Consuming well-cooked food has always been considered a guarantee of safety. Meat, fish, eggs and other products can carry bacteria or parasites that generate health risks, and even lead to epidemiological dangers.
However, there are certain products that are generally preferred raw . Foods, such as fruits and vegetables, have a cellular structure that is strong enough so that pathogens take time to penetrate inside and when they spoil, it is easy to detect from the outside, with the naked eye.
But, other products such as milk and its derivatives, fruit juices, certain pickles, soups, gazpachos, vegetable drinks, sauces, ice cream or low-grade alcoholic beverages do not have this advantage, and can easily become a breeding ground for microorganisms. pathogens.
On the other hand, there are certain preparations that are prepared with raw food, including meat, fish or shellfish. If these foods are not properly treated, they can become a risk . And even if they are going to be cooked, the presence of microorganisms can reduce the shelf life of that fresh food, causing premature deterioration of the product.
When cooking is not the optimal solution
Of course, cooking these foods would solve the problem, although it is not always the best option, since the nutritional and organoleptic properties of the food change. Its proteins may be denatured, changing its texture; sauces containing eggs would curdle, and products such as beer would lose gas and alcohol.
Without a method to eliminate microorganisms from these foods, we are forced to consume them within a few hours of preparing them, a maximum of a couple of days if they are refrigerated.
The problem is greater with milk and milk products. Any pathogen in milk can already be dangerous from the moment it leaves the udder of the cow, the goat, the sheep, or the female of any mammal.
For milk to be safe, it must boil for a long time, and since its composition makes it “rise” and spill when it reaches the right temperature, it is not possible to keep it boiling long enough.
Given these difficulties, the milk must be boiled at least three times in a row, then refrigerated as quickly as possible, and consumed within 48 hours . After that, in the trash. An investment of time that many people do not have, that does not generate too many guarantees, and whose result, moreover, is different. The milk loses its texture, the fat it contains is out of phase and remains in the form of a sheet on the liquid, and if the time is exceeded, the casein coagulates and the milk “cuts”. As has been said, the organoleptic properties are altered.
pasteurization
Fortunately, on a day like today, April 20, 1862, 160 years ago, the chemist Louis Pasteur and the biologist Claude Bernard discovered a method that allows pathogens to be eliminated from a food while minimally altering its structure and organoleptic properties. It received the name of pasteurization , and more than a century and a half later we continue to use it to disinfect a large number of foods.
The original pasteurization, developed by these researchers, is what we now call slow pasteurization . The procedure is based on filling a large container with the product to be treated and maintaining a temperature of 63 °C for at least 30 minutes . In this way, the main pathogenic organisms are killed by the continuous heat, but the organoleptic properties of the product are not altered. Slow pasteurization was successfully used in milk and alcoholic beverages such as wine or beer. In these cases, pasteurization also slowed down the fermentation processes, by denaturing the responsible enzymes, leaving the product at its optimum quality point.
Subsequently, a new faster pasteurization technique emerged; high temperature short time ( HTST ). In this new technique, the temperature is raised to 72 ºC, which allows the time needed for disinfection to be reduced to just 15 seconds. This process, although it can also be carried out in a container, since it takes so little time, it is usually applied in a continuous flow system. In it, the product passes through a heated conduit that raises its temperature to the required levels, and for the necessary time. In this way, it is possible to pasteurize large quantities of a product in a very short time, something very advantageous for industrial production.
Thanks to this continuous flow technology, the so-called ultra-pasteurization, or ultra-high-temperature (UHT) pasteurization, later emerged. In this process, the temperature reached exceeds 135 ºC but the time is barely 2 seconds. However, this process does alter some properties of certain foods and cannot be used in all cases.
In alcoholic beverages this process is not feasible. In the case of milk, it is usually indicated when it has been pasteurized —with the HTST method— or ultra-pasteurized —UHT— and an expert palate can tell the difference between two identical milks treated differently. However, for gazpachos, soups or juices, the UHT process is optimal.
The new pasteurizations
With new technologies , new pasteurization methods have emerged without the need for the high temperatures or times required in previous systems.
A novel form of pasteurization is the application of radiation . Unlike classical pasteurization —which requires the food to be in a liquid state— radiation can be applied to solid and even dry products, and can be used cold. Significantly extends the shelf life of perishables like meats, seafood, fruits and vegetables, and even spices and dried foods. It destroys parasites and microorganisms, although it cannot eliminate spores —latent forms of resistance to fungi and bacteria—, so refrigeration is still necessary to prevent germination.
Another novel system is the application of pulsed electric fields (PEF). Under laboratory conditions, it has shown great success on food of any kind and at room temperature and even refrigerated, and involves a treatment of a few seconds. However, its application at an industrial level is an engineering challenge. At the moment, it is not being used, but it should not surprise us that it will be in a few years.
Of course, the future is not written, and perhaps, in 160 years, someone will write about new pasteurization techniques that today we do not even imagine.
REFERENCES:
Crawford, L. M. et al. 1996. A review of the safety of cold pasteurization through irradiation. Food Control, 7(2), 87-97. DOI: 10.1016/0956-7135(96)00004-7
Steele, J. H. 2000. History, trends, and extent of pasteurization. Journal of theAmerican Veterinary Medical Association, 217(2), 175-178. DOI: 10.2460/javma.2000.217.175
Zhang, Q. et al. 1995. Engineering aspects of pulsed electric field pasteurization. Journal of Food Engineering, 25(2), 261-281. DOI: 10.1016/0260-8774(94)00030-D
