Introductory remarks to the descriptive part.
In the specific part of the program of the course are studied the most important agro-food products, and that describes the properties, characteristics, composition, function, etc. of each of them
The food classe.
In merceologia, agro-food products are classified and studied according to the criteria of their origin, of similar and processing properties.
If the foods are classified according to their origin, we have for example the class of plant-based foods, such as flour, bread, pasta, and the food of animal origin class, such as milk, butter, cheese, meats, eggs; these two are respectively the first and second of the Program class food.
If the foods are classified according to the criterion of similar properties (chemical, physical or similar organoleptic), have food classes "fats and oils", "Beverages" and "nervine substances", which are the third, fourth, respectively, and fifth of the program class food.
Finally, if foods are classified according to the criteria of the process, within the class of plant foods have the wheat succession - flour - bread and pasta (wheat as raw material processing, flour as an intermediate, and bread and pasta as finished products), and the class of foods of animal origin have the milk succession - products (cheese, butter, cottage cheese, yogurt).
As can be seen, for each grouping (class), it has been applied to one or more of the abovementioned criteria for classification, depending on the circumstances and convenience; Unfortunately, there is no single classification standard by which logically group all food products.
Processing and technological treatments of food: good and bad.
The production, processing, and preservation of foods involve stages of processing and technological treatments that serve to improve their use and their properties. However, it is also true that, during processing, the rise in temperature and other causes may adversely affect the nutritional value and properties. Modern food technology tends to get better results, trying to minimize the negative effects.
Examples of technological treatments (in the sense of more complex operations, or more delicate) are fermentation, cooking, distillation, rectification, pasteurisation, sterilization, lyophilization, etc..
Among the technological treatments an important place is occupied by fermentation.
The production of certain foods and beverages is favored by fermentations operated by enzymes belonging to microorganisms, such as yeasts, bacteria, and molds.
Thus, for example, Saccharomyces cerevisiae and Saccharomyces carlsbergensis the content in some yeasts favor the leavening of bread, and the wine and beer; with other enzymes of bacterial origin, (Bulgarian lactobacillus and streptococcus thermophilus), let the yogurt; with others, belonging to mold, we make the cheese.
The detailed study of enzymes is the basis of fermentation chemistry, so important for the production of such foods.
Consider the distillation. The spirits are obtained by distillation of fermented mash of different cereals or fruit.
The distillation is a technique of separation of the components of a mixture having sufficiently different boiling points. In our case, the must is no water, ethyl alcohol and other components. During the boiling of the wort, the ethical alcohol, which is the most volatile, it passes into the vapor phase in greater quantities. These vapors, condensates, constitute the distillate. By subjecting the distillate to successive ridistillazioni, you get the brandy.
Pasteurization and sterilization are food preservation techniques.
Consider the milk, which, being rich in water, plus complete food, it is more easily subject to alterations induced by microbial load. This microbial charge consists of harmful bacteria and bacteria less harmful or harmless to human health.
While with UHT sterilization (at 135 ° C milk for 2-3 seconds) is eliminated the entire microbial load, with pasteurization (milk at 75-80 ° C for a 15 ") are eliminated all harmful bacteria, and only part those not harmful (saprophytes).
The freeze-drying consists in applying to the food, such as milk, thermally insulated from the external environment, a certain degree of vacuum, which is sufficient to do so freeze; then, it still increases the degree of vacuum and simultaneously heats up a bit ', so as to cause the sublimation of the ice. At this point, the sealed container contains freeze-dried milk (in practice, perfectly anhydrous milk powder and in the absence of air).
The freeze-dried milk lasts a long time and have lost only a small part of its nutritional value.
Examples of processing steps (in the sense of simpler operations) are grinding, sieving, the heating and the cooling through heat exchangers, precipitation, mixing, filtration, decantation, concentration, crystallization, l ' drying, etc.
Technological treatments can modify the properties of food both positively and negatively.
In fact, foods such as organic substances, making that part of the renewable resources of the plant and animal kingdom, can easily be changed in the composition in nutrients (carbohydrates, proteins, fats, vitamins, minerals and water) at the hands of these technological treatments, especially those that take advantage of the heat, with losses also sensitive to their nutritional value.
In contrast, these technological treatments may also make improvements to the original food substance, making it more wholesome, palatable and digestible.
The development of technology will reduce some of the negative aspects of the treatments.
For example, the loss of the nutritional value of milk sterilized in the bottle was remarkable. Today, modern food technology - passage of the milk in heat exchangers thin foil - by reducing the contact time with the heat source, allow to obtain "fresh pasteurized milk" and "sterilized milk UHT" with moderate losses of nutritional value.