The physical and molecular properties of the polymorphism of stearic acid, oleic acid and SOS (1.3-distearoyl-2-oleoyl glycerol) are comparatively discussed. Temperature dependence of Gibbs energy (G-T relation) of three polymorphs of stearic acid; A, B and C, revealed close relationships to each other. The molecular structures subtly differed in these polymorphs. In contrast, three plymorphs of oleic acid, b , and y exhibited remarkably different characteristics. G-T relation showed more diversified features: in particular, the melting points of 9 and B differ by 3 C. An order-disorder transformation occured between 9 and y, as a result of conformational disordering the portion of the oleic acid molecule from the double bond to the terminal methyl group in 9. Finally, five plymorphs of SOS were newly presented,y pseudo-B, B2 and B1 X-ray spectra and thermal behaviors proved that the above five forms are the independent polymorphs. The author discussed the multiple polymorphism of SOS, taking into account the lamellar sorting of stearic/oleic acids chains accompanied with the change in the chain lenghth structure. In relation to the polymorphism of SOS and other 1,3-disaturated-2-oleoyl glycerides, the authro emphasizes the possibility that the conversion from Form V to VI in cocoa butter might be caused principally through the polymorphic transformation from B2 to B1 of the higher melting fat fractions of cocoa butter.
"Physical and Molecular Properties of Lipid Polymorphs - A Review,"
Food Structure: Vol. 6
, Article 7.
Available at: http://digitalcommons.usu.edu/foodmicrostructure/vol6/iss2/7