Photocatalytic Antimicrobial Coating for Food Contact Surfaces
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PHOTOCATALYTIC ANTIMICROBIAL COATING FOR FOOD CONTACT SURFACES ________________________________________ A Dissertation presented to the Faculty of the Graduate School at the University of Missouri-Columbia ________________________________________ In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy ________________________________________ by EDUARDO TORRES DOMÍNGUEZ Dr. Heather K. Hunt and Dr. Azlin Mustapha, Dissertation Supervisors JULY 2020 The undersigned, appointed by the dean of the Graduate School, have examined the dissertation entitled PHOTOCATALYTIC ANTIMICROBIAL COATING FOR FOOD CONTACT SURFACES presented by Eduardo Torres Domínguez, a candidate for the degree of Doctor of Philosophy, and hereby certify that, in their opinion, it is worthy of acceptance. _______________________________________ Associate Professor Heather K. Hunt, chair _______________________________________ Professor Azlin Mustapha, co-chair _______________________________________ Assistant Professor Bret Ulery, member _______________________________________ Assistant Professor Karl D. Hammond, member _______________________________________ Associate Professor David Mendoza, outside member ACKNOWLEDGMENTS I thank all the students who helped me with this academic research. I list them below in alphabetical order. Abigail Penfield University of Missouri From Fall 2019 to Spring 2020 Annika Hylen Saint Louis University Summer 2019 Kritika Sigdel David H. Hickmann HS Summer 2018 Liam Adams University of Missouri Fall 2017 Marisa Pina Truman University Summer 2018 Miki Hodel University of Missouri Fall 2019 Phong Nguyen University of Missouri From Fall 2017 to Spring 2019 I thank my academic advisers Dr. Heather K. Hunt and Dr. Azlin Mustapha for their guidance and support. Additionally, I thank the U.S. Department of State through the Bureau of Education and Cultural Affairs, the Fulbright Program, and the Comisión México Estados Unidos para el Intercambio Educativo y Cultural (Comexus) for their financial support through the Fulbright García Robles scholarship for Mexican students. ii TABLE OF CONTENTS ACKNOWLEDGMENTS .................................................................................................. ii LIST OF FIGURES ............................................................................................................ v LIST OF TABLES ........................................................................................................... viii LIST OF ABBREVIATIONS ............................................................................................. x ABSTRACT ....................................................................................................................... xi Chapter 1. INTRODUCTION ...................................................................................................... 1 2. THE CONTEXT OF PHOTOCATALYTIC ANTIMICROBIAL COATINGS IN FOOD CROSS-CONTAMINATION PREVENTION: A LITERATURE REVIEW ..... 12 2.1. Cross-Contamination Prevention on Food Contact Surfaces ....................................... 16 2.2. Food Contact Surfaces Cross-Contamination: Prevention Practices ............................ 18 2.2.1. Prevention Practices Via Cleaning Methods ..........................................................................20 2.2.2. Prevention Practices Via Sanitizing Methods ........................................................................22 2.2.3. Prevention Practices Via Sterilizing Methods ........................................................................30 2.2.4. Concluding Remarks ..............................................................................................................30 2.3. Photocatalytic Antimicrobial Coatings for Food Contact Surfaces ............................. 30 2.3.1. The Sol-Gel Method ...............................................................................................................33 2.3.2. Influence of the Sol-Gel Synthetic Factors on Photocatalytic Activity .................................36 2.3.3. Influence of the Sol-Gel Synthetic Factors on Mechanical Properties ...................................37 2.4. Food-Borne Pathogens and Related Outbreaks ............................................................ 38 3. ANTIMICROBIAL COATINGS FOR FOOD CONTACT SURFACES: LEGAL FRAMEWORK, MECHANICAL PROPERTIES, AND APPLICATIONS ................... 43 3.1. Legal Framework .......................................................................................................... 44 3.2. How Legal Requirements Can Be Translated into Technical Metrics ......................... 51 3.3. Mechanical Properties of Antimicrobial Coatings ....................................................... 52 3.3.1. Adhesion .................................................................................................................................55 3.3.2. Abrasion .................................................................................................................................57 3.3.3. Hardness, fracture toughness, and related properties .............................................................59 3.3.4. Hydrophobicity .......................................................................................................................61 3.3.5. Microstructure ........................................................................................................................63 3.3.6. Migration ................................................................................................................................64 3.3.7. Surface roughness ...................................................................................................................69 3.4. Potential applications of antimicrobial coatings for food contact surfaces .................. 75 3.4.1. Anti-adhesion .........................................................................................................................78 3.4.2. Antimicrobial-Loaded ............................................................................................................78 3.4.3. Contact Inactivation ................................................................................................................79 3.4.4. Photocatalytic .........................................................................................................................80 3.4.5. Multifunctional .......................................................................................................................80 3.5. Concluding Remarks .................................................................................................... 81 4. OPTIMIZATION OF COATING’S PHOTOCATALYTIC ACTIVITY ................ 82 iii 4.1. Introduction .................................................................................................................. 82 4.1.1. Response Surface Methodology: The Experimental Optimization Process ...........................84 4.2. Materials and Methods ................................................................................................. 89 4.2.1. Design of Experiments ...........................................................................................................89 4.2.2. Screening of Factors Experiment ...........................................................................................90 4.2.3. Quadratic mathematical experiment .......................................................................................91 4.2.4. Coating Fabrication for the Screening of Factors Experiment ...............................................92 4.2.5. Coating Fabrication for the Mathematical Model Determination Experiments .....................93 4.2.6. Coating Fabrication for Nanoindentation Testing ..................................................................93 4.2.7. Photocatalytic Assessment .....................................................................................................93 4.2.8. Characterization of the Coatings ............................................................................................96 4.2.9. Mechanical Characterization of the Coatings .........................................................................98 4.3. Results and Discussion ................................................................................................. 98 4.3.1. Screening of Factors Experiment ...........................................................................................98 4.3.2. Mathematical Model Experiment and Photocatalytic Activity Optimization ......................102 4.3.3. Coating’s Characterization ...................................................................................................103 4.3.4. Coating’s Mechanical Characterization ...............................................................................105 4.3.5. Comparison of the Photocatalytic Activity with Values Reported in the Literature ............110 4.3.6. Local Optimum .....................................................................................................................111 4.4. Concluding Remarks .................................................................................................. 111 5. PHOTOCATALYTICALLY AND MECHANICALLY OPTIMIZED ANTIMICROBIAL COATING FOR FOOD CONTACT SURFACES ........................ 113 5.1. Introduction ................................................................................................................ 113