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Designing Novel Emulsion Performance by Controlled Hetero-Aggregation of Mixed Biopolymer Systems Yingyi Mao University of Massachusetts Amherst, [email protected]

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Designing Novel Emulsion Performance by Controlled Hetero-Aggregation of Mixed Biopolymer Systems Yingyi Mao University of Massachusetts Amherst, Ericamao@Gmail.Com University of Massachusetts Amherst ScholarWorks@UMass Amherst Open Access Dissertations 9-2013 Designing Novel Emulsion Performance by Controlled Hetero-Aggregation of Mixed Biopolymer Systems Yingyi Mao University of Massachusetts Amherst, [email protected] Follow this and additional works at: https://scholarworks.umass.edu/open_access_dissertations Part of the Food Science Commons Recommended Citation Mao, Yingyi, "Designing Novel Emulsion Performance by Controlled Hetero-Aggregation of Mixed Biopolymer Systems" (2013). Open Access Dissertations. 826. https://doi.org/10.7275/0pym-jj83 https://scholarworks.umass.edu/open_access_dissertations/826 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Open Access Dissertations by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. ! ! ! ! ! ! ! ! ! DESIGNING NOVEL EMULSION PERFORMANCE BY CONTROLLED HETERO-AGGREGATION OF MIXED BIOPOLYMER SYSTEMS A Dissertation Presented by YINGYI MAO Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY September 2013 The Department of Food Science © Copyright by Yingyi Mao 2013 All Rights Reserved DESIGNING NOVEL EMULSION PERFORMANCE BY CONTROLLED HETERO-AGGREGATION OF MIXED BIOPOLYMER SYSTEMS A Dissertation Presented by YINGYI MAO Approved as to style and content by: ________________________________ D. Julian Mcclements, Chair ________________________________ Paul Dubin, Member ________________________________ Hang Xiao, Member _____________________________ Eric A. Decker, Department Head Department of Food Science DEDICATION To my supportive family ACKNOWLEGEMENT First and Foremost, I acknowledge, with gratitude, my debt of thanks to my advisor, Dr. Julian McClements, for his academic guidance and assistant in the past four years. His attitude and passion for research really help me to understand the meaning of being a scientist and also encourage me to pursue my academic goal in the future. I would also like to thank my committee members: Dr. Xiao and Dr. Dubin, for serving on my committee and their academic suggestion and foresight for my research. All special thanks go to all Julian Lab members. This thesis would not have been possible without your help. In particular, I would like to than Jean Alamed for her support and friendship in the past four years. She was the one person I would always go for help and advice. I would also thank Cheryl, Alison, Cheng, Jiajia, Ying, Yan, Mingru, Tanu for helping me for my research and my life. To Fang, thanks to your patience for listening my complaints and encouraging me all the time. Lastly, I would express my deepest appreciation to my family. To my parents, thank you for all your sacrifices to help me to achieve so many goals and dreams in my life. I feel so blessed for having you. To my husband Dingqiang Li, whenever I am confused and in difficulties, you always know how to make things become easy and never stop supporting me. I am so lucky to have you. Thank you for all the people helped me in my life. v ABSTRACT DESIGNING NOVEL EMULSION PERFORMANCE BY CONTROLLED HETERO-AGGREGATION OF MIXED BIOPOLYMER SYSTEMS SEPTEMBER 2013 YINGYI MAO, B.S., NORTHWEST AGRICULTURE AND FORESTRY UNIVERSITY M.S., SICHUAN UNIVERSITY Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor D. Julian McClements The increase in obesity and overweight in many countries has led to an upsurge of interest in the development of reduced fat food products. However, the development of these products is challenging because of the many roles that fat droplets normally plays in these food products, including contributing to flavor, texture, appearance, and bioactivity. The goal of this research was to develop novel reduced-fat emulsions based on hetero-aggregation of oppositely charged food-grade colloidal particles or polymers. Initially, lactoferrin (LF) and β-lactoglobulin ( β-Lg) were selected as emulsifiers to form protein-coated fat droplets ( d43 ≈ 0.38 µm) with opposite charges at neutral pH: pK aβ-Lg ≈ 5 < pH 7 < pKaLF ≈ 8.5. Droplet aggregation occurred when these two emulsions were mixed together due to electrostatic attraction. The structural organization of the droplets in these mixed emulsions depended on the positive-to- negative particle ratio, particle concentration, pH, ionic strength, and temperature. The nature of the structures formed influenced the rheology, stability, and appearance of the mixed emulsions, which enabled some control over emulsion functionality. The largest microclusters were formed at particle ratios of 40% LF-coated and 60% β-Lg-coated fat vi droplets, which led to mixed emulsions with the highest apparent viscosity or gel strength. At low total particle concentrations (0.1%), there was a relatively large distance between microclusters and the mixed emulsions were fluid. At high particle concentrations (>20%), a three-dimensional network of aggregated droplets formed that led to gel-like or paste-like properties. The influence of environmental stresses on the physicochemical stability of the microclusters formed by hetero-aggregation was investigated: pH (2-9); ionic strength (0-400 mM NaCl); and temperature (30-90 ºC). Large microclusters were obtained at pH 7 ( d43 ≈ 10 µm) with the absence of salt at room temperature. More acidic (< pH 6) or alkaline (> pH 8.5) solutions resulted in smaller aggregates by minimizing the electrostatic attraction between the protein-coated fat droplets. Microclusters dissociated upon addition of intermediate levels of salt, which was attributed to screening of attractive electrostatic interactions. Heating the microclusters above the thermal denaturation temperature of the proteins led to an increase in gel-strength, which was attributed to increased hydrophobic attraction. The influence of hetero-aggregation of lipid droplets on their potential biological fate was studied using a simulated gastrointestinal tract (GIT). Results showed that the mixed emulsions had high viscosity in the simulated oral environment but exhibited similar rheological properties and particle characteristics as single-protein emulsions in the simulated gastric and small intestinal tract regions. The mixed emulsions also had similar lipid digestion rates in the simulated small intestine as single-protein emulsions suggesting that they could be used as delivery systems for bioactive lipophilic compounds in reduced fat food products. vii The possibility of using more practical food ingredients to promote hetero- aggregation system was also examined. Whey protein isolate (positive) and modified starch (negative) were selected as building blocks due to their opposite charges at pH 3.5. The largest aggregates and highest viscosities occurred at a particle ratio of 70% MS and 30% WPI, which was attributed to strong electrostatic attraction between the oppositely charged droplets. Particle aggregation and viscosity decreased when the pH was changed to reduce the electrostatic attraction between the droplets. Finally, the influence of interfacial properties on the chemical stability of bioactive components in emulsion-based delivery systems containing mixed proteins was studied. Lactoferrin (LF: pI ≈ 8) and β-lactoglobulin ( β-Lg: pI ≈ 5) were selected to engineer the interfacial properties. Interfaces with different structures were formed: LF only; β-Lg only; LF-β-Lg (laminated); β-Lg -LF (laminated); β-Lg /LF (mixed). The influence of pH, ionic strength, and temperature on the physical stability of β-carotene- enriched emulsions was then investigated. LF- emulsions were stable to the pH change from 2 to 9 but the aggregation was occurred in intermediate pH for other emulsions. β- Lg- emulsions aggregated at low salt concentration ( ≥ 50mM NaCl), however other emulsions were stable (0 - 300mM NaCl). β-Lg /LF (mixed) emulsions were unstable to heating ( ≥ 60 ºC), but all other emulsions were stable (30 to 90 ºC). Color fading due to β-carotene degradation occurred relatively quickly in β-Lg-emulsions (37 ºC), but was considerably lower in all other emulsions, which was attributed to the ability of LF to bind iron or interact with β-carotene. viii Overall, this study shows that hetero-aggregation may be a viable method of creating novel structures and rheological properties that could be used in the food industry. ix TABLE OF CONTENTS Page ACKNOWLEGEMENT ..................................................................................................... v! ABSTRACT ....................................................................................................................... vi ! LIST OF TABLES .......................................................................................................... xvii! LIST OF FIGURES ........................................................................................................ xviii ! CHAPTER 1. INTRODUCTION ................................................................................................... 1! 2. LITERATURE REVIEW ........................................................................................ 4! 2.1 Principles of Hetero-aggregation ...................................................................... 4 2.1.1 Colloidal Interactions ......................................................................... 4 2.1.2 Modeling Aggregate
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