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Continuous High Pressure Processing of Liquid Foods: An CONTINUOUS HIGH PRESSURE PROCESSING OF LIQUID FOODS: AN ANALYSIS OF PHYSICAL, STRUCTURAL AND MICROBIAL EFFECTS by GEORGE A. CAVENDER (Under the Direction of William L. Kerr) ABSTRACT While the effects of high pressure on the safety and quality of food have been studied occasionally for over one hundred years, it is only recently that the widespread study and use of the technology has become feasible. One of the more interesting and least studied type of high pressure processing is continuous high pressure processing (CHPP), sometimes referred to as "high pressure homogenization" or "dynamic Pascalization." The current work examines the history and work in the field to date and goes on to investigate the effects of various CHPP systems on the microbial, physical, structural and sensory properties of liquid foods. Because the high shear conditions created in the release component(s) of a CHPP system generate significant heat, it has often been difficult to separate the anti-microbial effects of pressure and shear from those of temperature, particularly with regard to vegetative cells. By using a modified valve with inline cooling, the instantaneous temperature rise was dramatically lessened, showing that only a modest amount of inactivation results from the increased pressure and shear. The work further explains the effects of microfluidization, a type of CHPP system based upon a fixed geometry pressure release component, on ice cream mixes and the ice creams made from those mixes. Microfluidization is shown to effect changes in the texture, melting properties and viscosity of finished ice cream and to thereby improve the sensory characteristics of the same. It is later shown that the changes are evoked on a microstructural level, with visible differences apparent in electron micrographs, and that these changes affect the particle size distribution, apparent viscosity and dynamic rheology with treated samples showing more uniform particle size, significantly higher viscosity and more solid-like behavior than untreated samples. INDEX WORDS: High Pressure Processing, Microfluidization, Inactivation, Sensory, Rheology, Viscosity, Microstructure CONTINUOUS HIGH PRESSURE PROCESSING OF LIQUID FOODS: AN ANALYSIS OF PHYSICAL, STRUCTURAL AND MICROBIAL EFFECTS by GEORGE A. CAVENDER B.S.B.E, The University of Georgia, 2004 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPY ATHENS, GEORGIA 2011 © 2011 George A. Cavender All Rights Reserved CONTINUOUS HIGH PRESSURE PROCESSING OF LIQUID FOODS: AN ANALYSIS OF PHYSICAL, STRUCTURAL AND MICROBIAL EFFECTS by GEORGE A. CAVENDER Major Professor: William L Kerr Committee: Mark A. Eiteman Joseph F. Frank Robert L. Shewfelt Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August, 2011 iv DEDICATION Why this page is optional, I'll never know. I dedicate this work to those who struggle, those who strive, those who stumble and fall, to those who stand back up and keep on going and most importantly to those people, beings, ideas and things that help us along the way... v ACKNOWLEDGEMENTS Newton is credited with saying “If I have seen further it is only by standing on the shoulders of giants.” I agree fully with that sentiment and add that I also had a lot of help climbing up onto those shoulders. I’d like to thank my parents, not only for having rolled the dice and won my genome, but also for the things they did that led me to this point. So Dad, thanks for stressing the need to be educated, even if you didn't understand why I chose to keep at it for so long. And thanks for watching science fiction with me, so that I could be inspired by the idea of what the future could be. Mom, thanks for teaching me to read, and for all those hours spent ferrying me to school, or some program or the library. Both of you, thanks for all the sacrifices and know that I have no hard feelings about the mistakes you made- I hope you feel the same about my mistakes, after all it was the first time for both of us. I'd like to thank my girlfriend for standing by me these past mumble-mumble years and for all the support (both emotional and though it is embarrassing to admit, financial) you've given me. Thanks to the graduate faculty of the UGA food science department for taking a chance on my admission and master's bypass. I hope that you look back upon those decisions and feel it was worthwhile. Thanks to my advisor, Dr. Bill Kerr, for giving me the autonomy to pursue the project I wanted (and for somehow finding the funds to make it happen). Thanks to Dr. Rakesh Singh for helping with those funds, and for being so available anytime I had a problem. Thanks to Carl Ruiz, my compatriot in so many projects, for the help and advice you've given- even if I didn't always take it, it was nice of you to share. Thanks to Dr. Shields and Dr. Fan from vi the UGA Center for Ultra-Structural Research for your assistance with my TEM work. Thanks to Mr. Cash and Mr. Mulwee from the Clemson University EM lab for similar assistance with my SEM work. And finally, thanks to my friends and lab-mates for the support and for the positive environment. If I've left anyone out, my deepest apologies- I did write this last minute. vii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS.................................................................................................v LIST OF TABLES...............................................................................................................x LIST OF FIGURES ........................................................................................................... xi CHAPTER 1 INTRODUCTION TO THE CURRENT WORK References....................................................................................................5 2 CONTINUOUS HIGH PRESSURE PROCESSING OF LIQUID FOODS: A REVIEW ........................................................................................................7 Abstract........................................................................................................8 Introduction..................................................................................................9 Common Definitions..................................................................................11 Components of a CHPP System ................................................................12 Mechanisms Involved in CHPP.................................................................15 Effects of CHPP.........................................................................................17 Conclusions................................................................................................35 Further Readings........................................................................................36 References..................................................................................................38 Figures and Tables.....................................................................................42 viii 3 INACTIVATION OF VEGETATIVE CELLS BY CONTINUOUS HIGH PRESSURE PROCESSING: NEW INSIGHTS ON THE CONTRIBUTION OF THERMAL EFFECTS AND RELEASE DEVICE ..................................47 Abstract......................................................................................................48 Introduction................................................................................................49 Materials and Methods...............................................................................51 Results and Discussion..............................................................................55 Conclusions................................................................................................57 References..................................................................................................59 Figures and Tables.....................................................................................61 4 MICROFLUIDIZATION OF FULL-FAT ICE CREAM MIXES: EFFECTS OF GUM STABILIZER CHOICE ON PHYSICAL AND SENSORY CHANGES.......................................................................................................67 Abstract......................................................................................................68 Introduction................................................................................................69 Materials and Methods...............................................................................71 Results and Discussion..............................................................................76 Conclusions................................................................................................80 References..................................................................................................82 Figures and Tables.....................................................................................84 5 MICROFLUIDIZATION OF FULL-FAT ICE CREAM MIXES: RHEOLOGY AND MICROSTRUCTURE ...................................................91 Abstract......................................................................................................92 ix Introduction................................................................................................93 Materials and Methods...............................................................................95 Results and Discussion..............................................................................98
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