Photon Factory Activity Report 2017 #35 (2018)

BL-10C/2016G076

Study on Novel Crystallization Promoters for Fats and Oils by Simultaneous SAXS
and WAXS Measurements
Fumitoshi Kaneko and Shinichi Yoshikawa
Graduate School of Science, Osaka Univ., 1-1 Machikaneyama, Toyonaka Osaka, 560-0044, Japan
Research Institute for Creating the Future, Fuji Oil Holdings Inc., Izumisano, Osaka 598-8540,
Japan1,*12

21 Introduction
In order to promote the lipid crystallization, surfactants
and materials having long hydrocarbon chains have beenused as additives. It is considered that their alkyl chainsact as templates for the heterogeneous nucleation byordering the hydrocarbon-chain moieties of lipids.
Recently, it has been clarified that inorganic and organic
crystals (i.e., talc, graphite, carbon nanotube, theobromine,
terephthalic acid, and ellagic acid dihydrate) remarkably
promoted
thelipid
crystallization
toform
thermodynamically stable crystals [1, 2]. These additives
are sparingly soluble in lipids and possess no longhydrocarbon chains in their molecules, which suggeststhat the promotional effects are caused by the strong
intermolecular interactions between the surfaces of thesecrystalline materials and lipids.
Although the new crystallization promoters have agreat potential in the application to the production andseparation processes of oleochemical industry, thecrystallization processes induced by them have not been
fully studied yet. The crystallization of lipid systems is acomplicated process, often involving polymorphic
structural changes. Since lipid molecules assemble toform crystals in layered structures having long and shortspacings, X-ray scattering measurements in a wide rangeof scattering angles are required. Taking this into account,
we have studied how the promoters affect the lipid
crystallization by simultaneous SAXS and WAXS
measurements.
2 Experiment
Powder samples of graphite, talc, theobromine andfumaric acid and a thin sheet of highly oriented pyrolytic
graphite (HOPG) were used as the promoters.
Crystallization of trilaurin(LLL), palm oil and cocoa
butter was carried out with and without these promoters.
Powder promoters were added at a concentration of 1
wt. % and an HOPG sheet was placed on lipid samples.
A lipid/promoter mixture enclosed with polyimide
films into a hole (2 mm φ ) in an aluminum plate (1.5 mmthickness) was heated at 80°C for 10 min to erase
memories of lipid crystals. The mixture was then cooled
down to 0°C at a rate of 1°C/min and subsequently heated
up to 80°C at a rate of 5°C/min.
Time resolved simultaneous SAXS and WAXS
measurements were carried out at BL-10C. The mixture
temperature was controlled by using a LINKAM hot/cold
stage.
3 Results and Discussion
Figure 1 shows the SAXS and WAXS profile changes
during the crystallization of LLL/fumaric acid andLLL/graphite powder mixtures. It turns out that there areremarkable differences in the crystallization process
between the two mixtures. For the LLL/fumaric acidmixture showing a weak promotion effect, a reflection
appeared at 0.031 Å-1 in the SAXS region and its intensity

increased as crystallization progressed. The position of
the reflection suggests that LLL started to crystallize inthe metastable phase β’, which is the same result
observed for neat LLL. Actually, the WAXS region
shows the profile unique to the O⊥ subcell characteristicof the β’ phase, such as intense reflections at 0.24 and(a)(b)

Figure1. X-ray scattering profile changes during thecrystallization of LLL/fumaric acid mixture (left) andLLL/graphite powder mixture (right) in the regions of (a)SAXS and (b) WAXS.
0.26 Å-1. The stable phase β did not grow during thecooling process of this sample.
On the other hand, the addition of graphite powder
having a strong promotion effect induced thecrystallization of the β phase. In both the SAXS andWAXS regions, the reflections characteristic of the βphase are observed from the inception of crystallization,such as a long-spacing reflection at 0.032 Å-1 and shortspacing reflections due to the T// subcell at 0.22, 0.26 and0.27 Å-1.

Photon Factory Activity Report 2017 #35 (2018)

The results described above suggest that a strong
interaction is exerted between LLL molecules andsurfaces of graphite particles, reducing significantly theactivation energy for nucleation of the β phase. When acrystal face of this promoter acts as a heterogeneous
nucleation site, the generated new nuclei of LLL may
have a specific orientation to the crystal face.
In order to clarify the arrangement of LLL molecules in
the generated β phase on surfaces of graphite particles,
the crystallization of LLL/HOPG system was alsoinvestigated. The flat surface of HOPG is covered withthe carbon hexagonal network correpondfing to the (001)plane. Figure 2 shows the results of measurements usinga sample cell where an HOPG sheet was placed inside
one of the polyimide windows to contact LLL and X-rays
were applied to the windows perpendicularly.
Accordingly, X-rays passed through the hexagonal
network of HOPG along its normal.
The striking feature of the LLL/HOPG system is thatthe peaks appearing in both SAXS and WAXS regions
were remarkably weaker than the counterparts in theLLL/graphite powder mixture, though the amount of LLL
in the cell was almost the same. This result indicates thatthe crystalline phase of LLL was highly controlled by theHOPG surface; when crystal nuclei were generated with aspecific orientation to the HOPG surface, most latticeplanes did not meet the Bragg condition. It can beassumed that the most part of LLL crystals occurred in
the LLL/HOPG system grew keeping the specificorientation of their nuclei generated heterogeneously at
the surface of HOPG and a small portion of LLL

happened to grow with disordered orientations giving
the X-ray profile very weak reflections.
This assumption is supported by the preliminary
obtained FTIR-ATR results on LLL β-form crystals,
which formed a thin layer on the surface of a graphite
sheet. Figure 3 shows the p- and s-polarized spectra,
emphasizing the vibrational modes whose transition
moments are normal and parallel to the sample surface,respectively. The p-polarized spectrum shows CH2
wagging progression bands much more intense than thosein the s-polarized spectrum. Since the transition momentsof the wagging modes of triacylglycerols such as LLL are
parallel to their long hydrocarbon chains, the spectralfeature indicates that the long axis of LLL molecules
preferentially oriented toward the normal of thehexagonal network of graphite. From these results, wenow consider that heterogeneous nucleation of LLL βform crystals at graphite surfaces predominantly takes
place to orient their lamellar planes parallel to thehexagonal network.
As shown in Fig. 2, a SAXS peak for the LLL β’ phase
was observed prior to that for the β phase and theintensity increased at the early stage of crystallization. At
the moment, it is not clear wether the β’ phase occurredheterogeneously on the surface of HOPG orhomogeneously from the bulk of LLL.
Concerning crystal growth mechanisms for othercombinations of lipids and promoters, the data analyses
are now in progress, which will be presented in the nextreport.
References[1] S. Yoshikawa, H. Kida, K. Sato, J. Oleo Sci., 63, 333(2014)[2] S. Yoshikawa, H. Kida, K. Sato, Eur. J. Lipid Sci.
Technol., 117, 585 (2015)* toshi@chem.sci.osaka-u.ac.jp

Figure 2. X-ray scattering profile changes during thecrystallization of LLL kept in contact with an HOPG
sheet.

Figure 3. Polarized FTIR–ATR spectra of a crystalline
LLL layer grown on a graphite sheet