Milk fat was fractionated with supercritical CO* (SC-CO*) into 8 fractions at temperatures of 50" and 7O"C, over a pressure range of lo&350 bar. Two fractions (Ll and 2) were liquid, 3 fractions (1 I-3) were semi-solid and 3 fractions (Sl-3) were solid at 20°C. The peak melting temperature progressively increased (9.7" to 38.3"C) from fraction Ll to S3. The concentration of short chain (C24-C34) triglycerides decreased from fraction Ll to S3 while that of long chain (C42-C54) triglycerides increased gradually. The medium chain triglycerides were more concentrated in fractions L2 and 11-3. The proportion of short (C4-C8) and medium (ClO-C12) chain fatty acids decreased and that of long (C14-C18) chain fatty acids increased gradually from fraction Ll-S3. The weight average molecular weights and geometric mean-carbon number of milk fat fractions were in the range from 625.6 to 805.0 and 34.2 to 47.6, respectively, in comparison to 729.3 and 41 .O, respectively, for native milk fat, suggesting SC-CO* effected a fair degree of molecular weight separation.
INTRODUCTIONMILK FAT has been used traditionally for the most part as butter, being the most important product in the dairy industry. Milk fat is a mixture of triglycerides of a range of molecular weights and degree of unsaturation, exhibiting a broad and variable melting range (Mulder and Walstra, 1974). The pleasing flavor of milk fat is among its most important advantages. However, its unique physical characteristics, especially its melting properties and plastic range do not suit it to a number of food-fat applications. Furthermore, the nature of feed and plan of nutrition of the cow affect the fatty acid composition and hence, milk fat characteristics (Jenness and Patton, 1959). Economic fractionation of milk fat into oil and plastic fat fractions which differ markedly from one another in chemical composition and physical characteristics will facilitate an increased utilization of milk fat in many food applications, such as confectionary and bakery products, and in creating convenient (e.g., frigo-spreadable) and dietetic (e.g., cholesterol-reduced or short and medium chain-triglyceride enriched) butter types. Differences in molecular weight, melting temperature (molecular weight and entropy of fusion), volatility and intermolecular interaction energy of constituent triglycerides, provide the physical property basis for separation of milk fat triglycerides.There has been a growing interest in supercritical gas extraction, over the past few years. Liquid-like densities of dense gases result in liquid like solvent powers. This property and faster mass transport characteristics relative to liquids due to low dense gas viscosity make dense fluids attractive extraction agents. Substances can be selectively dissolved by changing the density of the gas. Dense gas extraction involves the phenomena of distillation and extraction simultaneously (Zosel, 1978); enhancement of vapor pressure, ideal solubility and phase separation play a role. A mixture of compounds differin...
