Discuss preservation by refrigeration. Add its advantages and limitations.

1. 1 · Open in two lines. Refrigeration preserves food by keeping it at about 0-5 °C, which slows microbes, enzymes and chemical changes. It is bacteriostatic and short-term.
2. 2 · Principle. Rates roughly halve for every 10 °C fall; most microbes survive and grow again on warming; psychrotrophs grow slowly even in the cold.
3. 3 · Levels of cold storage. Cellar (about 15 °C), chilling (0-5 °C) and freezing (−18 °C or colder), with examples.
4. 4 · Draw the refrigeration cycle. [Cycle: compressor → condenser → expansion valve → evaporator → compressor]
5. 5 · Good storage practice.
   • Right temperature and humidity; do not overload.
   • Avoid chilling injury (banana, mango, cucumber).
   • Controlled-atmosphere storage for apples; cold chain from farm to home.
6. 6 · Advantages and limitations.
   • Fresh quality and nutrients kept; simple; no chemicals.
   • Short-term; does not kill; Listeria grows; chilling injury; needs power and a cold chain.
7. 7 · Nutrition link. Chill cooked food within about two hours and keep raw meat below ready-to-eat food in hospital kitchens.
8. 8 · Close in one line. Refrigeration is the simplest way to keep perishables fresh for a short time.

Scoring tip: Draw the four-part cycle and name one pathogen that grows in the cold (Listeria); both stand out.