Method for detecting lactic streptococci in salt roasted chicken legs

Abstract

The invention discloses a method for detecting lactic streptococci in salt roasted chicken legs. The method comprises the following steps: S1, sample pretreatment; s2, enrichment culture; s3, selective separation; s4, biochemical identification; and S4, obtaining a biochemical identification result. The method provided by the invention has the beneficial effects of obvious effect, simple and easy operation, no need of complex and expensive equipment and high professional skills, error reduction and reliable result. The detection time is greatly shortened, the result can be obtained within 72 hours and is far faster than 5-7 days of a traditional method, the product quality can be controlled in time, the sensitivity is high, the lactic streptococci as low as 10 CFU / g can be detected, the detection has good repeatability and stability, the results of different batches of samples are consistent, the cost is low, popularization is facilitated, the industry quality control level can be improved, and the method is suitable for popularization and application. Health of consumers is guaranteed, and food safety risks and economic losses are reduced.

Description

Technical Field

[0001] The present invention relates to the field of detection, and in particular to a method for detecting lactic acid streptococci in salt-baked chicken legs. Background Art

[0002] Salt-baked chicken legs are a popular food among consumers, so their food safety is crucial. Lactococcus is a common microorganism that, under certain conditions, can cause food spoilage and affect consumer health.

[0003] At present, common microbial detection methods have problems such as complex operation, long detection time, and low sensitivity, which can hardly meet the needs of food production and quality control such as salt-baked chicken legs. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems in the background technology and to propose a method for detecting lactic acid streptococci in salt-baked chicken legs.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for detecting lactic acid streptococci in salt-baked chicken legs comprises the following steps: S1. Sample pretreatment: Weigh 25 g salt-baked chicken thigh sample, chop it and stir it thoroughly; add 225 ml sterile saline and homogenize at a speed of 8000-10000 r / min for 1-2 min to prepare a sample homogenate; S2. Enrichment culture: Take 1 ml of sample homogenate and inoculate it into a culture flask containing 10 ml of modified Todd-Hewitt broth medium, and culture it at 37°C for 18-24 hours; S3. Selective isolation: Inoculate 0.1 ml of the culture medium after enrichment onto a selective medium containing sodium azide and crystal violet. Incubate at 37°C for 24-48 hours and observe the colony morphology. S4. Biochemical identification: Suspicious colonies with a diameter of 0.5-1 mm were selected for Gram staining. If they were positive for cocci, a catalase test was performed, and if the result was negative, a carbohydrate fermentation test was performed. If they could ferment glucose, lactose, and sucrose to produce acid but not gas, they were confirmed to be lactic acid Streptococci. S4. Based on the biochemical identification results, determine whether lactic acid streptococci are present in the salt-baked chicken leg sample, and calculate its content using the plate count method.

[0006] Preferably, the modified Todd-Hewitt broth medium comprises: 17 g / L tryptone, 3 g / L soy peptone, 5 g / L sodium chloride, 2.5 g / L disodium hydrogen phosphate, 2 g / L glucose, and a pH value of 7.4±0.2.

[0007] Preferably, the selective culture medium containing sodium azide and crystal violet comprises: 10 g / L tryptone, 10 g / L beef extract, 5 g / L yeast extract, 1 g / L glucose, 5 g / L sodium chloride, 0.4 g / L sodium azide, 0.001 g / L crystal violet, and 15 g / L agar, with a pH of 7.0±0.2.

[0008] Preferably, in the sample pre-treatment, the sample slurry after homogenization needs to be filtered, and the filter pore size is 0.45 μm.

[0009] Preferably, during the bacterial enrichment culture process, the culture bottle needs to be shaken once every 6 hours.

[0010] Preferably, in the selective separation step, if there is still no obvious colony growth after 48 hours of culture, the culture time needs to be extended to 72 hours.

[0011] Preferably, in the biochemical identification, in addition to the catalase test and the carbohydrate fermentation test, a bile esculin test is also performed. If the result is positive, it is further confirmed that the detected colony is Streptococcus lactis.

[0012] The method for detecting lactic acid streptococci in salt-baked chicken legs provided by the present invention has many significant beneficial effects: First, it excels in operational ease. The entire testing process eliminates the need for complex and expensive instrumentation, making the method suitable not only for successful implementation in well-equipped professional laboratories but also for routine quality control in food production companies. Its simple operation reduces the need for specialized operator skills, significantly minimizing potential errors introduced by complex procedures and improving the accuracy and reliability of test results.

[0013] Secondly, the detection time is significantly shortened. Compared with traditional detection methods that usually take 5-7 days to obtain results, the detection method of the present invention can complete the entire process from sample processing to result determination within 72 hours. This significant time advantage enables food production companies to grasp the microbial contamination of their products more promptly, allowing them to quickly implement corresponding quality control measures, effectively avoiding the large-scale production and circulation of problematic products, and reducing potential food safety risks and economic losses.

[0014] Furthermore, the detection sensitivity is significantly improved. The detection method of the present invention can accurately detect lactic acid Streptococcus in salt-baked chicken legs at levels as low as 10 CFU / g. Even when the microbial content is extremely low, its presence can be keenly captured, providing a more stringent guarantee for food safety. For example, when testing a sample of salt-baked chicken legs with trace contamination, traditional methods may not be able to detect low concentrations of lactic acid Streptococcus, but the method of the present invention can accurately identify it, ensuring the quality and safety of the food.

[0015] Furthermore, the detection method of the present invention exhibits excellent repeatability and stability. Testing of multiple batches of salt-baked chicken thigh samples from different sources demonstrated a high degree of consistency and repeatability in the test results. This feature enables reliable and similar test results to be obtained under varying experimental conditions and by varying operators, further enhancing the method's credibility and practicality in practical applications.

[0016] Finally, the detection method of the present invention is relatively low-cost. By eliminating the need for sophisticated instruments and expensive reagents, the cost of testing is reduced, making it affordable for more food manufacturers. This will facilitate widespread adoption within the industry, improve quality control across the food industry, and protect consumer health and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a line graph of the experimental number and the detected lactococcus content (CFU / g) of the present invention. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0019] Reference Figure 1 A method for detecting lactic acid streptococci in salt-baked chicken legs comprises the following steps: S1. Sample pretreatment: Weigh 25 g salt-baked chicken thigh sample, chop it and stir it thoroughly; add 225 ml sterile saline and homogenize at a speed of 8000-10000 r / min for 1-2 min to prepare a sample homogenate; S2. Enrichment culture: Take 1 ml of sample homogenate and inoculate it into a culture flask containing 10 ml of modified Todd-Hewitt broth medium, and culture it at 37°C for 18-24 hours; The modified Todd-Hewitt broth medium comprises: 17 g / L tryptone, 3 g / L soy peptone, 5 g / L sodium chloride, 2.5 g / L disodium hydrogen phosphate, 2 g / L glucose, and a pH of 7.4±0.2; S3. Selective isolation: Inoculate 0.1 ml of the culture medium after enrichment onto a selective medium containing sodium azide and crystal violet. Incubate at 37°C for 24-48 hours and observe the colony morphology. The selective culture medium containing sodium azide and crystal violet comprises: 10 g / L tryptone, 10 g / L beef extract, 5 g / L yeast extract, 1 g / L glucose, 5 g / L sodium chloride, 0.4 g / L sodium azide, 0.001 g / L crystal violet, and 15 g / L agar, with a pH of 7.0±0.2; S4. Biochemical identification: Suspicious colonies with a diameter of 0.5-1 mm were selected for Gram staining. If they were positive for cocci, a catalase test was performed, and if the result was negative, a carbohydrate fermentation test was performed. If they could ferment glucose, lactose, and sucrose to produce acid but not gas, they were confirmed to be lactic acid Streptococci. S4. Based on the biochemical identification results, determine whether lactic acid streptococci are present in the salt-baked chicken leg sample, and calculate its content using the plate count method; When counting plates, select plates with colony counts between 30 and 300. If two plates with the same dilution have colony counts between 30 and 300, take the average as the colony count for that dilution. In sample pretreatment, the homogenized sample slurry needs to be filtered with a pore size of 0.45 μm; During the bacterial enrichment culture process, the culture bottle needs to be shaken every 6 hours; In the selective isolation step, if there is still no obvious colony growth after 48 hours of incubation, the incubation time needs to be extended to 72 hours; In biochemical identification, in addition to the catalase test and carbohydrate fermentation test, a bile esculin test is also required. If the result is positive, it is further confirmed that the detected colony is Streptococcus lactis.

[0020] This experiment aimed to verify the effectiveness and accuracy of the proposed method for detecting lactic acid streptococci in salt-baked chicken legs. A total of 10 experiments were conducted, each of which was performed strictly in accordance with the procedures and conditions specified in the claims.

[0021] During the sample preparation phase, 25 g of salt-baked chicken thigh samples were weighed and 225 ml of sterile saline was added to each sample. The homogenization process was performed at a speed ranging from 8,000 to 10,000 rpm, and the homogenization time was adjusted between 1 and 2 minutes.

[0022] During the enrichment stage, the culture temperature is uniformly set at 37°C, and the incubation time ranges from 18 to 24 hours. This process provides ideal conditions for the growth and reproduction of lactic acid streptococci, increasing their numbers and facilitating subsequent testing.

[0023] The selective culture stage was also carried out at a constant temperature of 37°C, and the culture time varied between 24 and 48 hours.

[0024] Through this series of operations and incubations, the final detected lactic acid Streptococcus content varied. In Experiment 1, the detected content was 50 CFU / g; in Experiment 2, it was 80 CFU / g; in Experiment 3, it reached 120 CFU / g; in Experiment 4, it was 65 CFU / g; in Experiment 5, it was 90 CFU / g; in Experiment 6, it was 70 CFU / g; in Experiment 7, it was 75 CFU / g; in Experiment 8, it was 85 CFU / g; in Experiment 9, it was 60 CFU / g; and in Experiment 10, it was 100 CFU / g.

[0025] The following table shows the specific experimental data:

[0026] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for detecting lactic acid streptococci in salt-baked chicken legs, characterized in that: The following steps are involved: S1. Sample pretreatment: Weigh 25 g salt-baked chicken thigh sample, chop it and stir it thoroughly; add 225 ml sterile saline and homogenize at a speed of 8000-10000 r / min for 1-2 min to prepare a sample homogenate; S2. Enrichment culture: Take 1 ml of sample homogenate and inoculate it into a culture flask containing 10 ml of modified Todd-Hewitt broth medium, and culture it at 37°C for 18-24 hours; S3. Selective isolation: Inoculate 0.1 ml of the culture medium after enrichment onto a selective medium containing sodium azide and crystal violet. Incubate at 37°C for 24-48 hours and observe the colony morphology. S4. Biochemical identification: Suspicious colonies with a diameter of 0.5-1 mm were selected for Gram staining. If they were positive for cocci, a catalase test was performed, and if the result was negative, a carbohydrate fermentation test was performed. If they could ferment glucose, lactose, and sucrose to produce acid but not gas, they were confirmed to be lactic acid Streptococci. S4. Based on the biochemical identification results, determine whether lactic acid streptococci are present in the salt-baked chicken leg sample, and calculate its content using the plate count method.

2. The method for detecting lactococci in salt-baked chicken legs according to claim 1, wherein: The modified Todd-Hewitt broth medium comprises the following components: 17 g / L tryptone, 3 g / L soy peptone, 5 g / L sodium chloride, 2.5 g / L disodium hydrogen phosphate, and 2 g / L glucose, with a pH value of 7.4±0.

2.

3. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 1, wherein: The selective culture medium containing sodium azide and crystal violet includes the following components: 10 g / L tryptone, 10 g / L beef extract, 5 g / L yeast extract, 1 g / L glucose, 5 g / L sodium chloride, 0.4 g / L sodium azide, 0.001 g / L crystal violet, and 15 g / L agar, with a pH value of 7.0±0.

2.

4. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 3, wherein: When counting plates, select plates with colony counts between 30 and 300. If two plates with the same dilution have colony counts between 30 and 300, take their average value as the colony count for that dilution.

5. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 1, wherein: In sample pretreatment, the sample slurry after homogenization needs to be filtered, and the filter pore size is 0.45 μm.

6. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 1, wherein: During the bacterial enrichment culture process, the culture bottle needs to be shaken every 6 hours.

7. The method for detecting lactococci in salt-baked chicken legs according to claim 1, wherein: In the selective isolation step, if there is still no obvious colony growth after 48 hours of culture, the culture time needs to be extended to 72 hours.

8. The method for detecting lactococci in salt-baked chicken legs according to claim 1, wherein: In biochemical identification, in addition to the catalase test and carbohydrate fermentation test, a bile esculin test is also required. If the result is positive, it is further confirmed that the detected colony is Streptococcus lactis.

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