Structure and Phase Characterization of Triacylglycerols by Raman Spectroscopy

摘要

Triacylglycerols (TAGs) are one of the main forms of energy storage in living organisms. Natural fats, which are nothing but the multicomponent TAG systems, are widely used in industrial products such as food, medicine and cosmetics. Industrial demands promote the studies on thermophysical properties of the multicomponent TAG systems for along time; however, the whole picture of their phase behavior is yet to be drawn. With a view to understand the complicated phase behavior of natural fats, I have investigated on the physical mixtures of TAGs by Raman spectroscopy.Firstly, the background of this study is introduced (Chapter1).Raman spectroscopy is the appropriate method to characterize TAGs, particularly when they exist in multicomponent systems. The structure and phase behavior of TAGs are then summarized with emphasis on the recent developments (Chapter 2). The interesting phase properties of TAGs, polymorphism and "molecular compound" formations, are introduced. The factors affecting these phase properties, such as crystallization conditions, are also mentioned. Next, the spectral features of TAGs are described in relation to their phase specific structures (Chapter 3). On the basis of the accumulated spectroscopic data, Raman spectroscopy has contributed to reveal the detailed structure of TAG polymorphs. Based on the knowledge described in these chapters, two TAG systems are studied. They include a TAG binary system that is known to form a molecular compound (Chapter 4) and several natural fats that are widely used in industrial products (Chapter 5).The results of the present study indicate that a third component, a molecular compound, is formed in the TAG binary system and its structure seems to be influenced decisively by crystallizing procedures. The molecular compound may be the phase dynamically formed by crystallization, rather than existing stationary in the liquid phase as previously considered (Chapter 4). In addition, the present study implies that the molecular compound may exist not only in a model binary system but also in real multicomponent systems. It is also shown that one can differentiate the origin of natural fats by detecting the difference in their polymorphic phases by using Raman spectroscopy (Chapter 5).Finally, future prospects of Raman spectroscopic studies on TAG systems for deepening the present understanding are presented (Chapter 6). Recent developments on the spectrometer offer bright future prospects for Raman spectroscopic studies on multicomponent TAG systems. Raman spectroscopy helps us to draw the whole picture of the phase behavior of natural fats.