Food Protection Trends - July 2008 - 476

The US Public Health Service—FDA Grade A Pasteurized Milk Ordinance (PMO) (12) contains general regulations regarding most aspects of the building. For example, the PMO states: “The floors… shall be constructed of concrete or other equally impervious and easily cleanable material; and shall be smooth, properly sloped, provided with trapped drains and kept in good repair…”. Although plain concrete is allowed, eventually it will be eroded by whey and cleaning solutions. The resulting cracks and loosened tiles are impossible to clean and can serve as harborage and incubators for LM. A better solution is to use concrete covered with an epoxy coating. The floor should slope sufficiently to allow for quick draining and prevention of puddle formation on the floor surface. Appropriate wall materials include fiberglass reinforced plastic (FRP), which is easy to clean and resistant to moisture, heat and chemicals. In general, piping and equipment should be mounted approximately 2 ft from the wall to allow for cleaning. The most common areas of dairy plants found positive for LM contamination are the floor drains (10, 26, 28). Up to 80% of environmental Listeria sites have been attributed to floor drains (16) where LM can attach to cast iron (46). Refrigerated areas are another common environmental incubator for LM (45). It is important to construct facilities and equipment so that they are easy to clean and sanitize. Special attention should focus on preventing condensate from dripping onto products, product contact surfaces, shelving and/or floors. In addition, ventilation systems can disperse LM-contaminated condensate inside the cooler. Draining of drip pans and formed condensate via sanitary pipes to a drain lowers this contamination risk. Some cheeses are ripened for an extensive time on shelves that can be a source of LM contamination (23). Formerly, wooden shelves were used for supporting the cheese for ripening and aging. Because raw or bare wood is difficult to clean and sanitize, only finished and poly-urethane-coated wood should be used. Currently, stainless steel (SS) shelves are preferable because of the ease of cleaning and sanitizing and of their overall durability. All items must be stored at least 18 inches above the floor, to prevent water splash from the floor. Water in contact with the floor is at high risk for LM contamination. It is recognized that water from high-pressure nozzles is a serious source of post-pasteurization contamination. Aerosols produced by high pressure water striking the floor can reach and contaminate most food contact surfaces within the plant. Equipment construction and design. It can be difficult to find equipment for smaller-sized dairy processing operations. Equipment suppliers have become accustomed to building machinery of ever-increasing sizes and capacities. Hence, small-scale equipment has become a high-priced specialty product. This has driven processors to purchase and install used and/or retrofitted equipment. Used equipment can contain damaged stainless steel (SS) surfaces, as well as worn or stressed seams and/or welded joints that are very difficult to clean and sanitize. Both new and used equipment must follow design specifications that meet 3-A sanitary standards (1). A number of different unit operations within dairy plants, such as tanks, tables, product fillers, and conveyers, have been observed to test positive for LM, although the contamination rate is lower than for environmental samples (28, 39). LM attaches very tenaciously to SS even after short contact times (33, 51), and SS cleanability is dependent on the SS surface finish (37, 47). Prior to purchase of equipment, it is important to consider both the construction and design features for relative ease of cleaning. Selection of equipment that is difficult to clean can prevent a proposed plant from becoming licensed by food industry regulators. A suggested strategy is to make payment(s) to equipment suppliers contingent on approval by regulatory agency representatives; this approach has been successfully used by some specialty cheese processors. Effective cleaning and sanitation. It is important that a comprehensive cleaning and sanitation program be implemented and strictly followed. This program is normally developed in collaboration with suppliers of detergents and sanitizers. Two fundamentals apply when cleaning and sanitizing dairy plants: (1) cleaning alone does not destroy bacteria, and (2) it is impossible to sanitize a dirty surface. Thus a plant must first be thoroughly cleaned and then sanitized. There are two methods utilized in cleaning equipment and piping; Clean In Place (CIP) and Clean Out of Place (COP). In CIP, cleaning and sanitizing solutions are pumped through the equipment. Detergent concentration, solution temperature, and flow rate are set to ensure that all internal equipment surfaces are cleaned without disassembly. In some circumstances, CIP is not feasible, so that the equipment is disassembled and cleaned by hand or in a parts washer instead. As mentioned earlier, drains are particularly vulnerable to bacteria biofilms. Cleaning of a drain is basically the same as hand cleaning. Chemical supply companies recommend the use of hot, soapy water and a brush that makes contact with as much of the drain surface as possible. Following cleaning, the drain should be rinsed with potable water and sanitized, using sanitizer at higher concentrations than are used on food contact surfaces. While cleaning drains and floors, there is a risk of contaminating food contact surfaces from exposure to aerosols and condensate. Therefore, it is recommended that floors and drains be cleaned before equipment. Tompkin et al. (49) outlines an easy-tofollow cleaning procedure for equipment: dry clean, pre-rinse equipment, visually inspect equipment, foam and scrub equipment, rinse equipment, visually inspect equipment, clean floors, sanitize equipment and floors, and dry floors. Thus, cleaning from top down minimizes the risk of re-contaminating equipment during the cleaning and sanitation process. All brushes used during cleaning should be color coded, with black being used for floors and drains. At least once a week, the plant walls and floors should be foamed with quats at concentrations from 400 to 800 ppm. This is especially important if condensate regularly collects on the wall, window, ceiling and equipment surfaces. To prevent corrosion of SS it is important to follow the following recommendations: (1) use only soft fiber brushes, pads, and/or sponges for manual cleaning and for removal of milk residues; (2) apply chemical cleaners only as directed by the manufacturer/supplier; (3) thoroughly rinse all alkaline and acid cleaners from equipment surfaces with tap water; and (4) limit exposure time of SS to sanitizers. For example, chlorinated compounds should contact SS equipment surfaces for no longer than 20 min (18). The cheese plant’s water supply needs to be of high quality in terms of both chemical content and microbiological profiles. Although no published studies report cheese contamination from LM in 476 FOOD PROTECTION TRENDS | JULY 2008

Food Protection Trends - July 2008

Table of Contents for the Digital Edition of Food Protection Trends - July 2008