Sampling (Sampling) takes a small amount of representative samples from the product for inspection and analysis. This process is called sampling.
1. Principles for collecting food inspection samples
1. Some preparations before sampling
– Dry ice: refrigerant. Wet ice can also be used.
– Box or refrigeration dish: store and transport samples.
– Sterilization containers: from plastic bags to sterilized gallon paint buckets, etc.
– Sampling tools: teaspoon, angle spoon, needle-nose pliers, tweezers, graduated cylinder, beaker, etc.
– Sterile gloves:
– Sterile cotton swabs: generally used to wipe instrument facilities and factory environment areas.
– Sterilized full-package bags: for samples.
• When samples are collected, the conditions at the time of sample collection, such as product temperature, location, etc., together with the sample number marks, are recorded in the inspector's notes.
• When collecting sterile samples, one of the most important rules is: never contaminate the samples. This requires the sample collector to collect all additional samples very carefully to ensure that this rule is not violated.
2. Principles of food sample collection
1) The sampled products should be representative.
2) Sampling must meet the requirements of aseptic operation to prevent all external pollution
– Only one sample can be used for one sample to prevent cross contamination.
3) During the storage and transportation process, it should be ensured that the state of the microorganisms in the sample does not change
– The collected non-frozen foods are generally refrigerated at 0 to 5 ° C. Foods that cannot be refrigerated are tested immediately. The inspection is generally carried out within 36h.
4) The sampling label should be complete and clear
– The label of each sample must be clearly marked and provide as much detailed information as possible.
2. Collection methods of food inspection samples
A) Sampling plan
Generally speaking, if the import and export trade contract clearly stipulates the sampling volume of the food, the sampling shall be conducted according to the contract; if there is no specific sampling requirement, the sampling plan may be determined according to the inspection purpose, the nature of the product and the sample taken and the analysis method.
Currently the most popular sampling plans are (International Food Microbiology Standards Committee) ICMSF recommended sampling plan and random sampling plan.
No matter what method is used for sampling, the number of samples for each batch of goods shall not be less than 5 pieces. For foods that need to be tested for salmonella, the number of samples should be appropriately increased, with a minimum of no less than 8.
2) Sample selection
C) Sampling (sampling) method
International Commission on Microbiological Specifications for Foods, ICMSF
The ICMSF method is considered from a statistical point of view, how many samples are inspected for a batch of products to be representative, and can the objective sampling reflect the quality of the batch of products.
The basic principle of sampling proposed by ICMSF is to specify different sampling numbers based on the following considerations:
(1) Various microorganisms themselves have different degrees of harm to people;
(2) After the food is processed under different conditions, the degree of harm can be divided into three situations: the degree of harm decreases; the degree of harm does not change; the degree of harm increases.
ICMSF is a classification of microbial hazards in food by combining the three hazards of microorganisms, food characteristics and processing conditions. This idea is very scientific and conforms to the actual situation. It is more reasonable for manufacturers and consumers.
Sampling scheme of ICMSF: The ICMSF method includes two methods: two-level method and three-level method. The second-level method has only n, c, and m values, and the third-level method has n, c, m, and M values.
– N: refers to the number of samples of a batch of products. c: Refers to the number of samples in the batch of samples that exceed the limit.
– M: refers to the limit of qualified bacterial counts. M: Refers to the limit of the number of bacteria determined to be qualified after additional conditions.
The secondary sampling plan is used in cases of moderate or severe hazards, and the tertiary sampling plan is recommended for those with low health hazards.
1) Secondary method:
Only the m value of the standard for passing the judgment is set, and if it exceeds the m value, it is a non-conforming product. Determine whether the lot is qualified by checking whether there is more than m value in the test sample.
For example, the standard of total bacteria in raw fish fillets is n = 5, c = 0, m = 100cfu / g. Among them, m = 100cfu / g is the limit standard, n = 5 means 5 samples, c = 0 means that among the 5 samples in the batch, if no sample with more than m value of 100cfu / g is found, then the The batch of products is qualified.
cfu: colony forming unit, colony forming unit
2) Three-level method:
The microbial standard values ​​m and M are provided. As in the two-stage method, a test sample that exceeds the m value is considered unqualified. All inspection samples are less than the m value, the batch of products is qualified; the number of inspection samples in the range of m value to M value is in the range of c value, which means that the additional conditions are qualified, otherwise it is unqualified; where any inspection sample exceeds the M value Otherwise, the batch of products is unqualified.
For example, the standard of coliform bacteria in Australian frozen sugar foods is n = 5, c = 2, m = 100, M = 1000, which means that 5 samples are taken from a batch of products. If the results are all less than m = 100, it is judged that the batch of products is qualified; if the results of ≤ 2 samples are between m and M values ​​(that is, between 100 and 1000), it is judged that the additional conditions are qualified; if there are 3 The results of the above test samples are between the m and M values, and the batch of products is determined to be unqualified; if any of the test samples exceeds the M value (ie, 1000), the batch of products is determined to be unqualified.
Table 3-1 ICMSF is classified according to the microbiological hazard degree and food processing progress
2) Sample selection
Sample selection can be divided into targeted selection and random selection.
1. When sampling on site, random sampling can be used for random sampling.
2. Targeted selection is based on the situation that has been grasped. For example, if a food is suspected to be the cause of food poisoning, or it has been preliminarily determined that the food has hygienic quality problems, the sample is selected.
C) Sampling (sampling) method
Random sampling, that is, a method that enables each part of the population to have an equal chance of appearing in the sample, extracts several parts from a large number of samples.
Representative sampling (targeted sampling), that is, sampling using systematic sampling, so that each part taken represents the corresponding part of the food.
The random sampling table is compiled by computer at random, including 1,000, 10,000 or 100,000 numbers. The method of use is as follows:
a. First, number each unit of a batch of products (such as boxes, bags, boxes, etc.) in sequence. For example, a batch of 600 packs of products are compiled into 1, 2, ... 600.
b. Randomly point out a number on the table. View the row and column where the number is located. For example, click on the numbers in row 18 and column 10.
c. According to the maximum digits of the unit product number (for example, the maximum number is three digits), find the consecutive column numbers of the row, then the unit product with the same number as the number is a sample that should be taken .
d. Continue to check the same consecutive column numbers in the next row. The unit product represented by this number is another sample that should be taken.
e. Check in sequence as described above. When the number checked exceeds the maximum number, the number is discarded, and the number of the same column in the next row is continued to be checked until the number of samples to be drawn is completed.
C) Sampling (sampling) method
1). The gravimetric method takes a certain weight of food as a sample. After slaughter, take 100g / muscle of the inside muscle of the legs or the longest muscle of the back; samples of eggs and egg products should not be less than 200g per serving.
2). Swab method Swab method sampling does not damage the integrity of the meat and is easy to operate. But the total number of viable bacteria detected is not high.
3). The lavage method for the full-cleaned poultry should be sampled immediately after washing. This method has a higher detection rate than the swab method.
Sampling methods are essential to the effective implementation of sampling plans and to ensure the representativeness of the effectiveness of samples.
Sampling must follow aseptic procedures. Sampling tools such as stainless steel spoons, tweezers, scissors, etc. should be autoclaved to prevent all possible external contamination. The container must be clean, dry, leak-proof, wide-mouthed, and sterilized, and the size is suitable for holding samples for inspection. Throughout the sampling process, necessary measures should be taken to prevent changes in the number and growth capacity of inherent microorganisms in food. Attention should be paid to the homogeneity and source of the product to ensure the representativeness of the sample.
Sample preparation during microbiological inspection: uniform food: quartile method; meat, aquatic food: sterilized scissors cut, quartile method.
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