Individual Fat Globules Research Articles

Influence of interfacial adsorption of glyceryl monostearate and proteins on fat crystallization behavior and stability of whipped-frozen emulsions

The effect of interfacial competitive adsorption of glyceryl monostearate (GMS) with proteins and GMS-fat (anhydrous milk fat; coconut oil) interactions on the fat crystallization behavior and stability of whipped-frozen emulsions were investigated. The results indicated GMS retarded the nucleation of emulsified anhydrous milk fat, but accelerated crystal growth. A contrasting outcome was elicited by emulsified coconut oil. Increasing GMS concentration strengthened and weakened the structural networking within anhydrous milk fat and coconut oil emulsions, respectively, which was evidenced by the oscillatory rheology results. Anhydrous milk fat whipped-frozen emulsions were characterized by increased partial coalescence degree with increasing GMS concentration. However, lower partial destabilization index and insignificant effect of GMS was found in coconut oil systems. Confocal laser scanning micrographs revealed that big clumps of fat globules were present at air bubble surfaces in anhydrous milk fat whipped-frozen emulsions, while only some individual fat globules were observed in coconut oil systems.

The Effect of Salt on the Structure of Individual Fat Globules and the Microstructure of Dry Salted Cheddar Cheese

Salting is an essential step in the production of Cheddar and other cheese varieties and is a well-studied process but the effect of salt addition on the microstructure of the milk ingredients and resulting cheese is not well known. This study provides insights into how the primary components in milk and the cheese matrix respond to salting. High concentrations of salt (15–25% (w/w) NaCl) disrupted fat globules due to the increased osmotic pressure. This led to fat coalescence, resulting in large fat globules >10 μm in diameter, together with submicron sized fat globules ~ 120–500 nm in diameter. Salt addition also prevented the visualization of the milk fat globule membrane when added at high concentrations (25% (w/w) NaCl) and induced asymmetry in liquid ordered domains at lower concentrations (10% (w/w) NaCl). The microstructure of the surface of the milled curd was compacted by salt, appearing coarse with 5% (w/w) NaCl or more hydrated with a denser protein structure with 2.5% (w/w) NaCl. After pressing, the curd junctions were fine and thin within the unsalted sample but coarse and thick where 5% (w/w) NaCl was added. Such coarse junctions appear to reduce binding between curd particles leading to a less cohesive cheese. Our results show that NaCl can significantly impact on the structure of fat and protein matrix of the curd surface if salt is not evenly distributed during dry salting. High concentrations of salt can also change the microstructure and texture of the cheese, resulting in a more heterogeneous product.

The surface properties of milk fat globules govern their interactions with the caseins: Role of homogenization and pH probed by AFM force spectroscopy

The surface of milk fat globules consists of a biological membrane rich in polar lipids and glycoproteins. However, high shear stress applied upon homogenization disrupts the membrane and leads to the adsorption of casein micelles, as the major protein fraction of milk. These changes in the interface properties could affect the interactions between native or homogenized milk fat globules and the surrounding protein matrix, at neutral pH and upon acidification. In this study, macroscale rheometry, microscopic observations, nanoscale AFM-based force spectroscopy and physico-chemical analysis were combined to examine the interfacial composition and structure of milk fat globules and to evaluate their interactions with casein micelles. We showed that the surface properties of milk fat globules (biological membrane vs. caseins) and pH govern their interactions with casein micelles. The adhesion between individual fat globules and casein micelles was higher upon homogenization, especially at acid pH where the work of adhesion increased from 3.3 x 10-18 to 14 x 10-18 J for native and homogenized fat globules, respectively. Consequently, casein-coated homogenized fat globules yield stiffer milk acid gels. These findings cast light on the importance of colloidal particle’s surface properties and pH on their connectivity with the surrounding matrix, which modulates the bulk microstructure and rheological properties with potential functional consequences, such as milk lipid digestion.

Composition, microstructure and chemical interactions during the production stages of Mozzarella cheese

Changes in chemical composition, microstructure and chemical interactions before and after the stretching stage of mozzarella cheese processing were investigated. The increased acidity and the decreased pH resulted in the solubilisation of total calcium. The protein matrix became more compact and the size of the fat globules decreased with the incorporation of small individual fat globules, aggregates and fat globules of irregular form into the matrix. The predominant bonds in the curd before the stretching stage were hydrophobic interactions, whereas the number of calcium bonds was minimal. After the stretching stage, the primary bonds responsible for maintaining the cheese structure were calcium bridges, electrostatic interactions and hydrogen bridges. These results clarify important aspects of the bonds involved in the production of this type of cheese.

Industrial Applications of Selected JFS Articles

Industrial Applications of Selected <i>JFS</i> Articles

Effects of emulsifiers on vegetable-fat based aerated emulsions with interfacial rheological contributions

A relationship between oil/water interfacial properties and the whipping performance of vegetable-fat based o/w emulsions was investigated for two emulsifier mixtures: lactic acid esters of mono and diglycerides (LACTEM), and partially unsaturated/saturated monoglyceride mixture (PUS/SMG). The whipping emulsions were evaluated on storage viscosity, overrun, and firmness. The model interfacial layer between water and oil with LACTEM gave higher shear modulus and the emulsion showed low bulk viscosity, high overrun and high firmness after whipping. The interfacial modulus with PUS/SMG was lower and the emulsion provided higher bulk viscosity, lower overrun and lower firmness. Microscopy and particle size distribution in sheared unwhipped emulsions showed individual fat globules without aggregation in the case with LACTEM, while globules with PUS/SMG became highly aggregated. These suggest that the weaker interfacial layer with PUS/SMG can be more susceptible to the fat crystal mediated partial coalescence of fat globules: Partial coalescence can happen already during quiescent storage. The subsequent whipping led to further aggregation then a strong fat network can help to stabilize air bubbles. The more stable interfacial layer in LACTEM-based emulsions leads to a lower tendency to coalesce during quiescent conditions, and only to aggregation and coalescence during the whipping stage. Fat aggregation was confirmed to be essential in achieving a good aerated structure but there were differences depending on the surface layer properties of fat globules induced by emulsifiers. This caused the rheological differences observed during storage.

Microstructural Changes in Fat During the Ripening of Iranian Ultrafiltered Feta Cheese

In this study, fat globules in Iranian ultrafiltered Feta cheese (3 to 60 d) were directly observed during the ripening period by scanning electron microscopy. According to images of ultrafiltered Feta cheese samples obtained by scanning electron microscopy, individual fat globules and aggregates of fat were easily distinguishable on d 3 and had completely disappeared within 20 d of storage. On d 20, only the fingerprints of the fat globules and pools of free fat in the casein matrix remained. After 40 d of ripening, the texture was homogeneous and no fat globules or fat voids were detected. Chemical analysis of cheese samples showed that with an increase in the ripening period, the contents of dry matter and fat decreased significantly, whereas the pH values and salt content did not indicate any significant changes.

Microstructural properties of fat during the accelerated ripening of ultrafiltered-Feta cheese

A commercial pregastric lipase was used to accelerate lipolysis of Iranian ultrafiltered-Feta (UF-Feta) cheese. Scanning electron microscopy images showed that with an increase in lipase levels from 2.0 to 6.0 g 100 kg −1 of retentate, disruption of fat globules increased significantly. On day 3 of ripening and enzyme level of 2.0 g 100 kg −1 of retentate, individual fat globules and fat aggregates were clearly observed on the cheese samples. An increase in the lipase level or ripening period resulted in an increase in the rate of disappearance of fat globules. After 20 days of ripening, no apparent fat globules were observed and fewer fingerprints and voids of free fat were detected, compared to when no enzyme was used.

Crystallisation and melting properties of dromedary milk fat globules studied by X‐ray diffraction and differential scanning calorimetry. Comparison with anhydrous dromedary milk fat

AbstractCrystallisation and melting properties of triacylglycerols (TG) in dromedary milk fat (DMF) globules are studied by X‐ray diffraction (XRD) as a function of temperature coupled with high‐sensitivity differential scanning calorimetry (DSC), using synchrotron radiation. The crystallisation properties studied on cooling at ∣dT/dt∣ = 1 °C.min−1 from 60 °C to −8 °C show the successive formation of two double‐chain length (2L) lamellar structures: α 2L1 (46.7 Å) from 22 °C and β' 2L2 (41.7 Å) from 9 °C, which coexist until the end of the cooling process. These two types of crystals are related to the two exothermal peaks recorded simultaneously by DSC. The melting properties are studied on subsequent heating of DMF globules at dT/dt = 1 °C.min−1. The detailed analysis of the intensity and position of the XRD peaks recorded as a function of time shows that (i) the α 2L1 structure melts first, (ii) some TG from 2L1 melt and are incorporated again in the 2L2 structure, and (iii) the 2L2 structure melts with a final melting temperature over 44 °C. The influence of the dispersion of TG molecules in individual fat globules, with the presence of an interface with water, was determined by comparing their crystallisation behaviour to that of the same TG extracted from cream (anhydrous DMF) under the same experimental conditions. Results show that the same lamellar structures, α 2L1 and then β' 2L2, are formed on cooling in the dispersed and bulk states. However, crystallisation in the unstable α form is favoured in fat globules.