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This study evaluates the influence of the polymorphs of triacylglycerol (TAGs) seed crystals on the crystallization of coconut oil (CO) using seeding techniques. Tripalmitin (PPP) and tristearin (S...

Understanding the correlation between the molecular structure of triacylglycerols (TAGs) and their crystallization behavior is a prerequisite for engineering the nanostructures of fats to enhance s...

This paper reports the preparation of oleogels composed of edible oils (olive oil, squalene, and caprylic/capric triglyceride) and high-melting fat crystals (tribehenoyl-glycerol (BBB)) to explore the potential use of BBB/edible oil mixtures as low-cost and stable gelators. These mixtures exhibited gel-like behaviors upon rapid cooling and subsequent heating. The mixtures of BBB in the liquid oils formed oleogels at BBB concentrations > 4.0 wt%. The thermal behaviors, crystal structures, and crystal morphologies of mixtures of BBB produced from 6.0 wt% BBB crystals in 94.0 wt% liquid oils were examined following the treatment of these systems according to different temperature regimes. In addition, rheological analysis was conducted to evaluate the physical properties and storage stabilities of the prepared oleogels. It was found that rapid cooling to the crystallization temperature (Tc) from 70°C and subsequent heating to the final temperature (Tf) were necessary to reveal the gel-like behavior. In addition, the crystals treated with rapid cooling were smaller and more uniform in size than those treated with a simple cooling procedure. The differential scanning calorimetry melting peaks were broad or split, and exhibited the eutectic mixing behavior of multi-component triacylglycerols. The X-ray diffraction spectra showed that the melt-mediated α to β transformation of the mixtures was a prerequisite for revealing the gel-like behavior. Moreover, the tempering procedure was found to influence the physical properties of the oleogels, wherein no visible changes were observed for any of the oleogels after rapid cooling and storage for 6 months at 25°C.

The crystallization behavior of the metastable &alpha, form of triacylglycerols (TAGs) plays a critical role as a precursor for the crystallization of more stable &beta, &prime, and &beta, forms for various applications in food and pharmaceutical products. However, precise analysis of the crystallization kinetics of &alpha, has not been performed, likely due to its rapid and complex behavior. This paper presents the observation results of the initial stages of the isothermal crystallization kinetics of &alpha, forms of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP), 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (rac-PPO), and molecular compound (MC) crystals of a POP/rac-PPO (1/1) mixture (MCPOP/PPO) using synchrotron radiation time-resolved X-ray diffraction and polarized optical microscopy. In all the TAGs, &alpha, crystals with a worm-like morphology started to grow rapidly in the first stage. Then, the &alpha, crystals slowly transformed into more stable forms in different manners for different TAG samples. In POP, the conversion was simple, as the &alpha, 2 form transformed into &gamma, 3, whereas in rac-PPO, the lamellar distance values of the &alpha, 2 form continuously decreased with time and changed into the &alpha, 3 form. In the MCPOP/PPO crystals, in contrast, separate crystallization of &alpha, 2 of a rac-PPO fraction initially occurred, followed by the crystallization of &alpha, 2 of POP, and the two &alpha, forms merged into &alpha, 2 of MCPOP/PPO. This separate crystallization was caused by large differences in the crystallization kinetics of the &alpha, forms of POP and rac-PPO.

We have investigated the polymorphism of triacylglycerol (TAG) crystals as they affect the qualities such as shelf life, mouth feel, and texture of chocolate and other products. Saturated monoacid TAGs, like trilaurin, are considered as models for TAG crystallization, however, there is still debate about the number of their polymorphs that exist. In this study, we characterized a set of novel polymorphs, &beta, forms of saturated monoacid TAGs, which were obtained via different pathways depending on the crystallization history, by polarized light microscopy, X-ray diffraction, and differential scanning calorimetry. Saturated monoacid TAGs were crystallized as the unstable polymorphs, the a or &beta, &rsquo, forms first, and then they were transformed into &beta, forms by solid&ndash, solid transformations. The &beta, form that had transformed from &beta, changed its morphology by a polymorphic transformation, while the &beta, form made from the a form kept its spherulite morphology. The &beta, forms obtained showed different melting points. Additional heat treatment promoted further polymorphic transformation. Four novel &beta, forms were found for each of the saturated monoacid TAGs, trilaurin, trimyristin, tripalmitin, and tristearin. They showed similar polymorphism with the same subcell packing.

Owing to the increasing reports of the harmful effects of trans and saturated fatty acids, the demand for trans- and saturated-fatty-acid-free oil and fat products is increasing among consumers. However, it is difficult to maintain the product stability and shape retention of such oil and fat products. As a result, there is a high demand in the processed oil and fat industry to develop solutions to such problems. Herein, we used molecular compound (MC) crystals in an attempt to find alternatives to trans and saturated fatty acids. The MCs used were 1,3-dioleoyl-2-palmitoyl-sn-glycerol (OPO) and 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP)&mdash, the main components of lard and palm oil, respectively. We believe that OPO and POP can be used to obtain no-trans, low-saturation, and high-oleic-acid oil and fat products. Optimal conditions for efficient MC crystallization were examined by changing the oil and fat composition under rapid cooling conditions assuming industrial cooling process by using differential scanning calorimetry and synchrotron radiation time-resolved X-ray diffraction methods. It was concluded that the increase in OPO concentration destabilized MC formation, while the increase in POP concentration stabilized it under rapid cooling conditions. As a result, it was shown that MC crystals can be efficiently obtained by reducing the degree of POP supercooling.

We performed in situ observations of the crystallization and melting behaviors of palm mid fraction (PMF) on sorbitan ester (SE) crystals comprising different fatty acid moieties (sorbitan tripalmitate (STP), sorbitan tristearate (STS), or sorbitan tribehenate (STB)) to reveal the epitaxial relationship between fat crystals and emulsifier crystals. The effects of SEs on the thermal behavior and polymorphism of PMF were investigated by differential scanning calorimetry and synchrotron radiation X-ray diffraction. These measurements showed that the addition of STP and STS greatly increased the crystallization temperature of PMF, which was caused by the crystallized SEs that were nucleated prior to PMF. Microscopic observations demonstrated that PMF crystals were oriented in the same direction as crystals of STP and STS because the chain lengths of the fatty acid moieties were similar to those of PMF. In contrast, when STB was used as a substrate, PMF crystals were not oriented in the same direction as STB c...

Edible oils containing high concentrations (>80%) of diacylglycerols (DAG oil) have beneficial health effects on obesity and obesity-related diseases; however, at low temperature, undesired precipitation of high-melting fractions in DAG oil can occur. Thus, preventing the precipitation of high-melting saturated fatty acid moieties in DAG oil is crucial for its expanded use. In this study, we investigated the mechanism of retardation of crystallization of DAG oil through the addition of polyglycerol fatty acid esters (PGFEs). We observed the occurrence of birefringence under polarized crossed-Nicols conditions in the PGFE-added DAG oil. We also found that prior to the crystallization of high-melting DAG fractions, PGFE-added DAG oil showed shear-rate-dependent changes in viscosity, providing strong evidence for the existence of self-assembled structures that lead to the birefringence. Furthermore, small- and wide-angle X-ray diffraction patterns suggest the formation of a supramolecular assembly comprising...

This study examined the destabilization of an oil-in-water (O/W) emulsion by freeze-thawing with a focus on the influence of the morphology and polymorph of fat crystals. For a model of food emulsion, this study used a mayonnaise-type O/W emulsion containing 70wt% canola oil (canola emulsion) or soybean oil (soybean emulsion) stored at -15, -20, and -30°C. The freeze-thaw stabilities of the emulsions were evaluated by measuring the upper oil layer after freeze-thawing. The soybean emulsion kept at -20°C had the highest stability; the other emulsions were destabilized during 6h of storage. Crystallization in the emulsions was determined using differential scanning calorimetry (DSC), time variation of temperature, X-ray diffraction measurement, and polarized light microscopy. DSC thermograms indicated that crystallization in emulsions occurred first in the high-melting fraction of oil, followed by water and, last, in the low-melting fraction of oil during cooling to -40°C. In the canola emulsion, the amount of fat crystals derived from the low-melting fraction of oil increased during storage at all temperatures, resulting in partial coalescence. The soybean emulsion was expected to be destabilized by polymorphic transformation (sub-α to β' and β) of fat crystals derived from the high-melting fraction during storage at -15 and -20°C. However, the soybean emulsion did not exhibit polymorphic transformation stored at -30°C, and the amount of fat crystals did not increase during freezing; thus, it was destabilized via a different mechanism.

We examined the influence of dynamic thermal treatment (variation of cooling/heating rates) on the polymorphic crystallization and transformation pathways of 1-palmitoyl-2,3-dioleoyl glycerol (POO), 1-stearoyl-2,3-dioleoyl glycerol (SOO), and 1-palmitoyl-2-oleoyl-3-linoleoyl glycerol (POL), which are major saturated-unsaturated-unsaturated (SUU) triacylglycerols (TAGs) of vegetable oils and animal fats (e.g., palm oil, olive oil, and Iberian ham fat). Using mainly a combination of differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffraction (SR-XRD), we analyzed the polymorphic behavior of TAGs when high (15 °C min− 1), intermediate (2 °C min− 1), and low (0.5 °C min− 1) cooling and heating rates were applied. Multiple polymorphic forms were detected in POO, SOO, and POL (sub-α, α, β'2, and β'1). Transient disordered phases, defined as kinetic liquid crystal (KLC) phases, were determined in POO and SOO for the first time. The results demonstrated that more stable forms were directly obtained from the melt by decreasing the cooling rates, whereas less stable forms predominated at high cooling rates, as confirmed in our previous work. Regarding heating rate variation, we confirmed that the nature of the polymorphic transformations observed (solid-state, transformation through KLC phase, or melt-mediation) depended largely on the heating rate. These results were discussed considering the activation energies involved in each process and compared with previous studies on TAGs with different saturated-unsaturated structures (1,3-dioleoyl-2-palmitoylglycerol, 1,3-dipalmitoyl-2-oleoyl-glycerol, trioleoyl glycerol, and 1,2-dioleoyl-3-linoleoyl glycerol).

The polymorphic crystallization and transformation behavior of extra virgin olive oil (EVOO) was examined by using differential scanning calorimetry (DSC) and X-ray diffraction with both laboratory-scale (XRD) and synchrotron radiation source (SR-XRD). The complex behavior observed was studied by previously analyzing mixtures composed by its main 2 to 6 triacylglycerol (TAG) components. Thus, component TAGs were successively added to simulate EVOO composition, until reaching a 6 TAGs mixture, composed by trioleoyl glycerol (OOO), 1-palmitoyl-2,3-dioleoyl glycerol (POO), 1,2-dioleoyl-3-linoleoyl glycerol (OOL), 1-palmitoyl-2-oleoyl-3-linoleoyl glycerol (POL), 1,2-dipalmitoyl-3-oleoyl glycerol (PPO) and 1-stearoyl-2,3-dioleoyl glycerol (SOO). Molten samples were cooled from 25 °C to − 80 °C at a controlled rate of 2 °C/min and subsequently heated at the same rate. The polymorphic behavior observed in multicomponent TAG mixtures was interpreted by considering three main groups of TAGs with different molecular structures: triunsaturated OOO and OOL, saturated-unsaturated-unsaturated POO, POL and SOO, and saturated-saturated-unsaturated PPO. As confirmed by our previous work, TAGs belonging to the same structural group displayed a highly similar polymorphic behavior. EVOO exhibited two different β'-2 L polymorphic forms (β'2-2 L and β'1-2 L), which transformed into β'-3 L when heated. Equivalent polymorphic pathways were detected when the same experimental conditions were applied to the 6 TAG components mixture. Hence, minor components may not exert a strong influence in this case.

We studied the effects of adding emulsifiers, specifically polyglycerine fatty acid esters (PGFEs), on the crystallization of palm stearin (PS), using synchrotron radiation X-ray diffraction and DS...

Many physical properties (e.g., hardness, texture, rheology, and spreadability) of lipid‐based products largely depend on the extent of crystallization and transformation of lipids, and their network formation. Therefore, many studies have focused on controlling the crystallization of lipids in order to determine the functionality of lipid crystals. Both internal and external factors greatly affect the processes of lipid crystallization. The most important internal factors are polymorphism, which depends on variation in fatty acid moieties, and the composition or blending of different lipid materials. Important external factors are thermal treatment, additives, application of shear, sonication, and pressure. This paper briefly reviews recent advances in research on these external factors. We discuss the results by considering the relationships between external factors and thermodynamics, as well as kinetic properties of the crystallization and transformation of polymorphic forms of lipid crystals.

POP (1,3-dipalmitoyl-2-oleoyl glycerol), a major triacylglycerol component of vegetable and animal fats found in chocolate, fat spread, and other edible fats, crystallizes in seven polymorphic forms: α, γ, δ, β′2, β′1, β2, and β1. The crystallization and transformation pathways of the polymorphs of POP are influenced by many factors. In the present work, we studied the influence of the rates of cooling and heating on the polymorphic crystallization and transformation of POP. The rate of cooling (heating) was changed from 15 to 2, 1, and 0.5 °C min−1 (15 to 2, 1, 0.5, and 0.1 °C min−1). The crystallization and transformation processes were examined with differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffraction (SR-XRD). The results indicated that more stable forms were formed in a higher quantity when POP was slowly cooled and heated, whereas less stable forms occurred at higher rates of cooling and heating. Specifically, less stable α and γ forms were directly obtained at cooling rates of 15 to 0.5 °C min−1. The more stable forms of β′ or β did not occur even at a rate of cooling of 0.5 °C min−1, whereas α or γ transformed to β′ or β at heating rates of 0.5 and 0.1 °C min−1. The polymorphic transformations occurred either in solid-state or melt-mediation and were largely influenced by the heating rates. We discuss the present results by considering the differences in activation free energies for the transformations from α or γ to more stable forms, which may determine the heating-rate-dependent transformation pathways.

Using macrobeam and microbeam techniques, we performed synchrotron radiation X-ray diffraction (SR-XRD) analyses of fat crystallization in water-in-oil (W/O) emulsion, in combination with DSC and polarized optical microscopic observation. Particular focus was on the crystallization of the fats around water droplets in the W/O emulsion systems using food emulsifiers of polyglycerol polyricinoleate (PGPR) alone (PGPR emulsion), and PGPR and monobehenoylglycerol (MB) (PGPR+MB emulsion). We obtained the following results: (1) macrobeam SR-XRD confirmed that adding MB promoted fat crystallization during cooling, (2) microbeam SR-XRD indicated that the lamellar planes of fat crystals near the water and oil interfaces are arranged almost parallel to the interface planes in both PGPR emulsion and PGPR+MB emulsion, and (3) adding MB resulted in the formation of tiny fat crystals because it promoted crystallization, which occurred both in the bulk oil phase and at the W/O interfaces. The present study is the first to apply microbeam SR-XRD to observe the microscopic features of fat crystallization in W/O emulsion, following fat crystallization in the oil droplets in the oil-in-water (O/W) emulsion (Arima, S.; Ueno, S.; Ogawa, A.; Sato, K. Langmuir 2009, 25, 9777-9784).

Rice bran wax (RBX) obtained during rice bran oil purification can form organogels in edible oils. The kinetics of crystallization and the viscous properties of RBX organogels were studied using differential scanning calorimetry (DSC), viscosity changes with varying temperature, hardness measurements by penetrometry, and synchrotron radiation X-ray diffraction (SR-XRD). The organogels were prepared by RBX in concentrations of 1%, 3%, 6%, and 10% on a weight basis in salad oil, olive oil, and camellia oil. The liquid oil type had no significant effect on the melting and crystallization temperatures of the RBX. However, the viscosity and the texture of the organogels differed with liquid oil type, temperature, and RBX concentration. Changes in the viscosity of the RBX organogels were monitored during cooling from 80°C to 20°C. Drastic viscosity changes occurred in accordance with the onset of crystallization in DSC thermographs obtained at a rate of 5°C/min. RBX in the olive oil and camellia oil mixtures had higher viscosity than RBX in the salad oil mixture, which correlates with the hardness obtained in texture measurements at 20°C. SR-XRD was used to clarify the crystal structures of the building blocks of the RBX organogels in salad oil. It was found that the RBX formed crystals with a long spacing of 7.3 ± 1 nm and short spacings of 0.41 ± 1 nm and 0.37 ± 1 nm. The intensity of the long-spacing pattern was remarkably weaker than that of the short-spacing patterns, which demonstrated strong anisotropy in the crystal growth of RBX crystal particles.

This article reviews new information about polymorphic structures, kinetic and microscopic properties of fat crystals in colloidal dispersion states such as aggregates (spherulite), oil-in-water (O/W) emulsion and water-in-oil (W/O) emulsion. The kinetic processes of fat crystallization under external factors such as different cooling rates, shear and ultrasound irradiation are reviewed. Microstructures of fats revealed by synchrotron radiation microbeam X-ray diffraction techniques in bulk and emulsion states are also reviewed for the first time.

Margarine and fat spread contain typical water-in-oil emulsions, including semi-solid fats, as continuous oil phases. The application of palm oil, one of the most promising trans-fat alternatives, for semi-solid fats is increasing. However, granular crystals often occur in palm-oil-based solid fats and cause deterioration. In this study, we carried out differential scanning calorimetry (DSC), optical microscopy, and X-ray diffraction (XRD) experiments on granular crystals in margarine. A conventional laboratory-scale technique was applied to examine thermal properties of high-melting fat fractions in granular crystals. In addition, microstructures of the granular crystal were precisely observed with a synchrotron radiation small-angle XRD (SR-μ-SAXD) technique by using a microbeam having a cross section of 5 × 5 μm2. The following results were obtained. (1) DSC indicated that granular crystals are composed of high-melting fractions having a melting temperature of 23 °C. (2) Conventional XRD of granular crystals indicated that β-fat crystals of a triple chain length structure (β-3) melted below the melting of β′-fat of a double chain length structure (β′-2). (3) SR-μ-SAXD indicated that the fat crystals in normal margarine were β′-2. However, the fat crystals of the double and triple chain length structures were simultaneously observed at the center region of a granular crystal, whereas only the fat crystals of β-3 were observed at the outer region of a granular crystal. We analyzed the microstructures and formation processes of granular crystals in relation to the fractional crystallization of the β form of 1,3-dipalmitoyl-2-oleoyl-sn-glycerol promoted by crystallization and transformation of tripalmitin and tristearin fractions.

親油性と親水性乳化剤の併用添加による安定性の飛躍的な向上は2種類以上の異なる性質を示す乳化剤を組み合わせることにより，（1）乳化膜のパッキング密度の向上，（2）鋳型効果による微細結晶の油滴内部での分散，（3）針状であるβprime;型結晶への多形転移を抑制，遅延が，低温におけるエマルションの安定性の向上をもたらしと考えられる．

We have carried out X-ray microbeam analysis of the crystallization behavior of n-hexadecane (C16) in oil-in-water emulsion droplets that were formed using surfactants with different types of hydrophobic moieties. It was confirmed that molecular-shape matching between the hydrophobic moiety and C16 caused the following crystallization behavior: when the molecular shape of the hydrophobic moiety was similar to C16, high-intensity X-ray diffraction of the rotator phase of C16 was detectable at the initial stage of crystallization and the long-chain axes of C16 crystals aligned normal to the membrane interface. The present results provided the first evidence of interfacial heterogeneous nucleation caused by molecular interactions at the emulsion membrane, which is thought to be related to the interfacial freezing that was observed at the oil−water interface with surfactants in a bulk system.

This paper reports experimental results of in situ observations of thermochromic processes of two binary mixture systems of 1-(4-hydroxyphenyl)-3-octadecylurea (PU18) + fluoran dye (FD), and 4-hydr...

The morphology, crystalline structure and crystal growth kinetics of melt-crystallized thin isotactic polybutene-1 films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. It is demonstrated that a bypass of tetragonal phase crystallization and direct melt crystal growth of the trigonal phase can be achieved via self-seeding at atmospheric pressure using solution-grown trigonal crystals as nuclei. Electron microscopy and optical microscopy observations show that melt-crystallized isotactic polybutene-1 single crystals of the trigonal phase have rounded or hexagonal morphologies around 75°C. The growth rate of trigonal crystals in the melt has been obtained by in-situ optical microscopy. The growth rate of trigonal crystals in the melt is 1/100 and 1/1000 that of tetragonal crystals in the melt around 70 and 90°C, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal properties, powder X-ray diffraction patterns and FT-IR absorption spectra of crystals of two isomers of conjugated linoleic acid (CLA), 9-cis, 11-trans-CLA (c9t11), 10-trans, 12-cis-CLA (t10c12) were examined. To search for polymorphic modifications, we carefully performed crystallization from melt and solution phases, and isolated one type of crystalline form in c9t11 and t10c12. The melting temperature (T m) was 14.9 °C, enthalpy of fusion (ΔH) was 38.7 kJ/mol, and entropy of fusion (ΔS) was 134 J/mol K for c9t11, and T m = 19.8 °C, ΔH = 35.6 kJ/mol and ΔS = 122 J/mol K for t10c12. The X-ray diffraction and FT-IR measurements indicated O⊥ subcell packing in the crystals of c9t11 and t10c12, and long spacing values of 4.22 nm for c9t11 and 3.88 nm for t10c12. The unique molecular structures of the two isomers of CLA are discussed in comparison to the polymorphism of oleic acid, petroselinic acid, elaidic acid and linoleic acid, all of which are unsaturated fatty acids having the same carbon number of 18 as that of the two CLA isomers.

An oil-in-water (O/W) emulsion, in which the oil phase is semi-solid fat, is easily destabilized when stored below the crystallization temperature of the oil phase. Such destabilization, characterized by loss of fluidity at chilled temperature and oil-water separation after re-heating, is caused by inter-droplet bridging of fat crystals protruding out of the emulsion droplets. In the present study, we found that the simultaneous use of additives of highly hydrophobic sucrose oligoester (SOE; P-170) and highly hydrophilic SOE (P-1670) containing palmitic acid moiety remarkably retarded the crystallization-induced destabilization of the O/W emulsion that contains palm-mid-fraction (PMF) as the oil phase. Without the additives, destabilization occurred when the emulsion was cooled from 60 to 0 degrees C and kept at 0 degrees C for 1 day. Microscopic observation revealed that destabilization was caused by coalescence of the oil droplets, which was triggered by the growth of needle-shaped PMF crystals protruding out of the emulsion membranes. However, the addition of P-170 to PMF increased the crystallization temperature of PMF and at the same time retarded the destabilization. Furthermore, the simultaneous addition of P-170 and P-1670 retarded the crystallization-induced destabilization even more. Optical observation, DSC, and synchrotron radiation X-ray diffraction measurements indicated that the P-170 additive enhanced interfacial heterogeneous crystallization to form tiny PMF crystals in the droplets, and that the P-1670 additive retarded morphological change of the PMF crystals into long needle shapes in association with polymorphic transformation from alpha to beta'.

1,3-Dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP) are two major molecular species that account for roughly half of the total triacylglycerols in palm oil. The binary phase behavior of a POP/OOP mixture plays an important role in the crystallization of palm oil. We conducted thermodynamic and kinetic studies of OOP and its mixtures with POP using differential scanning calorimetry and X-ray diffraction with a conventional generator and synchrotron radiation. We found that OOP has two polymorphs, α as a metastable form and β′ as the most stable form, and that the two forms are stacked in a triple-chain-length structure. The POP/OOP mixtures exhibited immiscible eutectic natures in both their metastable and their most stable states, in contrast to POP/1,2-dipalmitoyl-3-oleoyl-rac-glycerol and POP/1,3-dioleoyl-2-palmitoyl-sn-glycerol mixtures, in which molecular compounds of a double-chain-length structure were formed. A time-resolved synchrotron radiation X-ray diffraction study undertaken during the cooling and heating processes indicated that the α and β′ forms of the POP and OOP fractions crystallized and melted in separate manners, and that crystallization of the β′ form and the polymorphic transformation from α to β′ of POP and OOP are promoted in the presence of another component. The absence of molecular compound crystals in the binary mixtures of POP/OOP is explained by taking into account the molecular interactions of acyl chain packing, glycerol conformation, and methyl end stacking, among which glycerol conformation appeared to be most influential.

The extent of crystallization and transformation of lipids, and their network formation, play decisive roles in determining physical properties (e.g., hardness, texture, rheology, and spreadability) of lipid-based food products. In these products, the lipid materials are present in rather complicated physical states such as mixtures of solid and liquid lipids or emulsified with water phases. In addition, various external influences are applied during actual production in a factory. Therefore, exploration of lipid crystallization under multiple external influences is necessary to improve the functionality of lipid-based food products.

Conjugated linoleic acid (CLA) is commercially available as a mixture consisting of almost equal amounts of the cis-9,trans-11-CLA (c9, t11) and trans-10, cis-12-CLA (t10, c12) isomers. Separation of the two isomers is highly significant since each exhibits different biochemical properties. Highly efficient separation could be accomplished by crystallization in acetone (solvent) of the two CLA isomers (solutes) in the presence of medium-chain fatty-acid (MCFA) additives. The relative concentration ratios of the two CLA isomers in the solvent-crystallized materials varied depending on which MCFA were added. Addition of lauric and decanoic acids resulted in the crystals predominantly containing t10,c12, whereas octanoic acid yielded those predominantly containing c9,t11. We have confirmed that onetime solvent crystallization using decanoic acid and octanoic acid additives increased the t10,c12 and c9,t11 concentrations, and that repeated solvent crystallization resulted in the ratio of c9,t11 to t10,c12 of at least 4∶96 or 98∶2.

We observed the crystallization and polymorphic transformation processes of palm stearin (PS) dispersed in nanometer-size oil-in-water emulsion droplets (nanometer-size droplets, average diameter 120 ± 30 nm) using DSC and in-situ synchrotron radiation X-ray diffraction (SR-XRD) techniques. The nanometer-size emulsion droplets were prepared by using four types of highly hydrophilic polyglycerine fatty-acid mono-esters, in which a polar moiety was made of 10 polymerized glycerins (decaglycerine, 10G) and nonpolar moieties were lauric, myristic, palmitic, and stearic fatty acids. When decaglycerin monolaurate (10G1L) was employed, crystallization temperatures (Tc's) of high-melting and low-melting fractions of PS were 8 and 2 °C, which were decreased from 31 and 3 °C for the bulk PS. However, the Tc of the high-melting fraction of PS was increased as the fatty-acid moiety was changed to myristic (10G1M), palmitic (10G1P), and stearic (10G1S) acids; in particular, the Tc became 38 °C with 10G1S. Furthermore,...

The crystallization and polymorphic behavior of palm stearin (PS) in a bulk state and in oil-in-water (O/W) emulsion droplets (average diameter, 1.7±0.3 μm) was observed by using DSC, optical microscopy, and in situ X-ray diffraction with synchrotron radiation (SR-XRD). For the bulk sample the DSC measurements revealed three main exothermic peaks at approximately 31 (large), 21 (small) and 3°C (medium) on cooling, and broad endothermic peaks at approximate −3 (small), 8, 15 to 25 (medium), and 37 and 53°C upon heating. The SR-XRD patterns taken during cooling from 60 to −5°C clarified that the DSC exothermic peaks around 31 and 3°C corresponded to crystallization of the α form of high-melting and low-melting fractions, respectively, and that the occurrence of β′ corresponded to the small exothermic peak around 21°C. The XR-XRD patterns taken during heating from −5 to 60°C demonstrated that the DSC endothermic peaks corresponded to the following transformation processes: melting of α of the low-melting fraction (−3°C), melt-mediated transformation from α to ∇′ (15–25°C), melting of β′ (36°C), and melting of β (53°C) of the high-melting fraction. As for the O/W emulsion sample, the DSC and SR-XRD measurements during the cooling and heating processes exhibited basically the same behavior as that of PS in the bulk state, except that β′ did not crystallize during the cooling process, and the temperatures of crystallization of α, melt-mediated α→β′→β transformation, and melting of β were lower in the emulsion droplets than in the bulk state.

The course focuses on the polymorphism and polymorphic transformation of edible fat crystals, such as chocolate. The morphology, crystallization behavior and polymorphic transformation will be observed under optical microscopy, and melting point of each polymorph will be determined.

It was found that even-numbered n-alkanes (number of carbon atoms = 16−22) had a crystal structure that has not been reported for their bulk phase when the n-alkanes were nucleated in oil-in-water emulsion droplets with additives. We measured wide- and small-angle X-ray diffraction signals, using synchrotron radiation, at the same time that the nucleation was determined by differential scanning calorimetry. When high-melting-point surfactants were added to the droplets, pseudohexagonal and orthorhombic crystals were nucleated. In contrast, triclinic crystals formed in the droplets without the additive, and in bulk liquid both with and without the additives. The results were discussed by taking into account interfacial heterogeneous nucleation accelerated by freezing of the adsorbed films of the additive molecules at the oil−water interface. These findings indicate that emulsion can be used to form a new crystalline polymorphic structure by using suitable additives that modify interfacial heterogeneous nuc...

Crystallization, polymorphic transformation, and melting behavior of nanoparticles of trilauroylglycerol (LLL) in oil-in-water (O/W) emulsion were examined initially by DSC, and then by simultaneous synchrotron radiation small-angle (SAXS) and wide-angle (WAXS) X-ray diffraction and DSC (SR-SAXS /WAXS/DSC). The O/W nanoparticles emulsions having average diameters of 42 to 120 nm were prepared by application of mechanical shear using a high-pressure homogenizer. The following results were obtained: (i) The DSC study showed that the melting temperature of the stable β form of LLL was reduced from 46.7 (bulk) to 26.5–44.0°C (nanoparticles); this variation as assumed to be due to the size distribution of the nanoparticles. Crystallization temperature was also reduced from 18.9 (bulk) to −9.5±0.5°C (nanoparticles). These results were consistent with those of previous studies of nanoparticles of fats obtained in the O/W emulsion. (ii) The results obtained by the SR-SAXS/WAXS/DSC technique during the cooling process to −20°C showed that the first-occurring polymorph of LLL in the bulk liquid was β′, whereas α was first nucleated and transformed to β′ around −10°C during cooling in the nanoparticles. (iii) The SR-SAXS/WAXS/DSC data taken during the heating process from −20°C after the crystallization showed that β′ transformed to β around 0°C and that the melting of β started at 30°C and ended at 44°C. The present study showed that forming nanoparticles of LLL in the O/W emulsion having the diameters of 42 to 120 nm reduced the melting and crystallization temperatures and increased the transformation rate of α→β′→β in comparison to the LLL crystals formed in the bulk phase.

The crystallization behavior of tripalmitin (PPP) and trilaurin (LLL) without and with the application of ultrasonic power is investigated in situ using synchrotron radiation time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) simultaneous measurement. Without ultrasound application, both polymorphic forms β‘ and β crystallized in the melt of each substance. With ultrasound treatment of the melt, the following effects were observed: (i) a marked decrease of induction times for crystallization of both PPP and LLL, (ii) an increased nucleation rate, and (iii) a crystallization of only the β form for both PPP and LLL under conditions of initial crystallization temperatures of 50 and 30 °C, respectively, and applied ultrasound of 2 s. The last finding demonstrates that ultrasound irradiation can be used as an efficient tool for controlling the polymorphic crystallization of fats. In addition to this, the crystallization of LLL under a lower initial crystallization tempera...

Many overwintering livings accumulate fat (triacylglycerol) before winter and use it for basal metabolism. However, triacylglycerol in solid state is not digested by lipase. Therefore, it is expected that livings using fat during overwintering have some special strategies to avoid crystallization of fat at low temperatures. In order to clarify the strategies, Ohtsu et al. have studied the phase behavior of fat extracted from the cold-adapted Drosophila flies [Ohtsu, T., Katagiri, C., Kimura, M. T. & Hori, S. H. (1993). J. Biol. Chem. 268, 1830-1834]. It is, however, uncertain that the results obtained from the extracted fat can reflect the in vivo phenomena. In the present study, we investigated the crystallization of fat in a fly body with small- and wide-angle X-ray scattering, and detected the Bragg diffraction peaks that can be assigned to those originated from the solid triacylglycerol crystallized in the fly body below 253 K (– 20 oC).

The effects of polyglycerol behenic acid esters on the crystallization of palm oil were studied using optical microscopy and X-ray diffraction. Polyglycerol behenic acid esters were added in an attempt to promote the crystallization of palm oil. Optical microscopy observation confirmed that palm-oil crystals with the addition of 1 wt% of polyglycerol behenic acid esters were smaller and the number of palm oil crystals larger than without the additives. This indicated that the polyglycerol behenic acid ester promoted nucleation and inhibited crystal growth of palm oil. X-ray diffraction patterns of palm oil without the additives revealed that palm oil crystallized in the α-form after rapid quenching of melted palm oil at 10°C. During the heating process from 10°C to 45°C, the α-form transformed to the β′-form around 15°C, and the β′-form changed to the β-form around 40°C. The X-ray diffraction patterns of palm oil with the addition of polyglycerol behenic acid esters showed that palm oil crystallized in the β′-form at 10°C, and did not transform to the β-form during the heating process. Furthermore, the crystallization of the β′-form was promoted at 20°C and 25°C, but retarded at 28°C by the additive.

The binary phase behavior of SOS (1,3-distearoyl-2-oleoyl-sn-glycerol) and SLS (1,3-distearoyl-2-linoleoyl-sn-glycerol) was examined by using DSC and conventional and synchrotron radiation X-ray diffraction. The solid-solution phases were observed in the metastable α and γ forms in all concentration ranges. Results indicated that the miscible γ form did not transform to the β′ form when the mixtures were subjected to simple cooling from a high-temperature liquid to a low-temperature solid phase. However, and α-melt-mediated transformation into β′ and β2 resulted in the formation of immiscible phases in concentration ranges of SLS below 30%. By contrast, at SLS concentration ranges above 30%, the α-melt-mediated transformation caused crystallization of only the γ form, and β′ and β2 crystals did not appear. These results show that the specific interactions between SOS and SLS are operative in the phase behavior of the mixture states of SOS and SLS.

Crystallization kinetics of binary mixture phases of SOS (1,3-distearoyl-2-oleoyl-sn-glycerol) and SSO (1,2-distearoyl-3-oleoyl-rac-glycerol) were examined with time-resolved X-ray diffraction (XRD) and DSC methods. Formation of three polymorphic forms, named αc, β′c and βc, of a molecular compound was observed at a SOS/SSO=50/50 concentration ratio. The XRD data showed that all three polymorphs were arranged in a double chain-length structure, although a triple chain-length structure is formed in α and β′ forms of SSO, and β′ and β forms of SOS. The time-resolved XRD studies showed that αc and βc forms of the molecular compound crystallized more rapidly than the corresponding polymorphic forms of SOS and SSO. The results were discussed in terms of molecular chain–chain interactions of SOS and SSO, by assuming that kinetic processes of nucleation may prefer the formation of the αc and βc forms arranged in the double chain-length structure.

Effects of application of ultrasonic power (20 kHz, 100 W) on the crystallization behavior of tripalmitoylglycerol (PPP) and cocoa butter have been examined in terms of rate of nucleation and polymorphic control. High-purity PPP (>99%) and low-purity PPP (>80%) samples were employed to mimic real fat systems, which usually have higher concentrations of minor components in addition to the main component. For both the high-purity and low-purity PPP, the application of ultrasonic power accelerated the rate of nucleation as measured by induction time for the occurrence of crystals and by the number of crystals nucleated. As for the polymorphic influences, the nucleation of both the β′ and β forms was accelerated by the ultrasound, yet the β′ form nucleation was more accelerated when the low-purity PPP samples were employed. As for cocoa butter, sonication for a short period accelerated the crystallization of Form V. The present results indicate that ultrasound irradiation is an efficient tool for controlling polymorphic crystallization of fats.

Crystallization and polymorphic properties of linoleic acid (cis-9, cis-12-Octadecadienoic acid) (LA) and alpha-linolenic acid (cis-9, cis-12, cis-15-Octadecatrienoic acid) (alpha-LNA) have been studied by optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The DSC analyses presented three polymorphs in LA, and two polymorphs in alpha-LNA. The XRD patterns of the higher- and lower-temperature forms in LA and alpha-LNA showed orthorhombic O'(//)+O-like and O'(//) subcell, which were similar to those of alpha- and gamma-forms of mono-unsaturated fatty acids, respectively. From the solvent crystallization of LA and alpha-LNA in acetonitrile, single crystals of the higher temperature polymorphs have been obtained. The crystal habits of truncated rhombic shape were also similar to those of alpha-forms of the mono-unsaturated fatty acids. The enthalpy and entropy values of fusion and dissolution of the alpha-forms of LA, alpha-LNA and oleic acid showed that the two values decreased with increasing number of the cis-double bond.

Crystallization rates of n-hexadecane dispersed oil-in-water (O/W) emulsion were studied by ultrasonic velocity measurement, differential scanning calorimetry and synchrotron X-ray diffraction. The hydrophobic food emulsifier, polyglycerol ester possessing a stearic acid moiety (DAS-750), was added to n-hexadecane as an impurity, to determine what effect it would have on the rate of the crystallization of n-hexadecane. A comparison of results obtained with O/W emulsion systems with those by bulk systems, indicated the following; (a) the addition of DAS-750 accelerated nucleation in the emulsion but not bulk system, (b) crystal growth rates were retarded by DAS-750. These results are discussed in terms of heterogeneous nucleation at interfaces of O/W emulsion droplets.

Kinetic properties in polymorphic crystallization of SOS (1,3-Distearoyl-2-oleoyl-sn-glycerol) in a melt-mediated transformation have been examined in situ with a time-resolved (10 s intervals) X-ray diffraction method using synchrotron radiation (SR-XRD). It was observed that the formation of lamellar ordering occurred more rapidly than that of the lateral subcell packing, as revealed in the sequential occurrence of SR-XRD long spacing and short spacing spectra. The time lag in the occurrence of the two spectra increased with increasing stability of the polymorphic forms which crystallized; e.g., the formation of the stable chain packing of T‖ in a stable β polymorph was delayed by 500 s from the formation of the lamella, yet the time lag was 10–20 s in the crystallization of a metastable β′ form. This behavior was singly detectable by the SR-XRD, not by a conventional XRD technique.

This article has reviewed the recent work on the molecular interactions and kinetic properties of the polymorphic transformations of the TAGs in the single and mixed states. Progress has recently been made in the molecular-level understanding of the polymorphic transformations of the TAGs. Particularly, the use of the time-resolved X-ray diffraction with Synchrotron radiation (SR-XRD) has provided precise information of the structural changes of the fat crystals at a time scale of 10 sec. Therefore, fruitful information was obtained on the kinetic and molecular aspects of crystallization and mixing processes of the various types of mixed-acid TAGs, which were not obtained with the traditional thermal and structural techniques because of their complicated structural properties. One may anticipate that, although the experimental sites and machine times are limited, the SR-XRD techniques will be more applied to the fat systems involving the following materials and systems; (a) multicomponent natural fats with and without additives of emulsifiers, proteins and carbohydrates, (b) fats in dispersed phases such as oil-in-water (O/W) and water-in-oil (W/O) emulsions, (c) crystallization and transformation processes under external influences of hydrostatic pressure and shear stress [68].

A cool-temperate fly, Drosophila triauraria, stores fat, triacylglycerol (TAG), primarily in the fat storage organ, the fat body, and then diapauses to pass the winter in imago stage. TAG crystallization and ice formation taking place in a living fly by lowering temperatures were studied, in order to clarify the relationship between crystallizations and the fly's death at lower temperatures. X-ray diffraction, a direct non-invasive method, was used to detect the liquid-to-crystal transformations of TAG and water. During cooling, TAG crystallization preceded ice formation. It was also found that ice formation causes the fly to die instantaneously whereas the TAG crystallization does not.