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

Verified step by step guidance

1. Identify the decimal reduction time (D) on the graph, which is the time required at a certain temperature to reduce the microbial population by 90% (or one log cycle). This corresponds to the time interval for the survivor curve to drop by one log unit.
2. Locate the two temperatures on the x-axis of the graph for which you need to find the decimal reduction times. For each temperature, find the corresponding survivor curve (log number of survivors vs. time).
3. For each temperature, select two points on the survivor curve that differ by exactly one log unit on the y-axis (for example, from 10^6 to 10^5 survivors).
4. Calculate the time difference between these two points on the x-axis (time axis). This time difference is the decimal reduction time (D) at that temperature.
5. Repeat the process for the second temperature to find its decimal reduction time. This will give you the D values for both temperatures as required.

Key Concepts

Decimal Reduction Time (D-value)

The decimal reduction time (D-value) is the time required at a specific temperature to reduce a microbial population by 90%, or one log cycle. It quantifies the effectiveness of a sterilization or disinfection process and is typically derived from survival curves plotting microbial count versus time.

Thermal Death Time and Temperature Relationship

Microbial death rates increase with temperature, meaning higher temperatures reduce the D-value. Understanding how temperature affects microbial inactivation helps interpret survival curves and calculate D-values at different temperatures from the graph.

Interpreting Microbial Survival Curves

Survival curves plot the logarithm of the number of surviving microorganisms against time. The slope of the linear portion of the curve is used to calculate the D-value, as it represents the rate of microbial death under specific conditions.