Food Microbiology and Food Safety
Scope of the domain
This domain tests how microorganisms spoil food, cause illness and are controlled. It covers bacteria, yeasts, moulds, viruses and parasites; intrinsic and extrinsic factors; foodborne pathogens; HACCP; GMP and hygiene.
Core rules and concepts
- Intrinsic factors include pH, water activity, nutrients, redox potential and natural antimicrobials. Extrinsic factors include temperature, relative humidity and gaseous atmosphere.
- Spoilage organisms make food unacceptable but may not cause illness. Pathogens may grow without obvious spoilage.
- Important pathogens include Salmonella, Clostridium botulinum, Staphylococcus aureus, Escherichia coli O157:H7 and Listeria monocytogenes.
- C. botulinum forms heat-resistant spores and produces toxin in anaerobic, low-acid foods.
- The temperature danger zone is roughly 5–60°C; keep foods outside it.
- HACCP has seven principles: hazard analysis, determination of CCPs, critical limits, monitoring, corrective actions, verification, and record keeping.
- GMP and good hygiene practices are prerequisite programmes that support HACCP.
Worked example
A dairy heats milk at 72°C for 15 seconds, cools it and fills it into chilled cartons. Is this a CCP? Reasoning: the step is designed to reduce vegetative pathogens such as Salmonella and E. coli. A measurable critical limit exists: 72°C for at least 15 seconds. Temperature and holding time can be monitored and recorded. Failure requires a corrective action such as reprocessing or diversion. Therefore pasteurisation is a CCP in this process.
Traps that cost marks
- Saying HACCP guarantees zero risk; it controls significant hazards but does not replace hygiene.
- Relying on end-product testing alone; testing samples cannot assure every unit.
- Assuming a food that smells normal is safe; pathogens may produce no off-odour.
- Forgetting that C. botulinum risk is highest in low-acid, anaerobic, improperly canned foods.