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Control of Listeria Monocytoenes in the Food Industry

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Control of Listeria Monocytoenes in the Food Industry Department of Food Hygiene and Environmental Health Faculty of Veterinary Medicine University of Helsinki Helsinki CONTROL OF LISTERIA MONOCYTOGENES IN THE FOOD INDUSTRY Riina Tolvanen ACADEMIC DISSERTATION To be presented, with the permission of the Faculty of Veterinary Medicine of the University of Helsinki, for public examination in Walther Auditorium, EE-building (Agnes Sjöbergin katu 2), on 2nd September 2016, at 12 noon. Helsinki 2016 Supervising Professor Hannu Korkeala, DVM, Ph.D., M.Soc.Sc. Professor Department of Food Hygiene and Environmental Health Faculty of Veterinary Medicine University of Helsinki Helsinki, Finland Supervisors Professor Hannu Korkeala, DVM, Ph.D., M.Soc.Sc. Department of Food Hygiene and Environmental Health Faculty of Veterinary Medicine University of Helsinki Helsinki, Finland Docent Janne Lundén, DVM, Ph.D. Department of Food Hygiene and Environmental Health Faculty of Veterinary Medicine University of Helsinki Helsinki, Finland Reviewed by Laura Raaska, Ph.D. Docent, University of Helsinki Director, Biosciences and Environment Research Unit Academy of Finland Helsinki, Finland Associate professor Marcello Trevisani Department of Veterinary Medical Sciences Faculty of Veterinary Medicine University of Bologna Bologna, Italy Opponent Riitta Maijala, DVM, PhD Docent, University of Helsinki Vice President for Research Academy of Finland Helsinki, Finland ISBN 978-951-51-2385-5 (pbk.) ISBN 978-951-51-2386-2 (PDF) Unigrafia Helsinki 2016 ABSTRACT Contamination routes of Listeria monocytogenes were examined during an 8-year period in a chilled food-processing establishment that produced ready-to-eat meals using amplified fragment length polymorphism (AFLP) analysis. The three compartments (I to III) of the establishment exhibited significantly different contamination statuses. Compartment I, producing cooked meals, was heavily contaminated with three persistent AFLP types, and compartment II, producing uncooked chilled foods, was contaminated with persistent and non-persistent AFLP types. Only one environmental sample was positive for L. monocytogenes in compartment III, producing heat-treated ready-to-eat products. The persistent contamination appears to be influenced by the cleaning routines, product types and lack of compartmentalisation in facilities producing cooked meals. The reconstruction of the production line in compartment II resulted in the elimination of two persistent AFLP types. The survival of five L. monocytogenes strains was studied in dry-fermented sausages prepared using two different starter cultures with or without a bacteriocin- producing Lactobacillus plantarum DDEN 2205 strain. L. monocytogenes was detected throughout the ripening process in sausages containing no bacteriocin- producing strain. The use of one starter with a high concentration or another starter with a low concentration of bacteriocin-producing culture resulted in L. monocytogenes-negative sausages after 17 days of ripening. Differences in survival were found among the L. monocytogenes strains. Two of the strains survived in sausages with bacteriocin-producing cultures better than the other strains, whereas two other strains were inhibited by all the cultures used. Bacteriocin-producing strains provide an appealing hurdle in dry sausage processing, but differences in survival of L. monocytogenes strains require the use of other hurdles as well. The acid and heat tolerance of 17 persistent and 23 non-persistent L. monocytogenes strains were studied. L. monocytogenes strains exhibited large variation in both acid and heat tolerance. The persistent strains exhibited higher tolerance to acidic conditions than the non-persistent strains, but significant differences in heat tolerance between persistent and non-persistent strains were not detected. Acid tolerance may have an effect on the persistence of L. monocytogenes contamination. Due to the great differences in acid and heat tolerances between L. monocytogenes strains, preventive measures should be designed to be effective against the most tolerant strains. Ultrasonic cleaning was tested on three conveyor belt materials: polypropylene, acetal and stainless steel at two temperatures and two cleaning times with two cleaning detergents. Conveyor belt materials were soiled with milk-based soil and three L. monocytogenes strains. The ultrasonic cleaning was efficient for cleaning conveyor belt materials, but the reduction of L. monocytogenes was significantly greater in stainless steel than in plastic materials. Cleaning treatments with potassium hydroxide detergent reduced L. monocytogenes more than combined 3 potassium and sodium hydroxide detergent. The ultrasonic cleaning of a conveyor belt was further studied by building a pilot-scale conveyor with an ultrasonic cleaning bath. A piece of the stainless steel conveyor belt was contaminated with meat-based soil and three L. monocytogenes strains. The detachment of L. monocytogenes from the conveyor belt caused by the ultrasonic treatment was significantly greater than without ultrasound. Ultrasonic cleaning efficiency was tested with different cleaning durations and temperatures. In both studies, lengthening of the treatment time did not significantly increase the detachment of L. monocytogenes. However, an increase in temperature improved the effect of the ultrasonic treatment significantly. Ultrasonic cleaning for 10 s at 50 °C reduced L. monocytogenes counts by more than 5 log units. These results indicate that the ultrasonic cleaning of conveyor belts is effective even with short treatment times. 4 ACKNOWLEDGEMENTS This study was performed at the Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, during 2002-2006. The financial support of the National Technology Agency of Finland (40425/02) is gratefully achnowledged. University of Helsinki, Doctoral School in Biological, Environmental and Food sciences is acknowledged for supporting the writing of this dissertation with dissertation completion grant (31/1/2015), which made full-time writing possible for two months in late autumn 2015. My supervisors professor Hannu Korkeala and docent Janne Lundén are acknowledged for all their support and guidance. I thank professor Hannu Korkeala for introducing me into the field of food hygiene and having confidence in completion of this project during all these years. Docent Janne Lundén is thanked for sharing your knowledge, fruitful discussions and all those cups of coffee. Professor Marcello Trevisani and docent Laura Raaska are acknowledged for reviewing the thesis. Stella Thompson is thanked for carefully revising the English language of the manuscript. All my co-writers professor Johanna Björkroth, Gun Wirtanen, Ari Hörman, Sanna Hellström and Riikka Keto-Timonen are warmly thanked for their contributions and sharing their knowledge. I want to thank the entire personnel of the department for enthusiastic and supporting atmosphere at the department. I thank especially the Listeria researchers Tiina Autio and Annukka Markkula, and neighbour in fourth floor and good listener Riikka Laukkanen-Ninios. Kirsi Ristkari, Raija Keijama and Anu Seppänen are acknowledged for great laboratory assistance. I am grateful to Heimo Tasanen for all the assistance with the huge ultrasonic cleaning device. Johanna Sepppälä is thanked for always knowing where, who and when. I also thank Nina Aalto who participated in this project as part of her licenciate thesis. I want to thank my colleagues and friends at Evira, with whom I have been working for the last years. I thank Auli and Leena for enabling my study leave, Carmela, Eva, Eeva, Eveliina, Karolina, Tiina, Noora, Marko, Elina, Annika, Raija, Marina and Paula for lively and stimulating conversations. Special thanks to Anne for refreshing evenings at the horse racetrack. I want to thank my parents for always supporting me, since my decision to become a veteriarian at the age of four. I thank my husband Petri for practical advice and always being there for me. My beloved son Aaron, thank you for your love and supportive warm hugs. 5 CONTENTS ABSTRACT ........................................................................................................ 3 ACKNOWLEDGEMENTS .................................................................................. 5 CONTENTS ....................................................................................................... 6 LIST OF ORIGINAL PUBLICATIONS ................................................................ 9 ABBREVIATIONS ............................................................................................ 10 1 INTRODUCTION ..................................................................................... 12 2 REVIEW OF THE LITERATURE ............................................................. 13 2.1 Listeria spp. and Listeria monocytogenes ....................................... 13 2.1.1 Listeria monocytogenes ............................................................ 13 2.1.2 Detection and characterisation .................................................. 14 2.1.3 Listeriosis .................................................................................. 17 2.2 Transmission of Listeria monocytogenes ........................................ 20 2.2.1 Sources ..................................................................................... 20 2.2.2 Contamination in the food industry ............................................ 21 2.2.3 L. monocytogenes
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