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

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

[0003] At present, common microbial detection methods have problems such as complex operation, long detection time, and low sensitivity, which makes it difficult to 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:

[0006] A method for detecting lactic acid streptococci in salt-baked chicken legs comprises the following steps:

[0007] S1. Sample pretreatment: weigh 25 g salt-baked chicken leg sample, chop it and stir it thoroughly; add 225 ml sterile physiological saline, and homogenize it at a speed of 8000-10000 r / min for 1-2 min to prepare a sample homogenate;

[0008] S2. Bacterial enrichment culture: Take 1 ml of sample homogenate and inoculate it into a culture bottle containing 10 ml of modified Todd-Hewitt broth medium, and culture it at 37°C for 18-24 hours;

[0009] S3, selective separation: inoculate 0.1 ml of the culture fluid after bacterial enrichment culture on a selective medium containing sodium azide and crystal violet, culture at 37°C for 24-48 hours, and observe the colony morphology;

[0010] S4. Biochemical identification: Select suspicious colonies with a diameter of 0.5-1mm for Gram staining. If it is a positive cocci, perform a catalase test, and the result is negative. Then perform a carbohydrate fermentation test. If it can ferment glucose, lactose, and sucrose to produce acid but not gas, it is confirmed to be lactic acid streptococcus.

[0011] S4. Based on the biochemical identification results, determine whether lactic acid streptococci exist in the salt-baked chicken leg samples, and calculate their content using the plate count method.

[0012] Preferably, the components of the modified Todd-Hewitt broth medium include: 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 the pH value is 7.4±0.2.

[0013] 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, 15 g / L agar, and the pH value is 7.0±0.2.

[0014] Preferably, in the sample pretreatment, the sample slurry after homogenization needs to be filtered, and the pore size of the filter is 0.45 μm.

[0015] Preferably, during the bacterial enrichment culture process, the culture bottle needs to be shaken once every 6 hours.

[0016] 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.

[0017] 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 lactic acid streptococcus.

[0018] The method for detecting lactic acid streptococci in salt-baked chicken legs provided by the present invention has many significant beneficial effects:

[0019] First, it excels in terms of ease of operation. The entire testing process does not rely on complex and expensive instruments and equipment, which enables the method to be successfully implemented not only in well-equipped professional laboratories, but also easily applied to the daily quality testing of food production companies. Its simple operation steps reduce the excessive requirements for the professional skills of operators, greatly reduce the errors that may be introduced due to complex operations, and improve the accuracy and reliability of the test results.

[0020] Secondly, the detection time is greatly shortened. Compared with the traditional detection method which usually takes 5-7 days to obtain the results, the detection method of the present invention can complete the whole process from sample processing to result determination within 72 hours. This significant time advantage enables food production enterprises to grasp the microbial contamination of products more timely, so as to quickly take corresponding quality control measures, effectively avoid the mass production and circulation of problematic products, and reduce potential food safety risks and economic losses.

[0021] Furthermore, the detection sensitivity is significantly improved. The detection method of the present invention can accurately detect lactic acid streptococci in salt-baked chicken legs with a content as low as 10 CFU / g. Even when the content of microorganisms is extremely low, its presence can be keenly captured, providing a more stringent guarantee for food safety. For example, when testing trace-contaminated salt-baked chicken leg samples, low-concentration lactic acid streptococci that may not be detected by traditional methods can be accurately identified by the method of the present invention, ensuring the quality and safety of the food.

[0022] In addition, the detection method of the present invention also has good repeatability and stability. By testing multiple batches of salt-baked chicken leg samples from different sources, the results show that the detection results of the method have high consistency and repeatability. This feature enables reliable and similar detection results to be obtained under different experimental conditions and in the hands of operators, further enhancing the credibility and practicality of the method in practical applications.

[0023] Finally, the detection method of the present invention has a relatively low cost. Since it does not require the use of high-end complex instruments and a large number of expensive reagents, the economic cost of the detection is reduced, making it affordable for more food production companies, which is conducive to the widespread promotion and application in the industry, improving the quality control level of the entire food industry, and protecting the health and safety of consumers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a line graph of the experimental number and the detected lactic acid streptococcus content (CFU / g). DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely 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.

[0026] Reference Figure 1 A method for detecting lactic acid streptococci in salt-baked chicken legs comprises the following steps:

[0027] S1. Sample pretreatment: weigh 25 g salt-baked chicken leg sample, chop it and stir it thoroughly; add 225 ml sterile physiological saline, and homogenize it at a speed of 8000-10000 r / min for 1-2 min to prepare a sample homogenate;

[0028] S2. Bacterial enrichment culture: Take 1 ml of sample homogenate and inoculate it into a culture bottle containing 10 ml of modified Todd-Hewitt broth medium, and culture it at 37°C for 18-24 hours;

[0029] The components of the modified Todd-Hewitt broth medium include: 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;

[0030] S3, selective separation: inoculate 0.1 ml of the culture fluid after bacterial enrichment culture on a selective medium containing sodium azide and crystal violet, culture at 37°C for 24-48 hours, and observe the colony morphology;

[0031] 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, 15 g / L agar, and a pH value of 7.0±0.2;

[0032] S4. Biochemical identification: Select suspicious colonies with a diameter of 0.5-1mm for Gram staining. If it is a positive cocci, perform a catalase test, and the result is negative. Then perform a carbohydrate fermentation test. If it can ferment glucose, lactose, and sucrose to produce acid but not gas, it is confirmed to be lactic acid streptococcus.

[0033] S4. According to the biochemical identification results, determine whether lactic acid streptococci exist in the salt-baked chicken leg sample, and calculate its content by plate count method;

[0034] When counting plates, select plates with colony counts between 30 and 300 for counting. 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.

[0035] In sample pretreatment, the homogenized sample slurry needs to be filtered, and the filter pore size is 0.45 μm;

[0036] During the bacterial enrichment culture process, the culture bottle needs to be shaken every 6 hours;

[0037] 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;

[0038] 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 lactic acid streptococcus.

[0039] This experiment aims 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, and each experiment was strictly carried out in accordance with the steps and conditions specified in the claims.

[0040] In the sample processing stage, 25 g salt-baked chicken leg samples were weighed for each experiment and 225 ml of sterile saline was added to them. During homogenization, the speed varied between 8000 and 10000 rpm, and the homogenization time was adjusted between 1 and 2 minutes.

[0041] During the bacterial enrichment stage, the culture temperature is uniformly set at 37°C, and the culture time ranges from 18 hours to 24 hours. This process provides suitable conditions for the growth and reproduction of lactic acid streptococci, increasing their number and facilitating subsequent detection.

[0042] The selective culture phase was also carried out at a constant temperature of 37°C, and the culture time varied between 24 and 48 hours.

[0043] Through this series of operations and cultivation, the final detected lactic acid streptococcus content was different. In experiment 1, the detected content was 50CFU / g; in experiment 2, it was 80CFU / g; in experiment 3, it reached 120CFU / g; in experiment 4, it was 65CFU / g; in experiment 5, it was 90CFU / g; in experiment 6, it was 70CFU / g; in experiment 7, it was 75CFU / g; in experiment 8, it was 85CFU / g; in experiment 9, it was 60CFU / g; in experiment 10, it was 100CFU / g.

[0044] The following figure shows the specific experimental data:

[0045]

[0046] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope 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 leg sample, chop it and stir it thoroughly; add 225 ml sterile physiological saline, and homogenize it at a speed of 8000-10000 r / min for 1-2 min to prepare a sample homogenate; S2. Bacterial enrichment culture: Take 1 ml of sample homogenate and inoculate it into a culture bottle 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 solution after bacterial enrichment culture on a selective medium containing sodium azide and crystal violet, culture at 37°C for 24-48 hours, and observe the colony morphology; S4. Biochemical identification: Select suspicious colonies with a diameter of 0.5-1mm for Gram staining. If it is a positive cocci, perform a catalase test, and the result is negative. Then perform a carbohydrate fermentation test. If it can ferment glucose, lactose, and sucrose to produce acid but not gas, it is confirmed to be lactic acid streptococcus. S4. Based on the biochemical identification results, determine whether lactic acid streptococci exist in the salt-baked chicken leg samples, and calculate their content using the plate count method.

2. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 1, characterized in that: The components of the modified Todd-Hewitt broth medium include: 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.

3. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 1, characterized in that: 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, 15 g / L agar, and 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, characterized in that: When counting plates, select plates with colony counts between 30 and 300 for counting. 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, characterized in that: In sample pretreatment, the sample slurry after homogenization needs to be filtered, and the filter pore size is 0.45μm.

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

7. The method for detecting lactic acid streptococci in salt-baked chicken legs according to claim 1, characterized in that: 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 lactic acid streptococci in salt-baked chicken legs according to claim 1, characterized in that: 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 lactic acid streptococcus.

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