Store foodDefinitions and general aspects Traditional conservation conservation techniques Modern conservation techniques Conservation and nutrient techniques Conclusions
- Definitions and general aspects
- Traditional conservation conservation techniques
- Modern conservation techniques
- Conservation techniques and nutrients
Food has always been part of our life and is an irreplaceable good, but it can create problems for human health; if the proper hygiene rules are not followed during production, they can in fact cause dangerous food diseases, sometimes only annoying, sometimes even fatal. The foods deteriorate quickly and it is therefore necessary to intervene with appropriate treatments, to preserve them over time. Finally, the numerous energy resources needed to produce them negatively affect the environmental balance; to give an idea, 39 types of cured raw ham are produced worldwide, about 1, 200 types of cured meats, 1, 600 varieties of more or less seasoned cheese and over 100 types of fermented milk (yogurt is just one of them). There are also countless types of bread, pasta, baked goods, desserts and variously preserved vegetables, which form a more or less conspicuous part of our daily diet.
Among the conservation techniques, heat is one of the most common and the one that has the greatest impact on the nutritional (and sensorial) characteristics of a food: we have therefore dedicated a separate chapter to it, in which we will consider all the other techniques of food storage and processing.
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Definitions and general aspects
Preserving a food means keeping its hygienic-sanitary, sensorial and nutritional characteristics unchanged for as long as possible. The period in which a food product remains unchanged is called commercial durability, shelf life or shelf-life.
Despite the efforts made by man, foods (fresh or preserved) are destined to deteriorate, that is, to lose the sensorial characteristics that are typical of them: think of the cut fruit that darkens, a salami that becomes rancid or a product moldy oven. When altered, a food stops, by law, from being such:
it can no longer be consumed by man and must be withdrawn from commerce.
Deterioration processes are the main cause of subtraction from the consumption of foodstuffs, and conservation techniques are aimed precisely at avoiding, or at least slowing down, these processes. To understand how conservation techniques work, you need to know why foods change. Whether they are of animal, vegetable or mixed origin, they go bad for two reasons, often independent of each other, but sometimes added together:
- excessive charges of bacteria, yeasts or molds develop on the surface or inside them. These microorganisms, not directly visible, produce enzymes that break down proteins, fats and / or carbohydrates, releasing chemical compounds that can be unpleasant for our senses, and modify odor, flavor and consistency. The putrefaction of meat and fishery products is the most classic example of alteration of microbial origin;
- proteins or fats undergo chemical reactions that release unpleasant compounds. Rancidity is the most classic example of these reactions: fats become more and more yellow, a characteristic smell develops and the product becomes spicy while before it was not.
We realize that the food is deteriorating because it begins to develop strange, non-typical colors, smells and / or flavors. These changes appear when chemical compounds are formed and accumulated that were not there before:
- volatile aromatic compounds such as ammonia, sulfur compounds (rotten egg smell) and solvents such as acetone;
- compounds that alter the flavor of the food making it spicy (butyric acid) or bitter or giving it a strange taste as aldehydes, ketones and alcohols do (fruit, potato, rancid butter, detergent, kerosene flavor) ;
- compounds that give it an unusual color (mozzarella and ricotta that are tinged with yellow or red, raw and cooked meats that become greenish, mayonnaise and yogurt that are covered with brown, reddish or black spots);
- various types of gas (carbon dioxide, hydrogen, hydrogen sulphide) that accumulate inside the package, causing the so-called swelling or swelling.
In 90% of cases, a food spoils due to the excessive growth of altering microorganisms inside; only in 10% of cases does it deteriorate due to chemical causes not dependent on microorganisms.
The altering microorganisms (bacteria, yeasts and / or molds) come to pollute the food with the raw materials, during the handling during production and possibly from the environment in which the food is left to mature and mature before being ready for consumption. . In general, a food begins to spoil when on its surface or inside the overall microbial load exceeds very high values (say, not less than 10 million microorganisms per gram of food). It is rare for a food to be polluted by such high microbial loads from the beginning; the more scrupulous the hygiene of production is, the lower these initial microbial loads will be and, therefore, the lower the risk of product alteration. A food generally deteriorates because this initial microbial flora is able to multiply more or less quickly.
Food preservation techniques aim primarily at eliminating the altering microorganisms or, at least, at blocking their multiplication, by adopting various strategies. Some techniques have been discovered by prehistoric men and have practically remained unchanged over the centuries: they are those that exploit natural elements such as drying, salt, smoking and marinating in vinegar. Other systems are of ancient invention, but man has perfected them thanks to the discovery of new packaging materials, such as the plastic film vacuum, the addition of food additives or the cold techniques. Still others have been invented only in recent decades thanks to the development of technology, such as packaging in a protective atmosphere, microwave cooking and so on. Therefore, food preservation techniques can be divided into traditional and modern, as we will see later.
It is rare that a food is preserved by applying only one of the systems listed below: very often two or more techniques are used, even if the consumer does not notice it. For example, the seasoning of meats and cheeses is a practice that favors a gradual loss of water by the food, but these products have also undergone the addition of salt and sometimes have also been smoked. In canned preserves, commercial sterilization heat treatment, vacuum packaging, the addition of salt and / or marinating, often the addition of food preservative additives such as nitrite or sulphites are used.
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