Abstract: 【Objective】Milk fat is not suitable for some food applications and has limited functionality because of its complex compositions, structures and processing properties. The objective of this study is to provide a technical method and theoretical reference for fractionation of milk fat through studying the chemical compositions and physicochemical properties and its correlation of milk fat and fractions obtained by short-path distillation in different distillation temperatures.【Method】Commercial milk fat was fractionated by short-path distillation at 150℃, 165℃, 180℃, 190℃, 200℃, 210℃, 225℃, and 240℃, respectively, and the relationship of distillation temperature and yield of distillate was analyzed. Fatty acid composition was determined by gas chromatography to study the effect of distillation temperature on the composition and properties of milk fat and its fractions. Acid value, iodine value, peroxide value, slipping melting point, DSC thermograms of melting and crystallization and polarized light micrographswere also measured.【Result】The lowest temperature that milk fat could be fractionated was 165℃. Distillate yield increased from 1.19% to 36.89% with the distillation temperature increased from 165℃ to 240℃. Acid and peroxide value of distillate and retentate obtained by short-path distillation had different changes with no regularity, while the iodine value of retentate was generally higher than that of distillate. Short-path distillation did not change the kinds of fatty acids in the fractions, but the concentration of certain fatty acid presented substantial differences: the distillate was enriched in short- and medium-chain fatty acids (40%-60%), while the retentate was enriched in long-chain fatty acids (65%-75%) and unsaturated fatty acids (about 30%), which was consistent with the result of iodine value. Distillation temperature had a significant effect on the content of fatty acids in the fractions and the concentration of all kinds of fatty acids showed a trend of approaching to milk fat with the increase of distillation temperature. Relative to milk fat, the slipping melting point of the distillate was depressed and that of the retentate was augmented, while both of them showed an increasing trend as the distillation temperature increased. There was a significant positive correlation (P＜0.01) between the concentration of long-chain fatty acids in the fractions and their slipping melting point, r=0.977. DSC results showed that the melting and crystallization peaks of fractions were offset to the high temperature area as the increase of distillation temperature which indicated that the melting and crystallization properties of fractions were different but changed regularly. Polarized light micrographs showed that the distillate and retentate had different fat crystals, the crystals formed on cooling at 5℃ for 24 h corresponded to spherulites for the retentate whereas the solid fat phase of the distillate corresponded to needle-shape crystals. 【Conclusion】 Milk fat could be fractionated effectively by short-path distillation and distillation temperature had a significant effect on the resulting fractions. Fractionation of milk fat by short-path distillation at different distillation temperatures is able to change the chemical compositions, physicochemical properties and processing properties of the fractions.

Key words: milk fat, short-path distillation, fatty acid composition, physicochemical properties