Question

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Which of the following statements are true and which are false? The decimal reduction time D...

Which of the following statements are true and which are false?

The decimal reduction time D is the heating time in min at a certain temperature required for the number of viable microbes to be reduced to 10% of the original number.

The z value is the temperature increase required for a ten-fold decrease in D.

Thermal death time is the heating time required to give commercial sterility.

Thermal death time does not depend on the initial microbial load.

The D value does not depend on the initial microbial load.

The D value of a microorganism is independent of the food item.

The D value of a microbe is a measure of the thermal resistance of the microbe.

If the number of microbes in a process has to be reduced from an initial load of 106 to a final 104, the required thermal death time will be 10D.

Solutions

Expert Solution

1. Ans: True

In microbiology, D-value refers to decimal reduction time and is the time (or dose) required at a given condition (e.g. temperature), or set of conditions, to kill 90% (or 1 log) of the exposed microorganisms i.e., viable microbes are reduced to 10% of the original number.

2. Ans: True

Z-value is a term used in microbial thermal death time calculations. It is the number of degrees the temperature has to be increased to achieve a tenfold (i.e. 1 log10) reduction in the D-value.

3. Ans: True

Thermal death time is how long it takes to kill a specific bacterium at a specific temperature to make the system sterile.

4. Ans: False

The thermal death time depends both on the initial and the final microbial load.

5. Ans: True

The D-value of an organism is the time required in a given medium, at a given temperature, for a ten-fold reduction in the number of organisms and is independent of the microbial load.

6. Ans: False

In microbiology, D-value refers to decimal reduction time and is the time (or dose) required at a given condition (e.g. temperature), or set of conditions, to kill 90% (or 1 log) of the exposed microorganisms. If the number of microorganisms in the food increases, the heating time required to process the product will also be increased to bring the population down to an acceptable level.

7. Ans: True

8: Ans: True

Note: It is 106 and 10-4 over there in the question.

Whatever values you have just plug in the values in the below expression.

The required thermal death time can be found from the following expression:

where:

No = Initial load

Nt = Final load

t = death time

we have

No = 106

Nt = 10-4

substitution in the above expression we get,

D = t/10

or t = 10 D


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