Decoding the role of triacylglycerol composition in the milk fat crystallisation behaviour: A study using buffalo milk fat fractions

Abstract

The role of triacylglycerols (TAGs) composition in milk fat crystallisation is evaluated from a new perspective by correlating the crystal structures and their predicted TAG contributors. Four different TAG groups, defined by their fatty acid (FA) chain length and saturation are proposed to explain the crystallisation behaviour of different milk fat samples, namely TAGs containing (i) fully saturated long chain FAs, (ii) single unsaturated long-chain FA and (iii) multi unsaturated long-chain FAs, as well as (iv) short-chain FAs. Samples containing different TAGs proportions were obtained from two-step dry fractionation of buffalo milk fat. Liquid chromatography and mass spectrometry (LCMS) was employed to determine the TAGs composition. The crystallisation characteristics were evaluated using small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) and polarised light microscopy. The results confirm that fully saturated long chain TAGs are responsible for the formation of high melting point 2L-crystals (d-spacing: 44.1–49.7 Å), whilst the low melting point 3L-crystals (64.4–72.8 Å) are mainly contributed by long chain TAGs containing unsaturated fatty acids. Further, the crystallisation inhibiting effect of asymmetrical TAGs, containing short chain fatty acid (C4-6) is evident. As a final point, effects of the four TAG groups, each given with a specific composition, were examined closely also with respect to their influence on the nucleation and polymorphic transformation kinetics of milk fat crystals.