ADVANCEMENT OF THE PRACTICE
Open Access
THE PRACTITIONER’S TOOL KIT
Using Water Activity to Control Foodborne Illness
James J. Balsamo, Jr., MS, MPH, MHA, RS, CP-FS, CSP, CHMM, DEAAS Nancy Pees Coleman, MPH, PhD, RPS, RPES, DAAS
Brian Collins, MS, REHS, DLAAS Gary P. Noonan, CAPT (Retired), MPA, RS/REHS, DEAAS Robert W. Powitz, MPH, PhD, RS, CP-FS, DABFET, DLAAS Vincent J. Radke, MPH, RS, CP-FS, CPH, DLAAS Charles D. Treser, MPH, DEAAS
Editor’s Note: The National Environmental Health Association (NEHA) strives to provide relevant and useful information for environmental health practitioners. In a recent membership survey, we heard your request for information in the Journal that is more applicable to your daily work. We listened and are pleased to feature this column from a cadre of environmental health luminaries with over 300 years of combined experience in the environmental health field. This group will share their tricks of the trade to help you create a tool kit of resources for your daily work. The conclusions of this column are those of the authors and do not necessarily represent the ocial position of NEHA, nor does it imply endorsement of any products, services, or resources mentioned.
the U.S. Department of Agriculture and the Food Safety Inspection Service including water activity as a means of microbial control in the Generic HACCP Model for Heat Treated, Shelf Stable Meat and Poultry Products . Earlier ver- sions of the FDA Food Code stipulated what sci- ence already knew—that below a certain water activity level (a w ≤ 0.85), most foods would not support pathogenic bacterial growth. The concept of using water activity as a means of controlling foodborne illness in the retail food industry is a recent addition to the applied science of food safety. As part of the regulatory community, it was not even a blip on the radar screen until 2005, when water ac- tivity was partnered with pH and was declared a major factor in assessing temperature-sen- sitive foods. The 2005 Food Code considered the interaction of water activity and pH under certain conditions of heat treatment and pack- aging. This synergism was sought to control or eliminate pathogens that would otherwise be ineective when used alone. Additionally, heat treatment (a process that destroys vegetative cells) and the eect of packaging (a control for recontamination) are now widely considered in the evaluation of foods oered to the pub- lic. In addition, by considering water activity, we are given a broader latitude in assessing the risk of foodborne illnesses beyond the more traditional time and temperature controls. To better understand the term, science de- fines water activity as the relative availability of water in a substance. It is the vapor pressure of water divided by that of pure water at the same temperature; therefore, pure water has a water activity of 1.0. As a rule, when the ambi- ent temperature or the temperature of the food increases, water activity typically decreases,
T he longer we work with the Food and Drug Administration (FDA) model Food Code , retail food establishments, and environmental health professionals, the more we realize that the most misunderstood criterion for food safety is water activity (a w ). While we cannot answer all your questions and concerns on this topic, together we can make a bit of sense of this enigmatic concept. Simply defined, water activity is the “humid- ity” of food. Unlike the water content of food, water activity can determine shelf stability. It can predict which microorganisms will be potential sources of spoilage and infection. For example, it can give us the dierence between the growth of bacterial pathogens and fungal physiology, or in the parlance of water activ- ity, 0.91 versus 0.70 (the former being ideal for bacterial growth while the latter might provide a cozy environment for mold). The water activity of a food is also instru- mental in maintaining its chemical stability, where it is partially responsible for minimiz- ing nonenzymatic browning reactions (i.e., appearance) and spontaneous autocatalytic lipid oxidization reactions, thereby prolong- ing the activity of enzymes and vitamins, and optimizing the physical properties of food products such as moisture migration, texture, flavor, odor, and shelf life.
In other words, water activity helps us pre- dict what will happen to food products as they sit on the shelf, even under ideal conditions of temperature and humidity. While shelf sta- bility means that food “won’t get moldy,” it also aects the texture, moisture migration, caking, and clumping of food. Not bad for a little relative humidity measurement. So, in the greater scheme of things, water activity and its measurement in the field do more than judge food with a thermometer. Water activity opens the door to both food safety and food quality. It has only been in the last two decades that water activity has had a significant impact on regulatory criteria. And it has been only a few short years that water activity has had any impact on the way we go about our retail regulatory business. Using water activity as a microbiological control initially was cited in parts and paragraphs of the Good Manufactur- ing Practice regulations from Title 21 of the Code of Federal Regulations. Further, the use of water activity in relation to control measures and food safety was introduced through in-pro- cess detection in hazard analysis critical control point (HACCP) systems, where water activity is specifically targeted as a microbial control measure during the production process. This introduction was followed in short order by
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Volume 86 • Number 6
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