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Preparation and Fractionation of the High Melting Glyceride Fraction of Milk Fat

New Zealand Dairy Research Institute, Palmerston North, New Zealand

ABSTRACT

High melting glyceride (HMG) was prepared from anhydrous milk fat and from a commercially prepared hard fraction of a different milk fat. The latter glyceride was further fractionated by progressive crystallization from acetone. The first precipitation of HMG reduced the softening point of the supernatant fat to about 18 C, primarily by eliminating fats melting above 20 C. The melting properties of the supernatant to the recrystallization of HMG depended upon the source of fat. That from anhydrous milk fat had a limited melting range whereas that from the hard fraction had an extended melting range. Thermograms of the glyceride preparations indicated the possible existence of co-crystallization in both quickly cooled and tempered samples. Five fractions were prepared from HMG by progressive crystallization from acetone. The three highest melting fractions had thermograms typical of pure solid phases. All samples of HMG or its fractions could be crystallized unstably by rapid cooling of the melt. Two types of transitions were detected on the thermograms of samples in an unstable form, a direct transition between the unstable and stable forms and a melting of the unstable form followed by re-crystallization into the stable form. The melting points of the stable forms of the HMG fractions varied from 27 C to 56 C, whereas the intact HMG melted at 46 to 49 C. The saturated fatty acid residues of the HMG fractions varied from 97% (mole) for the highest melting to 77% for the lowest melting.

¹ On leave from Cornell University. Present address: Department of Food Science, Cornell University, Ithaca, New York 14850.