Food systems are very complex. They consist of many components that are incompatible with each other. Thus there are a lot of interfaces. Food emulsifiers can affect these interfaces. Consequently emulsifiers exhibit a variety of functions as well as the emulsification of oil and water. These emulsifiers function in the form of self-organized structures, such as lamellar, micellar and cubic. To understand the nature of this functionality, it is very important to know the chemical structure and physical properties of emulsifiers. It has been shown that mono-esters of sucrose fatty acid ester have a conical shape and diand tri-esters are cylindrical. These molecular shapes affect the curvature of the interfacial membranes; this is a determining factor of the resultant emulsion type. The hydrophilic moiety of polyglycerol fatty acid esters is very complex with a range of molecular weights. Some experiments have been done to clarify the molecular structure of polyglycerol esters, too. In this review, I show some examples, in which self-organized structures of emulsifiers have been identified in food systems.

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Fractal analysis of shape of ice crystal particles in frozen fish meat (yellowfin tuna) was carried out by using the technique of image analysis. From a microscopic image of the ice crystal particles, it was confirmed that the perimeter of ice crystal particles could be characterized as a fractal and the fractal dimension of perimeter was evaluated. Effects of the storage time and storage temperature on the fractal dimension (d_p) of the perimeter of the ice crystal particles were also investigated. With increase of the storage time, the d_p value tended to decrease. The higher the storage temperature, the more rapidly the value of d_p decreased. The changes were in agreement with the visual observation of the shape change for the ice crystal particles reported by many researches, indicating that the fractal dimension d_p can be used as a quantitative index reflecting the surface roughness of ice crystal particles.

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The apparent distribution coefficients, K_app, of glucose, cellobiose and 3-ketocellobiose onto the cation-exchange resins with various divinylbenzene (DYB) contents in Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺ and Ba²⁺ forms were measured at room temperature. The K_app values of 3-ketocellobiose were greater than those of cellobiose in spite of the similar molecular masses, and were near those of glucose for the resins with any DYB content in all the ion forms tested. The K_app values of cellobiose, which were estimated from the K_app values of glucose under the assumption of no complex formation with the ions according to our previous model, coincided with the experimental values. This indicated that cellobiose formed no complex with the counter-ions within resins or that the binding constants of cellobiose to the ions were extremely low. On the other hand, it was shown that 3-ketocellobiose formed complexes with all the ions tested. The binding constants of 3-ketocellobiose to the ions were estimated based on the model, and could be correlated with the dynamic hydration numbers of the counter-ions.

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The oxidation process of the powdery ethyl eicosapentaenoate (EPA) included in α-, β- or γ-cyclodextrins (CD) was investigated under various oxidation conditions. The washed EPA powders of α- and β-CDs were quite stable and could not be oxidized for 670 h. To protect the unincluded EPA from oxidation, polysaccharides were added to the cyclodextrin for the preparation of hybrid carbohydrate-EPA-CD powder by kneading, resulting in further protection of the powdery EPA from oxidation. A mathematical model based on the Gaussian distribution of the activation energy of oxidative reaction could be successfully applied to correlate the oxidation process of the powdery ethyl eicosapentaenoate included in α-, β- and γ-cyclodextrins.

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