L7: DSCI 229 Pasturization

Topic: Recap on build receptions, standardization, and calculations using Pearson Square.
Reminder: Problem set is due in November, many students have completed it.
- Advice: Hold onto completed problem sets; calculations will appear in the midterm examination.
- Optional submission: Students may take pictures of their assignments and send them in.
- Reminder: Send pictures of all questions, not just the last ones.

Discussion point: The density of milk fat compared to water.
- Correct statement: The density of milk fat is lower than the density of water (true).
- Implication: Milk fat rises to the top due to lower density.

Mechanism: The cream separator uses centrifugal force to separate cream from skim milk.
- Explanation: Spins at high speed to create the separating force.

Definition: Pasteurization is a heat treatment process named after Louis Pasteur, first applied in 1862 to milk and wine.
- Purpose: Extends the shelf life by killing pathogens but is not a sterilization process.
- Clarification: Products are not sterile post-pasteurization; they still contain viable microorganisms.

General Conditions for Sterilization: 121 °C (250 °F) for 15 minutes.
- Consequence: Such high conditions are impractical for consumable food due to nutrient destruction.
Commercially Sterile Foods:
- Aim: Destroy pathogens and toxin-forming organisms, often found in canned foods.
- Example: Canned tomatoes typically heated to 121 °C (250 °F) for 3 minutes.
- Shelf Life: Generally, over 2 years, although heat-resistant bacterial spores may survive.

Explanation: Spores can survive heat treatment, leading to food poisoning when the can is opened post-storage.
- Example Scenario: College students often eat leftovers from an opened can without reheating, risking foodborne illness from germinated spores.
- Bacteria of Concern: Bacillus and Clostridium species can form spores.
- Botulism: Associated specifically with Clostridium botulinum, known for causing severe food poisoning in improperly stored canned goods.

Low order heat treatment executed below boiling.
- Purpose: To destroy pathogenic microbes without achieving sterility.
- Typical Shelf Life Extension: 11-14 days depending on state regulations.

Key components of pasteurization:
- Heating every particle of milk to a minimum required temperature for a specified period in properly designed equipment.
- Historical Context: Prior instances such as orange juice pasteurization in Florida that were not compliant with this definition.

Target Heat-Resistant Pathogens:
- Mycobacterium tuberculosis (causes tuberculosis);
- Coxiella burnetii (causes Q fever).
- Target Reduction Level: A 5-log reduction is the goal in pasteurization treatments.

Concept: Bacterial populations decrease logarithmically rather than linearly under heat treatment.
- Example:
- Heating at 60 °C takes 10 minutes to reduce bacteria from 100,000 to 10,000 (90% reduction = 1 log).
- Continued heating reduces the population further, cumulatively achieving expected reductions systematically.
- 5-log reductions = 100,000 to 1.

Definition of D Value: Time required at a certain temperature to kill 90% of the organisms being studied.
- Example Calculation: D value of 10 minutes at 60 °C means reaching a 5-log reduction involves heating for a total of 50 minutes.

Notable Reduction Standard: 12-log reduction of Clostridium botulinum in commercially sterile foods.
Heat Treatment Progressions: Understanding reduced bacterial viability through gradual heat exposure over time.

Methods to confirm pasteurization effectiveness:
- Collecting milk samples before and after treatment, followed by bacterial counts (time-intensive).
- Quick alternative: Measuring alkaline phosphatase activity—an enzyme deactivated by pasteurization.

The Two Major Processes:
1. HTST (High Temperature Short Time): 161 °F (72 °C) for 15 seconds. Common in commercial operations.
2. LTLT (Low Temperature Long Time): 145 °F (63 °C) for 30 minutes. Suitable for smaller operations like cheese-making.

Core Components:
- Plate Heat Exchanger: Primary mechanism for heating, separating hot and cold streams using thin plates.
- Tubular Heat Exchanger: Used for more viscous products with chunks.
- Holding Tube: Sloped upwards for preventing contamination and ensuring proper flow timing.

Explanation of the Regenerator Process:
- Incoming cold raw milk is warmed by outgoing hot pasteurized milk, improving energy efficiency of the overall process.
- Essential to quickly cool pasteurized milk back to safe storage temperatures following treatment.

Variations in temperature adjustments based on solid contents (e.g., cream or half-and-half).
Equipment regulations: State inspections and safety mechanisms to avoid contamination must be adhered to in commercial settings.

Ultra-Pasteurization: Involves heating at 280 °F (138 °C) for 2-4 seconds, prolonging shelf life for up to 3 months for high-acid foods.
- Commonly used for organic milk; no reflection on quality, just the heat treatment process.

UHT Process: Similar to ultra-pasteurization with aseptic packaging ensuring product safety and stability for up to 6 months.
Common practices in countries outside of the US; increasingly popular due to convenience and longer shelf life.