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The basic process of food microbiological testing

2024-01-09 14:50

To learn microbiological testing well, one must have a foundation in food microbiology and other disciplines, and be familiar with the biological characteristics of various pathogenic bacteria; Master the testing procedures for various pathogenic bacteria, molds, and viruses.

General steps for food microbiological testing

Preparation before inspection

(1) Prepare all necessary instruments, such as a refrigerator, constant temperature water bath, microscope, etc.

(2) All kinds of glass instruments, such as straws, petri dishes, wide mouthed bottles, test tubes, etc., need to be brushed clean (121 ℃ for 20 minutes) or sterilized by dry method (160 ℃ -170 ℃, 2 hours). After cooling, they should be sent to the sterile room for future use.

(3) Prepare various reagents and drugs required for the experiment, prepare regular agar medium or other selective media, and divide them into test tubes or sterilize them before pouring them into plates or storing them in a 46 ℃ water bath or a 4 ℃ refrigerator for future use.

(4) Sterilization in a sterile room; If using UV lamp sterilization, the time should not be less than 45 minutes, and the lamp should be turned off for half an hour before entering work; If using an ultra clean workbench, it needs to be turned on half an hour in advance. If necessary, conduct an air test in the sterile room and expose the agar plates to the air for 15 minutes. After cultivation, each plate should not exceed 15 colonies.

(5) The work clothes, hats, shoes, masks, etc. of the inspectors are sterilized and stored for future use. Staff are not allowed to enter the sterile room without permission until the experiment is completed.

Sample collection and processing

In food inspection, sample collection is an extremely important step. The collected samples must be representative, which requires inspectors to not only master the correct sampling method, but also understand the batch number of food processing, the source of raw materials, processing methods, storage conditions, transportation, and various links in sales, as well as the salesperson's sense of responsibility and hygiene knowledge level. Samples can be divided into three types: large sample, medium sample, and small sample.

A large sample refers to a whole batch, while a medium sample is a mixed sample taken from various parts of the sample. Generally, a 200g small sample, also known as a test sample, is used for inspection, with 25g as the standard. The number and method of sampling vary depending on the type of sample. However, the collection of all samples must be representative, meaning that the samples taken can represent all the components of the food. If the collected samples are not representative, even if a series of testing works are very precise and accurate, the results will be of no value, and even erroneous conclusions may appear.

Sampling and sample processing are the most important components of any inspection work. In terms of the accuracy of inspection results, the representativeness and condition of the samples received by the laboratory are key issues. If the sampling is not representative or the sample is mishandled, the test results obtained may be meaningless. If the quality of a large amount of food or the nature of a food poisoning case is explained based on the test results of a small sample, designing a scientific sampling plan and adopting the correct sample preparation method are essential conditions.

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