All foods naturally contain a microbial load, which over time and under certain conditions can replicate, proliferate and deteriorate our food, even if they do not pose a danger to our health.
For these reasons, some techniques have been developed, especially in the last century and a half, to minimize the microbial content in foods before they reach our tables.
Fight bacteria at high temperatures
The first technique that has been used is pasteurization. Actually, this is only applicable to certain types of foods such as milk, honey and wine, and eliminates the majority of the potentially pathogenic microorganisms, even though it does not work for spores or thermophilic bacteria.
It consists in submitting food to high temperatures (ranging from 60 to 90°C) for a certain amount of time: these two parameters vary depending on the type of food and how much it could be “contaminated”.
Above all, raw milk needs to be treated with pasteurization: it can be easily contaminated during urination and the most frequent illnesses associated with untreated milk consumption are salmonellosis, brucellosis, anthrax, listeriosis…
Ultra High Temperature (UHT)
The UHT (Ultra High Temperature) technique, applied to milk and fruit juices, allows sterilization, that is, the complete elimination of the microorganisms contained therein. To achieve this result a jet of steam is blown into the beverages at 140-145°C for a few seconds.
The choice of steam is not a random one: if, for example, milk was heated over a flame or in an oven, then the milk near the walls of the container would reach the temperatures useful for sterilization, but the center would remain colder.
Instead, steam allows homogeneous heating of all the liquid. Nowadays this treatment is the most used for the sterilization of milk because it allows to obtain a completely safe product without altering its nutritional properties.
Another important advantage is prolonged shelf-life: if pasteurized milk is kept in the fridge for no more than a week and should be consumed within 2-3 days of opening, UHT milk can last, unopened, up to three months!
Blast chilling techniques
Thermal abatement with cold
The techniques seen so far make use of heat, but the same results can also be obtained by using cold.
We are talking about what is called blast chilling: food is quickly cooled (in about 90 minutes) from 70°C (or more) to 3°C. Again, microbial remediation is obtained and shelf-life is prolonged. Another important advantage is that it does not alter the organoleptic properties of foods.
During slow freezing (what we get for example in our freezer), large ice crystals can form in the cells, which can even break them causing the nutrients to escape from them.
In blast chilling, on the other hand, the cooling is so rapid that the ice crystals that are formed remain small in size, thus not altering cellular structures.
Abatement is not just an industrial process, but it can also be done at home with a specific appliance, called a blast chiller, to cool food without altering its properties and aromas.
The sanitization of fish and meat at high and low temperatures
The technique applies to practically every kind of food and for some categories its use is even required by law. In fact, some foods, like fish, need special attention.
The Ministry of Health’s Circular of 11 March 1992 provides the methods for obtaining sanitization or recovery, namely: “a) freezing the fish to an internal temperature of -20°C for no less than 24 hours at authorized establishments, prior to transfer from fish markets under health care; (B) thermal treatment of fish at least 60°C for ten minutes or another equivalent treatment, after removal of the parasitized parts, in storage or processing establishments.”
Nowadays, the Ministry prohibits the administration in public places of any kind of raw fish that has not undergone these treatments. The legislation was set up to protect consumers, especially from Anisakis, a pathogen parasite for humans whose larvae may be lurking in fish meat.
On the other hand, for meat, the main source of trouble is an infection by Trichinella spiralis, which like Anisakis is a Nematode (round worm).
It can be extracted with heat (it is enough to cook the meat at 65°C for one minute) or with cold, in this case the meat must remain frozen at -15°C for at least one month. Potentially infected meat must be subject to this treatment, especially pigmeat from small farms.
It is not generally done for meat coming from large farms or those that are part of the industrial food chain because animals are supposed to undergo strict veterinary control to exclude the presence of infection.
Now more than ever, food security is a hot topic. In this article, we have tried to understand how the techniques most used in food sanitization work, but the matter is much broader and more complex and food operators are required to comply with the sanitary standards provided by the competent bodies. These procedures follow the system guide lines such as HACCP, ISO 22000, or EFSA (European Food Safety Authority) guidelines.
Federica De Napoli