Microbial contamination of food refrigeration equipment.
Judith A. Evansa, Steven L. Russella, Christian Jamesa, Janet E.L. Corryb
Journal of Food Engineering, Volume 62, Issue 3, May 2004, Pages 225–232
Abstract
Refrigeration systems in chilled rooms in 15 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.
In general, no correlation could be found between any of the physical
measurements and the numbers and types of bacteria detected. Maximum
mean temperatures in the chilled rooms varied from −1 to +16.9 °C and
few chilled units were regularly cleaned. Twenty five percent of sites
examined had more than 105 colony-forming units per cm2, although, very
few pathogens or faecal indicator bacteria were detected. Listeria spp.
were not found and coliforms were found only once, in low numbers. Low
numbers of S. aureus or B. cereus were present in 9 of the 15 plants, B.
cereus was found on evaporators and associated drip trays in two catering
plants and two plants processing cooked meat. Enterococci and S. aureus
were found most frequently in a raw red meat slaughterhouse (always in
low numbers). In general, microbial contamination was lower in rooms
where wrapped rather than unwrapped products were stored. The type of
product also affected the degree of contamination, with raw red meat and
poultry or dry ingredients giving highest counts, and raw vegetables and
cooked products lowest.
The work demonstrated that bacteria were present on evaporator cooling
coils in all factory cold rooms visited. 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.
Keywords
Evaporator; Drip tray; Food processing; Temperature; Bacteria
Corresponding author. Tel.: +44-117-928-9300; fax: +44-117-938-9314