The Three Requirements of Pathogens

Pathogens thrive when three basic living conditions are readily available: protein, water , and appropriate pH. A large percentage of foods typically contain these three elements in ratios favourable to the rapid growth of pathogens. The greater the abundance of protein and water and the more favourable the pH, the higher the likelihood that foods will become contaminated . In addition , some bacteria do best with a good supply of oxygen , others when oxygen is absent. Some  can get along either way. The handling procedures noted in sections on cooling, re-heating and thawing help to prevent any single condition from becoming so predominant that it will favour the pathogen’s growth and reproduction.

Protein

Most food contain some protein. Meats, fish, poultry and eggs are among the foods with greatest percentage of protein , making them highly susceptible to food poisoning and intoxication. But, grains and legumes also contain protein in significant quantities. They become especially vulnerable when cooked. Rice and potatoes are among the most likely carriers of disease. Vegetables has very small quantities of protein and fruits contain very little , if any protein at all.

Water

Foods that are moist enough to be soft and easy to chew are also moist enough to support  the growth of many types of pathogens. There are some foods that are naturally ‘dry’ and have a lesser chance of becoming infected ; certain root vegetables have relatively low moisture content ; Other foods , once processed, lose much of their moisture content , very hard cheeses such as Romano or Parmesan cheese ; dried, salted or preserved foods such as olives and hams ; nuts and seeds , and uncooked grains, cereals and meals. These are the foods that we treat as ‘non perishables’, a recognition of the fact that they can be stored at room temperature without fear of immediate loss of quality or wholesomeness.

Moderate pH

The pH of most foods falls with in a range called ‘moderate ‘ ; a state that makes foods attractive for growth and reproduction of many different type of microorganisms. A substance that is extremely acid(e.g. lemon juice ) will be closer to a value of zero. Those that are extremely alkaline (e.g. baking soda) will measure closer to 14. Most foods tend to fall with in a range of about 4 to 10. Foods that are either more acidic or more alkaline than that will generally no longer be susceptible to micro organisms. Vinegar, lemon or lime juice and other very tart and sour – tasting foods are acid; baking soda , alum, cream of tartar are bitter-tasting and cause the mouth to pucker , these items  are alkaline. We use this general principle to keep foods when we pickle , salt or brine them in order to change their pH level to above 10 or below 4, increasing the shelf life of the food.