Polymorphic Transformation in Mixtures of High- and Low-Melting Fractions of Milk Fat

Abstract

The kinetics of crystallization of high-melting fraction (HMF) and a mixture of 40% HMF and 60% low-melting fraction (LMF) of milk fat were studied at 5 degrees C by time-resolved in-situ synchrotron X-ray diffraction. HMF crystallized in the alpha polymorph, had a longer lifetime than the ones previously reported in pure milk fat, and was almost completely solid. The HMF/LMF mixture crystallized initially in the alpha form and transformed into the beta' polymorph, with a solid fat content much lower than that of HMF. The polymorphic change was therefore attributed to a delayed sudden formation of beta' mixed crystals from the uncrystallized melt. These findings are important for the food industry and as fundamental knowledge to improve our understanding of the origin of the macroscopic physical properties of solid milk fat fractions used in many manufacturing processes.

Unsaturated fatty acid enriched vs. control milk triacylglycerols: Solid and liquid TAG phases examined by synchrotron radiation X-ray diffraction coupled with DSC

“…with a hexagonal chain packing, which corresponds to the least stable polymorph with the lowest energy barrier. This result is in agreement with earlier studies reporting that cooling of milk fat with high dT/dt leads to the formation of the α polymorphic form (Cisneros, Mazzanti, Campos, & Marangoni, 2006;Lopez, Lavigne, Lesieur, Bourgaux, & Ollivon, 2001;Lopez et al, 2005;Ten Grotenhuis, van Aken, van Malssen, & Schenk, 1999). The α polymorphic form has vertical chains (angle of 90°) in relation to the absence of organisation of end-group plane.…”

Effects of Addition of a Palmitic Sucrose Ester on Low-Trans-Fat Blends Crystallization in Bulk and in Oil-in-Water Emulsions

“…After 1 min at 30°C (a), the SAXS spectrum of HMF displayed a single peak in the 0.1°to 3.5°region (2θ) with a d of 47.14 Å. According to the literature 15,17,18 , these X-ray diffraction patterns are consistent with a bilayer (2L 001 ) lamellar packing arrangement and a hexagonal subcell or α polymorph. The intensity of the diffraction pattern of HMF increased until 4 min of isothermal crystallization.…”

“…Zero time was the moment at which sample reached crystallization temperature. Assignment of the subcell packing (α, β′, or β polymorphs) was done on the basis of information from the literature 15,17,18 . In addition to short spacing signals, each polymorphic form showed characteristic long spacing signals.…”

“…After this time, a second SAXS peak began to grow, while the initial diffraction peak began to decrease in intensity. The second diffraction peak with a d of 40.60 Å corresponded to the 2L 001 packing of the orthorhombic subcell (β′ polymorph) 15,17,18 . After 5 min at 30°C, the α peak disappeared.…”

“…The use of techniques that does not allow studying in detail the early stage of crystallization can lead to misleading interpretations of the phenomenon. This early stage of crystallization is very important since it determines the later evolution of the system 15 . A synchrotron source allows diffraction patterns to be acquired during real-time crystallization, and therefore, further and less speculative information about mechanisms of action can be obtained.…”