System tristearin

Fig. 15.6 Comparison of the solubility data for the system tristearin and CO2 with literature data (open...

Ilieva, P., Kilzer, A., Weidner, E. (2015). Measurement of solubility, viscosity, density and interfacial tension of the systems tristearin and CO2 and rapeseed oil and CO2. Journal of Supercritical Fluids (03 May 2016, In Review). 

Monotectic mixtures arise when the individual components have similar melting points, molecular volumes and polymorphic forms. Figure 17.12(a) represents a possible phase diagram for monotectic mixtures. A typical monotectic solution occurs when SSS is mixed with SOS. Lutton (1955) determined that the a form was present and associated with limited solid solution formation, and contrasted with the a forms of other glyceride mixtures that formed continuous solid solutions (Rossell 1967). It was found, for this system, that tristearin incorporates about 50% of the SOS into a solid solution on the other hand, SOS incorporates very little SSS into a solid solution. 

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. 

Two different systems of triacylglycerols, i.e. tricaprin and tristearin on the one hand and trilaurin and tripalmitin on the other, were studied in the solid state at three different concentrations 25 75, 50 50, 75 25 (w/w). For the tricaprin/tristearin system, the mixtures were melted at 80°C and then cooled to -50°C for 10 min. The temperature was finally increased to 10°C for 30 min. For the trilaurin/tripalmitin system, the mixtures were melted at 80 C and then cooled to -20°C for 10 min. The sample was first reheated to 0°C for 20 min and then to 20°C for 30 min before NMR measurements. 

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... 

In this exothermic reaction there is a net decrease in volume equivedent to the ehmination of (163 — 114) mol = 49 mol of gas molecules for every 2 mol of tristearin molecules that reacts. The decrccise in volume at 25°C is about 600 cm for the consumption of 1 g of fat. Because the volume of the system decreases, the atmosphere does work on the system is the reaction proceeds. That is, energy is transferred to the system is it contracts. For this reaction, the decrease in the internal energy of the system is less thcui the energy relccised as heat because some energy has been restored by doing work. 

LG Ogden, AJ Rosenthal. Influence of tristearin crystals on the apparent interfacial shear viscosity of aqueous lysozyme-hydrocarbon model systems. J Colloid Interface Sci 168 539-541, 1994. 

In his doctoral thesis, Lucassen-Reynders [73] showed that monoolein can adsorb onto tristearin. Johansson and coworkers [74-76] carried out detailed work on model fat systems dispersed in oil. They studied the adsorption of various emulsifiers to the crystals (fats and sugar) dispersed in oils. The adsorbed amount, the strength of the adsorption, and their relationship to the character of the emulsifiers, crystals, and oils were obtained. 

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