• Preservation by High Temperature

High-temperature preservation involves the application of heat to destroy microorganisms, enzymes, and spoilage agents. The treatment varies depending on the type of microorganisms, the nature of the food, and additional preservation methods. There are three levels of heat treatment used in food preservation:

• Pasteurization (Below 100°C) Pasteurization involves mild heat treatment to kill most, but not all, microorganisms. The remaining microbes can be controlled using additional preservation techniques.

• Temperature Range: Below 100°C
• Heating Methods: Steam, hot water, dry heat, or electric currents
• Cooling: Products are rapidly cooled after heating

Preservative Methods Supplementing Pasteurization:

1. Refrigeration: E.g., pasteurized milk stored at low temperatures
2. Sealed Packaging: Prevents microbial contamination
3. Anaerobic Conditions: Vacuum-sealed containers
4. High Sugar Concentration: E.g., sweetened condensed milk

Methods of Pasteurization:

• HTST (High-Temperature Short Time): Heating above 70°C for a few seconds.
• LTH (Low-Temperature Holding): Heating at 60-70°C for longer periods.

Example: Milk is commonly pasteurized using the HTST method at 72°C for 15 seconds.

• Heating at About 100°C Heating food at approximately 100°C destroys most non-spore-forming bacteria. This can be achieved by boiling liquid food, immersing containers in boiling water, or exposing food to steam.

• Examples:
  • Blanching vegetables before freezing or drying (brief heating at 100°C)
  • Preheating acidic foods like sauerkraut before packaging

Key Point: Foods with higher acidity can be safely preserved at this temperature.

1. Sterilization (Above 100°C)

Sterilization involves heating food at temperatures above 100°C to destroy all microorganisms, including spores. This is achieved using steam pressure sterilizers like pressure cookers and autoclaves.

• Temperature: Above 100°C
• Time and Temperature: Varies depending on the type of food
• Equipment: Pressure cookers, autoclaves

Examples:

• Fruits and tomatoes: Sterilized at 100°C for 30 minutes due to their high acidity.
• Non-acidic vegetables (e.g., peas, okra, beans): Require 116°C for 30-90 minutes.
• Empty cans and bottles: Sterilized in boiling water for 30 minutes before use.

Difference Between Pasteurization and Sterilization

Other Heat-Based Preservation Methods:

1. Aseptic Canning: Food is sterilized outside the can, then packed in sterilized cans under aseptic conditions.
2. Hot Pack (Hot Fill): Pasteurized or sterilized food is filled while hot into clean containers under non-sterile but clean conditions.

2. Preservation by Low Temperature

Low-temperature preservation slows microbial growth and enzymatic reactions. The lower the temperature, the greater the retardation of spoilage.

Cellar Storage (About 15°C)

• Used for surplus food storage in underground rooms.
• Not effective for long-term preservation as the temperature is not low enough to prevent spoilage.
• Examples: Storage of root crops (potatoes, carrots), cabbage, apples, and onions during winter months.

Refrigeration or Chilling (0 to 5°C)

• Achieved using ice or mechanical refrigeration.
• Used as the main preservation method or for temporary storage before further processing.
• Slows, but does not prevent, microbial and enzymatic changes. Examples of Chilled Products: Perishable foods like eggs, dairy products, meat, seafood, fruits, and vegetables.

Factors to Consider for Chilling Storage:

1. Temperature: Ideal range of 0 to 5°C.
2. Relative Humidity: Controls moisture loss and microbial growth.
3. Air Velocity: Ensures uniform cooling.
4. Atmosphere Composition: Modified or controlled atmosphere storage enhances shelf life.
5. Radiation: Use of UV rays or other radiations can further retard spoilage