Natural oils polymorphism

D Souza, V., deMan, J.M., deMan, L. 1990. Short spacings and polymorphic forms of natural and commercial solid fats A review. J. Am. Oil Chem. Soc. 67, 835-843. 

In this section, the polymorphic properties of natural fats are briefly discussed by highlighting miMat, cocoa butter, and palm oil fraction based on recent research into the effects of external factors on the polymorphic crystallization such as shear stress, ultrasound stimulation, and addition of food emulsifiers. 

This chapter described polymorphic properties of principal TAGs and natural fats based on recent research work to clarify fundamental aspects of polymorphsim of fats and oils. The authors hope that the basic understanding of the polymorphism of the principal TAGs would be useful to elucidate rather complicated polymorphic properties of natural fats and oils that contain TAGs with very heterogeneous fatty acid compositions. 

The once traditional suppository base, cocoa butter (theobroma oil) is a variable natural product which undergoes a polymorphic transition on heating. It is primarily a triglyceride. Four polymorphic forms exist y, m.p. 18.9°C a, m.p. 23°C / , m.p. 28°C and the stable /i form, m.p. 34.5°C. Heating above 38°C converts the fat to a metastable mixture solidifying at 15-17°C instead of 25°C, and this subsequently melts at 24°C instead of at dl-dS C. Reconversion to the stable yS-form takes 1-4 days depending on storage conditions. 

D Souza, V., de Man, J.M., and de Man, L. Short spacings and polymorphic forms of natural and commercial solid fats a review. Journal of the American Oil Chemists Society, 67, 835-843. 1990. Hagemann, J.W. Thermal behavior of acylglycerides (eds. N. Garti and K. Sato). Crystallization and Polymorphism of Fats and Fatty Acids. Marcel Dekker, New York, pp. 9-95. 1988. 

However, even without structural studies, Friberg et al. [32], Shinoda [33], and others noted that the broad existence range with respect to the water/oil ratio could not be consistent with a micellar-only picture. Also, the rich polymorphism in general in surfactant systems made such a simplified picture unreasonable. It was natural to try to visualize microemulsions as disordered versions of the ordered liquid crystalline phases occurring under similar conditions, and the rods of hexagonal phases, the layered structure of lamellar phases, and the minimal surface structure of bicontinuous cubic phases formed a starting point. We now know that the minimal surfaces of zero or low mean curvature, as introduced in the field by Scriven [34], offer an excellent description of balanced microemulsions, i.e., microemulsions containing similar volumes of oil and water. 

On the other hand, numerous species of the genus are really polymorphic concerning their vola tile compounds. Mentha longifolia, Mentha spicata, Mentha arvensis, and also natural hybrids like Mentha dumetorum exhibit a wide spectrum of essential oil compounds, and many chemotypes has been reported (Tetenyi, 1970 Lawrence, 2007 Baser et al., 2012). 

The occurrence of several chemotypes is reported, for example, for commercially used Origanum species, from Turkey (Baser, 2002). In 0. onites, two chemotypes are described, a carvacrol type and a linalool type. Additionally, a mixed type with both basic types mixed may occur. In Turkey, two chemotypes of Origanum majorana are known, one contains c -sabinene hydrate as chemo-typical lead compound and is used as maijoram in cooking ( marjoramy ), while the other one contains carvacrol in high amounts and is used to distil oregano oil in a commercial scale. Variability of chemotypes continues also within the marjoramy O. majorana. Novak et al. (2002) detected in cultivated marjoram accessions additionally to cts-sabinene hydrate the occurrence of polymorphism of c -sabinene hydrate acetate. Since this chemotype did not influence the sensorial impression much, this chemotype was not eliminated in breeding, while an off-flavor chemotype would have been certainly eliminated in its cultivation history. In natural populations of 0. majorana from Cyprus besides the classical di-sabinene hydrate type, a chemotype with a-terpineol as... 

The main objectives of this chapter are to clarify the roles of the hydrophobic emulsifier additives added in the oil phase of O/W emulsions how they modify fat crystallization and where they interact within the emulsion droplets. One may ask why the hydrophobic emulsifiers accelerate the nucleation process. The answer may not be straightforward, because their influences on fat crystallization are controlled by their physical and chemical properties and the nature of the interactions with the fat molecules occurring in the oil phase and at the oil/water interfaces. However, the results we have obtained so far indicate that the addition of hydrophobic emulsifiers in the oil phase has remarkable effects on crystallization. Fat crystals typically form a number of polymorphs, whose crystallization properties are influenced by many factors, such as temperature, rate of crystallization, time evolution for transformation, and impurity effects, as is commonly revealed in various examples [27,28], It is reasonable to expect that these polymorphic properties of fats may interfere with the clarification of the essential properties of the interface heterogeneous nucleation that occurs in O/W emulsions. 

As an application to real food fats, the acceleration effects of the additives on the heterogeneous nucleation of palm oil, PMF, and PKO droplets may be used to control fat crystallization in food emulsions. As for PMF, the results clearly indicated that polymorphism was modified by the addition of hydrophobic emulsifiers. The preferential crystallization of P was explained by assuming that the nature of the acyl chain packing of templates and the shape of their polar headgroup influence the degree of P nucleation. The preferred crystallization of P by the additives may be applied to food fats. 

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