Structure Of Milk Fat Globules Research Articles

Effect of infant formula production processes on phospholipid composition and structure of milk fat globules

The phospholipid (PL) composition and milk fat globule (MFG) structure are important for MFG membrane function. However, the effects of various processing methods on these factors remain unclear. In the present study, we compared the effects of different processing methods for infant formula (IF) production on PLs and MFGs. Homogenization and heat sterilization significantly decreased the number of PL species in raw milk (RM, 104). Heat sterilization and spray drying significantly reduced PL content in RM (160.3 ± 12.2 mg/L; p < 0.05). During processing, the average volume diameter (5.67 ± 0.81 μm) and zeta potential (−7.37 ± 0.27 mV) of RM were significantly reduced (p < 0.05). After homogenization, PLs were distributed in a circular and dotted manner around the MFGs. After spray drying, PL fluorescent rings lost structural integrity. Therefore, the tested processing methods substantially damaged the PL composition and MFG structure. These results may provide a scientific basis for future IF development.

Changes in interfacial composition and structure of milk fat globules are crucial regulating lipid digestion in simulated in-vitro infant gastrointestinal digestion

The interfacial phospholipid and protein compositions of fat globule in human milk and three different infant formulas (F1: supplied with MFGM and OPO; F2: supplied with OPO and without MFGM; F3: supplied with MFGM and without OPO) were analyzed and compared, and the changes of interfacial composition and structure on their in-vitro infant gastrointestinal digestion were evaluated. The study from the interfacial properties of fat globule to illustrating the effect of interfacial composition and structure on lipolysis and proteolysis. The results showed that, both F1 and human milk had a similar interfacial phospholipid composition and higher sphingomyelin (SM) content. The interfacial protein composition of F1 was closer to human milk. F1 had the average particle size of 3.67 ± 0.12 μm and a phospholipid layer on the surface of triglyceride. Meanwhile, the relatively complete phospholipid ring structure in F1 could always be observed during gastric digestion, while was gradually destroyed during intestinal digestion. Moreover, F2 and F3 are significantly different from HM and F1 in composition and structure of fat globule. Although MFGM is added to commercial infant formula (F3), most MFGM still existed in the aqueous phase of emulsion in free form. Notable, F1 had similar in-vitro lipolysis and proteolysis properties to human milk. These results indicated that the simulation of human milk fat globule at the molecular level and structure feature was the key contributing to digestion behavior. • The abundant phospholipid ring structure were observed in F1. • F1 had sn-2 SFAs and OPO, which reduced the formation of calcium soap. • HM had the highest lipolysis rate of 86.3%, followed by F1 (82.9%) after digestion. • F1 had similar digestive properties to human milk and is superior to F2 and F3. • The simulation of HM fat at the molecular and structure is key to effect digestion.

Changes in Milk Fat Globules and Membrane Proteins Prepared from pH-Adjusted Bovine Raw Milk.

Milk fat globules (MFGs) have tri-layer biological membrane structures, and their compositions are gaining more interest for their physiological benefits. In this study, the changes in MFGs and milk fat globule membrane (MFGM) proteins after cream separation from different pH bovine raw milk were investigated. Raw milk samples were adjusted to pH 5.30 and 6.30 using citric acid at 25 °C. The effect of pH and centrifugation on the structure of MFGs was evaluated by means of particle size, zeta potential and confocal laser scanning microscopy (CLSM). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to analyze the proteins in the obtained fractions. It was found that both pH and centrifugation could affect the particle size of all samples. As the volume distribution (Dv; Dv (10), Dv(50)and Dv (90)) decreased, the corresponding specific surface area (SSA) increased, and span and uniformity values showed the same trend. The decrease in the zeta potential of MFG correlated with the Dv(50), which was further confirmed by CLSM observation. More butyrophilin (BTN) and periodic acid Schiff 6/7 (PAS 6/7) were lost in cream samples at pH 5.30. The findings could provide valuable knowledge for the application of MFGs ingredient in the food industry since their structures and compositions could affect their potential functional and physiological properties.

Effects of pulsed electric field on fat globule structure, lipase activity, and fatty acid composition in raw milk and milk with different fat globule sizes

To modify the structure of milk fat globules (MFGs), raw milk (RM) with native MFGs, and milk with small (MS) and large (ML) MFGs, were subjected to moderate pulsed electric field (PEF) treatment at 9 and 16 kV·cm−1 for 30 μs. The changes caused by PEF on MFG structure leading to MFG-MFG and MFG-protein aggregation were found to depend on the size, composition and/or previous damage caused by the separation and mixing processes during production of MS and ML, in addition to the intensity of the PEF treatment. Although, PEF treatment had a more pronounced effect on MFGM proteins of MS, these MFG were less affected by PEF due to significant adsorption of milk proteins. The structural changes caused by PEF were accompanied by changes in lipase activity and fatty acid (FA) profiles, i.e. increase in the proportion of C6:0, C8:0, C10 and some long-chain FAs and a decrease in medium and other long chain FAs. Industrial relevancePEF is gaining attention in the dairy industry. However, information regarding the effect of PEF processing on milk components and functionality is still limited. The present investigation contributes to understand the potential of PEF at moderate field intensities to modify the MFGs and consequences for milk stability, lipolysis and composition of FAs. The new insight is relevant in development of new products and ingredients containing milk fat.

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.

Current knowledge of lipids in human milk and recent innovations in infant formulas

Human milk (HM) is recognized as the exclusive natural source that provides infants with the essential nutrients for development and growth. Lipids in HM are present as a unique colloidal structure of milk fat globules enveloped by a biological membrane. Benefiting from the advances in spectroscopic imaging and lipidomics analysis technology, the knowledge about HM lipids regarding lipid class profile and distribution, and their digestion mechanism have been greatly updated; the nano/microstructures of human fat globule membrane and heterogeneous distribution of HM lipids are deciphered. Accordingly, innovative infant formulas, to larger extent mimicking HM to promote the cognitive development and maturation of the digestive system of infants, have been developed, including the supplementation with milk fat globule membranes.

Elevated concentrate-to-forage ratio in dairy cow rations is associated with a shift in the diameter of milk fat globules and remodeling of their membranes

We examined the effects of concentrate-to-forage ratio in dairy cow rations on milk-fat composition, with a specific focus on the structure of milk fat globules (MFG). Twenty-four Holstein cows, 153 d in milk, were assigned to 2 dietary treatments in a crossover design study. Treatments were (1) high-concentrate (65%), low-forage (35%; HCLF) diet and (2) low-concentrate (35%), high-forage (65%; LCHF) diet. The mean diameter of the MFG; plasma concentrations of insulin, glucose, and nonesterified fatty acids (FA); and the composition and concentrations of milk FA and polar lipids were determined. Concentrations of insulin were 56% higher, and those of nonesterified FA 46% lower, in the HCLF than in the LCHF diet. The milk yield was 8.5kg/d higher and yields of fat, protein, and lactose were 180, 350, and 403g/d higher, respectively, in the HCLF versus LCHF diet. Milk FA composition differed between treatments, with 1.5 and 1.0 percentage units higher saturated and polyunsaturated FA concentrations, respectively, in the HCLF versus LCHF diet. Mean MFG diameter tended to be smaller (0.2μm) in the HCLF diet than in the LCHF diet, associated with increased daily phospholipids yield (34%), lower phosphatidylserine and higher phosphatidylcholine concentrations. In conclusion, the decreased milk and fat yields in the LCHF diet were associated with remodeling of the MFG membrane and with the secretion of larger MFG. Membrane remodeling of the mammary epithelium membranes seems to play a role in regulating MFG size.