Microbial contamination of food refrigeration equipment
Refrigeration systems in chilled rooms in fifteen plants processing a variety of foods were studied. These included plants processing raw meat and salads, Chinese ready meals, dairy products, slicing and packing of cooked meats and catering establishments. An initial survey of total numbers of microbes at a total of 891 sites on evaporators, drip-trays and chilled room walls was followed up with a more detailed examination of 336 sites with high counts, selecting for Listeria spp, coliforms, enterococci, Staphylococcus aureus and Bacillus cereus. Temperatures (particularly air on and air off, maximum and near defrost heaters) relative humidity, airflow, layout and cleaning regimes were surveyed.
The work demonstrated that bacteria were present on evaporator cooling coils in all factory chill rooms visited. In general, no correlation could be found between any of the physical measurements and the numbers and types of bacteria detected. Further trials with an experimental evaporator indicated that bacteria could be transferred from the surface of the evaporator to the air within a cold room. These trials with the experimental evaporator also indicated that little microbial growth occurred on a clean evaporator.
Although evaporator cleaning procedures were carried out in some factories as part of routine maintenance these were not shown to be effective at maintaining low levels of bacteria on evaporators. To maintain evaporator hygiene it is suggested that more regular cleaning procedures, possibly by means of automated cleansing systems, should be considered.