1 The scorching summer has come, and ice cream will also become the main consumer product in the summer. With reference to the microbiological quality requirements of GB/T 31114-2014 frozen beverage-ice cream, we selected 3 ice creams to participate in the verification of the effectiveness of the rapid culture medium plate for the aerobic count and coliforms.
The DNP rapid culture medium plate uses the enzyme substrate method as the color development method. During the growth, the bacteria produce biological enzymes, which react with the chemical components in the plate to make the bacteria stained more obviously and easy to see and judge.
In this experiment, we used ice creams BAXY, MAGNU, and UBEST as the test substrates to see the effect of frozen beverage-ice cream substrates on the DNP culture medium plate.
2 Experimental design:
2.1 Bacterial liquid preparation
2.1.1 Incubate Escherichia coli in NB overnight to prepare a bacterial suspension.
2.2 Sample group preparation
2.2.1 Take 1 ml of the cultured bacteria liquid and add it to 25g ice cream, as a sample group for future use.
2.3 Preparation of bacterial liquid group
2.3.1 Take 1mL of the cultured bacterial solution and add it to 9mL PBS as a bacterial solution group for future use.
2.4 Blank control group
2.4.1 Take 1mL of sterile water and add it to 25g ice cream, as a blank control group.
2.5 Experimental procedure
2.5.1 Take the sample solution in the bacterial solution group for gradient dilution and count the viable bacteria.
2.5.2 Add 225mL sterile MV-225PBS to the ice cream in the sample group for homogenization. Use the MT-11 9mL diluent for the homogenized sample to carry out a gradient dilution, and keep the diluent.
2.5.3 Place the medium plate on a flat surface, open the cover film, take 1ml of the sample solution in each diluent, drop it on the center of the medium plate, slowly cover the film, the sample solution will spread automatically. Perform parallel tests.
2.5.4 After the sample solution is completely infiltrated, place AC plate at 35±1°C for 48 hours and place CC plate at 35±1°C for 24 hours.
2.5.5 Add 225mL sterile MV-225PBS to the ice cream in the blank control group for homogenization, take 1mL homogenized sample solution and drop on AC/CC medium plate.
2.5.6 Count the red colonies (coliforms)
2.5.7 Count the blue colonies (coliforms)
3 Experimental results
3.1 Experimental Group
3.1.1 Sample group
Brand | Aerobic Count | Coliforms |
BAXY |
|
|
MAGNUM |
|
|
UBEST |
|
|
3.2 Bacterial liquid group
Bacteria concentration |
|
|
3.3 Blank control group
3.3.1 No bacteria growth in all three products.
3.4 Summary of test data
Positive bacterial name | Dilution | n | Medi.Ca AC | ||
BAXY | MAGNUM | UBEST | |||
Escherichia coli | 10-6 | 1 | 130 | 136 | 115 |
2 | 134 | 141 | 118 | ||
10-7 | 1 | 12 | 16 | 10 | |
2 | 12 | 15 | 11 | ||
Positive bacterial name | Dilution | n | 4 Medi.Ca CC | ||
BAXY | MAGNUM | UBEST | |||
Escherichia coli | 10-6 | 1 | 99 | 110 | 87 |
2 | 105 | 113 | 83 | ||
10-7 | 1 | 9 | 16 | 7 | |
2 | 7 | 14 | 11 | ||
Positive bacterial name | Dilution | n | Plate count agar |
Escherichia coli | 10-6 | 1 | 140 |
2 | 177 |
4.1 Calculation results
4.1.1
Calculation formula: ratio of recovery test=
4.1.2
Reference value: the ratio of the recovery test is between 0.5-2
BAXY | MAGNUM | UBEST | |
Ratio of recovery test of Medi.Ca AC | 0.81 | 0.87 | 0.75 |
Ratio of recovery test Medi.Ca CC | 0.63 | 0.69 | 0.53 |
5 Result Analysis
5.1
According to the hygienic requirements of GB/T 31114-2014 frozen beverage ice cream, the three products we manufactured all meet the food safety requirements, so you can eat ice cream with confidence.
5.2
According to the verification results of Medi.Ca AC and Medi.Ca CC recovery tests on the three kinds of ice cream, they are all between 0.5-2, and the adaptability of the DNP culture medium plate in ice cream and other frozen beverages meets the requirements. It can be directly used for rapid testing of aerobic count and coliforms in frozen beverages.
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