Phase Behavior of Binary Mixture Systems of Saturated-Unsaturated Mixed-Acid Triacylglycerols: Effects of Glycerol Structures and Chain–Chain Interactions

Thermal Properties, Microstructure and Crystallization of Blends of Leaf Lard and Cottonseed Oil Stearin

Blend oils composed by leaf lard (LL) and cottonseed oil stearin (COS) were prepared and the thermal property, microstructure and crystallization of these blends were investigated in the present study. Solid fat content (SFC), thermal behaviors, triacylglycerols composition, crystal structure and morphology of the LL and COS blends were determined by pulsed nuclear magnetic resonance (pNMR), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), X-ray diffractometer (XRD) and polarized light microscope (PLM), respectively. SFC profiles and iso-solid diagrams indicated that SFCs of all blends were almost close to the weighted averages of the fat components at temperatures beyond 20°C; however, below 20°C, SFCs of blends exhibited higher than those of the weighted averages of the fat components. With the content of COS increasing, palmitic acid and linoleic acid in the blends increased, while stearic acid and oleic acid decreased; monounsaturated-disaturated (USS) and triunsaturated (UUU) glycerides in the blends enhanced, while monosaturated-diunsaturated (UUS) glycerides declined. The melting temperature of the blends decreased with the increase of COS content. The crystal forms in LL were β' and β, and the packing pattern was double and triple chain length (2L and 3L). With COS in blends increasing, β' form crystals and 3L pattern reduced. Polarized light micrographs showed that the number of crystal particles in the blends raised with the increase of COS content, meanwhile, the grainsize of the sample gradually decreased. Visual appearances of the blends indicated that blending LL with COS could efficiently reduce the graininess of LL. The addition of COS had a significant effect on the crystallization behavior of LL. LL presented one-step crystallization at 10°C and 20°C, while COS showed two-step crystallization at 10°C and one-step crystallization at 20°C. However, the blends exhibited obvious two-step crystallization at 10°C, one-step or slight two-step crystallization at 20°C.

Solid phase behavior of mixture systems based on tripalmitoyl glycerol and monounsaturated triacylglycerols forming a molecular compound

Differential scanning calorimetry and X-ray diffraction were used to investigate the mixing behavior of triacylglycerol (TAG) mixtures of PPP/PPO (tripalmitoyl glycerol/1,2-dipalmitoyl-3-oleoyl-rac-glycerol) and PPP/MCPOP/PPO (being MCPOP/PPO the equimolecular blend of 1,3-dipalmitoyl-2-oleoyl-glycerol...

Systematic Investigation of Co-Crystallization Properties in Binary and Ternary Mixtures of Triacylglycerols Containing Palmitic and Oleic Acids in Relation with Palm Oil Dry Fractionation

This work investigates the molecular interactions within the main triacylglycerols constitutive of palm oil, all having a key role in the multi-step dry fractionation process. Identification of these interactions is possible thanks to the establishment of binary and ternary phase diagrams, using differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) at variable temperature. The following systems were selected: PPP-POP, PPP-OPP, PPP-POO, POP-OPP, POP-POO, OPP-POO, PPP-POP-POO and PPP-OPP-POO (P: palmitic acid and O: oleic acid), and analyzed in direct mode (heating at 5 °C/min., after melting and quenching at -60 °C), and after tempering for three months at 20 °C (tempered mode). DSC makes it possible to bring out crystallization and melting phenomena associated to polymorphic transitions, which are further characterized (crystalline forms) by XRD. The results show that unsaturated are poorly soluble in fully saturated triacylglycerols, that the intersolubility decreases in proportion to the number of unsaturated fatty acids, that positional isomerism (POP/OPP) has a major impact, that OPP may induce formation of molecular compounds and that co-crystallization properties are highly modified by tempering depending on the polymorphic properties of the systems. This provides a better understanding and allows for effective control of the palm oil dry fractionation process.

Fat crystallization of blends of palm oil and anhydrous milk fat: A comparison between static and dynamic-crystallization

The application of dynamic-crystallization (a combination of shear with rapid cooling) often plays an important role in the production of industrial fat-based products such as shortenings/margarines but has been rarely reported. In this study, three blends of palm oil (PO) with anhydrous milk fat (AMF) (0, 25 and 50% AMF, w/w) were rapidly crystallized under static (using freezer) and dynamic conditions (using a benchtop scraped surface heat exchanger). Various techniques including differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarized light microscopy (PLM), rheology and texture analysis were applied to investigate physicochemical properties of fat blends as well as their crystal morphology upon the long-term storage (4 weeks) at 5 °C and 15 °C. The results revealed that high cooling rate of dynamic-crystallization not only affected melting behavior of fat blends but also prevented the polymorphic transformation from β' to β crystals. Besides, the application of shear during fat crystallization helped to improve significantly the gel strength of produced shortenings. Although post-crystallization of low melting triacylglycerols (TAGs) occurred for all produced shortenings during storage at 5 °C which was accompanying with a firmness increase, it was more considerable for samples owning higher AMF content. Moreover, this phenomenon promoted the sintering as well as Ostwald ripening between fat crystals of dynamic-crystallized fat blends resulting in the formation of unwanted large aggregates (or granular crystals) with the size ranging from 100 to 500 μm.

Mixing Ratio and Cooling Rate Dependence of Molecular Compound Formation in OPO/POP Binary Mixture

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)—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.

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.

Formation and properties of dark chocolate prepared using fat mixtures of cocoa butter and symmetric/asymmetric stearic-oleic mixed-acid triacylglycerols: Impact of molecular compound crystals

This paper reports an experimental study of the formation and properties of dark chocolate prepared using novel CB alternative fats (CBAs): symmetric (OS_atO) and asymmetric (S_atS_atO) mixed-acid triacylglycerols (TAGs), in which Sat and O represent saturated fatty acids (stearic:S + palmitic:P) and oleic acid moieties, respectively. It was found that the ternary fat mixtures of CB/S_atS_atO/OS_atO with a ratio of CB/(S_atS_atO + OS_atO) of 1:1 formed the most stable β-form of the double chain length (DCL) structure (β-2), which revealed sufficient hardness and sharp melting profiles around body temperature without tempering processes. Fat bloom formation was not observed in dark chocolate with CBAs at ratios of CB/S_atS_atO/OS_atO of 50/20/30-50/0/50 during the one-year storage test at temperatures between 15 °C and 30 °C. Overall, the present study has shown that fat mixtures made of CB/S_atS_atO/OS_atO, which are rich in oleic acid moieties, can be employed as a cocoa butter equivalent (CBE) fat without tempering procedures.

Continuous Gradient Temperature Raman Spectroscopy of Fish Oils Provides Detailed Vibrational Analysis and Rapid, Nondestructive Graphical Product Authentication

Background: Gradient temperature Raman spectroscopy (GTRS) applies the continuous temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a new means for rapid high throughput material identification and quality control. Methods: Using 20 Mb three-dimensional data arrays with 0.2 °C increments and first/second derivatives allows complete assignment of solid, liquid and transition state vibrational modes. The entire set or any subset of the any of the contour plots, first derivatives or second derivatives can be utilized to create a graphical standard to quickly authenticate a given source. In addition, a temperature range can be specified that maximizes information content. Results: We compared GTRS and DSC data for five commercial fish oils that are excellent sources of docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3). Each product has a unique, distinctive response to the thermal gradient, which graphically and spectroscopically differentiates them. We also present detailed Raman data and full vibrational mode assignments for EPA and DHA. Conclusion: Complex lipids with a variety of fatty acids and isomers have three dimensional structures based mainly on how structurally similar sites pack. Any localized non-uniformity in packing results in discrete “fingerprint” molecular sites due to increased elasticity and decreased torsion.

Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the α-Phase (Part II)

The early-stage crystallization behavior in a triacylglycerol mixture has been investigated on the nanoscale with a novel global small-angle X-ray scattering analysis technique. This method has been tailored for the determination of the electron density profiles (EDPs) replicating both (i) the nanostructural texture of molten triacylglycerols (TAGs) (refer to "Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the Molten State (Part I)" of this publication series) and (ii) the lamellar structure of the metastable α-polymorph. In a first stage, the α-phase scattering contribution alone was examined by classical Fourier analysis as well as by globally fitting the data, leading to practically identical EDPs. On the basis of these findings, we extended our analysis to the entire X-ray scattering contribution arising from molten TAGs and the solid α-phase fraction. Remarkably, the experimental and theoretical data agree very well, providing for the first time a detailed nanostructural understanding about the coexisting molecular assemblies. This, in turn, also allowed us to quantitatively determine the solid fat content (SFC) with X-ray scattering data. Our new theoretical approach for measurement of SFC is based on the global analysis of small-angle scattering/diffraction patterns, and the SFC results are in good agreement with values obtained from other techniques such as NMR spectroscopy.

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)".