Importance of Microorganisms in Sterilization and Pasteurization

The main aim behind sterilization and pasteurization process is to inactivate microorganisms and enzymes that cause spoilage and particularly which causes food poisoning. 

Thus the principal reason for characterizing the heat resistance of microorganisms is in order to design a safe sterilization step. 

The goal is to determine the required operating conditions (time/temperature) to achieve sterilization criterion.

One of the major factors that affects a microorganism’s heat resistance is pH. It is possible to classify food products into three groups according to pH:

• Low - acid products: pH ≥ 4.6
• Medium - acid products: 3.7 ≤ pH ≤ 4.6
• Acid products: pH ≤ 3.7

 This is important because the heat resistance of microorganisms is greater at this pH ( ≥ 4.6). On the other hand, fruits,juices and most soups are medium - acid or acid products and require a much softer heat treatment to achieve the sterilization criterion.

1. Vegetative cells 10 min at 80 °C
2. Yeast ascospores 5 min at 60 °C
3. Fungi 30–60 min at 88 °C
4. Bacillus stearothermophilus 4 min at 121.1 °C
5. Clostridium thermosaccharolyticum 3–4min at 121.1 °C
6. Clostridium botulinum spores 3min at 121.1 °C
7. Clostridium botulinum toxins types A and B 0.1–1min at 121.1 °C
8. Clostridium sporogenes 1.5 min at 121.1 °C
9. Bacillus subtilis 0.6 min at 121.1 °C