Prevention

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Food Poisoning

Spoilage Organisms

Lab 36

WAYS TO PREVENT FOOD SPOILAGE

Food preservation includes processes involved in protecting food against microbes and other spoiling agents that may allow its future consumption. The preserved food should retain a palatable appearance, flavor, and texture, as well as its original nutritional value. Food is considered spoiled when an undesirable change in the color, flavor, odor or texture has occurred. Foreign substances in food products make foods undesirable. The onset of food spoilage is rather indefinite. It is a gradual process occurring because of poor sanitation, enzymatic or chemical reactions, improper temperature controls, microbial growth or physical abuse.

There are many ways to prevent and avoid food spoilage all of which address the major principles of
     · Killing of micro-organisms
    · Inhibition of microbial growth
    · Removing micro-organisms
    · Destroying enzyme
    · Retardation of chemical changes

Drying and dehydration

One of the first ways to prevent/avoid food spoilage is by drying and dehydration. Drying and dehydration is the oldest method of food preservation. Quite simply, drying reduces moisture necessary for bacterial growth that eventually causes deterioration. Successful dehydration depends upon a slow steady heat supply to assure that food is dried from the inside to the outside. There are various methods of drying and dehydrating foods which range from simply laying the food out in the sun on a dry, sunny day to solar food dryers and the most reliable, food dehydrators.

The disadvantages of this preservation method include the time and labor involved in rehydrating the food before eating. Moreover, rehydrated food typically absorbs only about two-thirds of its original water content, making the texture tough and chewy.

Soup and milk are easy to dry and they last for years.

Heat Treatment

As food is heated up or cooked, the heat kills microorganisms and their spores, alters protein structure, and can destroy enzyme activity of microorganisms in food. Common foods that undergo some form of heat treatment include milk, beer, and wine. One type of heat treatment is the very widely known method of pasteurization. Pasteurization uses mild heat treatment for a short time and is designed to inactivate pathogens and certain enzymes. Pasteurized products, however, can still contain living microorganisms capable of causing food spoilage, which is why many food products, which utilize pasteurization, also utilize another form of food preservation such as refrigeration.

Other forms of heat treatment include blanching, which is used to denature enzymes and is often used on vegetables and fruits before they are frozen. Also, in some aseptic canning and bottling processes, commercial sterilization is performed to destroy all pathogenic and toxin forming organisms which could grow under normal handling conditions. In this process, heat resistant spores may remain but they will not grow under normal storage conditions.

Refrigeration and Freezing

Refrigeration and Freezing are both widely popular methods of preventing food spoilage. In each of these methods, the microbial activities of nearly all pathogenic microorganisms are dramatically slowed down or prevented, as are the chemical changes that result in spoilage. In refrigeration, the food is stored between 0 degrees Celsius to 4 degrees Celsius so the water in the food is not frozen so some psychrophiles, which can spoil the food, can still thrive. In freezing, the food is stored at temperatures lower than -20 degrees Celsius so 95% of the water is frozen and food can be stored much longer, for months, even years.

Smoking

Smoking is the process of curing, cooking, or seasoning food by exposing it for long periods of time to the smoke from a (usually wood) fire. "Hot smoking" is typically a several-hours-long process that can be used to fully cook raw meats or fish, while "cold-smoking" is an hours- or days-long process that is generally used to preserve or flavor foods (usually meats or fish, but sometimes cheeses, vegetables, fruits, and even beer). Preservative action is provided by such bactericidal chemicals in the smoke as formaldehyde (HCHO) and creosote (antiseptic obtained from wood tar), and by the dehydration that occurs in the smokehouse.

The largest drawback to smoking food in order to preserve it is that the food itself absorbs chemicals from the smoke including aldehydes and acids. While the acids effectively kill many microbes, the aldehydes are carcinogenic and diets high in smoked foods have been known to increase the risk of cancer of the mouth, stomach, and esophagus.

Canning

Canning is simply the process of preserving food by heating it and then sealing it in an airtight container. Heating the product destroys all of the enzymes and microorganisms currently present and sealing it assures that no oxygen or other microorganism can enter. If done correctly this can be an excellent way of preserving foods. Commercial canning is most popular but many people also choose to can and preserve food themselves.

Irradiation

Food irradiation is a new food safety technology that can eliminate disease-causing germs from foods. Treating food with ionizing radiation can kill bacteria and parasites that would otherwise cause food borne disease. Similar technology is used to sterilize medical devices so they can be used in surgery or implanted without risk of infection. The effects of irradiation on the food and on animals and people eating irradiated food have been studied extensively. These studies show clearly that when irradiation is used as approved on foods: disease-causing germs are reduced or eliminated, the food does not become radioactive, dangerous substances do not appear in the foods, and the nutritional value of the food is essentially unchanged.

When microbes present in the food are irradiated, the energy from the rays is transferred to the water and other molecules in the microbe. The energy creates transient reactive chemicals that damage the DNA in the microbe, causing defects in the genetic instructions. Unless it can repair this damage, the microbe will die when it grows and tries to duplicate itself. Disease-causing organisms differ in their sensitivity to irradiation, depending on the size of their DNA, the rate at which they can repair damaged DNA, and other factors. It matters if the food is frozen or fresh, as it takes a higher dose to kill microbes in frozen foods. The size of the DNA "target" in the organism is a major factor. It takes more irradiation to kill bacteria, because they have a somewhat smaller DNA, with D-values in the range of 0.3 to 0.7 kiloGray.

The type of radiation used for food preservation is ionizing radiation in the form of gamma rays, x-rays, and electrons.

Foods that have been commercially irradiated must be clearly labeled. The international symbol used to label irradiated foods is the radura.

Foods that have been recently approved by the FDA as being safe to irradiate include flour, potatoes, pork, fruits and vegetables, herbs and spices, poultry and meat.

Sugaring and Salting and Meat Curing

Sugaring and Salting of foods is an older method of food preservation. In this method food is treated with high concentrations of salt or sugar. These methods of food preservation rely on the phenomenon of osmosis to be effective. When salt or sugar is added, the water potential inside the microorganisms is less than the water potential outside so the water needed by the microbe for enzyme action and growth is removed by osmosis and this results in microbial death. Meat Curing is one specific example of using salt and sugar to cure foods. The meat is cured by osmosis and the microbes die of dehydration.

There have been health risks associated with meat curing. The large amount of nitrates that are taken into the body are converted to nitrites which can react to form nitrosamine. These nitrosamines have been known to be carcinogenic in some animals.

Pickling

Pickling is another method of food preservation that has been around for centuries. The idea behind pickling is quite simple. Vinegar is added to the food which lowers the pH value making it difficult for most microorganisms to live. Commonly pickled foods include cucumbers, beets, and some commercially bottled sauces.

Filtration

Filtration is a very simple method used in conjunction with some other food preservation techniques. Filtration is the physical removal of certain microorganisms from food. The filter used to filter many fluids has a millipore membrane with pore diameter that is smaller than that of the bacteria filtered. One example of the use of filtration is the filtering of beer after it has been heat treated to remove any impurities which may have been caused by the sterilization. This beer is necessary to be treated in order to avoid future quality problems with yeast and biological residues which may have been created in the fermentation process.

Use of Food Additives

Food additives are widely used to prevent food spoilage and to maintain the safety of foods by slowing the growth of harmful bacteria that could lead to food poisoning. Additives are also used to prevent color and flavor changes that can occur when food reacts with air. Common additives include mild acids, alkaline agents, anti-caking agents, antioxidants, color additives, emulsifiers, stabilizers and thickeners, maturing and bleaching agents, preservatives, humectants, and natural and artificial flavors.

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