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Thesis: Equipment hygiene and risk assessment measures as tools in the prevention of Listeria monocytogenes contamination in food processes



Kaarina Aarnisalo, Research Scientist from VTT presents her doctoral thesis “Equipment hygiene and risk assessment measures as tools in the prevention of Listeria monocytogenes contamination in food processes” on 25 January 2008 at the Helsinki University of Technology.

A problematic pathogen occurring in food processing is Listeria monocytogenes. Its efficient control at the processing plant level requires good equipment hygiene, including functioning good manufacturing and hygiene practices used by all employees, effective means of decontamination and rapid detection of contamination sources, as well as hazard analysis systems supported by risk assessment procedures.

The thesis of Kaarina Aarnisalo focuses on deficiencies and improvements in these equipment hygiene and risk assessment practices with the aim of elucidating and developing the most efficient practices against L. monocytogenes.

The hygienically most problematic types of equipment in the Finnish food industry were identified as the packaging machines, conveyers, dispensers, slicing machines and cooling machines. The main reason for the equipment being considered as problematic was poor hygienic design. Equipment designers must focus their performance on more suitable equipment design. Clear deficiencies were also found in hygiene performance of the maintenance personnel in food processing plants. The results of these studies also indicate that L. monocytogenes may be transferred through maintenance work. Training of maintenance personnel with reference to hygienic practices must be increased. The results of the thesis showed that lubricants used in food processing equipment may act as contamination vehicles of L. monocytogenes.

An investigation of the efficiency of eight commonly used commercial disinfectants against L. monocytogenes strains at +5°C was performed. The tested agents were generally efficient at the recommended concentrations and effect times, with only a few exceptions.

Risk assessment practices were developed by investigating and modelling recontamination of a product and by a plant-level quantitative risk assessment. Recontamination was modelled by investigating transfer of L. monocytogenes from slicing blade to slices of cold-salted salmon. As a concluding example, a practical approach to quantitative risk assessment at the plant level of L. monocytogenes in heated marinated broiler legs is presented. This approach helps food processors in illustrating the risks caused by the products for consumers.

PHOTO: Sampling from a slicing machine.

Further information:

VTT, Kaarina Aarnisalo, Research Scientist, tel. +358 20 722 7126

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