Conservation of raw materials

In this article we discuss the methods of food preservation and we emphasize temperatures and general aspects of food handling to prevent the development and spread of disease.

It is not possible to determine the form or method of preservation without mastering the degree of perishability of the raw material or processed food, since preservation is a process that begins where the food chain begins and does not end until the food is consumed. .

Perishable and non-perishable food

Food will be perishable or not in time, taking into account temperature, humidity and other aspects. Not perishable: salt, honey, legumes and cereals, dried fruits, canned ... Opinion disputed since everything is perishable over time, depending on the conditions of temperature, humidity, type of storage, and other factors. Perishable: meats, vegetables, milk and its derivatives, fish and creams, since they need adequate temperatures without interruption so as not to decompose.

The Codex Alimentarius [Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO)], taking into account the general principles of food hygiene, points out - according to epidemiological data - that many of the food poisoning epidemics are caused by violations related to the preparation, cooking, preservation and storage of food prepared for community feeding.

Types of food alterations

Any food raw material, alterable or perishable, that is not used immediately in the production of cooked dishes, is at risk of suffering any of the following alterations to the detriment of its quality.

Microbial disorders

They are produced as a consequence of the activity metabolic of the microorganisms that proliferate when the food is placed in an optimal environment of temperature, humidity or pH. These organisms are generally only visible under a microscope, are widely distributed in nature, and reproduce with great ease and speed. Due to their action on food they can be beneficial or harmful.

The main types of microorganisms are:
  • Bacteria: they are unicellular and microscopic. They multiply by division with great ease, especially those that develop between 5 and 60 ºC, but there are so-called thermophiles that survive at higher temperatures. These and the spores they produce are in the soil, air, water, fur, and feathers of animals.

Food raw materials

  • Virus: they do not multiply in food, but these are vehicles for transmission; p. eg, those that cause hepatitis, polio, gastroenteritis, and other diseases. Some authors do not consider them living organisms because they do not have their own metabolism and need a living host to reproduce. Its growth and development is related to the temperature, time, humidity and pH of the medium.
  • Fungi:
    • Molds: they live at the expense of other organisms; p. eg, on the surface of decomposing organic matter, and others attack fruits, vegetables, bread, giving them a bitter taste. They can be black, gray, green or brown.
    • Yeast [see chap. 2. "Food raw materials" ("Industrial raw materials", p. 29)].
    • Macroscopic fungi: beneficial for food such as mushrooms, truffles and mushrooms, widely used in kitchen.
  • Protozoa: Many parasites belong to this group, such as: giardias, amoebas, paramecia and others.

Chemical alterations

Under certain environmental conditions, chemical and enzymatic reactions originate, such as:

  • Fat oxidation (rancidity)s: process where a food with a high fat content is altered over time, acquiring an unpleasant taste; this may involve the destruction of fat-soluble vitamins, particularly vitamins A and E.
  • Protein denaturation: it causes loss of solubility, manifested under forms of food hardening.
  • Retrograde starch: alters the texture of the preparations; p. eg, the links in the sauces.

Physical disturbances

It is the loss of water with weight reduction and variation of the characteristics of the food by drying and browning, which negatively influences the taste quality of the product.

Food preservation methods

For the preservation of food there are several methods that avoid alterations. According to different authors' criteria, the principles of action offer differences and coincidences regarding the handling of temperatures for food preservation.

Physical methods

By temperature
Low temperatures

Adequate refrigeration maintains the temperature and relative humidity in the food; under these conditions very few contaminating bacteria harm conservation. However, the same does not occur with the chemical reactions that take place at any stage of refrigeration and even freezing; in both their reaction speed is reduced, but in the long run they end up altering the food, p. eg rancidity. Hence, the refrigeration process presents variable limits for the time food is kept in preservation.

Freezing is a long-term preservation. Once the water in the food has been converted to ice - stored in proportion according to the species - the water molecules cannot take part in chemical reactions or be used in microbial metabolism. The cold stops the proliferation of microorganisms, especially bacteria, but does not eliminate them; therefore, when the temperature rises during defrosting, they resume their development with more force. The defrosting of meat must be done in chambers for this purpose, at temperatures close to 4 ºC.

In a nutritive substance subjected to temperatures below 0 ºC, the water contained in its tissues turns into ice and is finally a frozen or hardened piece on sight, whether the freezing reaches -8 ºC or if it is reduced to -25 ºC . In reality, the internal structure of the part varies significantly with the speed at which it cools:

  • If the cooling rate is slow and it takes meats to freeze, the ice crystals that form in the tissues are large and sharp. By thawing the meat, they tear the membranes of the cells, and this allows the nutrients to leave the piece with the thaw. This causes the loss of organoleptic properties, such as color, flavor and texture.
  • If the cooling is fast, so that the food reaches between -25 to -30 ºC, the internal process in the cell occurs normally and maintains the piece its nutritional value.

Hence the importance of freezing and thawing correctly, taking into account:

  • Freezing should be rapid and at the indicated temperature.
  • Thawing in the chamber for this purpose at 4 ºC and for the established time.
  • Anything that has been thawed should never be re-frozen.

Another element to consider during storage and conservation in chambers is the separation of the products, depending on whether they give off odors (onion, fish or citrus) or absorb them (butter and milk). Fruits that give off ethylene, such as bananas, avocados, and tomatoes, accelerate the maturation of others, such as citrus. Compliance with temperatures is important at each stage of the food chain: reception, storage and distribution.

High temperatures

The application of heat removes water from the food, hindering chemical reactions and the development of microorganisms. This food preservation system is frequently used, taking into account temperature and time factors. The processes, that apply are:

  • Pasteurization: application of temperature up to 90 ºC, with variable times. This provides stability to the product (raw foods offer greater resistance to microbial activity than cooked foods, since the microorganisms that survived the heat are more active). That is why a continuous process of applying heat manages to reduce the microbial load as much as possible, completing with refrigeration.
  • More energetic heat treatments: are applied for long-term preservation. Opening is used, a procedure that is applied to food in closed containers and is subjected to the effects of heat (temperatures above 100 ºC) for the time necessary to destroy almost all microorganisms.

The invention of Nicolás Appert of food preservation by the action of heat is known as opening. His genius invention was the foundation of the modern packaged food preservation industry and gave rise to the graphic metal industry; This generates in the world the manufacture of more than 100 billion cans per year.

Storage types (depending on temperature)

Air-conditioned warehouses:

  • Refrigeration: preservation of food at temperatures close to 0 ºC, with a relative humidity generally between 80-85%. As the temperature increases, getting closer to the environment; it is considered adequate preservation for certain foods that do not perish easily and for a short time.
  • Freezing: long-term preservation, by converting the food's water into ice (below 0 ºC), depending on the type of food.

Unheated warehouses:

  • Pantries or commissaries: For non-perishable foods such as food, nuts, grains, canned, and other products.

FIFO principle:
It comes from the English phrase first in / first out, that is, the first thing that comes in is the first thing that comes out. It is the most important rule of the storage system: food must be used in the order of arrival at the warehouse. So they must be marked to know the date of receipt.

Food preservation temperatures

  • Meat and fish: they are kept at temperatures below -18 ºC and can reach -30 ºC. For meats: -18 ºC. For fish and seafood: from -21 to -24ºC.
  • Vegetables: Most of them are kept in chambers for this purpose, at temperatures between 4 and 10 ºC, depending on the species. Humidity control is required and in appropriate containers, without piling. The optimal conservation time is highly variable, depending on the type and quality of the vegetables, as well as the procedure for their conservation.
  • Fruits and vegetables: from 6 to 10 ºC; some meats and vegetables reach 15 ºC; orange and potato from 2 to 4 ºC; cucumber, melon, avocado, bomba fruit and pineapple from 7 to 8ºC; banana, mango, sweet potato, pumpkin and lemon, from 10 to 15 ºC.
  • Eggs, milk, cheese, yogurt, butter: from 0 to 4 ºC.
  • Mayonnaise: from 7 to 10 ºC.
  • Sausages: at less than 7 ºC.
  • Cake shop: between 0 and 4 ºC.
  • Nonperishable food: they go to the pantry between 15 to 20 ºC.
  • Canned: between 15 and 20 ºC.
  • Semi-processed, processed and smoked: between 0 and 4 ºC.
  • Preparation areas: there must be an environment below 15 ºC.
  • Exhibition areas: in the buffet, at 65 ºC hot and cold foods from 2 to 4 ºC.
  • Thawing: from 3 to 5 ºC in cameras dedicated to the effect.
  • Cooking: they will be carried out for the established time at more than 74 ºC.
  • Overheating or regenerations: from 70 to 74 ºC.
  • Microorganisms proliferation danger zone: between 5 and 65 ºC.

By pressure

The growing demand for food products with the characteristics of fresh foods, and without losing the sanitary guarantee, has led to the introduction of new technologies in food preservation and not only treatments by temperature but also by pressure are used, which It works by destroying microorganisms.

Chemical methods

The main methods are:

  • Salt-based (salted): For example, cod, bacon, beef jerky
  • Dehydrated products: garlic, onion, potato, and other foods that can undergo dehydration.
  • Smoked: pork, ham, fish, and other products that can be applied to this method.
  • Sugar-based preparations: quinces and jellies, among others.
  • Canned vacuum packed: in cans, glass, plastic (jars and bags).

The use of salt and smoke (smoked) is a prehistoric method that currently has been reserved as a method of production; instead, the preservative effect of sodium chloride or common salt is maintained, together with sugar, vinegar and spices. They deserve to be mentioned:

  • Salted meats: salt extracts water molecules from food; in this way its activity is reduced, preventing the development of microorganisms.
  • Pickles: food preservation by immersion in a liquid. Its main component is vinegar, which prints a degree of acidity or pH that is inadequate for the life of microorganisms. The aroma of herbs and spices also contributes to this. It is applied to vegetables that are used as appetizers, hors d'oeuvres and garnishes.
  • Marinades: used since ancient times; especially for meat and fish. They consist of various spices and aromatics, fat, wine, vinegar, pepper and other ingredients, which together with refrigeration keep food for ≈ 48 hours.
  • Marinade: formerly created to preserve cooked products, its base consists of immersing the product, for at least 24 hours, in a conservative broth. This contains oil, salt, vinegar, spices and certain aromatic herbs so that the food acquires the corresponding aromas. Sometimes it requires the addition of refrigeration to prolong preservation, eg. eg, pickled fish.

We hope that in these times of pandemic this information you find it interesting and contribute to your knowledge. If it was useful, share it.

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