DISSERTATION SENSORY and FUNCTIONAL PROPERTIES of MONOSODIUM GLUTAMATE Submitted by Maria Elizabeth Giovanni Department of Food
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DISSERTATION SENSORY AND FUNCTIONAL PROPERTIES OF MONOSODIUM GLUTAMATE Submitted by Maria Elizabeth Giovanni Department of Food Science and Human Nutrition In partial fulfillment of the requirements For the degree of Doctor ofPhilosophy Colorado State University Fort Collins, Colorado Summer2002 1111111111111111 U18402 4973681 Qr S(Od- ,65 (;40; zoc)Z \"'".\~5 COLORADO STATE UNIVERSITY ~/1 November 2, 2001 WE HEREBY RECOMMEND THAT THE DISSERTATION PREPARED UNDER OUR SUPERVISION BY MARIA ELIZABETH GIOVANNI ENTITLED SENSORY AND FUNCTIONAL PROPERTIES OF MONOSODIUM GLUTAMATE BE ACCEPTED AS FULFILLING IN PART REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PIDLOSOPHY. Committee on Graduate Work A~ vr;~,fi2 ~/ Co-Advisor Department~ev&JC~) · ead COLORADO STAT~!JNIV. UBRAR:ES ABSTRACT OF DISSERTATION Sensory and Functional Properties of Flavor Potentiators Flavor potentiators have been used for centuries to improve food flavor. However, neither the taste transduction mechanisms nor the behavior of flavor potentiators in food are fully understood. The objectives of this research were: 1. To determine the relationship between salivary glutamate and perception ofMSG and NaCl; 2. To characterize the time-intensity profiles (TI) of flavor potentiators; and, 3. To determine the effects of heat treatment and pH on levels ofL-glutamic acid in simple food systems. The first study consisted of collecting whole mouth saliva and determining thresholds to and perceived intensities ofMSG and NaCl. A preliminary experiment indicated that perception ofMSG may be influenced by salivary glutamate, gender, and ethnicity. The principal study with 60 subjects found no effect of ethnicity or gender on salivary glutamate or sodium levels. Female Asians had higher salivary sodium and rated the lower concentrations ofNaCl as more intense. Psychophysical measures of MSG and NaCI were independent of salivary levels. iii Twenty subjects, trained in TI methods, evaluated 20 samples of MSG, IMP, and GMP, singly and in combination. The TI profiles generated were atypical of other taste modalities. Time to maximum intensity was brief, followed by a plateau phase at maximum intensity with a long aftertaste. Sample intensities varied significantly, with mixtures of 10 and 5 mM MSG and 2.5 mM IMP and GMP having highest intensity and duration. These results indicated that flavor potentiators may increase total flavor in the mouth. Synergism among flavor potentiators was demonstrated. To determine the effect of pH and heat on L-glutamic acid, 0.1% MSG was added to eleven simple food systems. Percent recovery was highest for tomatoes and lowest for beef broth. Fish broth and tomatoes had higher recoveries at pH 6 than pH 3; thus, pH altered L-glutamic acid levels. No effect of heat on L-glutamic acid levels was found. The sensory and functional behavior ofMSG is governed, in part, by the individuality of the subject, its temporal response, and the food system in which it is used. Maria Elizabeth Giovanni Department of Food Science and Human Nutrition Colorado State University Fort Collins, CO 80523 Summer2002 iv ACKNOWLEDGEMENTS The guidance and knowledge of my committee, Drs. Joseph Maga, Martha Stone, Kenneth Allen, and Sue Kinnamon was essential for the completion of this program. As my advisor and co-advisor, I am especially grateful to Dr. Maga and Dr. Stone. I also thank the staff and faculty of the Department of Food Science and Human Nutrition for their answers to my many questions and asssitance to me, both as a student and as a teaching assistant in the department. To the 102 people who willingly participated as subjects in the various sensory test of this research, thank you! These studies were conducted in several laboratories. I appreciate Dr. Maga's support and resources for much of the research, including incentives to pay subjects and support to present a paper at the Institute of Food Technologists' Annual Meeting. Dr. Miriam Linschoten gave of her knowledge and her lab at the Rocky Mountain Taste and Smell Center at the University of Colorado Health Sciences Center; the timely advise of Robin Michaels at RMTSC is also appreciated. The presentation of this research was supported by the Association for Chemoreception Sciences. The time-intensity research was done under the advisement of Dr. Jean-Xavier Guinard in the Department of Food Science and Technology at the University of California, Davis. I appreciate his support of this work. During my work at Davis, I am especially indebted to Dr. Ann Noble, Dr. Gerald Russell, Rie Ishii, and Charlene Wee. The presentation of these findings at the Third Pangborn Symposium was supported by V and S Vina and Spirit. The flavor potentiators for this work were provided by Ajinomoto. The friendship and support of my classmates was vital, as was the love from my husband Ted and my sons, Vincent and Paul. v DEDICATION This manuscript and the effort put into it is dedicated to Professor Rose Marie Pangborn, one ofthe pioneers of sensory evaluation. She was committed to the evolution of sensory evaluation as a scientific discipline and to the growth of her students,ofwhich I was fortunate to be. May her commitment and her sense of humor continue through those of us who have been influenced by her. vi TABLE OF CONTENTS Chapter 1. Introduction .. .. ... .. ... 1 Chapter 2. Literature Review.................................................................... 5 I. Chemistry of Flavor Potentiators........................................................ 5 A. History of Flavor Potentiators........................................................ 5 B. Definition........................................................................................ 7 C. Production and Consumption of Flavor Potentiators..................... 9 1. Monosodium Glutam.ate............................................................... 9 2. 5'-ribonucleotides ........................................................................ 12 3. Other Flavor Potentiating Compounds . .. .. .. .. ... ............. 17 D. Safety of Flavor Potentiators .......................................................... 22 1. Glutamate Metabolism ................................................................. 23 2. MSG Symptom Complex ............................................................. 26 3. Regulatory Status and Labeling Requirements ............................ 33 E. Chemistry of Monosodium Glutamate ........................................... 3 5 1. Properties ...................................................................................... 3 5 2. Analytical Methods ...................................................................... 39 3. Levels in Food .............................................................................. 42 4. Chemical Interactions .................................................................. 45 5. Stability of Flavor Potentiators .................................................... 52 II. Sensory Properties of Flavor Potentiators ......................................... 57 A. Flavor Perception . .. .. .. 57 1. Umami: A Fifth Primary Taste? ................................................. 57 2. Threshold Measurements ............................................................. 62 3. Quality and Intensity of Flavor Potentiators in Water and Food Systems . 66 4. Hedonic Evaluations and Impact on Consumption...................... 76 5. Time-Intensity Studies ................................................................. 82 B. Taste Transduction Mechanisms .................................................... 94 1. Anatomy ....................................................................................... 95 vii Table of Contents, continued 2. Receptor Mechan.sims .................................................................. 97 3. Structure-Function Theories ........................................................ 105 C. Saliva .............................................................................................. 107 1. Function an.d Composition ........................................................... 107 2. Role of Saliva in Taste Perception ............................................... 115 Chapter 3. The Relationship Between Salivary Composition an.d Taste Perception of Flavor Potentiators ........................................... 124 I. Study 1. Preliminary Experiment ...................................................... 124 A. Materials an.d Meth.ods ................................................................... 124 1. Subjects ....................................................................................... 124 2. Procedures .................................................................................... 125 3. Chemical Analysis ....................................................................... 128 4. Statistical Analyses ...................................................................... 129 B. Results ........................................................................................... 129 II. Study 2. Principal Experiment. ......................................................... 13 5 A. Materials an.d Meth.ods ................................................................... 13 5 1. Subjects ........................................................................................ 135 2. Procedure ...................................................................................... 13 6 3. Stimuli .........................................................................................