Tristearin crystal forms

Fats and oils often show multiple melting points. As an example, tristearin has three melting points at 52°C, 64°C and 70°C, because fats and oils solidify in more than one crystal form this property is known as polymorphism. Crystallization of fats and oils occurrs in two stages of nucleation and growth. 

Since preliminary survey work had indicated that the crystal forms of tristearin were extremely sensitive to impurity and previous thermal history, several samples were prepared acetone-recrystallized tristearin, annealed melt (cooled at 0.5°C./minute to 10°C.) tristearin, and 97% (mole %) tristearin-3% stearic acid treated in all of the above fashions. 

Figure 7 Interfacial shear viscosity as affected by the interaction of sodium caseinate and different polymorphic form of fat crystals located at the interface. (O), P-polymorph hydrogenated pahn oil mid fraction (HPMF) crystallized in hexane ( ), P-polymorph tristearin crystallized in oil ( ), p -polymorph HPMF crystallized in hexane ( ), P -polymorph HPMF crystallized in oU. (Results from Ref. 36.)...

The existence of a substance in two or more forms, which are significantly different in physical or chemical properties, is known as polymorphism. The difference between the forms arises firom different modes of molecular packing in the crystal structure of certain triglycerides. Certain pure or mixed fatty acid triglycerides may show as many as five different melting points. Each crystal system has a characteristic melting point, x-ray diffraction pattern, and infrared spectrum. For example, tristearin can exist in three polymorphic forms with melting points of 54.7, 63.2, and 73.5°C. 

The evolution of spin-lattice relaxation times as a function of time was measured for the tricaprin/tristearin 50 50 (w/w) mixture at 40°C. At this temperature, tricaprin was liquid and tristearin was in the P form (checked by XRD measurements, results not shown). The Solid Fat Content (SFC) was 60%. The small deviation from theory (50%) was due to the presence of co-crystals which delay the melting of triceqjrin crystals. It is already known that the average crystal size increases as a fimction of time via the Ostwald Ripening phenomenon according to a power law model. The evolution of T for the present system is shown in Figure 1. 

Tricaprin/Tristearin Mixtures. The tricaprin/tristearin mixtures were studied at 10°C. According to melting temperatures, tricaprin is in the P form and tiistearin in the a form at 10°C. However, the polymorphic behaviour depends on the thermal history of the sample. It was confirmed by XRD measurements (data not shown) that in our system, tricaprin was in the p form and tristearin in the a form. We thus had a solid mixture of two different polymorphs, and it was interesting to obtain information on the crystal size distribution profile. The Ti distributions for the three different ratios are presented in Figure 3. 

The behaviour was different for the three mixtures. There was one peak broadened at the bottom for the 25-75 (w/w) mixture, there were two peaks for the 50-50 (w/w) mixture and three peaks for the 75-25 (w/w) mixture. The first peak was found for all three mixtures around 150 ms and was attributed to T of tristearin in the a form. This peak confirmed the presence of small crystals of tristearin in the systems. This peak shifted a little to a higher value when the tricaprin concentration increased. A second peak was characterized for the three mixtures, and attributed to the p polymorph of tricaprin. It was... 

Stearin (Tristearin) can be prepared from tallow by crystallisation from a solution in ether, forming small crystals which have a bright pearly lustre. The melting point of stearin appears to undergo changes and suggests the existence of distinct modifications. When heated to t55 G. stearin liquefies with increase of temperature it be- comes solid, and again becomes liquid at C. If this liquid be further heated to 76 G., and allowed to cool, it will not solidify until 55" G. is reached, but if the liquid at 71 G° G. be allowed to cool, solidification will occur at 70" C,... 

FIG. 3 Calorimetric curves of tristearin showing, during the first heating (soUd curve), the melting of the stable polymorphic form around 75°C and, during the second heating, (-------), the melting of two less stable forms around 55°C and 70°C, with partial crystal-... 

According to W/O emulsion work by Lucassen-Reynders [34] droplet coverage is achieved only if the number of particles is much higher than the number of droplets. In her study, the number of tristearate crystals was 1000 times the number of droplets, indicating that half of the fat crystals flocculated in 1 s compared with 1000 s for the water droplets. Hence, the fat crystals were able to cover the droplets and form a network before any real droplet coalescence could occur, thereby stabilizing the emulsion. The network formation, however, also hindered the free diffusion of crystals to the interface. Without the presence of surfactants in the initial emulsion mix, no stabilization was observed. With added surfactant, however, crystal flocculation was reduced as the interparticle bond energy was lowered. Results showed that partial flocculation was best for W/O emulsion stabilization by tristearin. Lagaly et al. [114] also observed that surfactants aided the colloidal stabilization of emulsions. 

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