Lipid Crystal Characterization

The structure (e.g., number, size, distribution) of fat crystals is difficult to analyze by common microscopy techniques (i.e., electron, polarized light), due to their dense and interconnected microstructure. Images of the internal structures of lipid-based foods can only be obtained by special manipulation of the sample. However, formation of thin sections (polarized light microscopy) or fractured planes (electron microscopy) still typically does not provide adequate resolution of the crystalline phase. Confocal laserscanning microscopy (CLSM), which is based on the detection of fluorescence produced by a dye system when a sample is illuminated with a krypton/argon mixed-gas laser, overcomes these problems. Bulk specimens can be used with CLSM to obtain high-resolution images of lipid crystalline structure in intricate detail. 

This protocol is written primarily for samples where the dyes can be added into the molten fat, which can then be observed either in the molten state, if a hot substage is attached to the microscope stage, or after allowing it to solidify. To obtain the best images, dyes should be dissolved in the fats before samples are crystallized. 

It is important to weigh Nile Red accurately. Nile Red modifies lipid nucleation kinetics when used at higher concentrations and, thus, modified crystal images may be obtained if the concentration is too high. The concentration recommended in this protocol has been proven not to modify lipid crystallization kinetics. 

This procedure will destroy all existing crystals. This temperature and time will be sufficient for most fats. 

Add dyes to hot sample. Hold sample in an oven at 60°C for 5 hr to dissolve dyes. 

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Simulations of Lipid Crystals Characterization of Potential Energy Functions and Parameters (or Lecithin Molecules. 

To rccrystallize the unknown lipid, dissolve the crude residue in a minimum amount (about 20 mL) of warm acetone on a steam bath (Hood ). After slow cooling of the acetone solution to room temperature and then in ice to allow crystals to form, filter by suction, and wash the solid product with icc-cold acetone. A typical yield is about 0.5 g of purified lipid. Save the purified lipid for characterization. 

Conductivity, in water activity measurement, 67-70 Confocal laser scanning microscopy to characterize lipid crystals, 575-579 description of, 575, 577 Conjugated dienes and trienes, determination of, 515-517 Conjugated linoleic acid (CLA), fatty acid analysis, 437-438, 445-446 Convection oven, gravimetric measurement of water, 7-8, 10-11... 

Lipids. See also Lipid composition Lipid oxidation/stability characteristics of, 425, 432 crystal characterization, 575-579 extraction of... 

The crystallization kinetics of bulk triglycerides and oil-in-water emulsions has been characterized by both NMR imaging and localized spectroscopy. The rate of lipid crystallization in an oil-in-water emulsion was affected by the addition of a second homopolymer (addition of trilaurin to trimyristin in this case). The addition of the second homopolymer of higher chain length was observed to slow the rate of crystallization [26]. 

Lipid Crystals. Tripalmitin (>99% pure) (PPP obtained from Sigma Chemical Co., Stockholm, Sweden) was used. Crystals were recrystallized in hexane to give well-characterized 3-crystals. Hieir surface area was measured by Brunauer, Emmett, and Teller analysis to be 2.077 mVg. 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

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