11

1 Introduction

Fats and oils are employed in food, cosmetics, phar-maceuticals, etc., as main bodies of end products, or asmatrices in which cosmetic and pharmacological fine

chemicals are dispersed. The molecular species of thefats and oils are waxes, fatty acids, glycerols (mono-,di- and tri-), phospholipids, and glycolipids etc., whichare categorized as long-chain compounds (1, 2). Triacyl-glycerols (TAGs) are employed in edible oil, butter,

193

JOS

Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online

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1 Department of Agro-bioscience, Iwate University(3-18-8 Ueda, Morioka, Iwate 020-8550, JAPAN)

2 Research Laboratory, Tsukishima Foods Industry Co., Ltd.(3-17-9 Higashi Kasai, Edogawa-ku, Tokyo 134-8520, JAPAN)

Makoto MIURA1Ayako KUSANAGI1Shoichi KOBAYASHI1Shigeru TOKAIRIN2 and Koichi TSURUMI2

Edited by M. Yonese, Nagoya City Univ., and accepted December 10, 2004 (received for review August 23, 2004)

Effect of Static Magnetic Field Processing on CrystallizationBehavior of Triacylglycerols

Correspondence to: Makoto MIURA, Department of Agro-bioscience, Iwate University, 3-18-8 Ueda, Morioka, Iwate 020-8550, JAPAN

E-mail: [email protected]

JOURNAL OF OLEO SCIENCECopyright 2005 by Japan Oil Chemists SocietyJ. Oleo Sci., Vol. 54, No. 4, 193-202 (2005)

Abstract: The influence of static magnetic field on crystallization of triacylglycerols(TAGs) was investigated. Melted TAGs were solidified under static magnetic field of 5 T with asuperconductive magnet system. Polymorphic behavior of TAGs was examined by temperaturemodulated differential scanning calorimetry (TMDSC) and X-ray diffraction (XRD). In TMDSCexperiment, saturated mono-acid TAGs (PPP and SSS) had no change in crystallization behaviorunder static magnetic field. Static magnetic field processing suppressed the crystallization of aform of SOS, PPO and POS. Furthermore, it suppressed the crystallization of sub-a form, aform, and bform of POP. In case of SSO, the crystallization of a form and bform wassuppressed. On the other hand, in the XRD experiment the crystallization of a form in PPP andPOP was suppressed by static magnetic field processing. PPO had no change in crystallizationbehavior under the static magnetic field. However, fluctuation in the ratio of the XRD peak area(wide angle region/small angle region) of a form was increased. This change suggested that thephase transition from a to bform had occurred. From these results, the following can beconsidered as the influences of static magnetic field on crystallization of TAGs: (i) the effect ofstatic magnetic field on crystallization of saturated mono-acid TAGs depended on the fatty acidchain length which constitutes TAG (PPP and SSS), (ii) the shorter the acyl chains of TAGs, themore sensitive to static magnetic field it was in saturated-unsaturated mixed-acid TAGs (PPOand SSO), and (iii) symmetrical type TAGs (POP and SOS) were more sensitive to staticmagnetic field rather than asymmetrical type of TAG (POS). It is speculated that the effect of amagnetic field on polymorphism of TAGs is due to the magnetic field gradient in a magnet andthe molecular orientation caused by magnetic anisotropy of a TAG molecule. Much work isneeded to clarify the mechanism of the polymorphic crystallization under static magnetic field.

Key words: triacylglycerol, crystallization, polymorphism, magnetic field

M. Miura, A. Kusanagi, S. Kobayashi et al.

margarine, cream, chocolate, and other edible oils andfats products, and the fat structures are the major factorsto determine their physical properties, such as food tex-ture, plasticity, morphology, and so on (3, 4). In choco-late manufacture, the solidification process significantlyinfluences the quality of the final product: gloss, snap,food texture, heat resistance, fat bloom resistance, andso on (5). The most troublesome problems are encoun-tered in the occurrence of different crystal structures ofsolid-fat components, mostly cocoa butter, called poly-morphism.

The crystallization behavior of fats and oils has twomajor industrial implications: (a) processing of the endproducts made of fat crystals, such as chocolate, mar-garine and shortening, whipping cream, etc., and (b)separation of specific fats and lipids materials from nat-ural resources (6). The natural fats and oils resourcesare vegetable and animal fats and oils, which containvarious molecular species having different chemical andphysical properties. It may be worth noting that there isan increasing necessity to develop the fractionationtechnology of high- and low-melting fats and oils putforward by the following market demands: (a) obtaininghigh melting fats by dry fractionation, instead of hydro-genation which produces trans-fatty acids as bi-prod-ucts, (b) coping with new regulation standards of theuse of fat materials for confectionery end products, (c)maintaining better functionality of physically refinedvegetable oils compared to conventional materials, etc.

The crystallization behavior of lipids is affected bythe presence of minor components. The crystallizationkinetics of palm stearin, a palm oil fraction, in blendswith sesame seed oil were investigated (7). The resultsindicated that the crystallization behavior of palmstearin in sesame oil was mainly associated with thecrystallization of tristearoylglycerol (SSS). Cocoa but-ter consists mainly of three symmetric TAGs, 1,3-dipalmitoyl-2-oleoyl glycerol (POP), 1,3-distearoyl-2-oleoyl glycerol (SOS), and 1-dipalmitoyl-2-oleoyl-3-stearoyl glycerol (POS) (8). The polymorphism ofcocoa butter is an important physical aspect for the con-fectioner, especially for chocolate manufactures,because the major fat in chocolate is cocoa butter. Tosolidify chocolate in desired polymorphs, careful tem-perature treatment is needed because the polymorphismof cocoa butter is quite complicated, and therefore itscrystallization phenomena are not easily controlled.

Monogalactosyldiacylglycerol (MGDG), digalacto-

syldiacylglycerol (DGDG) and trigalactosyldiacylglyc-erol (TGDG) were prepared from various natural mate-rials (9). MGDG and DGDG significantly retarded thepolymorphic transformation from form V to VI oncocoa butter compared with the control, with the addi-tion of MGDG being the most effective.

Sophisticated food processing operations have beendeveloped to control crystallization in food lipids, par-ticularly in the fields of chocolate, margarine, andshortening manufacture. To produce good solid choco-late, it is necessary to crystallize it in a stable polymor-phic form. This is achieved by a process of temperingwhere the melt is exposed to a controlled-temperatureprofile under shear, the aim being to create 1-3 % of thedesired crystals in an otherwise liquid continuum. Dif-ferent processing factors, such as cooling rate and crys-tallization temperature as well as the supersaturation ofthe system, may influence the crystallization behaviorof any system. The crystallization behavior of palm oiland its thermal features were examined by differentialscanning calorimetry (DSC), X-ray diffractometry(XRD) and infrared spectroscopy (IR) (10). Whenusing palm oil-based products, attention should bedirected to the effects of temperature on crystallizationof TAGs. The effects of cooling rate, degree of super-cooling, and storage time on the micro-structure andrheological properties of a vegetable shortening com-posed of soybean and palm oils were examined (11).The morphology and size of the microstructural ele-ments also affects the mechanical strength of the net-work. The induction times for the crystallization, underisothermal conditions, of refined, and deodorized palmoil from the melt were studied by viscometry (12). Attemperature below 295 K, the crystallization of palm oilwas observed to occur in a two-stage process. On theother hand, only a single-stage crystallization processwas observed at temperatures higher than 295 K. Theeffect of shear rate on the crystallization onset tempera-ture of a confectionary coating fat was studied using arheometer incorporating ultrasonic sensors (13). Theonset temperature increased significantly with shearrate, implying lipid crystallization can be accelerated bymixing. Crystallization, polymorphic transformation,and melting behavior of nanoparticles of trilauroylglyc-erol (LLL) in oil-in-water (O/W) emulsion were exam-ined by simultaneous synchrotron radiation small-angle(SAXS), wide-angle X-ray diffraction (WAXS) andDSC (14). The forming nanoparticle of LLL in the O/W

194J. Oleo Sci., Vol. 54, No. 4, 193-202 (2005)

Effect of Magnetic Field on Crystallization of TAGs

emulsion having the diameters of 42 to 120 nm reducedthe melting and crystallization temperatures andincreased the transformation rate of a b b incomparison to the LLL crystal formed in the bulkphase.

Nowadays consumers are demanding prepared foodsdevoid of any chemical additives, e.g., emulsifiers, andwith natural characteristics and natural flavor. Studyingthe influence of parameters of reaction field such aselectric field, magnetic field, electromagnetic field andextra-high pressure on lipid crystallization is quiteinteresting since development of processing method forcrystallization control of lipids is needed in the foodindustry without food additives. As for magnetic fieldprocessing, an investigation of the influence of a mag-netic field on selectivity ratio (SR) in the nickel-cat-alyzed hydrogenation process of sesame oil and soy-bean oil was reported (15). The SRs obtained werehigher than those without a magnetic field because themagnetization of the nickel particles reduced the con-centration of hydrogen on the catalyst surface.

New processing operations in controlling lipid crys-tallization have been developed. Therefore, the aim ofthe present work was to investigate the effect of staticmagnetic field on crystallization of lipids. In this study,TAGs were chosen as model substances mainly becausetheir important properties of crystallization and poly-morphic transformation in bulk state are well known.

2 Experimental

21 MaterialsSeven kinds of TAGs were purchased from Sigma-

Aldrich Corp. (St. Louis, MO, USA) with purity higherthan 99%. Tripalmitoyl glycerol (PPP) and tristearoylglycerol (SSS) were used as saturated mono-acid TAGs.1,3-dipalmitoyl-2-oleoyl glycerol (POP) and 1,3-dis-tearoyl-2-oleoyl glycerol (SOS) were used as symmetri-cal saturated-unsaturated mixed-acid TAGs. 1,2-dipalmitoyl- 3-oleoyl glycerol (PPO), 1,2-distearoyl-3-oleoyl glycerol (SSO), and 1-palmitoyl-2-oleoyl-3-stearoyl glycerol (POS) were used as asymmetrical sat-urated-unsaturated mixed-acid TAGs. All the TAGswere employed without further purification. Mercury(Standard Reference Material 743, National Institute ofStandards and Technology, USA), biphenyl (CertifiedReference Material LGC2610, Laboratory of the Gov-ernment Chemist, Middlesex, UK) and benzyl (Certi-

fied Reference Material LGC2604, Laboratory of theGovernment Chemist, Middlesex, UK) were obtainedas reference materials for temperature calibration. Indi-um (Certified Reference Material LGC2601, Laborato-ry of the Government Chemist, Middlesex, UK) wasused as a reference material for enthalpy of fusion.

22 Static Magnetic Field ProcessingThe influence of static magnetic field on occurrence

of polymorphs of TAGs was examined by the simplecooling of the melt from varying heating temperatures(Th) to varying cooling temperatures (Tc). Two mil-ligrams of the sample for temperature modulated differ-ential scanning calorimetry (TMDSC) were weightedinto an aluminum sample pan and hermetically sealed.The sample (200mg) was placed in the XRD sampleholder, which was temperature controlled. These sam-ples were attached on the heating/cooling plate of Pel-tier type thermoelectric device (SL-10W, Nippon BlowerCo., Ltd., Tokyo, Japan) equipped with a platinumresistance temperature sensor (f 2 mm L 30 mm,Nippon Blower Co., Ltd.) and a temperature controlsystem (SL-CPP1206M, Nippon Blower Co., Ltd.). Thethermoelectric device was placed in a superconductivemagnet system (JMTD-5T300, central magnetic fluxdensity of 5 T, Japan Superconductor Technology Inc.,Tokyo, Japan) as shown in Fig. 1 and temperature of thesamples controlled. Moreover, melted SOS was crystal-lized under static magnetic field of 2 T and 0.5 T. Theheating temperature (Th) were 60 for PPO and POS,70 for SSO and POP, 80 for SOS, 90 for SSS,and 100 for PPP at the heating rate of 2min1,respectively. The cooling temperature (Tc) were 10 for POP, 0 for PPO, SSO, SOS and POS, and20 for PPP and SSS at cooling rate of 5min1

except for SSS and POS at 2min1, respectively. Allthe TMDSC and XRD measurements were performedwithin 12 hours to avoid any crystal changes after staticmagnetic field-processing of the samples.

23 Temperature Modulated DifferentialScanning Calorimetry

The crystallization and melting behaviors of theTAGs were examined by TMDSC. Calorimetric analy-sis was performed with a MDSC Cell Base 2900equipped with Thermal Analyst Controller TA-5200(TA Instruments, Inc., New Castle, DE, USA). Thetemperature calibration of the equipment was done with

195J. Oleo Sci., Vol. 54, No. 4, 193-202 (2005)


mercury (melting temperature 38.83), biphenyl(68.93) and benzyl (94.85). The baseline wasdeveloped with an empty aluminum pan. The calibra-tion for heat involved in phase changes (i.e., melting/crystallization) was made only with indium (enthalpychange for melting 28.71 Jg1). Nitrogen was used asthe purge gas to prevent condensation in the cell, and anempty pan was used as reference.

For all scans, 10 min was allowed for insertion of thesample, starting of scan, and for thermal equilibrium tobe established at initial temperature. For the heatingrun, the sample was held at Tc for 10 min, then heatedat a constant rate from Tc to Th with the temperaturemodulation amplitude of 0.125 and modulation peri-od (frequency) of 100 s (0.01 Hz). The following heat-ing rate was varied to assess the effect of static magnet-ic field-processing during the solidification stage andthus the crystallization behavior of TAGs: at 0.8min1 for SSO, 1min1 for POP and POS, 1.5min1 for PPO, 2min1 for SOS, respectively.Enthalpy change (DH), onset temperature (To), peaktemperature (Tp), and completion temperature (Tc) werecomputed automatically.

Deconvolution of TMDSC signals provides not onlythe total heat flow obtained from conventional DSC, butalso separates that total heat flow into its heat capacity-related (reversible within the time scale of the perturba-tion) and kinetic (irreversible) components. Specifical-ly, Fourier transformation analysis of the modulatedheat flow signal is used to continuously calculate anaverage heat flow value which is equivalent to the totalheat flow signal in conventional DSC. Heat capacity iscalculated from the ratio of the modulated heat flow

amplitude divided by the modulated heating rate ampli-tude. The reversing heat flow is determined by multi-plying this heat capacity by the average heating rate.The nonreversing heat flow is determined as the differ-ence between the total and reversing heat flows.

24 Powder X-ray DiffractionThe polymorphic forms of the TAG crystals were

assessed by powder XRD using a X-ray diffractometer(M18XHF22, Bruker AXS K. K., Tsukuba, Japan). TheXRD patterns were obtained at X-ray tube voltage of 35kV, X-ray tube current of 40mA, scanning rate of 5degs1, measuring interval of 0.02 deg, and scanningangle (2q) of 0 to 40 deg with Cu-Ka radiation. X-raydiffraction spectrum of PPP was obtained at room tem-perature. As for POP and PPO, the spectra were meas-ured at 0 using a cryostat.

The peak (2q 6 deg) reflecting a long spacing andthe peak (2q 21 deg) indicating a form crystal wereobserved in all XRD patterns. Consequently, XRD peakintensity was evaluated from the standardized peak areaof these peaks. And a peak ratio of the peak intensity of2q 21 deg to that of 2q 6 deg was computed.

25 Statistical AnalysisData were statistically analyzed by a one-way analy-

sis of variance (ANOVA) using SPSS 12.0.2J for Win-dows (SPSS Inc., Tokyo, Japan). Significant difference(P


lowed by an exothermic peak at 46-52. These twopeaks corresponded to the melting of the a form andrapid crystallization of the most stable b form. Furtherheating showed an endothermic peak at 63-70,which is due to the melting of b form. Figure 3 (A)shows enthalpy changes of PPP on each peak inTMDSC curves. No significant differences wereobserved between the reference sample and the sampleprocessed with static magnetic field of 5 T regardingthe enthalpy changes accompanying the melting of aform, the phase transition from a to b form, and themelting of b form. Therefore, PPP was thought to haveno change in crystallization under static magnetic field

of 5 T.SSS (tristearoyl glycerol) reveals three polymorphic

transformations, a, b, and b. The melting temperaturesof a (55.0), b(61.64), and b (73.0) have beenreported (17, 18). Reference sample of SSS in thisexperiment showed an endothermic peak at 52-56,which was followed by an exothermic peak at 56-62in TMDSC curve. These two peaks corresponded to themelting of the a form and rapid crystallization of themore stable b form. Further heating showed anendothermic peak at 70-78, which is due to the melt-ing of b form. The pattern of the obtained TMDSCcurve was in good agreement with the DSC curvereported by Singh et al. (19). Figure 3 (B) showsenthalpy changes of SSS on each peaks in the TMDSCcurves. No significant differences were observed

197J. Oleo Sci., Vol. 54, No. 4, 193-202 (2005)

Fig. 2 TMDSC Curves of PPP without Static MagneticField Processing (A) and with the Processing (B).Deconvolution of TMDSC signals provides not onlythe total heat flow (upper curve), but also separatesthat total heat flow into its heat capacity-related(middle curve) and kinetic (bottom curve) com-ponents. No significant differences were observedbetween (A) and (B).

Fig. 3 Enthalpy Changes of Saturated Mono-Acid TAGsCrystallized under Geomagnetism (white) and StaticMagnetic Field of 5 T (gray). (A) Enthalpy changesof PPP : Mean values of six determinations (standard deviation) are represented. (B) Enthalpychanges of SSS : Mean values of eight determi-nations ( standard deviation) are represented.


between the reference sample and the sample treatedwith static magnetic field of 5 T in regard to enthalpychanges accompanying the melting of a form, the phasetransition from a to b form, and the melting of b form.

From these results, it can be concluded that staticmagnetic field processing during solidification had nosignificant effect on crystallization behavior of PPP andSSS.

312 Saturated-unsaturated mixed-acid TAGsIn 1,3-dipalmitoyl-2-oleoyl glycerol (POP), six poly-

morphs, a (melting point 15.2), g (27.0), pseudo-b2(30.3), pseudo-b1(33.5), b2 (35.1) and b1(36.7) were identified with XRD, DSC and Ramanspectroscopy by Sato et al. (20). Additionally, POPexhibited two transformation pathways; a g pseu-do-b2( pseudo-b1) b2 b1 in the sample with99% purity, and d (melting point 29.2) pseudo-b1 b2 b1 in the sample with 99.2% purity, imply-ing subtle influences of the impurity. Sub-a form wasobserved in SOS, AOA(1,3-diarachidoyl-2-oleoyl glyc-erol) and BOB (1,3-dibehenoyl-2-oleoyl glycerol) as aless stable form than a form (21). An exothermic peakwhich indicated solid-state transition from the sub-a toa form was observed in the present TMDSC curve of areference sample at 11-17. Thereafter the sampleshowed a endothermic peak at 26-29 followed by anexothermic peak at 29-31. These two peaks corre-sponded to the melting of the a form and the rapidcrystallization of a form to the more stable bform.Further heating showed an endothermic peak at 31-34 which indicate the melting of bform. Figure 4(A) displayed enthalpy changes of each peaks in theTMDSC curves of POP. As for solidified POP understatic magnetic field of 5 T, the exothermic peak whichindicated solid-state transition from the sub-a to a formcould not be observed. Consequently, static magneticfield processing suppressed the crystallization of the aform (ca. 73% compared with the reference sample),the transformation from the a form to the bform (ca.35%) and the crystallization of the bform (ca. 76%).

Five polymorphs, a, g, pseudo-b, b2, and b1 wereisolated in SOS (1,3-distearoyl-2-oleoyl glycerol) (20).The melting points of these crystal forms are 23.5,35.4, 36.5, 41.0, and 43.0, respectively. Therewas one transformation pathway in SOS; a g pseudo-b b2 b1. On TMDSC curves, referencesample of SOS showed a small endothermic peak at 21-23 soon followed by an exothermic peak at 24-29.

These two peaks corresponded to the melting of the aform and rapid crystallization of a form to the morestable bform. Further heating showed an endothermicpeak at 35-42 which was due to the melting of bform.TMDSC curves of SOS solidified under static magneticfield of 5 T showed disappearance of a thermopeakindicating the melting of a form or the thermopeaksindicating the melting of a form and the transformation

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Fig. 4 Enthalpy Changes of 1,3-disaturated-2-unsaturatedMixed Acid TAGs Crystallized under Geomagnetism(white) and Static Magnetic Field (gray). Data aretaken from the mean standard deviation. (A)Enthalpy changes of POP crystallized under andstatic magnetic field of 5 T (n=6). (B) Enthalpychanges of SOS crystallized under and staticmagnetic field of 2 T (n=4). (C) Enthalpy changes ofSOS crystallized under static magnetic field of 0.5 T(n=4).


from the a form to the bform. This result indicatedthat static magnetic field processing suppressed thecrystallization of the a form of SOS. Since the exother-mic peak of the phase transition was observed in threeof the processed sample but not the others, magneticflux density of 5 T would be near the critical valueaffecting the polymorphic behavior of SOS. According-ly, static magnetic field processing of 2 T and 0.5 T tothis TAG was also tried. TMDSC curves of the samplesprocessed under static magnetic field of 2 T and 0.5 Tshowed the same patterns as the reference sample. Stat-ic magnetic field of 2 T accelerated the crystallizationof the a form (ca. 126% compared with the referencesample) as shown in Fig. 4 (B). There was no apprecia-ble difference between the reference sample and thesample processed with static magnetic field of 0.5 T asshown in Fig. 4 (C). It appears that SOS would not beinfluenced by the static magnetic field processing of 0.5T.

The results described above suggest that both POPand SOS were influenced by static magnetic field pro-cessing of 5 T, and it became clear that a form of theseTAGs were suppressed. Polymorphic behavior of SOSwould be more sensitive to static magnetic field andhave a critical magnetic flux density.

1,2-dipalmitoyl-3-oleoyl glycerol (PPO) shows twokinds of polymorph: a (melting point 18.5) and b(35.2) forms (6). Reference sample of PPO in thisexperiment showed an endothermic peak at 17-19soon followed by an exothermic peak at 20-23 inTMDSC curve. These two peaks corresponded to themelting of the a form and rapid crystallization of themore stable bform, respectively. Further heatingshowed an endothermic peak at 31-36 which is dueto the melting of bform. Figure 5 (A) shows theenthalpy changes of each peaks in a TMDSC curve.Thermopeaks indicating the melting of the a form andthe transformation from the a form to the bform couldnot be observed. This suggests that static magnetic fieldprocessing at 5 T suppressed the crystallization of the aform of PPO.

1,2-distearoyl-3-oleoyl glycerol (SSO) is similar withPPO in chain length structure, and exhibits simplertransformation from a form to bform, maintaining thetriple chain length structure (22). The melting points ofthese form are 26 and 41.4, respectively (23). Ref-erence sample of SSO in this experiment showed anendothermic peak at 30-33 which was soon followed

by an exothermic peak at 32-36 in TMDSC curve.These two peaks corresponded to the melting of the aform and rapid crystallization of the more stable bform. Further heating showed an endothermic peakat 40-44 indicating the melting of bform. In SSO,static magnetic field processing suppressed the crystal-lization of the a form (ca. 92% compared with the ref-erence sample), the transformation from the a form tothe bform (ca. 89%) and the crystallization of the bform (ca. 91%) as shown in Fig. 5 (B).

1-palmitoyl-2-oleoyl-3-stearoyl glycerol (POS),which is the major component of cocoa butter, has fourpolymorphs, a (19.5), d (28.3), pseudo-b(31.6),and b (35.5) (21). There are two pathways of poly-morphic transformations in POS : a pseudo-b band d pseudo-b b. a form directly transformed

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Fig. 5 Enthalpy Changes of 1,2-disaturated-3-unsaturatedMixed-Acid TAGs Crystallized under GeomagneticField (white) and Static Magnetic Field of 5 T (gray).(A) Enthalpy changes of PPO : Mean values of fourdeterminations ( standard deviation) are repre-sented. (B) Enthalpy changes of SSO : Mean valuesof five determinations ( standard deviation) arerepresented.


to pseudo-b, not through the d form. The pattern of theobtained TMDSC curve of POS was in good agreementwith the DSC curve reported by Arishima et al. (24).Reference sample of POS in this experiment showed anendothermic peak at 19-21 which was soon followedby an exothermic peak at 22-24. These two peakscorresponded to the melting of the a form and rapidcrystallization of the more stable bform, respectively.Further heating showed an endothermic peak at 31-35 corresponding to the melting of bform. Figure 6shows enthalpy changes of each peaks in TMDSCcurves of POS. Static magnetic field processing sup-pressed the crystallization of the a form (ca. 69% com-pared with the reference sample), and the transforma-tion from the a form to the bform (ca. 82%).

32 X-ray DiffractionThe XRD patterns of reference sample and magnetic

field processed samples of PPP were shown in Fig. 7(A). In wide angle region, the a form crystal is charac-terized by a single strong reflection at diffraction angle(2q) of 21.4 deg (25). The wide angle spacings arerelated to the cross sectional arrangement of the carbonatoms, i.e. the crystal structure on the atomic level: theyare independent of the triacylglycerol composition. Inthe small angle region, XRD provides additional infor-mation with respect to the overall molecular arrange-ment. In this study, the ratio of the XRD peak area inthe wide angle region ( 2q 21 deg) to the peak areain the small angle region (2q 6 deg) was defined toquantify the magnetic field effect. The ratios of PPP,POP, and PPO were shown in Table 1. Static magnetic

field processing suppressed the crystallization of the aform (ca. 90% compared with the reference sample).This result seems to be in conflict with the resultobtained by TMDSC. However, it can be explained asfollows: TMDSC is a thermodynamic measurementtechnique which measures the incoming and outgoingheat capacity during melting and crystallization of asubstance. Differences in XRD patterns between thereference and static magnetic field processed samplescould not be detected by TMDSC due to limited detec-tion of the present calorimeter. The result obtained byXRD suggests that effect of static magnetic field pro-cessing on crystallization behavior of saturated mono-acid TAGs depends on the kind of fatty acid chain

200J. Oleo Sci., Vol. 54, No. 4, 193-202 (2005)

Fig. 6 Enthalpy Changes of POS Crystallized under Geo-magnetism (white) and Static Magnetic Field of 5 T(gray). Mean values of four determinations (standard deviation) are represented.

Fig. 7 X-ray Diffraction Patterns of TAGs Crystallizedunder Geomagnetic Field for Control (solid blackline) and Static Magnetic Field of 5 T (solid grayline): (A) PPP, (B) POP, (C) PPO.


length which constitutes TAGs.Characteristic peak of a form crystal was observed at

2q 21 deg in XRD pattern of POP (Fig. 7 (B)) (26).Static magnetic field processing suppressed the crystal-lization of the a form of POP (ca. 69% compared withthe reference sample) as shown in Table 1. It is likelythat static magnetic field processing suppressed thecrystallizations of the a form in symmetrical saturated-unsaturated mixed-acid TAGs. Also, the characteristicpeak of a form crystal was observed at 2q 21 deg inthe XRD pattern (Fig. 7 (C)) of PPO (22). No signifi-cant differences were observed in XRD patternsbetween the reference sample and the static magneticfield processed sample (5 T) as shown in Table 1. How-ever, PPO exhibited suppressed crystallization of aform. The coefficient of variation (13%) of the peakarea which shows the a form in static magnetic fieldprocessed sample was larger than that (5-8%) of the ref-erence sample. The diffraction peak of bform mighthave overlapped on the peak of a form crystal, thusexplaining the reason for the higher variation. There-fore, polymorphic transition from a form to bformwould be caused by static magnetic field processing inPPO.

4 Conclusion

In order to clarify the effect of static magnetic fieldon polymorphic behavior of TAGs and to provide acrystal control technique using magnetic field to foodindustries, melted TAGs were cooled and crystallizedunder the static magnetic field. The main results are asfollows: (i) the effect of static magnetic field on crystal-lization of saturated mono-acid TAGs depended on acylchain length which constitutes TAGs (PPP and SSS),(ii) the shorter the acyl chains of TAGs, the more sensi-tive the saturated-unsaturated mixed-acid TAGs ( PPO

and SSO) were to static magnetic field and (iii) sym-metrical type TAGs (POP and SOS) were more sensi-tive to static magnetic field rather than asymmetricaltype of TAGs (POS). It is speculated that the effect of amagnetic field on polymorphism of TAGs is due to themagnetic field gradient in a magnet and the molecularorientation caused by magnetic anisotropy of a TAGmolecule. Magnetic anisotropy is defined as a propertyin which magnetic internal energy changes with magnet-ized directions of substances. Crystalline materials havea magnetic anisotropy whose magnetic susceptibilitychanges with direction of crystal growth.

The present findings will be useful in tempering fatsand oils, such as shortening and chocolate. However, inorder to confirm the conclusion (i), it is necessary toconduct the same experiments on more saturated mono-acid TAGs (e.g., LLL, MMM, AAA, BBB: M, myristicacid; A, arachidic acid; B, behenic acid) which consistof a fatty acid chain length of 12-22. It is also necessaryto examine the polymorphic behavior of asymmetricalsaturated-unsaturated mixed-acid TAGs (e.g., LLO,MMO, LMO, LPO, LSO) which consist of a fatty acidchain length of 12-18 for confirmation of conclusion(ii). Further, in order to prove conclusion (iii), it is nec-essary to execute the same experiments for more sym-metrical saturated-unsaturated mixed-acid TAGs (e.g.,LOL, MOM, AOA, BOB), and the asymmetrical satu-rated-unsaturated mixed-acid TAGs (e.g., MOL, MOP,MOS, MOA, MOB) which consist of a fatty acid chainlength of 12-22. There are many problems left unsolvedboth theoretically and experimentally. These include anenergetic consideration of the occurrence and stabiliza-tion of the diversified polymorphism of TAGs. Muchwork is needed to clarify the mechanism of the poly-morphic crystallization under static magnetic field.

Acknowledgement

The authors are deeply indebted to Dr. KiyotakaSato, Hiroshima University for providing constructivecomments and helpful suggestions. Dr. Toru Takahashiof Akita Research Institute of Food and Brewing for hiskind assistance in XRD measurements and valuable dis-cussion. We thank Dr. Zhe Jin of Iwate Industry Promo-tion Center for his instruction on superconducting mag-net system. Advanced Applications of Magnetic Field- The creation of industries based on magnetic fieldsapplication - program supported by Collaboration of

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Table 1 The Ratio of the Peak Area of a form Crystal ofTAGs.

Magnetic fieldprocessing

Ratio of the peak areaa

PPP POP PPO

Without 35.5 2.3a 26.7 0.5c 27.9 1.3e

Processed under 5 T 31.9 1.5b 18.4 1.1d 26.1 3.4fa Values are mean and standard deviations for triplicates, means with

different letters within a column differ signigicantly (P


Regional Entities for the Advancement of Technologi-cal Excellence (CREATE) and Japan Science andTechnology Agency (JST) are greatly acknowledged fortheir financial support.

References

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