Interaction of fatty acid composition and temperature cycling on melting properties of milk fat.

Milk was collected and milk fat extracted from 40 individual cows that were specifically selected over time in lactation in order to produce a graduation of natural samples exhibiting a wider range of milk fatty acid composition (i.e., ratio of de novo to preformed fatty acids) than would normally be produced by changes in feeding under commercial dairy herd management conditions. The melting properties of the milk fats were determined using differential scanning calorimetry. Higher levels of de novo fatty acids (i.e., shorter chain) and higher levels of unsaturated fatty acids both caused softening of milk fat, but by different mechanisms. Unsaturation directly lowered the melting point by disrupting the 2L and 3L triglyceride crystallization process (polytypism) on first cooling, whereas differences in de novo fatty acid concentration likely caused a shift in the proportion of 2L and 3L crystal forms (polytypism) and affected polytrophic behavior. Milk fat with more de novo fatty acids was more responsive to softening by temperature cycling than milk fat with more unsaturation. The impact of de novo fatty acid concentration in milk fat and in the total milk supply should be considered in controlling the hardness of butter.