Food Preservation Techniques: Pasteurization & Sterilization

Study Notes

Preservation methods extend food shelf life by killing microorganisms and inactivating enzymes.
Two main heat processing methods are pasteurization and sterilization.

A mild heat treatment, heating food below 100°C.
Used to minimize health hazards from pathogenic microorganisms and extend the shelf life of foods (e.g., milk) for several days.
Used to extend the shelf life of acidic foods (pH < 4.5, e.g., bottled fruit) for several months by destroying spoilage microorganisms (yeasts or molds) and/or inactivating enzymes.
Specific processing conditions vary by food type, including different temperatures and times (e.g., 65°C for 30 min, 77°C for 1 min, 88°C for 15s).
Batch pasteurization involves holding food at a specific temperature for a longer time (e.g., 62°C-66°C for 30-35 minutes).
High-temperature, short-time (HTST) pasteurization rapidly heats food to a high temperature (e.g., 72°C) for a short time (e.g., 15 seconds) using a plate heat exchanger.
Hot water is used to heat glass containers, particularly to minimize thermal shock.
Metal or plastic containers are processed with steam-air or hot water to minimize thermal shock of the food.

A more severe heat treatment, exceeding 100°C.
Destroys almost all microorganisms, including spores.
Can change the organoleptic qualities of the product (e.g., flavor, color), including potential caramelization and browning.
Correct temperature and time are crucial to prevent food poisoning (e.g., Clostridium botulinum). Failure to achieve the appropriate temperatures can result in spoilage and food poisoning.
Simple batch sterilization involves a water bath heating process for crates of packaged food, held at a pre-set temperature for a pre-determined time. Continuous sterilization uses long troughs fitted with conveyor belts, carrying containers through heating and cooling stages.

Graphs display the time and temperatures needed for specific products to achieve pasteurization and minimize quality loss. Precise time-temperature relationships are crucial for each food type.

A continuous heat treatment.
Products are packaged after sterilization.
High temperatures (130°C to 150°C) are used for a short time (1-3 seconds).
UHT treatment causes fewer chemical changes compared to traditional sterilization, helping to maintain product quality.

Destroys microorganisms and their spores using heat.
Food is sterilized inside air-tight containers to prevent re-contamination. Proper sealing is critical.

Pasteurization is a relatively mild heat treatment; there are minimal changes to nutritional and sensory characteristics, and it primarily extends shelf life for a few days or weeks.

Enzymatic browning in fruit juices is mainly due to polyphenoloxidase enzymes, and it's exacerbated by oxygen presence.
Deaeration of fruit juices minimizes enzymatic browning by removing oxygen.
A slight loss of volatile aroma compounds during pasteurization of food may decrease quality and possibly unmask other "cooked" flavors.

Deaeration in fruit juices minimizes vitamin C and carotene loss due to oxidation.
Milk processing results in a 5% loss of serum proteins and minor changes in the vitamin content.
There is a 0–10% reduction in vitamin content during pasteurization.