Moist heat sterilization is used for general medium testing, that is, high-pressure steam sterilization, generally at 121°C for 15 minutes, and sugar-containing or special medium is sterilized according to national standards or instructions provided by the manufacturer. The prepared medium must be sterilized immediately to prevent the growth and reproduction of microorganisms from consuming nutrients and changing the pH of the medium. High temperature will destroy the nutrient content of the medium and reduce the gel strength of the agar, so the sterilization temperature and time must be strictly controlled, and repeated sterilization cannot be performed. The pressure gauge of the high-pressure steam sterilizer should be checked regularly, and the sterilization effect should be verified regularly with biological indicator method or chemical discoloration paper.

1. Medium detection pH measurement

Microorganisms must be in the proper pH range to grow and reproduce properly or to reflect their biology. The pH value required by the medium formula is the pH value after sterilization or disinfection, that is, the pH value of the medium before use, and should be measured with a precision pH meter at 25°C. Solid agar media should be measured using special colloidal surface electrodes. Take measurements. During use, if the pH value of the medium needs to be adjusted, it can be adjusted with 1mol/L NaOH or 1mol/L HCL. Be careful not to adjust the pH repeatedly, otherwise it will affect the osmotic pressure of the medium.

2. Preservation of the prepared medium for detection

After sterilization, the medium should be quickly cooled to the required temperature to avoid long-term storage in the sterilizer, which will cause excessive sterilization and affect the nutritional content or selective effect of the medium. The amount of prepared medium should be used up within the longest shelf life. The medium containing the dye should be stored away from light; if the poured agar plate is not used up on the day of preparation, it should be stored in the refrigerator; if it is stored for more than 2 days, it should be stored in a sealed plastic bag; the prepared meat should be stored in a sealed in a plastic bag. Broth media should be stored in screw cap test tubes or other airtight tubes or containers for more than 2 weeks to prevent evaporation.

The quality control of food microbiological testing is actually a series of systematic activities formulated and implemented to meet the quality requirements of the laboratory. Ensure the accuracy of detection. Quality control can be divided into two categories: internal quality control and external quality evaluation.

Internal quality control refers to the continuous control plan adopted by the laboratory for comparative analysis, tracking and laboratory work. This is the core and foundation of laboratory quality assurance. Pass the quality control of inspectors, operation manuals, testing environment, equipment and instruments and their function testing, culture medium reagent staining liquid and other quality control, quality control of inspection process, standard strains, laboratory safety protection and other requirements. This content includes all aspects of the daily operation of the microbiological testing laboratory, and a sound and complete laboratory should meet the requirements of these aspects.

The quality of the culture medium is the basis of the testing work in the microbiology laboratory, which is related to the accuracy and reliability of the testing work, and plays an important role in the testing work of the microbiology laboratory. If quality problems in any link are ignored in the work, it will lead to deviations in scientific and objective test results. Therefore, it is necessary to strengthen the quality control of the medium in the laboratory, do a good job in the quality control of the medium, and continuously improve and improve the quality control level of the medium to provide high-quality culture substrates. Culture media for microbiological testing laboratories.