Heat Processing of Foods Quiz

Heat Processing of Foods

• Heat processing is used to ensure food safety and extend shelf life
• Common techniques include high temperature (pasteurization, sterilization), low temperature (chilling, freezing), reduced water activity (drying), chemical preservatives, radiation, and high hydrostatic pressure (HHP)
•  High temperature, low temperature, and reduced water activity are the three most commonly used methods

Food Processing Techniques Using Heat

• Various methods exist for processing food using heat
• Key methods include: Pasteurization, Tunnel Pasteurizers, Batch Pasteurizers, Continuous Flow Pasteurizers (HTST)

Pasteurization

• A thermal processing method for extending shelf life of food
• Designed primarily to remove pathogenic bacteria, but not heat-resistant spore-formers
• Uses moderate temperatures to minimize changes in sensory properties and nutrient value (days or weeks of shelf life)
• Not suitable for creating shelf-stable products without refrigerated storage

Pasteurization Concept

• A form of thermal processing for liquids and foods in containers
• Uses moderate temperatures to extend shelf life
• Minimizes changes to sensory properties and nutrient value
• Primarily for removing pathogenic bacteria, not heat resistant spore-formers that are not destroyed at the applied temperatures

Temperature-Time Combination

• The temperature and time combination for pasteurization depends heavily on the pH of the product

• Acidic foods (pH < 4.5): Inactivation of enzymes (e.g., fruit juices), destruction of spoilage organisms (yeasts)

• Low-acid foods (pH > 4.5): Destruction of pathogens (e.g., Brucella abortus, Mycobacterium tuberculosis in milk)

• Specific temperature-time combinations are required for different food types

• Examples include milk (72°C for 15 seconds), ice cream mix (80°C for 20 seconds), and tomato juice (118°C for 60 seconds)

Pasteurizer Types

• In-Container (Tunnel) Pasteurizers

  • Used for canned/bottled juices, milk, carbonated beverages stored at refrigeration temperatures
  • Temperatures are below 100°C (atmospheric pressure)
  • Heating methods: hot water spray/bath, steam
  • Cooling methods: cold water spray
  • Heating/cooling of carbonated beverages and glass containers are slowed down to prevent thermal shock

• Tunnel Pasteurizers - Hot Water Bath:

  • Employ conveyor belts (3-4 meters wide, 10-30 meters long)
  • Capable of pasteurizing 3000-12,000 cans/glass containers within 30 minutes
  • Specific temperature zones for pre-heating, superheating, holding, pre-cooling, and cooling

• Tunnel Pasteurizers - Hot Water Spray:

  • Packaged product is heated by hot water spray on conveyor belt
  • Product remains at desired temperature for specified time
  • Cools with water sprays before exiting the tunnel
  • Residence time up to 1 hour

• Batch Pasteurizers (LTLT):

  • Also known as vat pasteurization or low-temperature long-time pasteurization
  • Uses a double-jacketed vat with either circulating hot water or steam
  • Liquid food (milk) is heated to 63°C and held at that temperature during a 30-minute holding time, while agitated
  • The liquid food can be cooled within the vat or removed from the vat while still hot.

Continuous Flow Pasteurizers (HTST)

• Designed to minimize damage to nutritional content and sensory quality (taste, color) of food when exposed to high temperatures for extended periods
• High-Temperature Short-Time (HTST) process is a solution to the food quality issue

HTST Pasteurizers - System Design

• Components include a balance tank, pump, homogenizer, regeneration section, heating section, holding tube, flow diversion valve, and final cooling section

HTST Pasteurizers - Operating

• Process involves heating, holding time, and cooling stages
• Specific temperatures ensure appropriate heat treatment while minimizing food quality loss

HTST Pasteurizers - Regeneration Efficiency (RE)

• A measurement of heat recovery in the regeneration section
• Calculated as (T2-T1) / (T3-T1), where T1 is the unpasteurized liquid entrance temperature, T2 is the unpasteurized liquid exit temperature, and T3 is the pasteurized liquid entrance temperature.
• High RE (e.g., 90%) indicates an efficient system

Pasteurization Efficiency

• Temperature control is crucial (±0.5°C) for optimal results.
• Residence time is calculated based on flow velocity (laminar or turbulent)
• Efficiency evaluation includes biochemistry (alkaline phosphatase test) and microbiology (pathogen destruction checks in milk, etc.)
• Contamination from raw milk and other processes needs to be avoided.

Test your knowledge on heat processing techniques used in food safety and preservation. This quiz covers methods like pasteurization, sterilization, and other crucial heat processing techniques. Explore various methods and their effects on food shelf life and safety.