STABILITY AND RELEASE OF MODEL AROMA COMPOUNDS A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Ségolène Leclercq IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Adviser: Gary A. Reineccius September 2008 Acknowledgments My experience in Graduate School at the University of Minnesota was not just about science and writing a thesis. It was also a chance to meet a variety of people, and learn about different cultures, different points of view and different philosophies. I have learned so much in these last four years. None of this would have happened without Gary Reineccius, who served as my adviser and mentor. I would like to thank him deeply for sharing his expertise on flavor and academic life, for his support and patience through the years and his friendship. I have also learned so much from his open-mind and his philosophy on life, or “work should not be the only thing you do in life”. This will stay with me for many years to come. I would like to thank Nestle, and Nestle Product Technology Center, Orbe, Switzerland for the project’s financial support. I would like to acknowledge Imre Blank, Josef Kerler and Remy Liardon from Orbe for their scientific guidance, as well as Christian Lindinger and Philippe Pollien from the Nestle Research Center, Lausanne, for their help in release analysis. I would like to give a special thank to Christian Milo, who served as a committee member for my examination, for his support, advice and friendliness. I will definitely remember a great dinner in Boston. I would like to acknowledge the Gordon Memorial Foundation for the scholarship they awarded me in 2007. Another special thank you goes to my committee members, Ted Labuza, Ulrike Tschirner and Ron Siegel, for their support and critical minds on my project. I would like to show gratitude to other faculty in the Food Science department and other departments. I discovered with the years how much I like learning. In particular, I would like to mention Roger Moon who helped me think through my experimental design, and Deb Wingert who broadened my horizon about teaching and learning. i I appreciated all the help and support from the Food Science department administrative staff (Geri, Sue, Sue, Michelle, Susan and Lori) who answered all my endless questions. Life in the flavor lab would not have been the same without all the lab mates present. I would like to thank all of them, former and current, for sharing their time, jokes, chocolate and ideas together. I would like to give a special warm thanks to Katie, Mike, Anna-Katharine and Sarah; I enjoyed learning about anything from and with them, and laughing about it; and JP for being JP. I will certainly miss them. I want to thank all my friends, met in France or here, for their friendship and emotional support. It meant a lot to me. I want to thank particularly Adriana, who also introduced me to Israeli dancing and taught me Spanish with so much patience. Lastly I am very grateful to my family and relatives, who supported me without limits through this adventure. I am thankful to my parents and grandparents for their ever support and faith in me. I am thankful to my siblings for their help, laughs, online photos and discussions; in particular to Adeline for her endless statistical help. I want to give also a warm thank you to the Schwartz family who accepted me as me, and became my American family. Lastly I want to thank Edan, for supporting my school-related grumpiness, being so kind, fun, and so unpredictable, and cooking the most amazing 7-veggie dinners. ii Abstract Overall, this thesis has two parts: The first evaluated the use of complex coacervation for aroma encapsulation to control aroma release. The second part focused on improving the storage stability of encapsulated aroma compounds by different techniques. In part 1 coacervate capsules were formed using gelatin and gum acacia as wall materials and either a liquid or solid core (aroma compounds). A brief storage study compared the oxidation barrier properties of coacervate capsules and spray dried powder. No significant oxidation of limonene was detected in coacervate capsules after 25 days, whereas significant oxidation was found in spray dried powder. Then the effect of coacervate capsule properties on volatile release (measured using proton transfer reaction MS) was studied. No significant effect of glutaraldehyde cross-linking or wall:core ratio on aroma release was found. Comparing aroma release data from coacervates to their release from a spray dried material, no significant difference in release pattern could be found. However, testing temperature, aroma volatility and hydrophobicity were found to be significant but not predictive factors. In the second part of this thesis, the storage stability (12 weeks at 30 ˚C) of volatiles was found to be significantly decreased by the presence of oxygen and the type of matrix in which compounds are diluted (water or various edible oils). Medium chain triglycerides, sunflower oil and soy bean oil were evaluated as the edible oils. Water was found to have a highly significant detrimental effect on volatile stability compared to the oils. The type of oil matrix was also found to significantly affect storage stability. No correlation could be detected between the oxidation level of the oil and the oxidation pattern of the volatiles. iii The stabilization of volatiles during storage was attempted by physically removing oxygen from the storage environment (< 0.5 %) and by adding selected antioxidants (rosemary extract, vitamin E, vitamin C, BHA and BHT). The addition of antioxidants in oil matrices showed compound specific action and a significant detrimental effect in some cases. Overall, no system would offer optimal protection for all aroma compounds studied simultaneously. iv Thesis Flow Chart Chapter 1 Literature Review Chapter 2 Chapter 4 Making coacervates Parameters affecting volatile Determining critical parameters storage stability Choosing aroma compounds Choice of analytical method Standardize manufacturing Choice of control process Choice of compounds of interest Develop drying method Characterization of capsules obtained Chapter 5 Use of delta-tocopherol to stabilize aroma compounds during storage Choice of antioxidant Chapter 3 Choice of lipid matrix Measure of release response Choice of analytical method Set up Effect of lipid oxidation level on Choice of controls stability Max Intensity - Time to Max intensity Persistence - % of Imax at t = 0.5 min Chapter 6 Comparison of selected antioxidants to stabilize aroma Effects of capsule characteristics on compounds real-time release Choice of antioxidants Choice of lipid matrix Comparison with controls Strategies to stabilize aroma compounds during storage v Table of Contents Acknowledgments............................................................................................... i Abstract.............................................................................................................. iii Thesis Flow Chart............................................................................................... v Table of Contents ............................................................................................... v Table of Contents .............................................................................................. vi List of Figures.................................................................................................. xiii List of Tables .................................................................................................. xvii Chapter 1: Literature Review............................................................................. 1 1. Encapsulation ............................................................................................. 2 1.1. Plating .................................................................................................... 2 1.2. Spray chilling and spray cooling ............................................................. 3 1.3. Liposome................................................................................................ 3 1.4. Molecular inclusion, also called inclusion complexation ......................... 3 1.5. Spray drying ........................................................................................... 4 1.6. Coacervation .......................................................................................... 4 2. Coacervation ............................................................................................... 4 2.1. Principle.................................................................................................. 4 2.2. Materials used ........................................................................................ 5 2.3. Formation of microcapsules by complex coacervation: state of the literature ........................................................................................................ 7 2.4. Applications and uses of coacervated microcapsules ............................ 8 vi 3. Aroma release ............................................................................................. 9 3.1. Importance of aroma release.................................................................. 9 3.2. Release from encapsulated material ...................................................... 9 3.3. Methods for measuring release ............................................................ 11 4. Storage