Hazards to Food Safety

Identifying the various hazards to food safety is the first step in guarding against foodborne illness. These hazards may be microorganisms (bacteria, molds, and viruses), animal parasites, natural toxicants, or chemical and physical contaminants. Of these, the number one cause of foodborne illnesses are microorganisms and they are everywhere. They live on our skin, in the air, in water, and in soil, and most importantly in the food people consume.

Bacteria

Bacteria are so small that they cannot be seen, smelled, or tasted. Bacteria are found not only everywhere, but in extremely large numbers. Over 2 billion bacteria can be found in a teaspoon of soil, and over 100 billion are carried on the human body.

More than 90 percent of all food-borne illness are caused by bacteria, but only about 4 percent of identified bacteria are pathogenic. The remaining 96 percent are harmless, and some are even used to produce such food items as cheese, yogurt, soy sauce, butter, sour cream, buttermilk, certain cured meats, sourdough bread, and fermented foods such as pickles, beer, and sauerkraut.

Numerous different types of bacteria exist, but most require similar conditions in order to thrive. The following environmental factors affect the growth and reproduction of bacteria:

• Water: Its presence, and the amount available to bacteria, is the most important factor governing the microbial contamination of foods. Bacteria cannot survive without water.
• Oxygen. Bacteria vary in their need for oxygen. Aerobic bacteria require oxygen to live, but anaerobic bacteria can only survive in the absence of oxygen, as is the condition in sealed cans or soil found several inches deep in the ground. Some bacteria can survive in either environment and are known as facultative.
• Temperature. The temperature danger zone, which includes the human body temperature of 98.6°F (37°C), allows rapid bacterial growth. Some bacteria are even known to survive below freezing temperatures (32°F (0°C)). Bacteria are usually destroyed by the high heat of boiling if they are subjected to it for at least ten minutes.
• Time. Bacteria need time to replicate and produce toxins, but microbial growth occurs exponentially; the number of bacteria can grow from harmless to staggering in a relatively short time.
• pH. The acidity or alkalinity of a substance often determines which bacteria, if any, will grow in a food. The antibacterial action of vinegar has been known for a long time. Generally, high-acid foods are less likely to engender the growth of bacteria than low-acid foods.

The effects on bacteria of water, oxygen, temperature, and pH influence the threat these microorganisms pose to food. For example, microbial contamination can be avoided by removing water from food or by reducing the food’s water activity. This is the case with honey and preserves such as jams and jellies, which look moist but whose water is largely bound by their high sugar content and is thus not available to bacteria.

To avoid the temperature danger zone, cold foods should be stored under 40°F (4°C), while the temperature of hot foods should be above 140°F (60°C). Home purchases should be organized so that cold foods are selected last, brought to their destination immediately, and stored in the refrigerator or freezer as soon as possible. The “Two-Hour Rule” should always be followed: any perishable food left out in danger zone temperatures for more than two hours actual time, or four hours cumulative time, should be discarded. Cumulative time includes the time from the truck to the store, the store to the freezer, the freezer to the kitchen, and the time on the counter where the food is being prepared.

The pH sensitivity of bacteria means that fruits and other high-acid content (pH < 4.6) foods are less likely to be sources of microbial contamination than foods with a lower acid content (pH > 4.6), such as meats and vegetables. Tomatoes at one time were considered to be uniformly high-acid foods, but newer varieties have been developed that are not so acidic. The antibacterial action of certain high-acid foods is being exploited to good effect by the food industry in several ways. Some slaughterhouses spray beef carcasses with acetic acid (vinegar) to reduce the number of microbes, and during epidemics of cholera, a known folk remedy thought to block the transmission of the bacterium responsible for the disease is to add lime juice to the drinking water.

Despite precautions, some bacteria may survive environmental stresses in spore form. Spores are dormant and very resistant to drying and heating, and the bacteria may remain in this state for long periods until their environment becomes more hospitable.