Methods of Preserving Food
Methods of preserving food.
Food preservation – processing food for storage, to prevent deterioration caused by microorganisms. The basis of different methods of preserving food are factors which influence or cause the destruction of microorganisms, or a temporary suspension of their life, or to suppress the activity of enzymes. Thus, in some cases uses the effect of low or high temperature, in other – ultraviolet and ionizing radiation, ultrasound, in the third – high osmotic pressure and concentration of hydrogen ions, dehydration, bactericidal substances.
Effects of low temperature is the basis of conservation methods such as freezing and cooling. Freezing food is based on the fact that most bacteria sensitive to low temperature and at -18 ° C and stops below the development of microorganisms, also reduced enzyme activity and related physical and chemical processes in tissues. Great value at this speed is freezing. In slow freezing water from the cells gradually transformed into intercellular space, forming large ice crystals and damaging the cells themselves. If the product is frozen quickly, water does not have time to see the intercellular space, ice crystals are smaller and tissue product is not damaged. Therefore, we recommend freezing do quickly by placing the product in special chambers with temperatures below -18 ° C and thawing – slowly. This liquid, which freed during melting of ice, sucked back into the cells of tissues, keeping nutrients: proteins, minerals, vitamins.
Freezing point of view of hygiene is the best method of preservation. Frozen food can be stored for several years. Merely freeze foods such as meat, fish, blend and other products to be frozen should be benign, with no signs of damage.
When cooled understand food storage at temperatures close to ° C. On cooling is used to store foods that contain plenty of water: fruits, vegetables and milk. Chilled product retains its original properties for several days.
Effects of high temperature (60 ° C and above) causes coagulation of cytoplasm of cells of microorganisms. Because this process is irreversible, it would result in germ becomes viable. Vegetative forms of microorganisms respond instantly to high temperature. More resistant to high temperature sporoutvoryuyuchi microorganisms as the water in their cells is in a bound state with neither the coagulation proteins. However, the viability of the dispute under high temperature decreases.
The most common methods of preservation, using a high temperature sterilization and pasteurization.
When sterilization of food sealed product (meat, fish, vegetables) is heated in an autoclave at a temperature of 112-120 ° C. This destroys enzymes and microorganisms and their spores are killed.
Pasteurization products (juices, pickles, wine), a temperature 63-85 ° C, resulting in vegetative forms of microorganisms are destroyed. Used long, or low, pasteurization, when the product is heated at a temperature of 63-65 ° C for 30 min, and short-term or high pasteurization. This product is heated to 80 ° C and above for several minutes. Immediate pasteurization can be applied at the same temperature, but for a few seconds.
Type of sterilization is proposed in Germany uperizatsii method that is used for preserving milk while heating it to 150 ° C for 3 / 4 sec, then cooled milk. With such processing many vitamins are stored.
Dehydration products, or drying, is based on the fact that moisture is removed from the product. Moisture removal up to 8 – 15% promotes the suppression of life and reproduction of microorganisms. This stops the exchange of substances between the cell microorganism and food products – sources of nutrients. Dehydration is used for preserving milk and milk products (milk powder, cream), vegetables, fruits, fish and semis (soups and porridge-concentrates).
Sublimation combines freezing and dehydration. This is a special method of drying frozen in a vacuum. In sublimator created vacuum to 0.67 kPa (5 mmHg. Art.). First product frozen to -18 (-20) ° C and then heated to 30-40 ° C. When this ice becomes steam, bypassing the liquid state. After sublimation drying in the product contained 5% moisture. Sublimation drying products are widely used in the diet of astronauts.
Effects of high osmotic pressure. This method of food preservation is sodium chloride or sugar, which contributes bacteriostatic effect. When you add to food 10 – 15% sodium chloride cells of microorganisms around the hypertonic environment is created. In normal conditions, cells of microorganisms are in the hypertonic state with respect to the product that causes the nutrient substances from the product in cells. When salinity causes substances from receipt of product in cells. When salting same product through increased osmotic pressure around the cell cytoplasm is dehydrated, food stops and reproduction of microorganisms. But microorganisms while not dying. Conservation of sodium chloride from hygienic point of view the method is ineffective, because while in the brine are valuable nutrients: proteins, mineral elements, vitamins.
When sugar solutions of large concentrations (60-65%) also creates a high osmotic pressure. Effects of antibiotics. For preserving food is allowed to use a limited number of antibiotics because they can alter the normal gut microflora, improve ability to respond to external factors, etc. biomitsyn added to ice (5 g per 1 ton of ice) during storage of fish. This residual amount of its raw product should be not more than 0.25 mg / kg. Biomitsyn with nystatin allowed to apply for the storage of meat (carcasses) in long-haul transportation in the car-disposal. Carcass while zroshuyutsya biomitsyn solution (100 mg / l) and nystatyna (200 mg / l).
The action of antiseptics. For canning permitted use antiseptics, which do not have a cumulative effect, not form toxic compounds that do not destroy vitamins and reduce the enzyme activity of the food channel. Yes, sulphurous acid is used for preserving plant products – vegetables, fruits and berries. Oxidation products in destroying enzymes, the acid promotes the preservation of ascorbic acid, thiamine, inhibits reproduction Escherichia coli and other microorganisms.
Sorbinova acid inhibits growth of microorganisms, fungi Plesneva. In the body, it disintegrates into carbon dioxide and water, while highlighting a certain amount of energy. Used for preserving fruit juices, soft drinks, surface cheeses, bakery and confectionery.
Boric acid is less favorable for conservation because it has weak bactericidal action and applied for a limited number of products: chum caviar melange. Benzoic acid is used in combination with other substances in the form and abakterina mikrobina.
Effects of increased concentration of hydrogen ions.
Pickling based on biochemical processes in which some of the carbohydrates and other substances produced lactic acid, which owns preserving action. For longer storage obtained by this method of preserving food is necessary that the content of lactic acid was not less than 0.7%. Therefore, pre-product sodium chloride is added, which prevents pickling early reproduction of microorganisms, and sugar, which forms lactic acid. This method merely vegetables, fruits, mushrooms.
Pickling is carried out by acetic acid in the amount of 1,2-1,8% and salt (8-10%). Principle of pickling is to create a high concentration of hydrogen ions (pH change in the acidic side), which changes the dispersion of the cytoplasm of cells of microorganisms. As a result, stops growth and reproduction of pathogenic microorganisms hnylisnyh and actively multiply in a neutral environment (pH = 7-8).
For canning pickled products can be applied not only to vinegar, but citric, lactic and other acids. Marinate most vegetables, fruits and mushrooms.
Atermalne or cold sterilization is achieved by the action of radiation energy radionuclides or accelerated electrons that have great energy. This results in ionization cell content of microorganisms, thus they cease to proliferate. With this method of conservation (milk, juices) are stored vitamins, but changing organoleptic properties of products – appears bad, changes color, taste is lost.