Food Preservation Chapter 4

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.