Effect Of Temperature On The Wide Angle X-ray Diffraction Of .
EFFECT OF TEMPERATURE ON THE WIDEANGLE X-RAY DIFFRACTION OFNANOCRYSTALLINE TRIACYLGLYCEROLSbyXiyan DengSubmitted in partial fulfillment of the requirementsfor the degree of Master of ScienceatDalhousie UniversityHalifax, Nova ScotiaDecember 2014 Copyright by Xiyan Deng, 2014
TABLE OF CONTENTSLIST OF TABLES . vLIST OF FIGURES . viABSTRACT . xLIST OF ABBREVIATIONS USED . xiACKNOWLEDGEMENTS. xiiiCHAPTER 1INTRODUCTION. 11.1 Objectives . 2CHAPTER 2LITERATURE REVIEW. 42.1. Fat Crystallization . 42.1.1 Triacylglycerols. 52.1.2 Polymorphism . 52.1.3 Mechanisms of Crystallization. 102.2 Principles of X-Ray Diffraction . 152.2.1 Miller Indices. 162.2.2 Wide Angle X-Ray Diffraction (WAXD) . 172.2.3 Temperature Effect on the X-Ray Diffraction Peaks . 192.3 Crystallization under Shear . 202.3.1 Shear Effect on Fat Crystallization . 202.3.2 Studies on Shear Effect on the X-Ray Diffraction. 21CHAPTER 3EXPERIMENTAL METHODS AND MATERIALS . 243.1 Materials. 24ii
3.1.1 Sample Preparation . 243.2 In-House Wide Angle X-Ray Diffraction Measurements . 253.2.1 Centering the Diffraction Patterns . 263.2.2 Detector Distance Calibration . 263.2.3 Experimental Procedure . 273.2.4 Data Processing . 323.3 Synchrotron Wide Angle X-Ray Diffraction Measurements . 363.3.1 Synchrotron X-Ray Beamline Information . 363.3.2 Experimental Setup . 373.3.3 Experimental Procedure . 413.3.4 Data Processing . 42CHAPTER 4RESULTS AND DISCUSSION – I - EFFECT OF TEMPERATUREON WAXD OF PURE TRIACYLGLYCEROLS . 434.1 Effect of Temperature on d-Spacing of WAXD Peaks . 434.1.1 Effect of Temperature on d-spacing of β Form WAXD Peaks . 434.1.2 Effect of Temperature on d-spacing of β’ Form WAXD Peaks . 494.1.3 Effect of Temperature on d-spacing of α Form WAXD Peaks . 524.2 Reversibility of d-spacing of WAXD Peaks of β Form . 544.3 Estimation of Temperature from Difference of d-spacing . 564.4 Calculation of Unit Cell Values of β form TAGs from the d-spacings . 62CHAPTER 5 RESULTS AND DISCUSSION – II - EFFECT OF TEMPERATUREON WAXD OF TRIACYLGLYCEROLS MIXTURES . 665.1 Effect of Temperature on d-spacing of WAXD Peaks . 665.1.1 Effect of Temperature on d-spacing of β Form WAXD Peaks (Dry Blends) . 665.1.2 Effect of Temperature on d-spacing of β Form WAXD Peaks from ComplexTriacylglycerols Mixtures. . 74iii
5.2 Estimation of Temperature from Difference of d-spacing . 78CHAPTER 6 RESULTS AND DISCUSSION – III - EFFECT OF TEMPERATUREON WAXD OF TRIACYLGLYCEROLS MIXTURES UNDER SHEAR FLOW .846.1 Effect of Temperature on d-spacing of WAXD Peaks . 846.1.1 Effect of Temperature on d-spacing of β Form WAXD Peaks without Shearin the Mini Couette Cell. 846.1.2 Effect of Temperature on d-Spacing of β Form WAXD Peaks with 40 r/sRotational Speed . 876.1.3 Effect Of Temperature on d-spacing of β Form WAXD Peaks with 50 r/sRotational Speed . 896.2 Estimation of Temperature from Difference of d-spacing . 916.3 Comparison of the Difference of d-spacing with Different Shear Rate . 94CHAPTER 7CONCLUSION AND FUTURE WORK . 98BIBLIOGRAPHY . 102APPENDIX AWAXD PATTERN FITTINGS AND CALIBRATIONS . 107iv
LIST OF TABLESTable 3 - 1 The melting point of each polymorphic form for LLL, MMM, PPP and SSS(Takeuchi et al, 2003). . 29Table 3 - 2 The melting point of each phase for cocoa butter (Garti and Widlak. 2012). 29Table 4 - 1Characteristic d-spacing (Å) for the β TAGs . 64Table 4 - 2Cell parameters of β TAGs . 65v
LIST OF FIGURESFigure 2 - 1 Schematic representation of the different levels of structure in a bulk fat(Acevedo and Marangoni, 2010). . 4Figure 2 - 2 The structure of a typical saturated triacylglycerol molecule (Metin andHartel, 2005) . 5Figure 2 - 3 (a). Chain-length packing structure in TAG. (b). The polymorph sub-cellstructure (Himawan et al., 2006). . 7Figure 2 - 4 Energy barrier diagram for the 3 main polymorphic forms of a TAG at agiven condition below their melting temperatures. (a) General concept (Rousset, 2002),(b) Calculated specifically for trimyristin at 273 K. . 8Figure 2 - 5Polymorphic transition pathway in fat (Marangoni & Wesdorp, 2013) . 9Figure 2 - 6 Geometry of the reflection of x-rays from crystal planes used in thederivation of Bragg’s law (Marangoni & Wesdorp, 2013). . 16Figure 3 - 1In-house XRD set up. . 25Figure 3 - 2Explanation of distance calibration. . 27Figure 3 - 3Temperature - time profile of in-house WXRD experiment for β LLL . 28Figure 3 - 4 A GUI interface of the capillary cell temperature control program(Provided by Pavan K. Batchu). 30Figure 3 - 5(a) Original x-ray image and (b) radial plot of 3L7M . 32Figure 3 - 6 User interface for Igor Pro Multi-peak fit displaying a curve plotcorresponding to WAXD of 3L7M. . 33Figure 3 - 7 The location, amplitude, area and FWHM information of the fittedWAXD peaks provided by Igor Pro (5L5S). . 35Figure 3 - 8 Floor plan of the Advanced Photon Source (APS) at ANL showingstorage rings and beam lines. x-rays originating from Sector 5 - Insertion DeviceBeamline are further split into three beam lines 5-ID-B, 5-ID-C and 5-ID-D ("ArgonneNational Laboratory"). . 37Figure 3 - 9 Schematic figures of the temperature control system configuration (Li,2011). . 38vi
Figure 3 - 10The mini-Couette cell used in APS. (Provided by Cendy Wang.) . 41Figure 4 - 1β, β’ and α form WAXD Peaks in the literature (Kellens, et al. 1990) . 43Figure 4 - 2 Radial plot for the four pure triacylglycerol samples (LLL, MMM, PPPand SSS) at -20 C . 44Figure 4 - 3 The fitted Wide Angle Diffraction patterns of β form LLL at -20 C byIgor Pro. . 44Figure 4 - 4 Differences of d-spacings with temperature for pure TAGs. (a) LLL. (b)MMM. (c) PPP. (d) SSS. . 47Figure 4 - 5 The fitted Wide Angle Diffraction patterns of β’ form PPP by Igor Pro.Broad peaks are often associated with form β’ one. . 49Figure 4 - 6 Differences of d-spacings with temperature of β’ form WAXD Peaks.(a) LLL. (b) MMM. (c) PPP. (d) SSS. . 51Figure 4 - 7The fitted Wide Angle Diffraction patterns of α form PPP by Igor Pro. . 52Figure 4 - 8Differences of d-spacings with temperature of α form WAXD Peaks. . 53Figure 4 - 9d-spacings of WAXD peaks versus sequence (SSS). . 55Figure 4 - 10 Differences of d-spacings of WAXD peaks with small d-spacing (SSS). 55Figure 4 - 11 Differences of d-spacings of WAXD peaks with small d-spacing (SSS)versus temperature in the case where the temperature was cycled up and down. . 56Figure 4 - 12 Temperature versus differences of d-spacings for peaks with smalld-spacing. (a) LLL. (b) MMM. (c) PPP. (d) SSS. (e) SSS Circle. . 59Figure 4 - 13 Temperature versus differences of d-spacings for peaks with small dspacing (All β form pure triacylglycerols samples). (a) Peaks with small d-spacing at3.85 Å. (b) Peaks with small d-spacing at 3.7 Å. (c) Regression of peaks with small dspacing at 3.7 Å with 95% confidence interval. . 61Figure 4 - 14Δd 3.7 vs Δd 3.85 of four pure TAGs . 61Figure 4 - 15 Crystal structure of β form TAGs with the acyl chains perpendicular tothe plane of paper Van Langevelde et al. (1999). . 62Figure 4 - 16 Triclinic unit cell of β form PPP with the acyl chains, with the cellvalues from Van Langevelde et al. (1999) . 63Figure 5 - 1The fitted wide angle diffraction patterns of β form 3L7M by Igor Pro. . 67vii
Figure 5 - 2 Differences of d-spacings with temperature. (a) 3P7S (b) 5P5S (c) 7P3S. 68Figure 5 - 3 Differences of d-spacings with temperature. (a) 3M7P (b) 5M5P(c) 7M3P . 70Figure 5 - 4 Difference of d-spacing with temperature. (a) 3L7M (b) 5L5M (c) 7L3M. 71Figure 5 - 5The fitted Wide Angle Diffraction patterns of β form 5L5S by Igor Pro. . 72Figure 5 - 6Difference of d-spacing with temperature of 5L5S. . 73Figure 5 - 7 Wide Angle x-ray Diffraction Patterns (short spacing) of six polymorphsof cocoa butter (Garti and Widlak. 2012). . 74Figure 5 - 8 The fitted Wide Angle Diffraction patterns of β form cocoa butter byIgor Pro. . 74Figure 5 - 9 The fitted Wide Angle Diffraction patterns of β form 99% dark chocolateby Igor Pro. . 75Figure 5 - 10Difference of d-spacing with temperature (Cocoa butter). . 76Figure 5 - 11Differences of d-spacings with temperature (99% dark chocolate). . 77Figure 5 - 12 Temperature versus differences of d-spacings for peaks with small dspacing (3P7S). . 78Figure 5 - 13 Temperature versus differences of d-spacings for peaks with small dspacing at 3.85 Å. (a) Triacylglycerol mixture composed by PPP and SSS. (b)Triacylglycerol mixture composed by MMM and PPP. (c) Triacylglycerol mixturecomposed by LLL and MMM. . 80Figure 5 - 14 Temperature versus differences of d-spacings for peaks with small dspacing at 3.7 Å. (a) Triacylglycerol mixture composed by PPP and SSS. (b)Triacylglycerol mixture composed by MMM and PPP. (c) Triacylglycerol mixturecomposed by LLL and MMM. . 81Figure 5 - 15Temperature versus differences of d-spacings for peaks with small dspacing at 3.7 Å (all dry blend samples and pure TAGs). . 82Figure 6 - 1 The fitted Wide Angle Diffraction patterns of 6B4P without shear byIgor Pro. (a) Whole diffraction patterns. (b) Re-fitting for peak 7 and peak 8 at thereciprocal lattice spacing range from 1.5 to 1.8. . 85Figure 6 - 2Differences of d-spacings with temperature (6B4P without shear). 85viii
Figure 6 - 3 The fitted Wide Angle Diffraction patterns of 6B4S under 40 r/srotational speed at 0 C by Igor Pro. (a) Whole diffraction patterns. (b) Re-fitting forpeak 3 and peak 4 Re-fiting for peak 7 and peak 8 at the reciprocal lattice spacingrange from 1.5 to 1.8. . 87Figure 6 - 4 Difference of d-spacing with temperature (6B4S with 40r/s rotationalspeed) . 88Figure 6 - 5 The fitted Wide Angle Diffraction patterns of 6B4S with 50 r/s rotationalspeed at 0 C by Igor Pro. (a) Whole diffraction patterns. (b) Re-fitting for peak 3 andpeak 4 Re-fiting for peak 7 and peak 8 at the reciprocal lattice spacing range from 1.5to 1.8. 89Figure 6 - 6 Difference of d-spacing with temperature (6B4S with 50r/s rotationalspeed) . 90Figure 6 - 7 Temperatures versus differences of d-spacings for peaks with small dspacing. (a) 6B4P without shear. (b) 6B4S with 940 s-1 shear rate (40r/s rotationalspeed). (c) 6B4S with with 1200 s-1 shear rate (50r/s rotational speed). . 93Figure 6 - 8 Difference of d-spacings versus rotational speed for peaks with smalld-spacing. (a) Peak with small d-spacing at 3.85 Å. (b) Peak with small d-spacing at3.7 Å . 94Figure 6 - 9 Change of difference of d-spacing with temperature using in-house x-rayand synchrotron x-ray. . 95Figure 6 - 10 Change of difference of d-spacing with temperature with and without shear. 96Figure A - 1Center of the capillary of β form 5M5P. . 107ix
ABSTRACTThe peak position of wide angle x-ray diffraction patterns of nanocrystallinetriacylglycerols is affected by the temperature. To observe this effect quantitatively, puretriacylglycerols and triacylglycerol mixtures were crystallized in a desired polymorph incapillaries or a Couette system. The crystallized samples were kept at differenttemperatures and shear rates. The detailed WAXD patterns were obtained using in-housex-ray and synchrotron x-ray sources. When the temperature increased, the d-spacing forthe peaks with small d-spacing increased as well. However, the d-spacing for other peaksremained unchanged or just had a very small change. The relationship between differencesof d-spacing for the peaks with small d-spacing and temperature can be used to estimatethe real sample temperature, especially under higher shear rate. This provides a new way tomonitor and control the temperature of the system under study and the effect of high shearrate on nanocrystalline triacylglycerol crystallization.x
LIST OF ABBREVIATIONS USEDANLArgonne National LaboratoryAPSAdvanced Photon SourceCCCTricaprinCCDCharge-Coupled DeviceDCLDouble Chain Length StructureDSCDifferential Scanning CalorimetryFAFatty acidFOTFiber Optic Temperature SensorFWHMFull Width at Half MaximumGUIGraphical User InterfaceLDLamellar DistanceLLLTrilaurinLSLiquid SignalMMMTrimyristinNMRNuclear Magnetic ResonancePPPTripalmitinSAXDSmall Angle x-ray DiffractionSFSolid FractionSR-XRDSynchrotron Radiation x-ray DiffractionSSSolid SignalSSSTristearinTAGTriacylglycerolsxi
TCLTriple Chain Length StructureTECThermoelectric CoolerWAXDWide Angle x-ray DiffractionXRDx-ray Diffraction3L7M30% trilaurin: 70% trimyristin triacylglycerol mixture by weight5L5M50% trilaurin: 50% trimyristin triacylglycerol mixture by weight5L5S50% trilaurin: 50% tristearin triacylglycerol mixture by weight7L3M70% trilaurin: 30% trimyristin triacylglycerol mixture by weight3M7P30% trimyristin: 70% tripalmitin triacylglycerol mixture by weight5M5P50% trimyristin: 50% tripalmitin triacylglycerol mixture by weight7M3P70% trimyristin: 30% tripalmitin triacylglycerol mixture by weight3P7S30% tripalmitin: 70% tristearin triacylglycerol mixture by weight5P5S50% tripalmitin: 50% tristearin triacylglycerol mixture by weight7P3S70% tripalmitin: 30% tristearin triacylglycerol mixture by weight6B4P60% tributyrin: 40% tripalmitin triacylglycerol mixture by weight6B4S60% tributyrin: 40% tristearin triacylglycerol mixture by weightγshear rateqreciprocal lattice spacing (Å-1)Ttemperature of crystallization (K)θincident angle of x-raysΔGchange in Gibbs energy (J)λwavelength of x-rays (Å)dThe lamellar spacing of crystal planesxii
ACKNOWLEDGEMENTSFirstly I would like to gratefully acknowledge my supervisor Dr. Gianfranco Mazzanti,for his encouragement, guidance, inspiration, and patience for not only my project, butalso my life. I also want to thank my advisory team Dr. Jan Haelssig and Dr. BenedictNewling (University of New Burnswick) for their guidance and assistance for my thesis.To my research colleagues, Omar Qatami, Amro Alkhudair, Pavan Batchu, Pranav Arora,Mohit Kalaria, Liangle Lin, Rong Liu and Yujing Wang, your very insightful discussionsmade this work possible and enjoyable. I am grateful to Ray Dube for the assistance ofexperiment setup and the undergraduate project member Shenglin Yao for all the relatedassistance. I also want to thank DND-CAT staffs in Argonne National Laboratory,especially Steven Weigand and James Rix, for their help in experiment setup andoperation of x-ray beamline.Deepest thanks to my parents, who give birth to me, raise me, teach me and support me,for their endless love to me. It is my parents that make all the wonderful things happen inmy life. Words cannot express how much I love you both.My appreciation goes to my friends and other family members for their kindness andgenerous supports. One page is not enough to name you all.xiii
CHAPTER 1 INTRODUCTIONWith the development of society, people have never lost their interest in finding novelmethods to prepare food. People expect food to bring more pleasure to their lives.Therefore, food scientists and technologists devote themselves to advance the science offood and ensure a safe and abundant food supply. The food industry is doing its best tosatisfy the need of providing good texture and taste of food products. The understandingof food ingredients and the methods to modify and manipulate the ingredients to getbetter food are more and more important. Luckily, food science provides us with a largeplatform to achieve better food.Dietary fat is one of the main nutrients for humans. Dietary fat provides people withenergy storage resources. More importantly, it provides essential fatty acids to helpregulate body functions and carry the fat-soluble vitamins. From the point of view offood, dietary fat is also an important ingredient in many daily foods, such as chocolate,margarine, butter, spreads and baked products. Dietary fat provides a creamy texture andspecial mouth feel of the products. It also plays a critical role in food structures. Fatcrystallization, the formation of solid fat crystals, always occurs during the industrialmanufacturing and the storage of the fat-based foods. It has a great impact in the texture,shelf life and food quality of the fat-based foods (Metin and Hartel, 2005). In order toimprove the quality and the ability of fat-based foods to meet the current marketdemands, a better understanding of the fat crystallization process of dietary fat fromphysics, chemistry and biochemistry is needed (Sato et al., 1999).Many researches show that the sensorial attributes of many common fat-based foods arederived from the network structure of the crystalline fat (Narine and Marangoni, 1999,1
Wright et al., 2000, Mazzanti et al., 2005). Many sensorial attributes, such as texture,spread ability and mouthfeel, are dependent on the mechanical strength of the fat crystalnetwork (Narine and Marangoni, 1999). Some factors play an important role indetermining the crystallized fat structure, such as the solid fat content, microstructure ofthe crystal and the types of polymorph. The processing conditions, such as crystallizationtemperatures, shear rates and cooling rates, have great effects on the fat crystallization.The complexity of natural fats in the fat-based foods limits the accuracy ofmanufacturing and results in uncertain quality of the products. This research aims toobserve the behaviour of nanostructure during the lipid crystallization process underseveral constant temperatures and shear rates using x-ray diffraction techniques. It wasnoticed in previous studies that the peak position of wide angle x-ray diffraction(WAXD) patterns is affected by the temperature (Mazzanti, unpublished). In order toobserve this effect quantitatively, crystallization of different kinds of triacylglycerols(TAGs) and their mixtures, which are normally the main or critical components of thefood products, are studied at different controlled temperatures and shear flow. This thesisdescribes how different WAXD peaks change their position as the temperature changesand provides a new attempt to study the change of sample temperature when a shear rateis applied. It is particularly interesting that the anisotropy of the nanocrystals is evidentby these changes. The findings of this research should help future studies of academicresearchers and the food industry to develop a deeper knowledge of lipid crystallization,leading to better products and manufacturing procedures.1.1 ObjectivesThe general research aim of our lab is to gain a better and wider understanding of the2
characteristics of the triacylglycerols crystallizing under different temperatures and shearrates.The specific objectives of this Thesis are: To study how different WAXD peaks of the pure triacylglycerol crystals change theirposition as the temperature changes. To observe how different WAXD peaks of triacylglycerol mixture crystals withdifference proportions change their position when the temperature changes. To investigate how the WAXD peaks of triacylglycerol crystals change their positionunder shear when the temperature changes under different shear rates. To compare the change of WAXD peaks of triacylglycerol crystals with and withoutshear. To utilize WAXD vs. temperature as an intrinsic thermometer to study thethermomechanical increase of temperature at high shear rates.3
CHAPTER 2LITERATURE REVIEW2.1. Fat CrystallizationIn the food industry, fat crystallization has been applied in two ways: one is to process fatcrystal containing products, such as chocolates and margarine; the other one is to separatespecific fats and liquid materials from natural resources (Sato, 2001). Fat moleculesrearrange themselves to form a solid crystalline lattice from a supersaturated liquid orsolution. Fat crystallization is a kinetic process in which the lipid melt must be significantlysupercooled to start crystallization.As shown in Figure 2-1, triacylglycerol (TAG) molecules crystallize from the melt viamass and heat transfer to form crystals which then aggregate to particles, larger clusters,until a three dimensional space filling network forms (Acevedo and Marangoni, 2010).Figure 2 - 1 Schematic representation of the different levels of structure in a bulk fat(Acevedo and Marangoni, 2010).4
2.1.1 TriacylglycerolsTriacylglycerol molecules (TAG), which have a complex polymorphism, are the maincomponent of edible fats. Triacylglycerols constitute more than 95% of the edible fatcomposition. They are composed by three fatty acids esterified to one glycerol unit. Thereare several kinds of TAGs. One is called monoacid TAGs or simple TAGs, which meansthat there is just one type of fatty acids attached to the glycerol unit, such as trilaurin andtristearin. The other is called mixed-acid TAGs or mixed TAGs. Two or three types of fattyacids are attached to the glycerol unit. FA can be saturated (no C C double bonds) orunsaturated (C C double bonds).Figure 2 - 2Hartel, 2005)The structure of typical saturated triacylglycerol molecules (Metin and2.1.2 PolymorphismPolymorphism is the ability of a molecule to crystallize in more than one crystalline form.The crystalline form is dependent on the arrangement within the crystal lattice (Metin andHartel, 2005). Polymorphic forms are crystalline phases with different structuralcharacteristics, but with identical chemical compositions when melted in their liquid state.In lipids, differences in hydrocarbon chain packing and the tilt angle of the packing are thecause of different polymorphs. The formation of one polymorph or another is mainly5
influenced by the molecular structure and the external factors, such as temperature,pressure, impurities and shear rate. The rate of crystallization can also affect polymorphformation (Sato, 2001).2.1.2.1 Polymorphic Types and Sub-Cell StructuresThe chain length structure produces a repetitive sequence of the acyl chains involved in aunit cell lamella along the long-chain axis. This plays an important role in the phasebehavior of different
5.1 Effect of Temperature on d-spacing of WAXD Peaks. 66 5.1.1 Effect of Temperature on d-spacing of β Form WAXD Peaks (Dry Blends). 66 5.1.2 Effect of Temperature on d-spacing of β Form WAXD Peaks from Complex
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4.3.1 Effect of Temperature at pH 4.5 57 4.3.2 Effect of Temperature at pH 5.0 58 4.3.3 Effect of Temperature at pH 5.5 59 4.3.4 Effect of Temperature at pH 6.0 60 4.3.5 Effect of Temperature at pH 6.5 61 4.3.6 Combination Effect of Temperature on Enzymatic Hydrolysis 62
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