Question

…………. value is defined as the increase in temperature necessary to cause a 90% reduction in the decimal reduction time.

• A. D Value
• B. F Value
• C. Z Value
• D. K Value

Hint:

Remember: D is for Duration (time) at a fixed temperature, while Z is for Zone/increment (temperature) to change that duration.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the thermal processing term that describes the sensitivity of a microorganism's death rate to temperature changes. It specifically defines the temperature increment required to reduce the decimal reduction time ($D$-value) by one log cycle ($90\%$).
Key Formula or Approach:
Thermal death time calculations often use the $D$-value and $Z$-value:
- D-value: Time required at a specific temperature to kill $90\%$ of the population.
- Z-value: Temperature increase needed to reduce the $D$-value by a factor of 10.

Step 2: Detailed Explanation:

• Thermal Kinetics: In food sterilization, we observe that as temperature increases, the time required to kill microbes ($D$-value) decreases exponentially.

• Z-Value Definition: The $Z$-value is the number of degrees (Celsius or Fahrenheit) required for the thermal destruction curve to traverse one log cycle. Mathematically, it is the reciprocal of the slope of the plot of $\log D$ versus temperature.

• Implication: A lower $Z$-value indicates that the organism is very sensitive to temperature changes. For example, if $Z = 10^\circ C$, then increasing the processing temperature by $10^\circ C$ will allow you to achieve the same lethality in one-tenth of the time.

• Other Values: $D$-value (A) is a time measure. $F$-value (B) is the total lethality at a reference temperature. $K$-value (D) often refers to the reaction rate constant in chemical kinetics.

Step 3: Final Answer:
The increase in temperature required to reduce the $D$-value by $90\%$ is the $Z$-value.