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Heat Sterilization Lethality Calculations

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Heat Sterilization Lethality Calculations

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    1. Heat Sterilization Lethality Calculations FDT 3305, Principles of Food Engineering Pawan S. Takhar Animal and Food Sciences Texas Tech University

    2. D Value

    3. Thermal Death Time (TDT)

    4. TDT Curve

    5. F Value F Value is Thermal Death Time (TDT) denoted as follows:

    6. F0 Value

    7. Why we find F0 Values?

    8. Importance of Lethality Calculations Allows us to compare the effect of different temperature-time combinations on microbial destruction For example: Clostridium sporogenes, z-value =10 C What is the effect of heating at 100 C for 10 min versus 80 C for 15 min?

    9. Importance of Lethality Calculations 2. Temperature changes continuously in the retort. What is the effect of temperature - time profile on killing of microbes?

    10. Lethality Calculations

    11. Lethality Calculations

    12. Example

    13. Lethality: Measure of Microbial Kill Power at reference temperature

    14. Lethality

    15. Homework Problems (Due: In two Weeks) A) Calculate the Lethal Rate (L values) for C. botulinum (Z-Value 5.5 C) at a reference temperature of 65 C for the following time-temperature combinations Time (min) Temperature (.C) 0 25 7 50 10 60 15 70 20 80 25 80 50 60 60 40 70 25 B) Plot the process curve C) Plot the L-rate curve D) What are the units of L-values and the area under the L-Rate Curve? Note: Use Excel or your favorite spreadsheet software to plot the curves A. Redo Question 1 for Clostridium sporogenes , with a z value of 10 C. B. What is the effect of z values on L values? Support your answer by comparing L values calculated in the problems 1. and 2A. Which of the two microbes is killed more easily by the same thermal process?

    16. Homework Contd…. 3. Calculate lethality (area under the curve) using the spreadsheet given to you for the following process information:

    17. Homework Contd…. 4. A. Calculate lethality (area under the curve) using the spreadsheet given to you for the following process information:

    18. Homework Contd…. 5. Calculate lethality (area under the curve) using the spreadsheet given to you for the following process information:

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