentation broth of the G3 strain was much lower than that of the TSB control group; Figure 4 As shown in (B), with the extension of time, the browning degree of TSB gradually increased, and the browning degree of the group treated with the fermentation liquid of the G3 strain remained basically unchanged; although the browning degree values ​​of the other two strains were also lower than that of the control group, they fluctuated greatly and were not as stable as the G3 strain. At the same time, this also shows that the fermentation liquid of the G3 strain has a good effect on inhibiting the browning of fresh-cut potatoes.

[0056] Example 5: Effects of Serratia marcescens G3 on potato slurry, browning, PPO activity and protease activity

[0057] The cells obtained after fermentation centrifugation were rinsed with sterile deionized water for 3 times, then dissolved with an equal amount of sterile deionized water and mixed. The CK2 without any treatment was used as the control group, and the G3 cells without boiling and boiling for 5 minutes were used as the treatment group. The browning degree, protease activity changes and PPO activity changes of potato slurry at different times were measured.

[0058] like Figure 5 As shown in (A), the browning degree of the G3 bacterial resuspended material treatment group boiled for 5 minutes was basically consistent with that of the CK2 control group without any treatment, while the browning degree of the potato slurry treated with the uncooked G3 bacterial resuspended material was much lower than that of the G3 bacterial resuspended material treatment group boiled for 5 minutes and the CK2 control group without any treatment, indicating that the G3 bacteria without heating treatment has a good inhibitory effect on the browning of fresh-cut potatoes, while the G3 bacteria boiled for 5 minutes has no inhibitory effect on the browning of fresh-cut potatoes.

[0059] The results of browning degree determination are as follows Figure 5 As shown in (B), the browning degree is related to the potato slurry Figure 1 There was no significant difference in the browning degree between the CK2 treatment group and the G3 bacterial resuspended material treatment group boiled for 5 min, and the browning degree value continued to increase with time, while the browning degree value of the G3 bacterial resuspended material treatment group without heating treatment was not only smaller but also basically remained unchanged, which indicates that the G3 bacterial cells without heating treatment can not only inhibit the browning of fresh-cut potatoes but also have good stability, while the boiled G3 bacterial cells die due to high temperature and no longer play the role of inhibiting the browning of fresh-cut potatoes.

[0060] The protease activity of potato slurry was measured and the results were as follows: Figure 5 As shown in (C), although the protease activity of the three treatment groups showed an upward trend, the increase in the uncooked G3 bacterial cell treatment group was greater than that in the CK2 treatment group and the G3 bacterial cell treatment group boiled for 5 minutes, and the protease activity at each time point was significantly greater than that in the CK2 treatment group and the G3 bacterial cell treatment group boiled for 5 minutes, indicating that the G3 bacterial cells that have not been heated have good protease activity.

[0061] The activity of PPO is Figure 5As shown in (D), the PPO activity of the CK2 treatment group and the G3 bacterial cell treatment group boiled for 5 min showed an upward trend, while the PPO activity of the uncooked G3 bacterial cell treatment group showed a significant downward trend, and the difference became more and more significant from 4 h, indicating that the unheated G3 bacterial cells can inhibit the browning of fresh-cut potatoes by inhibiting PPO activity.

[0062] Example 6: Effect of Serratia marcescens G3 cell disrupted liquid on browning of potato slurry

[0063] The fermented strains were broken by ultrasonic cell disruptor at 400 W for 45 min, and the supernatant was taken as the bacterial cell breaking liquid. The CK2 treatment group (water treatment group) was used as the control group, the G3 bacterial cell breaking liquid treatment group and the boiled bacterial cell breaking liquid treatment group (boiled at 100 °C for 5 min) were used as the experimental groups, and the color difference was measured by colorimeter.

[0064] The results are as follows Figure 6 As shown in (A), the G3 boiled cell disruption liquid treatment group and the CK2 treatment group both showed severe browning, and the degree of browning was basically the same, while the uncooked G3 cell disruption liquid treatment group only showed slight browning. Figure 6 As shown in (B), the L * The values ​​showed a significant downward trend, while those of the uncooked G3 bacterial cell crushing liquid treatment group remained basically unchanged and slightly increased, indicating that the G3 bacterial cell crushing liquid had a good inhibitory effect on the browning of fresh-cut potatoes; it also explained that the boiled bacterial cell crushing liquid treatment group no longer had an inhibitory effect on the browning of fresh-cut potatoes because high-temperature heating destroyed enzymes and other heat-sensitive substances.

[0065] Example 7: Effects of different ultrasonic treatments of Serratia marcescens G3 cell fragments on browning of potato slurry

[0066] The optimal ultrasonic disruption time of G3 bacterial cell disruption liquid was screened to ensure that the browning of potato slurry was inhibited to the greatest extent. The control groups were set as CK2 (water treatment group) and CK3 (bacteria treatment group), and the treatment groups were treated with G3 bacterial cell disruption liquid at different ultrasonic times. Figure 7As shown in the figure, the browning of the G3 bacterial cell disruption liquid treatment group with an ultrasonic disruption time of 15 min was the most serious, and the browning degree was basically consistent with that of CK2; the browning degrees of the G3 bacterial cell disruption liquid treatment groups with ultrasonic disruption times of 60 min and 75 min were similar, both lower than that of the G3 bacterial cell disruption liquid treatment group with an ultrasonic disruption time of 15 min; although the G3 bacterial cell disruption liquid treatment group with an ultrasonic disruption time of 30 min showed obvious browning in the 2nd hour, its browning degree was more serious than that of CK3 from the 3rd hour; and the G3 bacterial cell disruption liquid treatment group with an ultrasonic disruption time of 45 min showed obvious browning from the 8th hour, and the browning degree was the lightest among all experimental groups, indicating that G3 bacterial cells treated with ultrasonic disruption for 45 min had the best inhibitory effect on the browning of pre-cut potatoes.

[0067] Example 8: SDS-PAGE electrophoresis analysis of Serratia marcescens G3 cells before and after fermentation, cell fragments, and purified crude protein

[0068] Previous experiments have shown that heat-labile substances such as enzymes in the G3 bacterial cell resolubilization product and the bacterial cell crushing liquid cannot inhibit the browning of fresh-cut potatoes. In order to further determine what kind of heat-labile substances they are, the crude protein of the G3 bacterial cell crushing liquid was purified, and the bacteria, bacterial crushing liquid and purified crude protein before and after fermentation were analyzed by SDS-PAGE electrophoresis.

[0069] G3 bacterial cell disruption liquid can be obtained by ammonium sulfate precipitation, dialysis desalination, and concentration. Add ground and dried ammonium sulfate to the bacterial cell disruption liquid in small amounts and multiple times, stirring slowly while adding, and avoid whipping and foaming to cause protein denaturation, until the ammonium sulfate saturation system reaches 70%. This process is carried out in an ice bath throughout the process, and after the end, it is placed in a 4 ℃ refrigerator for precipitation overnight until the layers are clearly visible. Take the upper two layers of solution and centrifuge them. The precipitate is the crude protein.

[0070] Dissolve the crude protein in PBS at pH=7.5 and pour it into the cleaned dialysis bag with 80% liquid volume to avoid bursting the dialysis bag. Clamp the two ends of the dialysis bag with two 40 mm special dialysis clamps and place it in 1000 mL of PBS at pH=7.5 for dialysis. The dialysis device is placed at 4 ℃ throughout the process, and the dialysis fluid is replaced every 6 hours. The pH is monitored until the pH of the dialysis fluid before and after dialysis does not change much (48 hours) and the dialysis is terminated. Polyacrylamide gel electrophoresis is used to identify the protein molecular weight of the bacterial cells before and after fermentation, the bacterial cell fragmentation liquid, and the purified crude protein.

[0071] Electrophoresis pattern Figure 8As shown, there are three protein bands in these four lanes, with molecular weights of 50-70 kDa, 35-40 kDa, and 25-35 kDa close to 25 kDa, respectively. The protein band with a molecular weight of 25-35 kDa close to 35 kDa is not obvious in the bacterial disruption liquid lane, but exists in other lanes. The reason is that the protein concentration in the bacterial disruption liquid is too low.

[0072] Example 9: Effect of crude protein in Serratia marcescens G3 bacterial cell crushing liquid on browning degree and PPO activity of potato slurry

[0073] In order to further explore the inhibitory effect of crude protein in G3 bacterial cell disruption liquid on the browning of fresh-cut potatoes, CK2 (water treatment group) and phosphate buffer treatment group (pH=7.5 PBS treatment group) were used as control groups, and crude protein treatment group and G3 bacterial cell disruption liquid treatment group were used as experimental groups, and color difference and PPO activity were determined.

[0074] Fig. 9 As shown in (A), the browning of potato slurry in the CK2 and phosphate buffer treatment groups became more and more serious over time, while the potato slurry in the G3 bacterial cell disruption liquid treatment group and the crude protein treatment group showed almost no change. Fig. 9 As shown in (B), the L* value of CK2 showed a downward trend, while the L* values ​​of the G3 bacterial cell crushing liquid treatment group and the crude protein treatment group were much greater than CK2 and basically consistent. This shows that the crude protein extracted from the G3 bacterial cell crushing liquid has an inhibitory effect on the browning of fresh-cut potatoes, and it also shows that the protein substances in the G3 bacterial cell crushing liquid have an inhibitory effect on browning. Fig. 9 As shown in (C), the PPO activity of CK2 showed an upward trend, while the PPO activity of the G3 bacterial cell crushing liquid treatment group and the crude protein treatment group showed a downward trend, and the PPO activity of the crude protein treatment group was lower than that of the bacterial cell crushing liquid treatment group, indicating that the protein substances in the G3 bacterial cell crushing liquid can inhibit the browning of fresh-cut potatoes by inhibiting the activity of PPO.

[0075] As described in the review, the fermentation liquid of Serratia marcescens G3, the strain and the broken liquid of the strain, and the crude protein of the strain have a good inhibitory effect on the browning of fresh-cut potatoes, and can significantly inhibit the PPO activity of fresh-cut potatoes, maintaining a good commodity value. Serratia marcescens G3 has the advantages of stable properties, simple cultivation, obvious effect, wide application conditions and no environmental pollution. The bacterial agent prepared by it has the characteristics of high viable count, strong adaptability of the strain in the bacterial suspension, stable strain performance, simple preparation method, low cost, etc. It can be prepared into a biocontrol agent for controlling enzymatic browning of potatoes, and has a good market application prospect.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A strain of Serratia marcescens G3, characterized in that: Serratia marcescens Serratia marcescens , deposited in the General Microbiology Center of China Microorganism Culture Collection Administration, with the deposit number CGMCC No.29042.

2. The Serratia marcescens G3 according to claim 1, characterized in that: The Serratia marcescens G3 is a Gram-negative short rod, and its colony is oval, the bacterial body is milky white, opaque, the surface is smooth and moist, the texture is sticky, the edge is irregular, and flagella are grown around it.

3. The fermentation agent of Serratia marcescens G3 according to claim 1, characterized in that The fermentation agent comprises fermentation liquid, bacterial strain cells, bacterial cell crushing liquid and bacterial strain crude protein.

4. The fermentation agent of Serratia marcescens G3 according to claim 3, characterized in that: The bacterial content of Serratia marcescens G3 in the fermentation broth was 8×10 9 / mL-6×10 10 Pieces / mL.

5. The fermentation agent of Serratia marcescens G3 according to claim 3, characterized in that: The fermentation conditions of the fermentation broth are as follows: pH 6.8-7.0, culture temperature 37°C, and culture time 24-48 h.

6. The fermentation agent of Serratia marcescens G3 according to claim 3, characterized in that: The formula of the fermentation medium of Serratia marcescens G3 is: 1.7% tryptone, 0.5% yeast extract, 0.25% dipotassium hydrogen phosphate, 0.25% glucose, 0.3% soy peptone, and the balance is water, calculated by mass ratio.

7. Use of the Serratia marcescens strain G3 according to claim 1 and / or the fermentation agent according to claim 3 in inhibiting browning.

8. The use according to claim 7, characterized in that: The Serratia marcescens strain G3 is capable of inhibiting PPO activity.

9. Use of the Serratia marcescens strain G3 according to claim 1 and / or the fermentation agent according to claim 3 in the preparation of a browning inhibitor.

10. The use according to claim 8, characterized in that: The browning inhibitor can inhibit the browning of potatoes.

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