El  Obispado

Nearly all types of food can be preserved for a considera ble period of time by cooking. When raw foods deteriorate, it is through the action of the enzymes they contain and action of bacteria with which they become contaminated. Heating or cooking destroys or inacti-vates these enzymes, thus preventing this type of deterioration. Cook-ing also destroys certain types of microorganisms that cause spoilage.

At home, cooking is used as a preservation method as well as a method to make food more palatable. However, ordinary cooking does not des troy all bacteria. Deterioration, although delayed, will occur through the growth of surviving bacteria.

Pasteurization

In this method of preservation, which named after Louis Pasteur, foods are subjected to suffi cient heat to kill most of the bacte ria without markedly altering fl avor or other characteristics. The food is heated in a closed system, rapidly cooked, and then placed in covered or sealed container to prevent recontamina tion. This method is generally used for liquids such as milk, fruit, vegetable juices, and beer.

Canning

Canning is a method of preserving foods, which combines the tech-niques of heating to kill spoilage microorganisms and inactivate enzymes by sealing in an airtight container to prevent subsequent contamination.

Microorganisms may exist in two forms: a growing vegetative cell or an inactive form called a spore. Vegetative cells can be killed by rather mild heat (140°F-180°F) depending upon the time of exposure. However, some spores can withstand boiling water for hours and after cooking still germinate into vegetative cells that cause spoilage. Therefore, it is neces-sary to use much higher temperature to kill spores in foods. Food prod-ucts are heated to expel air, then sealed in containers of glass or plated steel and heated or sterilized in retorts and cooled. The resulting product is altered in fl avor and texture from that of the raw product. Neverthe-less, it is preserved so that it can be shipped or stored for several years at ordinary temperature.

Baking

Baking has two-fold purposes: developing a different type of food product from grains, then preserving it for future use. Grains for bread are ground into fl our, then made into dough by fermentation with yeast to develop desirable fl avors and textures. The dough is then subjected to heat. This coagu lates the bread, reduces the moisture, and kills the microorga nisms that would otherwise cause spoilage. Cakes and other items owe their oven structures to chemical leavening agents such as bak-ing powder or natural gas such as beaten egg whites. Unless the heat is suffi cient to kill yeasts, molds, and spoilage bacteria, the products have a short shelf life. How ever, in hermetically sealed containers they keep very well.

Refrigeration

The rate of deterioration by naturally occurring enzymes and the rate of growth of microorganisms are progressively retarded by low tem-perature. In supermarkets, fresh meat is displayed in a chilling case, and fresh poultry in crushed ice to maintain quality and retard deterioration.

Fresh fruits and vegetables are held in a refrigerated warehouse regulated to obtain maximum storage according to product requirements. To ex-tend storage life, products such as butter, cheese, dehy drated eggs, and canned goods are stored in cooled ware houses. No change of form or texture is involved when pro ducts are simply cooled to prolong fresh-ness.

Sun and Air-Drying

In certain localities where the warm sun and low humid ity prevail, local fruits are dried on trays in the open. Rapid drying is essential to prevent molding and to maintain quality. For fast drying where sun dry-ing is not practicable, mechani cal air-drydry-ing offers a solution. Fruit and vegetables are pre pared, spread on perforated trays as belts, and passed through temperature regulated air until dry. In some products, sulfur dioxide is applied to preserve color and retard deterioration. Some liquid foods such as milk, liquid eggs, and instant coffee are dried by spray-ing them into rapidly movspray-ing current of hot dry air then coverspray-ing the resulting powder. Drying on a rotat ing heated drum is also employed for certain products.

Vacuum Drying

With products that deteriorate from heat or oxidation, a vacuum drying process may be employed in batch or continu ous fl ow. A high

vacuum plus heat causes the product to dry rapidly by evaporation.

Raising the temperature increases the rate of evaporation but this must be regulated according to product requirements. This method lends itself to the drying of certain fruit juices.

Freeze Dehydration

Certain products require a porous structure to facilitate dehydra-tion; otherwise, they may suffer heat or oxidation dam age during dry-ing even at room temperature. Products such as raw or cooked meat, fi sh, and certain fruits and vegetables are frozen, placed in a chamber, and subjected to a high vacuum. This causes the ice crystals to sublime or evaporate leaving small cavities. The spongy material takes up wa-ter rapidly during dehydration. To facilitate evaporation, heat is applied through the shelves upon which the frozen food seats. Temperature of the shelves must be regulated to increase the drying rate without melt-ing. Many products can be dried in this way and very closely resemble raw products when dehy drated, yet will keep for long periods without refrigeration provided proper moisture proof packaging is used.

Fermentation

Wines and beers are produced by adding yeast to ferment the natu-ral sugar. Because fruits and juices spoil through the action of many types of organisms, these are placed in a con tainer to seal out air. Yeast can utilize sugar even with out oxygen and produce alcohol, which acts as preservative. When the container is opened, acetic acid bacteria will oxidize the alcohol within the beverage, producing vinegar.

Preserving, Concentration, and Carbonation

In jams, jellies, marmalades, and such, preservation is accomplished by addition of sugar, while concentration of products by the removal of water produces syrups and various fruit concentrates. Most of these products can be kept without refrigeration, but some require cool storage to retain fl avor. Such products add variety to the diet through use of this preservation method. Honey is a natural product owing pres ervation to soluble sugars gathered from fl owers and concen trated by the bees.

Beverages are often pressured, and made more palatable, by use of carbon dioxide gas under pressure. The gas is soluble in the liquid and inhibits bacterial and mold growth. Fine fi ltration with raw fruit juices coupled with saturation with CO₂ under about 7 atmosphere pressure is used for long term bulk refrigerated storage.

Salting, Curing, and Smoking

Meat, fi sh, and certain vegetables may be preserved by high salt concentration. The salt inhibits microorganisms and enzyme action.

Products are later utilized by leaching the salt out with water. In curing ham, bacon, brine fi sh, and produc ing pickles, the product is submerged in a solution of curing salts, allowed to undergo a “cure”; then certain products are processed in a smokehouse by dry heat. Corned beef is curing salt brine and distributed under refrigeration. Certain sausages, like salami, are made by adding a small amount of curing salt to control fermentation that imparts a characteristic fl avor and exerts preservative qualities. These products are par tially dehydrated in the smokehouse and are stable for a time without refrigeration.

Irradiation

Energy imparted by atomic radiations can kill cells and is used as preservation method. This has been referred to as cold sterilization method since it does not employ heat. Extensive work is now in progress employing gamma rays from radioac tive Cobalt 60, machine accelerated electrons, and X-rays. When used in small amount, a pasteurizing effect can be obtained for short storage; or when used in a higher dose of en-ergy, steriliza tion can be obtained. Certain low levels will inhibit sprout-ing of potatoes in storage. Use of this method is still in the experi mental stage, and extensive work is yet to be done to prove the commercial practicability and to assure the safety and whole someness of the product thus treated.

Chemicals

Chemical preservatives can contribute substantially in the preser-vation of food. High temperature and humidities favor microbial attack and increase the rate of development of oxidative rancidity — which can be controlled by the use of chemicals. Food processors have been using many types of additives aside from preservatives to improve the appear-ance, fl avor, texture, or storage properties of food products.

New Preservation Methods

Recent innovations in technology have come up with new preser-vation methods such as Pulsed Light, Pascalization, and Aseptic and Modifi ed-Atmosphere Packaging (MAP). (Brown, 2005)

Pulsed Light is still undergoing approval by the Food and Drugs Administration (FDA). This method works by exposing food to intense

and very brief fl ashes of light, which disrupts the cell membranes of bacterial cells but not the surrounding food. The intensity of the light, which lasts only a second, is 20,000 times brighter than sunlight. There is no thermal effect, so quality and nutrient content are retained. Pascal-ization is a food preservation process utilizing ultra high pressure to in-hibit the chemical processes of food deterioration. Pascalization is named after Blaise Pascal, a 17th-century French scientist who described how contained fl uids are affected by pressure. Pascalization subjects food to very high pressure, a process that kills many bacteria, yeasts, and molds.

Acidic foods are best suited for this method because bacterial spores remain resistant and must be treated with acid to block their ability to germinate.

Aseptic and Modifi ed-Atmospheric Packaging (MAP) has been used for many years on food products. Food that is aseptically packaged is sterilized, packed, and sealed in a sterilized container under sterile conditions. The “juice box” is an example of an aseptically packaged product. It is sometimes combined with modifi ed-atmospheric package, which consists of changing the air composition around the food to pro-long its shelf life. The shelf life of products packaged with MAP is con-siderably longer than foods packaged without this technology. Modifi ed-Atmospheric Packaging is commonly used for fruits and vegetables that are ready to use, fresh, peeled, sliced, shredded or grated sold within a week of preparation. Cured cheeses, most meat and poultry are also packaged using MAP.