Monitoring aw is a critical control point for many food industry operations.
The importance of water activity (aw) in food systems cannot be overemphasized. Throughout history water activity in food has been controlled by drying, addition of sugar or salt and freezing. These methods prevent spoilage and maintain food quality. Water activity is the ratio of the partial vapor pressure of water in equilibrium with a food to the partial saturation vapor pressure of water vapor in air at the same temperature. This is equal to the relative humidity of air in equilibrium with the food. The water activity of a food describes the energy state of water in the food, and hence its potential to act as a solvent and participate in chemical/biochemical reactions and growth of microorganisms. It is an important property that is used to predict the stability and safety of food with respect to microbial growth, rates of deteriorative reactions and chemical/physical properties.
The growing recognition of the water activity principle is illustrated by its incorporation into U.S. Food and Drug Administration (FDA) and U.S. Department of Agriculture (USDA) regulations, Good Manufacturing Practices (GMP) and Hazard Analysis & Critical Control Points (HACCP) requirements, and most recently in NSF International Draft Standard 75. The purpose of these regulations is to detail the specific requirements, critical control points and practices to be followed by industry to assure that products are produced under sanitary conditions and are pure, wholesome and safe. New instrument technologies have vastly improved speed, accuracy and reliability of water activity measurements and are definitely a needed tool for food safety and quality.
Background
Throughout history man has controlled the water activity of food through drying, addition of salt or sugar and freezing such that the food becomes stable to microbial and chemical deterioration. Food manufacturers today have the same goal of making a stable and safe product. This means that the products must be wholesome and not endanger the health of the consumer with microorganisms or their toxins. The advantage today is in the knowledge and understanding of the importance of water activity in controlling microbial growth and thus upon the shelf life and safety of a product.
The Centers for Disease Control (CDC) stated foodborne disease is responsible for approximately 76 million illnesses, 325,000 hospitalizations and 5,000 deaths annually in the United States. Known pathogens, such as Salmonella, Escherichia coli O157:H7, Campylobacter and Listeria monocytogenes, account for an estimated 14 million illnesses, 60,000 hospitalizations and 1,800 deaths alone. With staggering statistics like these one would not believe that the U.S. has the safest food supply. Based on FoodNet surveillance data from 1997 to 1999, illness from the most common bacterial foodborne pathogens declined nearly 20%. This decline represents at least 855,000 fewer Americans each year suffering from foodborne illness caused by bacteria since 1997. By using water activity and controlling major food risks, such as microbial contaminants, the food industry can better ensure the safety of its products.
The consequence of a microbiological failure, particularly as they relate to product recalls, can be very costly. Brand recognition and sales may ultimately suffer as a result of consumers relating the recall to other products manufactured by a particular company. In a world of increasing pressures and diminishing resources, the need to strengthen microbiological quality assurance programs has not abated. In fact, there is more pressure than ever on the management of microbiological quality. Food safety must be controlled during the production process from beginning to end, rather than relying on detection of problems in the finished product.
