Crystallization and fractionation of milk fat
Recent progress in understanding milk fat crystallization and fractionation is reviewed. Extent of fat solidification in butter can be altered by variations in thermal treatment of cream prior to churning. Because of its compositional complexity, milk fat rarely exhibits polymorphism. As with mixtures of closely related triglycerides, milk fat forms solid solutions. A typical milk fat begins melting below 40 C, maximum melting occurs at 1518 C, and the highest melting fraction appears 2037 C as a shoulder on the main peak. Dispersion of fat in emulsions increases its tolerance to supercooling, thereby altering the properties and composition of the solid phase. Most studies of milk fat fractionation have used progressive fractional crystallization, either of the melt or of solutions. Both procedures result in fractions showing larger changes in mp than in composition. The high melting glyceride fraction, ca. 5% total fat, influences crystallization out of proportion to concentration. The Alfa-Laval system, using an aqueous suspension of partially crystalline fat, produces two fractions. Typical high melting fractions have softening points ca. 3C higher than the original fat. The softening point of typical low melting fractions is lowered 10 C. Refractionation is easier with the high melting fraction. Melting thermograms of these fractions show them as resembling fractions prepared from melted fat.