Natural Inhibition of Listeria Monocytogenes in Ready to Eat Meat
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NATURAL INHIBITION OF LISTERIA MONOCYTOGENES IN READY TO EAT MEAT PRODUCTS by DANITZA MORA-COSSIO (Under the Direction of Romeo T. Toledo) ABSTRACT Ready to eat meat products have been the source for the isolation of some LAB which are known to produce metabolic byproducts with inhibitory activity against spoilage and pathogenic bacteria. Leuconostoc carnosum 4010 was selected as the antimicrobial agent (cells and metabolic products) to be incorporated into an edible film. MIC was 1 ml of LAB cell-free supernatant against ca. 100 CFU/cm2 of Listeria. Inhibitory activity was a synergistic effect of the bacteriocin and lactic acid. Viable LAB cells had an effect after 21 days at 4˚C. The antimicrobial film C, 0.51 ± 0.02 mm thick, demonstrated the highest inhibitory action against L. 2 monocytogenes. After 14 days of treatment, almost 2 log10 CFU/25 cm reductions were achieved from initial Listeria inoculation of 103 CFU/25 cm2. Antimicrobial film is a promising form of active food packaging as a response to the increasing demand for “natural” and “minimally processed” foods. INDEX WORDS: Listeria monocytogenes, lactic acid bacteria, ready to eat meat and active food packaging. NATURAL INHIBITION OF LISTERIA MONOCYTOGENES IN READY TO EAT MEAT PRODUCTS by DANITZA MORA-COSSIO B.S., La Molina National Agrarian University, Perú, 2002 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2006 © 2006 Danitza Mora-Cossio All Rights Reserved NATURAL INHIBITION OF LISTERIA MONOCYTOGENES IN READY TO EAT MEAT PRODUCTS by DANITZA MORA-COSSIO Major Professor: Romeo T. Toledo Committee: Mark A. Harrison Yen-Con Hung Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2006 iv DEDICATION To God who gave me life to live this wonderful experience. To my brother, Erik Mora, who gave me the opportunity to be better; his support, advice and encouragement help me to overcome all the difficulties and achieve my goals. To my parents, Edgar A. Mora and Lourdes A. Cossio, whose love and strong belief in me gave me the courage and strength to reach my dreams. To my extended family who helped me in different ways and to my special friends who shared with me wonderful memories. This work is also dedicated to all my teachers who gave me guidance and encouragement. v ACKNOWLEDGEMENTS I would like to express my gratitude and admiration to Dr. Romeo T.Toledo, who gave me guidance and support during the development of this project. To Dr. Mo Toledo, whose company and encouragement made my life even more enjoyable. My sincere and eternal gratitude to both of you. I would like to thank Dr. Harrison for his patient and constant guidance and Dr. Hung for his support in being part of my committee. I would also like to thank Revis Chmielewski and Ruth Ann Morrow for their help during the laboratory work and for their valuable advice. Thank you. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS.............................................................................................................v LIST OF TABLES......................................................................................................................... ix LIST OF FIGURES ........................................................................................................................ x CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW .....................................................1 1.1 Purpose of the study ............................................................................................1 1.2 General characteristics of Listeria monocytogenes .............................................3 1.2.1 Taxonomy.........................................................................................................4 1.2.2 Growth characteristics......................................................................................4 1.2.3 Ecology.............................................................................................................7 1.2.4 Virulence properties .........................................................................................7 1.2.5 Disease syndrome.............................................................................................9 1.2.6 Infectious dose................................................................................................10 1.3 Lactic acid bacteria............................................................................................10 1.3.1 Microbiology..................................................................................................11 1.3.2 Taxonomy.......................................................................................................11 1.3.3 Antimicrobial components – Mode of action.................................................12 1.4 Regulatory background .....................................................................................16 1.5 Ready to eat (RTE) meat and poultry products.................................................18 vii 1.6 Lactic acid bacteria in RTE meats and their competitive inhibition toward L. monocytogenes .............................................................................................20 1.7 Routes of Listeria contamination in food processing facilities.........................25 1.8 Recalls in the meat and poultry industry...........................................................27 1.9 Improvements in food safety – Antimicrobial food packaging.........................28 1.10 References .......................................................................................................31 2 THE INHIBITORY EFFECT OF SELECTED LACTIC ACID BACTERIA AND ITS MAIN METABOLIC PRODUCTS ON THE GROWTH OF LISTERIA MONOCYTOGENES...............................................................................................40 Abstract ...................................................................................................................41 Introduction .............................................................................................................42 Materials and Methods ............................................................................................44 Results and Discussion............................................................................................51 Conclusions .............................................................................................................54 References ...............................................................................................................65 3 CONTROL OF LISTERIA MONOCYTOGENES IN READY TO EAT MEAT PRODUCTS USING ANTIBACTERIAL FILM ...................................................67 Abstract ...................................................................................................................68 Introduction .............................................................................................................69 Materials and Methods ............................................................................................71 Results and Discussion............................................................................................79 Conclusions .............................................................................................................83 References ...............................................................................................................88 viii 4 SUMMARY AND CONCLUSIONS ..........................................................................90 ix LIST OF TABLES Page Table 2.1: Effect of L. carnosum ATCC 49367 against L. monocytogenes Scott A (Level: 101, 102 and 103 CFU/ml).......................................................................................................56 Table 2.2: Effect of L. plantarum ATCC 8014 against L. monocytogenes Scott A (Level: 101, 102 and 103 CFU/ml) .............................................................................................................57 Table 2.3: Effect of L. carnosum 4010 against L. monocytogenes Scott A (Level: 101, 102 and 103 CFU/ml) ..........................................................................................................................58 Table 2.4: Indirect measurement of Listeria inhibition by bacteriocin from L. carnosum 4010...59 Table 2.5: Inhibitory effect of bacteriocin from L. plantarum ATCC 8014, L.carnosum ATCC 49367 and L. carnosum 4010..........................................................................................59 Table 3.0: Different composition for cast films.............................................................................75 Table 3.1: Final thickness of films B and C (Applicator vessel settings: 1.0 and 1.2mm, respectively)....................................................................................................................84 2 Table 3.2: Viable cells (log10 CFU/25 cm ± S.D.) of L. monocytogenes at 0, 3, 7 and 14 days in turkey roll after antimicrobial film application...............................................................84 x LIST OF FIGURES Page Figure 2.1: Inhibition zones: L. carnosum 4010 and L. carnosum ATCC 49367 in MRS and TSBYE broth.................................................................................................................60 Figure 2.2: Effect of bacteriocin from L. carnosum 4010 and ATCC 49367 (Zoom of Well #2 and #3 from Figure