Biological Aerosols: A Review of Airborne Contamination and its Measurement in Dairy Processing Plants

Abstract

Processing plant air is a source of post-pasteurization contamination of dairy products. Little is known about the extent to which biological aerosols contaminate pasteurized products, however evidence indicates that air within a packaging area is a critical control point for both pathogens and spoilage microorganisms. Consequently, it is important to understand the characteristics of biological aerosols, learn how to control their occurrence, and discover practical and valid monitoring methods. Methods used for monitoring viable particles in air include the use of sedimentation plates, impingers, slit and sieve impactors, filters, and centrifugal samplers. Each of these methods has limitations on its usefulness for dairy plant air monitoring. Microorganisms are often injured due to the stresses of the aerosolized state and consequently may not grow on selective media. Sampling methods such as impingement and filtration which subject the organisms to additional stress may cause sufficient injury to prevent growth on non-selective media. However, gentler collection methods such as centrifugal samplers may not generate enough force to collect the smallest viable particles. Aerosols are generated within the dairy plant by worker activity, sink and floor drains, water spraying, and air conditioning systems. Environmental sanitation, air filtration, air flow control, and control over personnel cleanliness and activity are useful control measures. The adoption of “clean room” design principles for a packaging area will aid in controlling biological aerosols in new dairy processing plants.