Thermal and Structural Behavior of Milk Fat

Lopez, Christelle; Lesieur, P.; Bourgaux, Claudie; Keller, G.; Ollivon, Michel

doi:10.1006/jcis.2001.7664

Cited by 96 publications

(28 citation statements)

References 25 publications

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“…At small angles, sharp diffraction peaks are immediately recorded after quenching. These peaks correspond to a 3L stacking of TG molecules (d = 70.5 Å) in the α form, as previously observed for quenching from 60 to -8 o C of cream and AMF samples [15,16]. Four of the six orders of diffraction observable in the scattering vector q domain analyzed (Miller index hkl, with h = k = 0 and l = 1, 2, 3, 5 ; noted 3L 001 for the first order of a triple chain length packing) are clearly visible in both cream and AMF patterns at q = 0.0891 Å -1 , Milk fat polymorphism 323 [15,16], was observed (data not shown).…”

Section: Isothermal Evolution At 4 O C After Quenchingsupporting

confidence: 79%

“…2). The higher liquid content expected at 4 o C compared to -8 o C [15] favors the 2L (47 Å) → 3L (70.5 Å) transition. In the AMF sample (Fig.…”

Section: Isothermal Evolution At 4 O C After Quenchingmentioning

confidence: 87%

“…Either excellent XRD peak resolution at small angles, mainly obtained by increasing sample-to-detector distance, or rapid recordings of XRD patterns as a function of time or temperature are now allowed when not both together. It has also been shown that when the fat phase is not too diluted, it is possible to follow polymorphic evolutions within the dispersed droplets of an emulsion [15]. The technique used allowed one to follow simultaneously fast polymorphic evolution at subzero temperatures in cream samples at both small and wide angles, simultaneously with DSC experiments.…”

Section: Introductionmentioning

confidence: 99%

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Crystalline structures formed in cream and anhydrous milk fat at 4 °C

Lopez

Bourgaux

Lesieur

et al. 2002

Lait

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-Crystallization and polymorphic evolutions of triacylglycerols (TG), at 4 o C, in cream and anhydrous milk fat (AMF) samples were studied using high-sensitivity differential scanning calorimetry (DSC), time-resolved synchrotron X-ray diffraction (XRD) and density measurement, and compared as a function of time after quenching from 60 to 4 o C. The evolution of the two crystalline structures initially formed in both samples, corresponding to a metastable 2L (47 Å) and a 3L (70.5 Å) lamellar organization with hexagonal chain packings (α form), were monitored in isothermal conditions at 4 o C as a function of time t. For t > 15 min, short spacings showed the formation of a β' packing of the chains in coexistence with the α form. In AMF, the occurrence of some β form was also recorded. For long spacings, a 2L (39 Å) structure was formed in cream with the 3L (70.5 Å) structure still being preponderant after conditioning for 30 min at 4 o C. In AMF samples, a TG polymorphic transition 3L (70.5 Å) → 2L (39 Å) + 3L (66 Å), correlated with an exothermic peak recorded simultaneously by DSC, was clearly visible. At t > 100 h conditioning at 4 o C, the same crystalline structures were found in cream and AMF with the coexistence of at least a 2L (40.5 Å) and a 3L (54.2 Å) longitudinal organization, associated with α, β' 2 , β' 1 and β packings of the chains. The melting behaviors of cream and AMF were monitored on heating at 2 o C . min -1 by coupled XRD as a function of temperature and DSC experiments. The absence of further structural evolution and polymorphic transition until final melting demonstrates the relative stability of the structure formed. The evolution of cream density after quenching to 4 o C revealed two transitions, the amplitudes, rates and duration of which coincided with DSC and XRD experiments. All data are in agreement in demonstrating that two transitions, a fast and a slow one, occur in dairy products after fast cooling to 4 o C. Cristallisation / polymorphisme / triacylglycérol / diffraction des rayons X / calorimétrie

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Section: Isothermal Evolution At 4 O C After Quenchingsupporting

confidence: 79%

“…2). The higher liquid content expected at 4 o C compared to -8 o C [15] favors the 2L (47 Å) → 3L (70.5 Å) transition. In the AMF sample (Fig.…”

Section: Isothermal Evolution At 4 O C After Quenchingmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

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Crystalline structures formed in cream and anhydrous milk fat at 4 °C

Lopez

Bourgaux

Lesieur

et al. 2002

Lait

Self Cite

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“…• C/min) were studied in (17). In the present study, the same techniques are used to determine the influence of both cooling rates and droplet size on the crystalline structures formed within fat globules, starting from the characterization of the species formed at intermediate rate in order to complement these previous studies.…”

Section: Introductionmentioning

confidence: 99%

Thermal and Structural Behavior of Milk Fat

Lopez¹,

Bourgaux

Lesieur

et al. 2002

Journal of Colloid and Interface Science

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Crystallization of triacylglycerols (TG) within milk fat globules of creams is studied with an instrument coupling time-resolved synchrotron X-ray diffraction (XRDT) at both small and wide angles and high-sensitivity differential scanning calorimetry (DSC) at cooling rates of -3 and -1 degrees C/min from 60 to -10 degrees C and compared to that of the anhydrous milk fat (AMF). Simultaneous thermal analysis permits correlation of the formation of the different crystalline species monitored by XRDT to the DSC events. Under the above cooling conditions, milk fat TG sequentially crystallize, within the globules, from about 19 degrees C, in three different lamellar structures with double-chain length (2L) stackings of 47 and 42 A and a triple-chain length (3L) stacking of 71 A, all of alpha type, which are correlated to two or three overlapped exothermic peaks recorded by DSC. Compared to what is observed for AMF, TG crystallization in emulsion (i) favors sub-alpha formation at low temperature and (ii) induces layer stacking defects in 3L crystals. Subsequent heating at 2 degrees C/min shows numerous structural rearrangements before final melting, confirming that (i) cooling at -1 degrees C/min leads to the formation of unstable crystalline varieties in the dispersed state and (ii) a monotropic transition alpha-->beta' takes place. Similar behavior is observed for cooling at -3 degrees C/min and subsequent heating. An overall comparison of the thermal and structural properties of the crystalline species formed as a function of the cooling rate, between >1000 and 0.15 degrees C/min, and stabilization time at 4 degrees C is given. Depending on the cooling rate, at least five crystalline subcell species are observed at wide angles, alpha and sub-alpha, two beta' and one beta. At small angles, at least six lamellar stackings are identified, three 3L and three 2L. However, a single subcell packing (e.g., alpha) might correspond to several longitudinal chain stackings, demonstrating the usefulness of the small-angle XRD technique. Reconstituted emulsions homogenized under different pressures are used to determine the influence of droplet size on crystallization. The decrease of droplet size induces (i) a higher supercooling/supersaturation and (ii) a higher disorder and/or a smaller size of TG crystals within the emulsion droplets. At the supramolecular scale, polarized light microscopy shows that various cooling rates applied in situ using a temperature-controlled stage directly influence crystal sizes and their type of organization within milk fat globules. The faster the cooling rate, the smaller the size of the crystals within the globules.

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“…Anhydrous milk fat (AMF) is produced by removal of the milk fat globule membrane as well as the water phase, so that only triacylglycerols (TAGs; 99.8 %) are present. Despite the same fatty acids composition, the crystallization mechanisms of butter and AMF are different [5][6][7]. In general, in milk fat globules the supercooling needed to start crystallization is higher, the crystallization onset is delayed, and the crystallization rate is lower when compared to bulk fat [4,5,8].…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Material Properties of Milk Fat Systems During Temperature Fluctuations

2013

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Microstructure and material properties of milk fat systems containing different amount of milk fat globules and different emulsion types were studied towards the effects of temperature fluctuations stress. The three systems were (i) an emulsion based on anhydrous milk fat (AMF) consisting of crystals dispersed in liquid oil, (ii) butter which is a water in oil emulsion consisting of a continuous crystal network with partially disrupted fat globules interrupted by intact fat globules and water droplets, and (iii) freeze-dried cream which is an oil in water emulsion consisting of concentrated milk fat globules. The microstructure of the systems was observed by confocal laser scanning microscopy and linked to their material properties by large and small deformation rheology techniques. Different rheological techniques were used to characterize the material descriptors. The crystallization behavior was studied by thermal analysis and pulsed nuclear magnetic resonance. The freeze-dried cream was characterized as the softest, more elastic, and less stiff when compared to butter and AMF. Temperature fluctuations led to drastic material consolidation in butter as a consequence of flocculation of fat globules and formation of a more dense crystal network with stronger bonds. Only after several temperature fluctuations, material consolidation was observed in AMF, whereas no significant changes in material properties were observed in the freeze-dried cream. The intact fat globules decrease the hardness and stiffness, whereas the amount and type of contact points between crystal clusters of the dispersed crystal phase contribute to increase hardness, stiffness, and brittleness of the systems.

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Thermal and Structural Behavior of Milk Fat

Cited by 96 publications

References 25 publications

Crystalline structures formed in cream and anhydrous milk fat at 4 °C

Crystalline structures formed in cream and anhydrous milk fat at 4 °C

Thermal and Structural Behavior of Milk Fat

Microstructure and Material Properties of Milk Fat Systems During Temperature Fluctuations

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