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Questions and Answers
What is the D-value in microbial inactivation kinetics?
What is the D-value in microbial inactivation kinetics?
Which method is used to combine several approaches to control pathogens in food products?
Which method is used to combine several approaches to control pathogens in food products?
What effect does lowering water activity have on microorganisms?
What effect does lowering water activity have on microorganisms?
What is the primary goal of pasteurization in food preservation?
What is the primary goal of pasteurization in food preservation?
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Which factor does NOT significantly affect the heat resistance of microbial cells?
Which factor does NOT significantly affect the heat resistance of microbial cells?
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What process typically requires reaching 121 °C at the cold spot?
What process typically requires reaching 121 °C at the cold spot?
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What does the Z-value indicate in microbial thermal processing?
What does the Z-value indicate in microbial thermal processing?
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Which of the following would NOT typically be considered an induced microbial killing method?
Which of the following would NOT typically be considered an induced microbial killing method?
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Study Notes
Food Preservation (Chapter 4)
- Death of Microorganisms: Natural causes include depletion of nutrients, changes in pH, buildup of toxic substances, lack of oxygen, and combinations of these factors.
Induced Microbial Killing
- Methods: Heat treatment, chemical agents (acidulants), radiation, lowering water activity, lowering temperature, hydrostatic pressure (very high pressure), pulse electric fields, and hurdle effect (combining multiple approaches).
Thermal Processing: Logarithmic Order of Death
- A table shows the relationship between heating time and the number of surviving microorganisms, demonstrating a logarithmic decrease in survivors over time. The table includes time of heating (minutes), number of survivors (powers of 10), and log of survivors.
Inactivation Kinetics
- D-value: Time required at a specific temperature to achieve a one-log reduction in viable cells or spores.
- Z-value: Change in temperature required to change the D-value by one log.
Z-Value Graph
- A graph shows the relationship between temperature (°C) and log D-value, displayed as a negatively sloped line. The R² value is 0.9917.
Factors Affecting Heat Resistance
- Factors impacting heat resistance in microorganisms: type of microorganism, stage of growth, pH, water activity, presence of fatty/protein components, and salt concentrations. Examples of D-values at 70°C are given for S.tyhimurium in milk and chocolate.
Why Calculate D and Z-Values?
- Use of D and Z-values aid in developing pasteurization and sterilization processes.
- Pasteurization targets vegetative cells (e.g., 7D process for Mycobacterium paratuberculosis).
- Sterilization targets spores (e.g., 12D process for C. botulinum spores in low-acid canned foods).
Types of Thermal Processes
- Blanching: Heat treatment.
- Pasteurization: Heat treatment to inactivate vegetative pathogens in food
- Low Temp Long Time (LTLT)
- High Temp Short Time (HTST)
- Commercial Sterilization: A thermal process for low-acid canned foods, destroying C. botulinum spores, targeting a specific temperature (e.g., 121°C at the cold spot).
- Ultra High Temperature (UHT) treatment: Another heat treatment process.
Effect of Microwaves on Microorganisms
- Microwaves use water molecules' oscillation to generate heat for food processing that includes; cooking, defrosting, reheating, and drying.
- Advantages include uniform heating and heating within the package.
- Disadvantage includes potential for uneven heating in food product.
Ultraviolet Light (UV light)
- UV light damages the genetic material of bacteria.
- Applications include water disinfection, packaging material disinfection for UHT milk, and mold control in baked goods. A simplified chain illustrates different organisms killed by UV-light ranging from Viruses to molds ending in G+ and G- bacteria.
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Description
This quiz explores the concepts of food preservation, focusing on the death of microorganisms and various induced microbial killing methods. It covers thermal processing, including the logarithmic order of death and inactivation kinetics, such as D and Z values. Test your understanding of these key food science principles.
