Despite 30 years of food safety education from farm to table and having one of the safest food supplies in the world, the federal government estimates that around 48 million cases of foodborne illness occur annually, which is about 1 in 6 Americans each year. These illnesses result in an estimated 128,000 hospitalizations and 3,000 deaths annually.
A foodborne illness is any illness resulting from the consumption of food contaminated with pathogenic microorganisms. Pathogens, known as BAC (bacteria), do not change the food so we often do not know they are present. BAC loves to invade food products and kitchen surfaces and utensils. Following four simple food safety steps—clean, separate, cook, and chill—before, during, and after food preparation can reduce the risk of becoming sick from microorganisms such as bacteria, yeast, and mold. Pathogens of most common concern include Salmonella, Campylobacter, E. coli, Clostridium botulinum, Listeria, and yeasts and molds. A previous blog discussed these pathogens.
Pathogenic growth and survival depend on conditions related to the pathogen and environment. Environmental factors that influence the growth of pathogens include pH levels, water activity, oxygen levels, time and temperature. Foodborne bacteria grow best in warm, moist, protein-rich environments that are slightly acidic or have a neutral pH. Yeasts and molds, also pathogens, do not require the same factors for growth as bacteria as both live on surfaces for different amounts of time. To learn more about how quickly bacteria can grow, check out this short video. Pathogens require a food source to grow, multiply and survive. Proteins and carbohydrates are a good food source because they contain nutrients needed for cellular growth.
pH or Acidity. pH is a measure of how acidic or alkaline (basic) a substance is. The scale ranges from 0-14 with a pH of 7 as neutral (distilled water). A pH of less than 7 is acidic and a pH greater than 7 is basic or alkaline. Acidic or acidified foods having a pH of 4.6 or less are considered high acid foods; foods with a pH greater than 4.6 are low acid. The pH value of common foods and ingredients can be found in this chart. Microorganisms are sensitive to pH and have specific pH ranges that allow them to grow, multiply and survive. A food’s pH level determines which microorganisms can grow in it.
Foods with a low (acidic) pH make it harder for microorganisms to survive and grow. pH also impacts the quality (flavor, texture, shelf life, and appearance) of foods and is especially important in canned foods. The acidity of a product itself is both a means of preservation and a way of keeping food safe for consumption.
Moisture or Water Activity (aw). Water is present in all food as either 1) free or available water or 2) water that is bound to the proteins, salt or carbohydrates in a food product. Bound water is not available for microbial growth. Water activity is the measure of the free or available water in a food product that can support microbial growth and affect the quality and safety of food. Water activity differs from moisture content. Moisture content is a measure of the total amount of water in a food but does not capture how unbound water behaves in the food. Water activity is synonymous with relative humidity. The FDA has established that a water activity value greater than 0.85 on a scale of 0 (bone dry) – 1.0 (pure water) indicates a high-risk food product capable of facilitating the growth of microorganisms in the product. Most foods have a water activity of .95 or more which is sufficient moisture to support the growth of bacteria, yeasts, and mold. In most cases, food items with a water activity of .85 or more require refrigeration while products below .85 are considered shelf stable. Water activity is controlled by binding up the water with ingredients such as salt or sugar, reducing or evaporating water by “cooking down”, dehydrating or freezing.
Oxygen levels. Oxygen can significantly affect food quality and safety through oxidation processes or support of microbial growth. Oxygen causes food enzymes to speed up chemical reactions resulting in browning or off coloring and rancidity or foul odors and taste. Enzymatic activity can also cause spoilage. Microorganisms are oxygen level specific; some require oxygen (aerobic) while others require little or no oxygen (anaerobic) to grow resulting in spoilage or poisoning. Still others, known as facultative anaerobic bacteria, can grow with or without oxygen by switching metabolic processes. So it is important to know that while microorganisms may be oxygen specific, they can adapt to their environments and therefore to minimize the risk of contamination. The Clostridium botulinum survives and produces toxins in anaerobic environments, a major consideration in canning and vacuum packaging of food.
Time and Temperature. Time and temperature are closely related in controlling the growth of microorganisms. Most microorganisms multiply rapidly between 40⁰F and 140⁰F (Danger Zone). Bacteria can double in numbers every 15 to 20 minutes in the danger zone. Foods that are capable of supporting the rapid growth of pathogenic microorganisms and require either temperature or time control for food safety (TCS foods) must be kept out of the danger zone. Thus:
– Keep COLD FOODS COLD at or below 40⁰F.
– Keep HOT FOODS HOT at or above 140⁰F.
– Limit time in the danger zone to two hours or one hour if the temperature is above 90⁰F.
– Reheat food to a minimum internal temperature of 165⁰F.
– Cook raw meat and poultry to a safe minimum internal temperature.
A food thermometer should always be used to verify temperatures.
Food products are host to pathogens. Environmental conditions affect the growth and survival of pathogens. Food prepared in any setting is subject to microorganism contamination. Practicing good sanitation and proper food safety techniques before, during, and after food preparation is the only way to prevent microorganism contamination and reduce the chances of contracting a foodborne illness.
Sources:
Appendix E. Water Activity Values of Select Food Ingredients and Products. Water Activity in Foods: Fundamentals and Applications. Second Edition. Gustavo V. Barbosa-Cánovas, Anthony J. Fontana Jr., Shelly J. Schmidt, Theodore P. Labuza
Water Activity’s Role in Food Safety and Quality. Food Safety Magazine
Understanding pH and its Importance in Food Safety UGA. UGA Cooperative Extension
BAM Chapter 18: Yeasts, Molds, and Mycotoxins. (FDA) US Food and Drug Administration
The Importance of pH in Commercial Canning Operations. OSU Extension
The Importance of pH in Food Preservation. Oklahoma Gardening
The Importance of Food pH. Terra Food Tech
Water Content and Water Activity: Two Factors that Affect Food Safety. Manitoba
Water Activity (aw) in Foods. Food and Drug Administration (FDA), US Food and Drug Administration
How Do You Know If Your Food Is Safe to Sell? Factors that Affect the Bacterial Growth on Foods: FAT TOM. Virginia Tech, Virginia Cooperative Extension
Understanding the Water Activity of Your Food. Virginia Tech, Virginia Cooperative Extension
Blog written in collaboration with Jennie Savits, AnswerLine Specialist.
