Science

The different ways of preserving food – Sciences et Avenir

This article comes from the journal Sciences et Avenir – Les Indispensables n ° 205 of April / June 2021.

As soon as they are produced, our food begins an inexorable process of putrefaction under the effect of microorganisms, oxygen or light. A challenge taken up by human genius through various methods, starting with heat.

The can was born at the same time as sterilization.

Cooking destroys germs. As for dehydration, it prevents the development of microorganisms in the water contained in food. The treatment of the meat by drying would be attested 50,000 years ago, in the Pradelles hunting station (Charente), where traces of cuttings were found in reindeer bones, slaughtered here in quantity by the Neanderthals. Dehydration can also be achieved by salting, dry or in brine, or by means of sugar that binds to water molecules. The results are confectionery, bitter herring and other hams.

Another preservation process is smoking, which combines dehydration with the action of antimicrobial and antioxidant substances present in smoke. In the 19th century, the techniques of the pastry chef Nicolas Appert were added to these secular techniques: then he tried the preservation of cooked food in airtight glass containers, which were soon replaced by tin cans, dipped in boiling water. The can was born, at the same time as sterilization (between 100 and 150 ° C). It will follow the pasteurization method, between 62 and 88 ° C, which allows reducing the amount of microorganisms without excessively denaturing the food.

Freezing stops the enzymatic action of yeasts and molds.

It is also well known that the cold is preserved. Conservation in wells, caves or ice has been practiced for thousands of years. Ancient Rome was already stocking up on blocks of ice mined directly … from glaciers. Always colder, freezing at -20 ° C stops the enzymatic action of yeasts and molds as well as the oxidation process. But when slowly frozen, the water contained in the cells of the food forms large crystals that eventually burst them, denaturing the products. Deep freezing has notably improved in this area.

Inspired by Inuit practices, it consists of keeping food at -40 ° C or -50 ° C for between five and fifteen minutes, to prevent frozen crystals from forming. Freeze-drying adds to this rapid freezing the removal of interstitial ice by sublimation, that is, cold drying. These recent preservation processes have marginalized fermentation, which is as old as cooking. This process is often carried out without oxygen and allows microorganisms to transform food through the action of enzymes.

Cutting-edge technologies are not left out

Additionally, certain storage methods also promote food preservation. Less perishable food can be stored in silos and warehouses for several months if temperature, light, humidity and oxygen levels are controlled. Cutting-edge technologies are not left out, such as irradiation, elegantly renamed ionization, which subjects food to gamma radiation or a very high-energy electron beam to destroy microorganisms and slow ripening and inhibit germination.

Nanoparticles, meanwhile, can be found in food and containers. The NanoPack project, funded by the European Union, has made it possible to develop plastic films with mineral nanotubes that release antimicrobial essential oils into the packaging, slowing down oxidation, humidity changes and microbial growth. The result: mold-free bread for three weeks.

By François Folliet

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