Food Protection Trends - August 2010 - 473

FIGURE 1. Hotbox-Axial HBA Fan Blower Heaters HB90415 – 415V 9.0kW used in heat holding chillers

transferred into two holding chillers to await meal assembly and freezing.

Heating of blast chillers
The three blast chillers were each 2 m × 7 m × 4 m. The blast chillers also have a 50 mm sandwich panel mezzanine. Chiller wall panels were 100 mm insulated refrigeration panels consisting of a 1.6 mm sheet over an expanded polystyrene core. These were constructed from Retracom Standard Sandwich Panel 100 (Retracom, Crestmead, Australia) as part of the original building works. Floors were covered in Sikagard 62 (Sika Group, Zurich, Switzerland), a two component high build epoxy resin. Air heating was instituted every 14 days at the end of production and sanitation. The heating of air within blast chillers was achieved by switching ceiling mounted chilling units to heat mode. The blast chiller units were Greenhalgh 16/561500 aluminum finned coils (Greenhalgh Asia Pacific, Brisbane, Australia), but these had been changed earlier to stainless finned units because of caustic sanitation chemicals corroding the aluminum fins. The fan motors on these units were sufficient for heating and fans were not used. Heat treatment of blast chillers commenced January 1, 2006. The temperature was maintained at 50oC for a minimum of 2 h at each treatment time. An adjunct to the existing Good Manufacturing Practice (GMP) cleaning regimen was sought to reduce chiller contamination with L. monocytogenes. Periodic heat treatment of chillers is an intervention that involves raising the temperature of the chillers to a level which, in combination with the associated drying, may provide multiple stressors and result in a reduction of bacteria present in the chiller. We speculated that periodically holding chillers at an air temperature of 50oC for 2 h may result in reductions in Listeria contamination. In this study, we tested this hypothesis by applying this heating and drying regimen to post-cook chillers in an RTE frozen meal production facility, using simple heaters and fans and determining the prevalence of Listeria in the chillers before and after implementation of the intervention.

MATERIALS AND METHODS
Post-cook blast and holding chillers
A RTE meal production facility based in Brisbane, Australia was operating an externally audited HACCP food safety system, and was listed for export under the jurisdiction of the Australian Quarantine Inspection Service. The facility had a corporate zero tolerance policy for Listeria monocytogenes contamination on finished product. Previous work performed within the facility has demonstrated contamination of finished product with L. monocytogenes sub-types that also persistently colonize chillers. Within the facility, three identical post-cook blast chillers (also known as intensive chillers) were used to chill exposed meal components. These components were then

Heating of holding chillers
The two holding chillers were 3 m × 7 m × 4 m and 7 m × 7 m × 4 m. These were constructed from Retracom Standard Sandwich Panel 100 (Retracom, Crestmead, Australia) as part of the original building works. Wall panels and floors were identical to those described for blast chillers. Product was consolidated into a different holding chiller each week, allowing for an every14-days heating regimen at the end of production and sanitation. Empty crates were allowed to remain in the chillers. Heaters and fans were wheeled into alternating corners. The holding chillers use Luve Contardo S3HCW 179 N80A (Uboldo–Varese, Italy) forced draft cooler units. Circulating refrigerant valves within these ceiling mounted units were released prior to operation of heaters and

AUGUST 2010 | FOOD PROTECTION TRENDS

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Food Protection Trends - August 2010

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