Calculate the decimal reduction time (D) for the two temperatures in the following graph.

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Identify the decimal reduction time (D) definition: it is the time required at a certain temperature to reduce the number of living microbes by 90%, which corresponds to a 1-log reduction on a logarithmic scale.

On the graph, locate the initial number of living microbes for each temperature (45°C and 20°C) at the starting time point.

For each temperature, find the time it takes for the number of living microbes to decrease by one logarithmic unit (i.e., from 10^4 to 10^3, or from 10^3 to 10^2, etc.). This time interval corresponds to the decimal reduction time (D).

Calculate the difference in time between these two points on the x-axis (time in minutes) for each temperature curve. This difference is the decimal reduction time (D) for that temperature.

Repeat the process for both the 45°C and 20°C curves to find their respective D values, noting that the steeper slope (45°C) will have a smaller D value compared to the gentler slope (20°C).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Decimal Reduction Time (D-value)

The decimal reduction time (D-value) is the time required at a specific temperature to reduce the microbial population by 90%, or one log cycle. It is a key measure of microbial resistance to heat and is used to compare the effectiveness of different temperatures in killing microbes.

Logarithmic Scale in Microbial Death Curves

Microbial death over time is often plotted on a logarithmic scale to linearize the exponential decline in the number of living microbes. This allows easier calculation of the D-value by measuring the time interval for a one-log reduction in microbial count.

Effect of Temperature on Microbial Death Rate

Higher temperatures generally increase the rate of microbial death, resulting in a shorter D-value. The graph shows two temperatures (20°C and 45°C), illustrating that microbes die faster at 45°C compared to 20°C, which is reflected in the steeper slope of the 45°C line.

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