Polymorphism Of Triacylglycerols Research Articles

Phase behavior of binary mixture systems of saturated-unsaturated mixed-acid triacylglycerols: effects of glycerol structures and chain-chain interactions.

We systematically examined the phase behavior of binary mixtures of mixed-acid triacylglycerols (TAGs) containing palmitic and oleic acid moieties 1,3-dioleoyl-2-palmitoyl-glycerol (OPO), 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (PPO), and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP), which are widely present in natural fats and are employed in the food, pharmaceutical, and cosmetic industries. Differential scanning calorimetry and X-ray diffraction methods were applied to observe the mixing behavior of PPO/OPO, OOP/OPO, and PPO/OOP under metastable and stable conditions. The results led to three conclusions: (1) Eutectic behavior was observed in PPO/OPO. (2) Molecular compound (MC) crystals were formed in the mixtures of OOP/OPO and PPO/OOP. (3) However, the MC crystals occurred only under metastable conditions and tended to separate into component TAGs to form eutectic mixture systems after 17 months of incubation. These results were contrary to those of previous studies on 1,3-dipalmitoyl-2-oleoyl glycerol (POP)/OPO and POP/PPO in which the MC crystals were thermodynamically stable. We determined that specific molecular interactions may cause this different phase behavior (stability of POP/OPO and POP/PPO MC crystals and metastability of OOP/OPO and PPO/OOP MC crystals). All results confirm the significant effects of molecular structures of glycerol groups, interactions of fatty acid chains, and polymorphism of the component TAGs on the mixing behavior of mixed-acid TAGs.

Triacylglycerol polymorphism is a stereochemical phenomenon

AbstractUnit‐cell stereochemistry for triacylglycerols in β′ (beta prime here and throughout) and β forms has been compared using data from studies of phase behavior for enantiomeric mixtures and space group determinations. The β′ form has a unit cell containing one stereoisomer and the β form has a unit cell containing both stereoisomers. As a result, the crystallization and polymorphic behavior for achiral, chiral‐racemic, and chiral‐enantiopure triacylglycerols is remarkably different. Accordingly, any plausible mechanism for TAG polymorphism must take unit cell stereochemistry into account.

Symmetry, chirality and crystalline tendency: the polymorphism of triacylglycerols

The physical properties of foods containing fat are often dependent on the polymorphism of the constituent triacylglycerols (TAG). This is illustrated by the favourable physical and sensory properties associated with the β' form for margarine and butter and the β(V) form for chocolate. Recent investigations have revealed that the stereochemistry of TAG molecules has a profound influence on their polymorphism. For instance, a pure enantiomer of TAG (sn-10:0-10:0-16:0) was β'-tending while the corresponding racemic mixture (rac-10:0-10:0-16:0) was β-tending. In addition, the binary phase diagram for mixtures of the two enantiomers, sn-10:0-10:0-16:0 and sn-16:0-10:0-10:0, showed the formation of a eutectic (metastable β'-form conglomerate) and a molecular compound (stable β-form racemic compound). At heart, these differences in polymorph and crystalline tendency stem from differences in the stereochemistry of the unit cell -i.e. both enantiomers in the β unit cell, one enantiomer in the β' unit cell. Information on the relative stereochemical arrangement of molecules within the unit cell is also available from the crystallographic space group. This information (determined by X-ray diffraction) is available for a number of β- and β'-tending, chiral and achiral TAG systems. Like crystalline tendency (discussed previously), space group data indicates that the unit cell for TAG in the β' polymorph contains only one stereoisomer whereas the unit cell for TAG in the β polymorph contains both stereoisomers (conformers in achiral and enantiomers in chiral systems). Therefore, based on the current data, the stereochemical arrangement of TAG molecules in the unit cell is associated with the polymorphic form of the solid - both stereoisomers in the β form and one stereoisomer in the β' form. This perspective clearly explains the observed differences in polymorphic behavior for enantiopure and racemic TAG including the β'-stability of enantiopure systems. As a result, the current descriptive mechanism for TAG polymorphism is vastly improved when the stereochemical orientation of the constituent TAG molecules is considered.

Erratum to: Triacylglycerol Polymorphism: What Can We Learn from Space Groups and Crystalline Tendency?

The caption for Fig. 1 should read ‘‘Schematic for a b and b b0 unit cells of achiral TAG and racemic mixtures of chiral TAG. Squares symbolize one unit cell, open circles symbolize one stereoisomer, circles containing commas symbolize the opposite stereoisomer and dashed line symbolizes a twinning operation. This scheme indicates the relative proportion (and not the total number) of molecules in the unit cell’’.

Triacylglycerol Polymorphism: What Can We Learn from Space Groups and Crystalline Tendency?

Journal of the American Oil Chemists' SocietyVolume 89, Issue 4 p. 741-744 Letter to the Editor Triacylglycerol Polymorphism: What Can We Learn from Space Groups and Crystalline Tendency? Correction(s) for this article Erratum to: Triacylglycerol Polymorphism: What Can We Learn from Space Groups and Crystalline Tendency? R. John Craven, Robert W. Lencki, Volume 89Issue 4Journal of the American Oil Chemists' Society pages: 745-745 First Published online: December 31, 2011 R. John Craven, Corresponding Author R. John Craven [email protected] Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1 Canada [email protected] [email protected]Search for more papers by this authorRobert W. Lencki, Corresponding Author Robert W. Lencki [email protected] Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1 Canada [email protected] [email protected]Search for more papers by this author R. John Craven, Corresponding Author R. John Craven [email protected] Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1 Canada [email protected] [email protected]Search for more papers by this authorRobert W. Lencki, Corresponding Author Robert W. Lencki [email protected] Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1 Canada [email protected] [email protected]Search for more papers by this author First published: 16 November 2011 https://doi.org/10.1007/s11746-011-1952-3Citations: 2 An erratum to this article can be found at http://dx.doi.org/10.1007/s11746-011-1997-3. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume89, Issue4April 2012Pages 741-744 RelatedInformation

The Viscoelastic Properties of Processed Cheeses Depend on Their Thermal History and Fat Polymorphism

Both the composition and the thermal kinetics that are applied to processed cheeses can affect their texture. This study investigated the effect of the storage conditions and thermal history on the viscoelastic properties of processed cheese and the physical properties of the fat phase. The microstructure of processed cheese has been characterized. Using a combination of physical techniques such as rheometry, differential scanning calorimetry, and X-ray diffraction, the partial crystallization of fat and the polymorphism of triacylglycerols (TG; main constituents of milk fat) were related to changes in the elastic modulus and tan δ as a function of temperature. In the small emulsion droplets (<1 μm) dispersed in processed cheeses, the solid fat phase was studied at a molecular level and showed differences as a function of the thermal history. Storage of processed cheese at 4 °C and its equilibration at 25 °C lead to partial crystallization of the fat phase, with the formation of a β' 2 L (40.9 Å) structure; on cooling at 2 °C min(-1), the formation of an α 3 L (65.8 Å) structure was characterized. The cooling of processed cheese from 60 to -10 °C leads to the formation of a single type of crystal: α 3 L (72 Å). Structural reorganizations of the solid fat phase characterized on heating allowed the interpretation of the elastic modulus evolution of processed cheese. This study evidenced polymorphism of TG in a complex food product such as processed cheese and allowed a better understanding of the viscoelastic properties as a function of the thermal history.

Effects of Crystal Growth and Polymorphism of Triacylglycerols on NMR Relaxation Parameters. 1. Evidence of a Relationship between Crystal Size and Spin−Lattice Relaxation Time

Fat crystal networks confer their physical properties on fat-containing products. They are characterized by the solid fat content (SFC) and the design of the crystals, that is, their polymorphism and their size. Different techniques such as NMR, differential scanning calorimetry, and X-ray diffraction (XRD) are used to determine these parameters. Low-field NMR, the reference method for evaluation of SFC, has been proven to allow the determination of polymorphism through spin−lattice relaxation time (T1) and second moment (M2) measurements. However, this technique could provide more information on the system. On the basis of the effects of supercooling on the NMR parameters, the first evidence of a possible relationship between the size of the crystals and T1 was demonstrated. The effects of a liquid phase on the fat crystal network were investigated with liquid tricaprin and solid tristearin. It was demonstrated that the two triacylglycerols can cocrystallize, and that the liquid phase modified the polymorphic behavior of tristearin. The evolution of T1 over time could be related to the Ostwald ripening phenomenon. In view of this evidence, it was concluded that there was a relationship between T1 and the size of the crystals in the fat crystal network.

Effect of Static Magnetic Field Processing on Crystallization Behavior of Triacylglycerols

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