Crystallization Of Triacylglycerols Research Articles

Internal Factors Affecting the Crystallization of the Lipid System: Triacylglycerol Structure, Composition, and Minor Components.

The process of lipid crystallization influences the characteristics of lipid. By changing the chemical composition of the lipid system, the crystallization behavior could be controlled. This review elucidates the internal factors affecting lipid crystallization, including triacylglycerol (TAG) structure, TAG composition, and minor components. The influence of these factors on the TAG crystal polymorphic form, nanostructure, microstructure, and physical properties is discussed. The interplay of these factors collectively influences crystallization across various scales. Variations in fatty acid chain length, double bonds, and branching, along with their arrangement on the glycerol backbone, dictate molecular interactions within and between TAG molecules. High-melting-point TAG dominates crystallization, while liquid oil hinders the process but facilitates polymorphic transitions. Unique molecular interactions arise from specific TAG combinations, yielding molecular compounds with distinctive properties. Nanoscale crystallization is significantly impacted by liquid oil and minor components. The interaction between the TAG and minor components determines the influence of minor components on the crystallization process. In addition, future perspectives on better design and control of lipid crystallization are also presented.

Palmitic acid at high concentration modifies the nanoscale structure of anhydrous milk fat

We performed a nanoscale study based on X-ray scattering to understand the impact of a promotor of crystallization, palmitic acid (PA), at high concentration, on the networks of triacylglycerols (TAGs) in anhydrous milk fat (AMF). Melted blends containing 10 wt% PA were quenched at 25 °C. X-ray scattering data were compared with those obtained for pure AMF, pure PA, and AMF containing 1 wt% PA. While PA at low concentration did not modify the nanostructure of TAG crystals (direct crystallization in the β’-2L form), a high concentration of this promotor favored the formation of polymorphic forms suggesting that PA first crystallizes and then directs crystallization of AMF TAGs towards α and β forms.

New insights into the thermodynamics and kinetics of triacylglycerols crystallization

Understanding the transition from an isotropic liquid state to an organized crystalline state of triacylglycerols has great significance when designing lipid-based materials in general and food products in particular. In the current research, the balance between the demand for the tuning-fork (Tf) conformation, which is the suitable conformation for most crystalline organizations, and the supply of these molecules was discussed. Based on the negative dependency of the nucleation rates and the induction times on temperature, it was suggested that the limiting factor for the nucleation process is the conversion from the Tf conformation to any other conformation. On the other hand, based on the positive dependency of the melting temperatures and enthalpies on crystallization temperature, and the organized morphologies obtained at higher temperatures, it was suggested that the limiting factor during the crystal growth process is the conversion to the Tf conformation from another conformation.

The effect of emulsifier type on the secondary crystallisation of monoacylglycerol and triacylglycerols in model dairy emulsions

Dairy emulsions contain an intrinsically heterogeneous lipid phase, whose components undergo crystallisation in a manner that is critical to dairy product formulation, storage, and sensory perception. Further complexity is engendered by the diverse array of interfacially-active molecules naturally present within the serum of dairy systems, and those that are added for specific formulation purposes, all of which interact at the lipid-serum interface and modify the impact of lipid crystals on dairy emulsion stability. The work described in this article addresses this complexity, with a specific focus on the impact of temperature cycling and the effect of emulsifier type on the formation and persistence of lipid crystals at lipid-solution interfaces. Profile analysis tensiometry experiments were performed using single droplets of the low melting fraction of dairy lipids, in the presence and absence of emulsifiers (Tween 80 and whey protein isolate, WPI) and during the temperature cycling, to study the formation of monoacylglycerol (MAG) crystals at the lipid-solution interface. Companion experiments on the same lipid systems, and at the same cooling and heating rates, were undertaken with synchrotron small angle X-ray scattering, to specifically analyse the effect of emulsifier type on the formation of triacylglycerol (TAG) crystals at the lipid-solution interface of a model dairy emulsion. These two complementary techniques have revealed that Tween 80 molecules delay MAG and TAG crystal formation by lowering the temperature at which the crystallisation occurs during two cooling cycles. WPI molecules delay the crystallisation of MAGs and TAGs during the first cooling cycle, while MAG crystals form without delay during the second cooling cycle at the same temperature as MAG crystals in an emulsifier free system. The crystallisation of TAGs is inhibited during the second cooling cycle. The observed differences in crystallisation behaviour at the interface upon temperature cycling can provide further insight into the impact of emulsifiers on the long-term stability of emulsion-based dairy systems during storage.

Isothermal crystallization of anhydrous milk fat in presence of free fatty acids and their esters: From nanostructure to textural properties

We performed a multiscale study to understand the impact of pure exogenous compounds at low concentration on the crystallization of triacylglycerols (TAGs) in anhydrous milk fat (AMF). We selected butyric acid, an inhibitor of crystallization, and palmitic acid, a promotor, to investigate the influence of the chain length. Tripalmitin was also used as a promotor to assess the impact of fatty acid esterification. Melted blends containing the additives (1 wt%) were quenched at 25 °C. X-ray scattering data showed that AMF TAGs crystallized directly in the β’-2L form. The presence of additives did not modify the nanostructure of TAG crystals. However, they significantly altered the microstructure of AMF, as revealed by polarized light microscopy and rheology. This study emphasizes the interest of a multiscale approach to gain knowledge about the behavior of complex fat blends and of the use of modulators at low concentration to monitor their textural properties.

Multiple β Forms of Saturated Monoacid Triacylglycerol Crystals.

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, β 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 α or β’ forms first, and then they were transformed into β forms by solid–solid transformations. The β form that had transformed from β’ changed its morphology by a polymorphic transformation, while the β form made from the α form kept its spherulite morphology. The β forms obtained showed different melting points. Additional heat treatment promoted further polymorphic transformation. Four novel β forms were found for each of the saturated monoacid TAGs, trilaurin, trimyristin, tripalmitin, and tristearin. They showed similar polymorphism with the same subcell packing.

An Insight into the Solid-State Miscibility of Triacylglycerol Crystals.

The crystallization properties of triacylglycerols (TAGs) strongly determine the functional properties of natural lipids. The polymorphic and mixing phase behavior of TAG molecules have long been, and still are, a hot topic of research with special relevance for the cosmetic, pharmaceutical, and food industry. To avoid the difficulties arising from the study of whole real fats, studies at the molecular level on mixtures of a limited number of TAGs has become an indispensable tool to identify the underlying causes of the physical properties in lipid systems. In particular, phase diagrams of binary mixtures of TAGs exhibiting a different degree of heterogeneity (monoacid or mixed fatty acids; molecular symmetry; the presence of cis or trans double bonds) have resulted in a significant breakthrough in our knowledge about structure–interaction–function relationships. The present work aims to provide an overview of the main reports regarding binary and ternary TAG systems, from the early studies to the most recent developments.

Varying Levels of Medium‐Chain Fatty Acids Affect Triacylglycerol Composition and Crystallization Behavior of African Elephant Milk Fat

AbstractAfrican elephant milk fats from different stages of lactation are studied to investigate the link between high contents of medium‐chain fatty acids (MCFA), triacylglycerol (TAG) species, and crystallization in a milk fat system. The elephant milk fats contain high amounts of MCFA, specifically C8:0, C10:0, and C12:0, which mainly form medium molecular weight TAG species (C26–C34). The milk fats with the highest MCFA levels (97% and 82%) correspond to mid‐ and late‐lactation stages. These milk fats display simpler TAG compositions and crystallization behaviors. The great majority of mid‐ and late‐lactation milk fats are comprised of medium molecular weight (C28–C30) TAG. Both melting and crystallization are sharp events, and only β’ polymorph is observed. At early lactation, with 66% MCFA, a more diverse fatty acid composition is observed, and TAG species with medium molecular weight (C30–C34) and high molecular weight (C36–C44) are the dominant. Under dynamic conditions, crystallization and melting take place gradually over a wide temperature range, both α and β’ polymorph crystals are observed.Practical Applications: Mammals of different species provide milk lipids with a wide variety of fatty acid composition yet with common stereospecific features. The study of milk lipids, other than the common bovine milk lipids, allows the investigation of crystallographic properties in relation to fatty acid composition while preserving the stereospecific arrangement. Specifically, the study of elephant milk fats from different stages of lactation provides insight in to the effect of varying contents of medium‐chain fatty acids and fatty acid diversity on triacylglycerol composition and crystallization behavior.

Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the Molten State (Part I).

The study of triacylglycerols (TAGs) in their molten state is of fundamental importance for a deeper understanding of the TAG crystallization processes, being highly relevant for both manufacturing and medical applications. Although different models have been proposed to explain the nanostructured nature of the fluid state of TAGs, none of them are fully satisfactory. In this paper, we propose a new model consisting of positionally uncorrelated lamellar TAG assemblies embedded in an isotropic medium that assist as prenucleating structures. This model was validated by applying a novel global fitting method, resulting in an excellent agreement with the small-angle X-ray scattering data. A deeper analysis of the scattering patterns at different temperatures, both in cooling and heating directions, allowed us further to detect the crystalline traces of TAGs even after heating to 40 °C and record, on cooling, the onset of crystallization at 30-25 °C. The application of the presented novel model not only explains the outstandingly structured fluid of molten TAGs, but also lays the basis for analyzing first the crystallization steps in greater detail, which is outlined in our follow-up paper "Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the α-Phase (Part II)".

Synergetic interfacial adsorption of protein and low-molecular-weight emulsifiers in aerated emulsions

Whipped creams (aerated emulsions) are a complex emulsion-foam system whose oil-stabilizing potential and aeration capacity are determined by the surface activity of proteins and small surfactants. In this study, the interaction between three low-molecular-weight (LMW) emulsifiers [sodium stearoyl lactylate (SSL), phospholipid (PL), and sucrose ester (SE)] with caseinate was investigated to elucidate the mechanism of formation and stability of whipped creams. Competitive adsorption, interfacial tension, droplet aggregation, viscosity, and morphological variations of the emulsions were examined, and aeration capacity, hardness, and microstructure of whipped creams were measured. The combination of surfactants (0.05–1.0% w/w) with caseinate (0.6% w/w) produced concerted effects on the stability of emulsions. Water-soluble surfactant (SE) adsorbed more strongly than oil-soluble surfactants (SSL and PL) onto oil droplets. The lesser protein adsorption in the SE emulsion enabled a strong foaming activity in the subsequent aeration. Protrusions of triacylglycerol crystals and aggregation of oil droplets into an interactive colloidal matrix with considerable hardness and viscosity were prominently observed in SE creams. On the other hand, shear thinning followed by thickening was observed when PL was added to form the caseinate-based emulsion while no foaming was produced, and SSL, known to form α-gel at the interface, produced no stable foam. The improved emulsion stability yet the propensity to coalesce induced by cooperative actions of casein molecules and hydrophilic surfactant played a crucial role in producing aerated emulsions.

Structural characteristics of crystals formed in palm oil using sorbitan tristearate and sucrose stearate

ABSTRACTThe formation and stabilization of fat crystals in palm oil (PO) by the templating effects of sorbitan tristearate (STS) and sucrose stearate (S-370) were examined. We observed that the crystallization mechanism occurred via heterogeneous nucleation, which was induced by co-crystallization or seeding, after the addition of STS or S-370, respectively. Overall, both emulsifiers, STS and S-370, caused an increase in the hardness of PO, which was related to changes in the microstructure. In addition, the intensity of this effect was shown to be dependent on the emulsifiers concentration. In differential scanning calorimetry analysis, S-370 proved to be associated predominantly to the crystallization of high-melting triacylglycerols (TAGs), while STS showed to actuate the crystallization of high and low-melting TAGs. Moreover, the addition of STS improved the polymorphic stability of the PO, while the use of S-370 resulted in a soft texture at lower temperatures.

Influence of processing parameters on physicochemical properties of fractionated fish oil at low temperature crystallization

Purpose – The purpose of this study was to investigate the efficiency of low temperature fractional crystallization to increase polyunsaturated fatty acid (PUFA) content of fish oil. Effects of temperature, stages of crystallization, rate of cooling, agitation and addition of primary nucleus on separation efficiency were evaluated. Low temperature crystallization of triacylglycerols (TAGs) was used to increase PUFA content of fish oil (initial PUFA content ∼30 g/100 g oil). Design/methodology/approach – To optimize the fractionation process, the effect of fractionation temperature (7, 5, 0 and −5°C), crystallization procedures, cooling rate, agitation and addition of primary nucleus on PUFA content was evaluated. Findings – The best relationship between PUFA concentration (45.8 g/100 g oil) and PUFA yield (51.5 per cent) was attained by performing two-stage crystallization of TAGs at the final temperatures of 5 and 0°C under slow cooling rate (3°C h−1 for first fractionation procedure and 0.7°C h−1 for second stage, until the final fractionation temperature, 0°C, was reached) and slow agitation (3 rpm) and in the presence of primary nucleus, which resulted in 50 per cent increase in PUFA content over the original fish oil. Practical implications – Determination of iodine and saponification values, refractive index, solid fat content, melting point, cholesterol content of original oil and final fractionated product with the highest PUFA ratio showed that fractionation significantly alters physical and chemical properties of the fraction. Originality/value – Comparison of iodine value, saponification value, refractive index, solid fat content, melting point and cholesterol content of original oil and the final fractionated product (with the highest PUFA ratio) showed that the fractionation process significantly alters mentioned properties of the initial oil.

Crystal structures and morphologies of fractionated milk fat in nanoemulsions

The triacylglycerol (TAG) crystal structures and morphologies of fractionated milk lipids in nanoemulsions were investigated at 4°C. Droplet size (0.17 versus 1.20μm), lipid composition (stearin versus olein) and cooling rate (1 versus 10°Cmin−1) had an influence on the structural properties. Five crystal polymorphs (α, β′1, β′2, β1, and β2) were formed with either triple and/or double chain length structures in the solid phases of the emulsified systems. X-ray scattering peak intensities were reduced with the nanoemulsion particles. The internal structure of TAG exhibited stacking of individual lamellar layers (3.8–4.2nm). Various anisometric shapes of fat nanoparticles were formed due to a highly sharp curvature of the nano-size droplets. The shape of olein nanoparticles was more polyhedral compared to the stearin. TAG crystals arranged in a planar-layered organisation at the slower cooling rate. These differences imply that the nanometric confinement of oil droplets modifies the fat crystal habit.

Triacylglycerol Crystal Growth: Templating Effects of Partial Glycerols Studied with Synchrotron Radiation Microbeam X-ray Diffraction

Microstructural investigation of palm oil (PO) containing 8% monopalmitin (MP) was performed using synchrotron radiation microbeam (beam area of 5 × 5 μm2) X-ray diffraction (SR-μ-XRD). The blend was isothermally crystallized at 20 °C and analyzed shortly after reaching the crystallization temperature and after aging at 20 °C. The SR-μ-XRD technique allowed demonstration of the template effect of the monoacylglycerol (MAG) by showing that the PO crystals were orientated by the previously crystallized MP. Interactions through the palmitic acid moiety in PO and MP must have played decisive roles in this template effect as palmitic acid is a major fatty acid in PO. Analysis of aged samples revealed that the MP crystals migrate and concentrate into large spherulitic crystals during long-term storage, probably caused by a process of Ostwald ripening.

Effect of diacylglycerol addition on crystallization properties of pure triacylglycerols

The objective of this study was to investigate the effects of blending triacylglycerols (TAGs) and diacylglycerols (DAGs) on the melting and crystallization properties in a fat system. To this end, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized light microscopy (PLM) methods were used. Different DAGs (diolein—OO, dipalmitin—PP and distearin—SS) were added at 5% to each TAG (triolein—OOO, tripalmitin—PPP and tristearin—SSS). DSC results showed that the addition of DAGs delayed the onset of crystallization of saturated TAGs (PPP and SSS). By contrast, the addition of DAGs to unsaturated TAG (OOO) accelerated the onset of crystallization, with the appearance of an extra crystallization peak upon the addition of SS and PP. PLM results revealed that the addition of OO affected the polymorphic transition of the TAGs studied findings were consistent with DSC melting curves and XRD results.

49. Interactions between water and triacylglycerols may explain faster aging rates in stored germplasm at low temperatures

Longevity of orthodox (desiccation tolerant) seeds, pollen and fern spores characteristically increases with decreasing storage temperature. We have discovered numerous seed and fern spore species that age faster when stored in the freezer near −20 °C compared to storage at higher or lower temperatures. Seeds exhibiting this temperature anomaly are considered to be intermediate between orthodox and recalcitrant physiologies. Intermediate traits are often associated with high proportions of saturated fatty acids within the triacylglycerols (TAG), accumulated into cells as food reserves. TAG high in saturated fatty acids crystallize and melt within the temperature range of the observed longevity anomalies and we have hypothesized a link between TAG phase change and increased damage to germplasm cells. Damage is exacerbated as water content within stored seeds and fern spores increases from near 5% to about 12%. These observations have led us to hypothesize that damage results from an interaction between TAG, water, temperature and time. The purpose of this research is to explore the extent and significance of possible interacting factors on the viability of stored germplasm. Our work begins with characterizing the kinetics of TAG and water phase changes in peanut ( Arachis hypogaea ) and papaya ( Carica papaya ) seeds equilibrated to different water contents and stored at temperatures between −5 and − 80°C. Water and TAG phase was measured using a Perkin Elmer Differential Scanning Calorimeter. Cytoplasm ultra-structure was visualized without chemical fixatives using low temperature scanning electron microscopy (cryo-SEM) performed with a Zeiss DSN 960 scanning microscope equipped with a Cryotrans CT-1500 cold plate (Oxford, UK). The time dependency of phase changes was assessed over a 3 week period. We report that TAG crystallization in seeds is independent of water content and occurs over several days. The amount of water that freezes in seeds increases with storage duration in a manner consistent with TAG crystallization kinetics.

Increasing Stearidonic Acid (SDA) in Modified Soybean Oil by Lipase‐Mediated Acidolysis

AbstractThe objective of this work was to synthesize a structured lipid (SL) enriched in stearidonic acid (SDA, C18:4 ω‐3), from modified soybean oil (MSO) originally containing ~25% SDA. Low temperature crystallization (LTC) of MSO triacylglycerols (TAG) and free fatty acids (FFA) was performed. The TAG and FFA crystallization products (LTC‐TAG and LTC‐FFA, respectively) had SDA contents of 48.72 and 60.78%, respectively. Enzymatic acidolysis between MSO and LTC‐FFA was studied utilizing Novozym 435 and Lipozyme TL IM as biocatalysts. Substrate molar ratio, incubation time, solvent, and enzyme load were explored. Equilibrium was reached at 96 and 48 h for Novozym 435 and Lipozyme TL IM‐catalyzed reactions, respectively. The best conditions from these studies were also applied to the acidolysis of LTC‐TAG and LTC‐FFA. Utilizing Lipozyme TL IM and solvent free conditions, SLs with SDA contents of 37.61 ± 1.00% (20.86 ± 6.48% at sn‐2 position) and 53.46 ± 1.85% SDA (36.37 ± 3.14% at sn‐2 position) were obtained from the acidolysis reaction between MSO and LTC‐FFA, and LTC‐TAG and LTC‐FFA, respectively. Compared to the original SDA content of MSO, this process leads to a 52 and 116% increase in SDA content, respectively.

Edible Liquid Marbles and Capsules Covered with Lipid Crystals

Liquid marbles are water droplets covered with solid particles. Here we show a method for the preparation of edible liquid marbles and capsules covered with fatty acid crystals and triacylglycerol crystals. We prepared liquid marbles using a simple method; namely, a water droplet was rolled on lipid crystals in petri dishes. The resulting marbles were converted to capsules covered with a lipid shell by heating. These marbles were stable not only on glass surfaces but also on water surfaces because they had rigid hydrophobic exteriors. The lifetime of the liquid marbles on water depended on the alkyl chain length of the lipid molecules and the pH of the water. These findings are useful for applying liquid marbles to food, cosmetic, and medical products.

Toward Nanoscale Engineering of Triacylglycerol Crystal Networks

Cryogenic transmission electron microscopy and X-ray diffraction techniques were used to analyze the effect of crystallization conditions on the nanostructure of triacylglycerol crystal networks. Nanoplatelet size was strongly affected by composition and degree of supersaturation in the melt, as well as external fields during crystallization, such as cooling and shear rate. Chemical interesterification induced a decrease in nanoplatelet size, while increases in the solid mass fraction also resulted in a decrease in nanoplatelet dimensions. Fast cooling rates and crystallization under shear produced a significant decrease in platelet length, width, and thickness. This work opens up the possibility of judiciously engineering the nanoscale of fat-structured products in order to formulate products with specific functionalities including hardness, liquid oil binding, water vapor barrier properties, and metabolic response in humans.

Characterization of the Nanoscale in Triacylglycerol Crystal Networks

Here we report on the characterization of the nanoscale in triacylglycerol crystal networks of edible fats. Blends of tristearin and triolein were prepared in proportions between 20 and 100% w/w to achieve a wide range of supersaturations. Crystal networks were subjected to mechanical disruption using isobutanol at 10 °C and visualized using cryogenic transmission electron microscopy (cryo-TEM). This method allowed the breakdown of spherulitic structures into their primary crystals: nanoplatelets of approximate sizes 150 × 60 × 30 nm to 370 × 160 × 40 nm depending on supersaturation conditions, and a length to width aspect ratio of 2.3. The method also allowed the visualization of bimolecular triacylglycerol lamellae within a cross-section of a nanoplatelet. The tristearin d-spacing (∼4.5 nm) and domain size (30−50 nm) of the (001) plane, by cryo-TEM and small-angle X-ray diffraction, agreed quantitatively. Scherrer analysis provided an accurate estimate of the cross-sectional thickness of the nanoplatele...