Crystallization of triglycerides

In 1963 Skoda and Van den Tempel observed [77] that the temperature at which crystallization of triglycerides started in emulsified systems was invariably lower than in nonemulsified solutions and depended on the emulsifying agent used. With some emulsifiers T was so low that the authors assumed the existence of homogeneous nucleation. Other molecules effected a rise in T, apparently catalyzing nucleation. It was observed that the catalytic activity was the greater... 

Crystallization of triglycerides from a solvent system generally yields P-form crystals. 

Van den Tempel, M. (1968). Effects of emulsifiers on the crystallization of triglycerides. Surf ace-Active Lipids in Foods. SCI Monograph No. 32. London. Soc Chem Ind, pp 22-33. 

PH van Dam, JJ Eshuis, W Hogervorst, S Noomen. Fractional crystallization of triglyceride fats. Patent WO 9835001, 1998. 

These reactions, which are believed to occur predominantly inter-molecularly, are capable of producing intermediates which hold some potential as precursors for important chemical products. For example, metathesis of olive oil, which consists chiefly of triglycerides of oleic acid, produces the glyceride of 9-octadecene-l,l8-dioic acid from which can be obtained, after saponification, acidification, and low-temperature crystallization, the free acid, which can be transformed by intramolecular condensation to civetone. 

Crystallization of milk fat largely determines the physical stability of the fat globule and the consistency of high-fat dairy products, but crystal behavior is also complicated by the wide range of different triglycerides. 

Interaction with such properties does, however, not allow the investigator to answer the question of where the drug is localized in the particles (on the surface or in the crystal lattice). Thermal interactions were also observed when an incorporated drug or a second type of triglyceride formed a separate phase within the nanoparticles [3,37,64,68]. Drug release studies can provide supportive information on the accessibility of the drug to the aqueous phase [72,108], but separation of the effects from the nanoparticles from those of additional colloidal structures — if present — may be difficult. 

Many methods exist to separate triglycerides into fractions on the basis of their degree of unsaturation. These include fractional crystallization from solvents, and separation by column and thin layer chromatography (TLC). The classes of triglycerides may then be studied and after methylation the fatty acid content determined by GLC. Yet even this is not the whole story since the position of fatty acids on the triglyceride molecule may uniquely affect the physical and biological properties of the lipid. 

Crystallization of fats (triglycerides) is a complex phenomenon, especially for milk fat, due to its very broad fatty acid composition (see Chapter 1). Principles of crystallization of milk fat have been reviewed extensively elsewhere (Chapter 7 Mulder and Walstra, 1974 Walstra et al., 1995). Whether a quantity of milk fat is present as a continuous mass (e.g., anhydrous milk... 

Skoda, W., van den Tempel, M. 1967. Growth kinetics of triglyceride crystals.. / Crystal Growth. 1, 207-217. 

Smith, P.R. 2000. The effects of phospholipids on crystallization and crystal habits of triglycerides. Eur. J. Lipid Sci. Technol. 102, 122-127. 

In a few instances, emulsions can be stabilized by solid particles as shown by S. U. Pickering in 1907 (see Petrowski, 1976). Examples are mustard seeds in traditional mayonnaise (Anon., 1968) or crystals of high melting-point triglycerides in margarine or butter (Precht and Buchheim, 1980 Heertje et al., 1987). The solid particles are considered to act as a barrier, which prevents the coalescence of droplets. Bancroft (1913) observed that the phase that wets the solid more easily will become the continuous phase. 

The complexity of chocolate manufacture arises from the polymorphic nature of its constituent fats, which can come in at least five crystal forms, each with an individual melting point. Cocoa butter is chemically a multicomponent mixture of triglycerides and trace compounds (Davis and Dimick 1986). Approximately 85% of the composition consists of just three triglycerides POP ( 20%), POS ( 40%) and SOS ( 25%), where palmitic (P), oleic (O) and stearic (S) are the fatty acids attached to the glycerol base. The precise composition depends on factors such as growing conditions and therefore can vary between batches, especially from different geographic regions (Chaiseri and Dimick 1989). 

Solvent Fractionation - The separation of component triglycerides that differ in solubility is accomplished by fractional crystallization of a solution of oil in an organic solvent, followed by separation of the solids from the liquid by filtration, and finally, removal of the solvent from the separated fractions by steam stripping. This process is the most versatile of the fractionation techniques presented. 

Knowledge about the detailed structures of the triglycerides present in palm oil is important because they define some of the physical characteristics of the oil. The melting points of triglycerides are dependent on the structures and position of the component acids present. They also affect the crystallization behavior of the oil. The semisolid nature of palm oil at room temperature has been attributed to the presence of the oleo-disaturated fraction. 

The triglycerides of palm oil consist of a combination of fatty acids with different chain length as well as degrees of unsaturation. This results in the presence of substantial quantity of both low- and high-melting triglycerides. Crystallization of the... 

Polymorphism. The structural stabihty of margarine is influenced by the properties of the crystal lattice and by the actual amount of solid fat present. Many organic compounds or mixtures such as fats can sohdify in more than one crystalline pattern. The primary crystal forms of triglycerides are designated a, p, and p, which correspond to three principal cross-sectional arrangements of the fatty acid chains (71). These may be differentiated by characteristic x-ray diffraction patterns (72) and heats of transition observed in calorimetric studies (73). Phase behavior of... 

It has been reported extensively that fats solidify in more than one crystalline type (2-23). Triglycerides exhibit three main crystal types—ot, p, and p—with increasing degrees of stability and melting point. The molecular conformations and packings in the crystal of each polymorph have been reported. In the ot form, the fatty acid chain axes of the triglyceride are randomly oriented and the ot form reveals a freedom of molecular motion with the most loosely packed hexagonal subcell structure. 

The heat of fusion normally increases with bigger chain lengths and decreasing unsaturation in the triglycerides. Blends of triglycerides have less latent heat of crystallization than the similar nonblended triglycerides (19). 

The influence of a shear field on emulsion crystallization is of great interest as it relates to behavior during product processing and distribution. Emulsions can be destabilized under shear in a controlled manner to deliver desirable properties uncontrolled or unintentional destabilization may lead to poor product performance. Comparisons of emulsions under perikinetic (at rest) and orthokinetic (under shear) conditions were made in an effort to understand the role of shear on the stability of the systems studied. Davies et al. (22) found stability of triglyceride emulsions containing crystals to be sensitive to both shear and crystal concentration. Crystal morphology also plays an important role in the destabilization of emulsions under shear. Boode and Walstra (4) reported the presence of needle-like... 

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