Suresh S. Narine

Relating structure of fat crystal networks to mechanical properties : a review

This paper reviews the identification of the various levels of structure present in fat crystal networks, and the development of analytical techniques to quantify these levels. The relationship of the various levels of structure to macroscopic physical indicators of the mechanical strength of the network is discussed. The analysis of the microstructural level of the network via fractal geometrical methods is discussed, as well as mechanical models relating the structure to mechanical properties. A method developed to quantify the fractality of fat crystal networks is also presented. The effect of processing conditions on microstructural indicators of the elastic modulus of the network is also discussed. This paper summarizes some 50 years of endeavor to relate the structure of fat crystal networks to their macroscopic rheological properties.

Physical properties of lipids.

Crystallization: modelling crystallization kinetics of triacylglycerols fat crystallization in O/W emulsions controlled by hydrophobic emulsifier additives. Structure-rheology-texture relationships in fats: structure and mechanical properties of fat crystal networks static crystallization behaviour of cocoa butter and its relationship to network microstructure. Emulsifiers: fat crystal behaviour in food emulsions food emulsifiers - structure-reactivity relationships, design and applications. Processing: deodorization fractionation of fats.

Microscopic and rheological studies of fat crystal networks

Abstract This talk discusses the quantification of microstructure in fat crystal networks by using the relationship of the elastic moduli ( G ′) to the solid fat content (SFC) via the fractal dimension (D) of the network. Results from application of a scaling theory developed for colloidal gels [W.H. Shih et al., Phys. Rev. A 42 (1990) 4772] to chemically and enzymatically interesterified and non-interesterified butterfat/canola oil mixtures and to cocoa butter and Salatrim TM are presented and discussed. In situ images from confocal laser microscopy and polarized light microscopy of the crystal network of butterfat and butterfat-canola oil blends yielded fractal dimensions of D =1.88 and D =2.02±2% respectively, which are in good agreement. The use of rheological measurements to calculate a fractal dimension of the crystal network of butterfat–canola oil blends yielded D =1.99, in good agreement with D calculated from the confocal laser microscopy and the polarized light microscopy images.

Evidence of critical cooling rates in the nonisothermal crystallization of triacylglycerols: a case for the existence and selection of growth modes of a lipid crystal network.

The isoconversional method, a model-free analysis of the kinetics of liquid-solid transformations, was used to determine the effective activation energy of the nonisothermal crystallization of melts of pure and complex systems of triacylglycerols (TAGs). The method was applied to data from differential scanning calorimetry (DSC) measurements of the heat of crystallization of purified 1,3-dilauroyl-2-stearoyl-sn-glycerol (LSL) and commercially available cocoa butter melts. The method conclusively demonstrated the existence of specific growth modes and critical rates of cooling at specific degrees of conversion. The existence of critical rates suggests that the crystallization mechanism is composed of growth modes that can be effectively treated as mutually exclusive, each being predominant for one range of cooling rates and extent of conversion. Importantly, the data suggests that knowledge of the critical cooling rates at specific rates of conversion can be exploited to select preferred growth modes for lipid networks, with concomitant benefits of structural organization and resultant physical functionality. Differences in transport phenomena induced by different cooling rates suggest the existence of thresholds for particular growth mechanisms and help to explain the overall complexity of lipid crystallization. The results of this model-free analysis may be attributed to the relative importance of nucleation and growth at different stages of crystallization. A mechanistic explanation based on the competing effects of the thermodynamic driving force and limiting heat and transport phenomena is provided to explain the observed behavior. This work, furthermore, offers satisfactory explanations for the noted effect of cooling-rate-induced changes in the physical functionality of lipid networks.

Lubricating and Waxy Esters. VI. Effect of Symmetry about Ester on Crystallization of Linear Monoester Isomers

The crystal structure development of jojoba-like esters incorporating either 1-decenoic acid and/or 1-decenol, namely octadec-9-enyl dec-9-enoate (JLE-281), and its isomer dec-9-enyl oleate (JLE-282) was investigated to reveal the effect of symmetry about the ester group on crystallization of aliphatic fatty monoesters. The phase transformation path was investigated with temperature-time resolved X-ray diffraction during stepped isothermal crystallization, and while cooling from the melt at a fixed rate. Startling differences in phase behavior were uncovered between the isomers. When stepped isothermals were used, selective extinctions occurred at a transition temperature for JLE-281 but not for JLE-282. The extinctions, which are due to dramatic changes in the electronic density of certain families of planes, indicate a phase transition attributed to a brusque rearrangement of the oxygen atoms in the crystal subcell. The phase transition did not occur when the JLEs were cooled continuously. The crucial role played by the position of the alkyl chain and its orientation relative to the easy rotation site of the C–O bond in the phase trajectories of the JLEs was particularly highlighted.