Quantitave Plating

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  • Topic: Milk, Pasteurization, Dairy product
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BioSci 101 – Lab Section 810

QUANTITATIVE PLATING

PURPOSE

The purpose of this lab is to see the effects of pasteurization while emphasizing the process for serial dilutions. PROCEDURE

See references (1)

RESULTS

As the dilution factor increased for both the raw milk (unpasteurized) and pasteurized milk samples, the number of colonies decreased. The number of cells/mL in the pasteurized milk sample is considerably less than the number of cells/mL in the raw milk sample. RAW (UNPASTEURIZED) SAMPLE

Dilution Factor| Number of Colonies| Number of cells/mL| 10-3| TMTC| TMTC|
10-4| TMTC| TMTC|
10-5| TMTC| TMTC|
10-6| 284| 284,000,000 cells/mL|
10-7| 44| 440,000,000 cells/mL|
| AVERAGE| 362,000,000 cells/mL|

PASTEURIZED SAMPLE

Dilution Factor| Number of Colonies| Number of cells/mL| 10-3| 71| 71,000 cells/mL|
10-4| 9 (TLTC)| TLTC|
10-5| 6 (TLTC)| TLTC|
10-6| 1 (TLTC)| TLTC|
10-7| 12 (TLTC)| TLTC|
| AVERAGE| 71,000 cells/mL|

DISCUSSION/CONCLUSIONS

Pasteurization, a process named after scientist Louis Pasteur, involves the application of heat to destroy the majority of human pathogens in foods. In the dairy industry, pasteurization involves the “heating of every particle of milk or milk product to a specific temperature for a specified period of time without allowing recontamination of that milk or milk product during the heat treatment process.” (2) For public health purposes, pasteurization is the process of making milk and milk products safe for human consumption by destroying all bacteria that may be harmful to health. (2)

A serial dilution is a laboratory technique in which a substance is decreased in concentration in a series of proportional amounts. Dilutions are usually made in multiples of 10. (3) The viable plate count procedure allowed for live cells in the milk samples to be analyzed.

The raw milk (unpasteurized) sample demonstrated too many colony...
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