Food preservation

(Notes for a Lecture on Food preservation)

What is food? Why it decays? How to preserve it?

Problems of food refrigeration)

Food (human and animal)

Food = eatable organic matter: living, freshly killed or preserved. Fresh food is classified as vegetable or animal.

Food spoilage (causes)

Evolution of food-preservation techniques

  1. Drying (physical) and Dehydration (chemical): dried fruits.

  2. Smoking: dries and protects with an antiseptic (creosote).

  3. Salting: dries and prevents reproduction.

  4. Pickling: with brine, vinegar and species that dry and hydrolyse.

  5. Canning of boiled food: T>70 ºC pateurizes and sterilises (kills bacteria and anabolic enzymes, but also kills vitamins). It was massively used by Napoleon troops, soon after bacteria were seen under the microscope. T>120 ºC kills even spores.

  6. Refrigeration: low T reduces metabolism but does not kill f.i. vitamins. Best preservation is frozen at -20 ºC for fish, meat and some vegetables (-25 ºC for icecream) and from -0.5 ºC to 5 ºC for vegetables, fruits and dairy (tropical fruits at 15 ºC).

  7. UV radiation: may directly kill living organisms, or decompose O2 to atomic oxygen and that decompose microorganisms.

  8. Ozone: reacts with organic matter and produce atomic oxygen that oxidises (burns) living organisms (the same as for H2O2).

  9. High voltage electric pulses (some 1000 kV/m).

  10. High pressure (some 100..1000 MPa). It has been found that high pressure inactivates microorganisms, without altering nutritional and sensory food quality; food (ready-to-eat food, oysters, etc.) is put on a small water or oil bath that is hydraulically pressed. High-pressure food freezing or thawing, by removing or applying pressure, respectively, gives a much faster and homogeneous transition than freezing or thawing by heat transfer.

PROBLEMATICS of food-preservation by refrigeration

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