S. Sarig

Colocalization of cholesterol and hydroxyapatite in human atherosclerotic lesions

SummaryCholesterol and calcium phosphate, the latter in the form of hydroxyapatite, accumulate in atherosclerotic lesions. In this report, we demonstrate that these organic and inorganic constitutents of lesions can accumulate together, closely associated in crystal agglomerates. Using the fluorescent cholesterol probe, filipin, we identified unesterified cholesterol that was associated with calcium granules in tissue sections of lesions. We also have shown that small crystallites of cholesterol can associate with preformed hydroxyapatite crystals in vitro. Scanning electron microscopy couple with energy-dispersive X-ray analysis demonstrated the physical association of many small crystallites of cholesterol with larger crystals of hydroxyapatite. These small crystallites of cholesterol associated with hydroxyapatite stained with filipin. This contrasted with the lack of filipin staining of unassociated larger cholesterol crystals or hydroxyapatite alone. How cholesterol and calcium come to be closely associated in crystal agglomerates within atherosclerotic lesions remains to be determined.

Rapid precipitation of apatite from ethanol-water solution

Abstract Calcium phosphate was precipitated by simultaneous mixing of 9mM–18mM calcium chloride and 5.4mM–10.8mM sodium dihydrogen phosphate at pH = 7.4. After periods of several minutes an amorphous phase was present, as expected. Ethanol added to the initial solutions, at 0.245 mol fraction, effected the crystallization on hydroxyapatite crystals. In the presence of fluoride, a well characterized apatite phase was obtained after one minute.

Dynamic control of polymorphic transformation in triglycerides by surfactants: The button syndrome

The kinetics of polymorphic transformations in monoacid saturated triglycerides and the influence caused by the presence of certain solid surfactants were investigated. Selected emulsifiers can be incorporated at the level of 10 wt% within the triglyceride, without changing the crystal lattice; on the other hand, their presence affects the heat capacity of the triglyceride and the NMR relaxation time T1. Following the polymorphic transformation both during aging and during heating in the DSC, it was observed that both the mechanism and rate of transformation of the triglyceride strongly depend on the kinetic conditions and on its own chemical structure. In conjunction with these results it also was observed that the effect of the emulsifier is strongly dependent on the transformation conditions. The kinetic effect of the additive on the solid-solid transformation has been found to be strictly associated with its hydrophilic moiety structure; a model of molecular incorporation has been proposed which describes the arrangement of the surfactant molecules parallel to the triglyceride chains and formation of vacancies. The selectivity of the additive concerning its effect of dynamic controller of polymorphic transformations has been explained by its capacity to create hydrogen bonds with the neighboring triglycerides, which was called the “Button Syndrome.” The wide range of different additives and triglycerides used supplied a better understanding of the factors which determine the polymorphic and crystallization behavior in triglycerides.

Mechanistic considerations of polymorphic transformations of tristearin in the presence of emulsifiers

Fat polymorphs influence the quality of some food and cosmetic products. Emulsifiers traditionally have been added in order to retard undesired polymorphic transformations. The present study is an attempt to understand the role of selected emulsifiers on such transformations. Tristearin was heated or aged under controlled conditions using differential scanning calorimetry (DSC) and X-ray techniques, and the extent of transformation was evaluated in view of the possible pathways of α transforming into β. The temperature regime controls the extent of mobility of fat molecules, the local crystal imperfections and the degree of liquefaction. As a result, it dictates the kinetics of the polymorphic transformation.The surfactant added as an impurity does not have a straightforward effect, as thought previously, but rather varies with the kinetic conditions. During aging some selected solid emulsifiers will retard the α-β transformation while others still enhance it (during heating, all of them will inhibit β form crystallization). Their effect probably is related to different crystalline organizations and the creation of imperfections. Liquid emulsifiers in any case will enhance the α-β transformation, due probably to their weak structure compatibility with tristearin, which causes a higher mobility of triglyceride molecules.

Reconsideration of Polymorphic Transformations in Cocoa Butter Using the DSC

Cocoa butter was crystallized in the differential scanning calorimeter (DSC) in the presence and the absence of sorbitan monostearate at different cooling rates. The solidification and fusion curves were recorded. It was found that cooling rate affects enthalpies and temperatures of phase transitions. The very slow cooling rate causes a significant decrease in crystallization enthalpy, suggesting that fractionation of glycerides occurs under these conditions. In the presence of sorbitan monostearate 5%, cooling and heating curves of cocoa butter are sharper, the solidification point is higher and the fusion point is slightly lower. Further, in the presence of sorbitan monostearate both crystallization and fusion enthalpies are lower than in pure cocoa butter. The presence of the emulsifier seems mainly to promote the fractional crystallization.Fusion curves after different periods of isothermal crystallization suggest that higher polymorphic forms differ in chemical composition from lower ones, and that the presence of sorbitan monostearate affects the fractionation in the fat.

Effect of food emulsifiers on polymorphic transitions of cocoa butter

The polymorphic behavior of cocoa butter in the presence of several food emulsifiers serving as crystal structure modifiers was investigated. Emphasis was placed on transitions among the relatively stable forms IV, V and VI, which are significant for a confectionery industry.As known from industry work, within the series of sorbitan esters and ethoxylated sorbitan esters, the solid emulsifiers were the most efficient in retarding transition of V form into VI modification. Blends of sorbitan monostearate (Span 60), ethoxylated sorbitan monostearate (Tween 60) and Span 60-Tween 65 used in the present study were particularly effective. Surprisingly, it was found that some combinations of emulsifiers accelerate the transition of form IV into form V. Transition of form V into form VI occurs via the solid state, and other transitions are known to take place via the liquid phase. Emulsifier was found to increase liquid fraction of the fat prior to its transition. Mechanistic considerations concerning these transitions are suggested.

Crystal Structure Modifications of Tristearin by Food Emulsifiers

The effect of several emulsifiers as crystal structure modifiers of tristearin has been investigated. The less thermodynamically stable modification, named a, is preserved when 1–10% of sorbitan monostearate was added before allowing the molten tristearin to cool and crystallize. Several other emulsifiers have been tested and it has been found that the combination of bulkiness of the hydrophilic groups with the right lengths of the hydrophobic chains of a given emulsifier is necessary to preserve the a-modification. Liquid emulsifiers and those having a pronounced hydrophilic character are not efficient as modifiers. The emulsifier has been shown to be incorporated into the tristearin during crystallization from solvent without an immediate effect, but it affects subsequent behavior upon melting and resolidification.

On the association between sparingly soluble carbonates and polyelectrolytes

Abstract The effects of polyvinyl sulfonate (PVS) and polyglutamic acid (PGA) on the precipitation of carbonates of magnesium, calcium, strontium, barium and lead were determined. The retarding effects vary and can be roughly correlated with the structural matching between the interanionic distances along the polymeric chain and the intercationic distances in the crystal lattice of the precipitate. An accelerating effect of PGA on the precipitation of basic lead carbonate was discovered, accompanied by very poor crystallinity of the precipitate. Both the retarding and the accelerating effects were explained on the basis of heterogeneous nucleation of the sparingly soluble carbonates on microsubstrates.

Analysis of sorbitan fatty acid esters by HPLC

Sorbitan esters of several fatty acids have been analyzed by high pressure liquid chromatography (HPLC) using an RP-18 column. No derivatization was necessary. Mono-, di- and trisorbitan esters of palmitic, stearic, oleic, isostearic and sesquioleic acid have been separated using isopropanol/water as the elution mixture.

Effect of food emulsifiers on crystal structure and habit of stearic acid

Several food emulsifiers have been found to serve as crystal structure modifiers for stearic acid crystallized from various organic solvents. Stearic acid that usually precipitates under appropriate crystallization conditions as the B- form is converted into the C- form when 1- 5% of sorbitan esters or ethoxylated sorbitan esters of fatty acids are present in the solution. Other emulsifiers such as polyglycerol esters, bdsubstituted monoglycerides and sucrose esters of fatty acids consisting of bulky hydrophilic groups are also effective emulsifiers in preserving the C- form of the crystallized stearic acid. The active emulsifiers modify the external crystal habit of stearic acid. Mass spectrograph analysis indicates that sorbitan monostearate (Span 60) is precipitated with the stearic acid.