Microbial parameter detection in fresh milk/food

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The routine inspection items include determination of total bacterial count, MPN determination of coliform group, and detection of pathogenic bacteria in fresh milk. According to GB. The total number of bacteria reflects the degree of bacterial contamination of fresh milk; The MPN of coliform bacteria indicates that fresh milk may be contaminated by intestinal bacteria; No pathogenic bacteria are allowed to be detected in milk and dairy products

2) Other microbiological examination methods

1. Methyl blue reduction test

Microorganisms present in milk can secrete reductase during growth and reproduction, which can reduce and discolor Methyl blue. The speed of the reduction reaction is related to the number of bacteria in milk.

. Based on the fading time of methylene blue, the amount of bacteria in milk can be estimated to evaluate the quality of milk. The operation method is as follows:

Operation method: Sterile operation: Take 5mL of the tested milk, inject it into a sterile test tube, add 0.25mL of 0.25% methylene blue solution, stuff the cotton stopper tightly, mix well, and place it in a 37 ℃ water bath. Observe the discoloration of the contents of the test tube every 10-15 minutes. The faster the fading time, the more severe the pollution

Result determination:

2. Blade azure test

Blade azure is an indicator of oxidation-reduction reaction, and when added to normal fresh milk, it appears bluish blue or slightly bluish purple. If the milk contains bacteria and grows and reproduces, it can cause blade azure reduction and color change. The quality of fresh milk can be determined based on the changes in color from cyan blue to red purple to pink white

The reaction speed of the blade azure test is faster than that of the methylene blue test, and it is an irreversible discoloration reaction, suitable for milk with high bacterial count

The specific method is as follows:

① Use 10ml sterile straws to take 10ml of the tested milk sample and place it in a sterile test tube. If there are multiple tested samples, each sample needs to use one 10ml straw and the milk sample should be numbered.

② Use an 1ml sterile pipette to take 0.005% aqueous solution of Tianqing and add it to the test tube. Immediately plug only the sterile rubber stopper, invert the tube 2-3 times, and mix well

③ Quickly place the test tube in a 37 degree water bath and heat it (loosen the rubber plug, do not make it too tight)

④ Observe the water bath for 20 minutes and record the color changes inside each test tube. Remove the test tubes that have turned white, and continue the water bath for the remaining test tubes until 60 minutes. Record the color changes of each test tube. The quality of dairy products can be determined based on the degree of discoloration and discoloration time of each test tube sample, and can also be inspected in a photoelectric colorimeter

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