MICROORGANISMS AND RELATED QUALITY ISSUES IN MILK AND CHEESE Bacteria

As the manufacture of cheese relies in part on the select outgrowth of microorganisms, such conditions can also allow for the multiplication of unwanted contaminants. Milk ultimately becomes contaminated with microorganisms originating from infection, the farm environment, and feedstuffs, as well as milking and processing equipment. Thus, poor sanitation, improper milk handling, and animal health issues can result in not only decreased yield and poor quality but also sporadic cases and outbreaks of dairy-related disease. The entry, establishment, and persistence of food-borne pathogens in dairy processing environments also present a considerable risk to products postprocessing. Food safety management systems coupled with regulatory policies and microbiological standards for milk and milk products currently implemented in various nations work to reduce risk while improving the quality and safety of cheese and other dairy products. With that, cheese has enjoyed an excellent food safety record with relatively few outbreaks of food-borne disease considering the amount of cheese produced and consumed worldwide. However, as cheese production and consumption continue to grow, wemust remain vigilant in ensuring the continued production of safe, high-quality cheese. The microbiological quality and safety of cheese begin with milk. With an abundance of nutrients, milk is intended to provide complete primary nutrition for young mammals. With its near neutral pH, milk also serves as an excellent growth medium for the select microorganisms utilized in the manufacture of cheese. Consequently, the same applies to contaminating microorganisms, including those associated with spoilage and defects as well as those that are pathogenic to humans. Milk, essentially sterile when secreted into the alveoli of the udder, ultimately becomes contaminated with microorganisms originating from infection, the farm environment, and feedstuffs, as well as milking and processing equipment. Generally, environmental contaminants found in soil, feces, and bedding material attach to the exterior of teats and are released into milk during collection. Some of these microorganisms may also enter the teat canal and cause infection and are thus excreted in the milk. Lastly, microorganisms adhered to the surfaces of the milking and processing equipment, present as a result of inadequate cleaning and sanitation, can also contaminate milk. Contamination is of great concern to the cheesemaker, as milk of high microbiological quality is important to achieve optimal cheese yield, quality, and safety. Many spoilage organisms are capable of producing negative changes in the organoleptic attributes of cheese through the enzymatic alteration of milk components. In addition, contaminants can access the cheese itself during manufacture and aging, resulting in additional defects and food safety concerns. This review discusses the various types of contaminating microorganisms, with a focus on those associated with quality and/or safety issues related to cheesemaking. It also covers the regulatory policies regarding milk and milk products currently implemented in various developed nations designed to increase the quality and safety of cheese and other dairy products. Received: 22 July 2011, Accepted: 4 April 2012, Published: 7 February 2014 Editor:CatherineW. Donnelly, University of Vermont, Burlington, VT Citation:D’AmicoDJ. 2014.Microbiological quality and safety issues in cheesemaking. Microbiol Spectrum 2(1):CM-0011-2012. doi:10.1128/microbiolspec.CM-0011-2012. Correspondence: Dennis J. D’Amico, ddamico@uconn.edu © 2014 American Society for Microbiology. All rights reserved. ASMscience.org/MicrobiolSpectrum 1 Downloaded from www.asmscience. org by