Physicochemical Properties of Milk Fat Emulsions Stabilized with Bovine Milk Fat Globule Membrane

Milk fat globules (MFG) were reconstituted with milk fat globule membrane (MFGM) and milk fat (MF). Viscosity of the reconstituted MFG was highest at pH 5.0 and 4 min emulsifying, and rose with an increase of MFGM between 40–80 mg/g fat. Adsorbed protein/unit fat increased at acid pH with increase of MFGM. The composition of proteins adsorbed on the surface of MFG was not influenced by factors of reconstitution. The size and specific surface area of globules were influenced by emulsifying time, MFGM and MF concentrations, and pH. The size range of MFG prepared by standard method was 0.9–17 μm in diameter. Median diameter was 5 μm and specific surface area was 15,600 cm²/cm³ of emulsion.     

Role of Milk Fat Globule Membrane in Autoxidation of Milk Fat

The influence of the milk fat globule membrane (MFGM) on oxidation of milk fat under various conditions was monitored by fatty acid analysis and oxygen consumption at 50°C. The rate of copper-catalyzed oxidation of cream containing the membrane was faster than when the membrane was removed. In the dry state, the isolated MFGM, membrane lipids (ML) and the nonlipid membrane solids (NLMS) inhibited oxidation at 50°C and 95°C. In the presence of water, however, all membrane components enhanced oxidation at 50°C. The balance between the accelerating effects of membrane components and the inhibiting influence of other factors appeared to depend on processing conditions.     

Simple Method for Separate Determination of Three Flavins in Bovine Milk by High Performance Liquid Chromatography

Milk, dialyzed milk and milk fat globule membrane (MFGM) (1.0g each) were boiled 3 min to inactivate pyrophosphatase. Release of flavins bound to milk proteins and deproteinization were performed simultaneously by Pronase digestion for 1 hr at 45°C. After centrifugation, the extracted flavins were analyzed by HPLC, using a C18 column at 40°C connected to a spectrofluorometer. Recovery of FAD, FMN and riboflavin was 97–99% from whole milk, 95–100% from dialyzed milk, and 99-100% from MFGM. The method is simple, rapid, sensitive and reproducible. Bovine milk contained 202 μg of total flavins per 100g milk, of which FAD was 13.8, FMN 4.3, and RF 81.9mol%(n=6).     

不同均质工艺处理对巴氏杀菌乳脂肪球膜蛋白质组成的影响

乳脂肪球大小和膜蛋白组分的变化决定了脂肪球稳定性,从而影响巴氏杀菌乳在贮藏期内的品质稳定性。本研究通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和液相色谱-质谱联用法分析不同预热温度（50、60、70?℃）和不同均质压力（20、30、40、45?MPa）对脂肪球膜蛋白的影响,并通过稳定性分析仪探究脂肪球膜蛋白变化与稳定性的关系。结果表明,均质工艺对脂肪球膜蛋白种类无显著影响,但对脂肪球膜蛋白的含量有一定影响：黄嘌呤氧化还原酶（xanthine dehydrogenase/oxidase,XO）、嗜乳脂蛋白（butyrophilin,BTN）、脂肪滴结合蛋白（adipophilin,ADPH）在预热60 ℃时的含量最低,黏液素（mucin 1,MUC1）在预热60 ℃时的含量最高,脂肪酸结合蛋白（fatty acid binding protein,FABP）、组织糖蛋白高碘酸烯夫6/7（periodic acid Schiff 6/7,PAS6/7）的含量随着预热温度的升高而减少,组织糖蛋白高碘酸薛夫IV（cluster of differentiation 36,CD36）的含量随着预热温度的升高而增多;XO、PAS6/7、BTN、ADPH、FABP在均质压力40 MPa时含量最低,CD36的含量随均质压力的增加而减少;脂肪球膜蛋白构成中,牛血清白蛋白（bovine serum albumin,BSA）、αs1-酪蛋白（casein,CN）和β-CN含量增加,其中BSA含量增加最明显。综上,推测均质工艺导致αs1-CN、β-CN和BSA组分参与了脂肪球膜的构建,并对脂肪球稳定性产生了积极的影响。     

Milk fat globule membrane proteins are involved in controlling the size of milk fat globules during conjugated linoleic acid–induced milk fat depression

Milk fat globule membrane (MFGM) proteins surround the triacylglycerol core comprising milk fat globules (MFG). We previously detected a decrease in the size of fat globules during conjugated linoleic acid (CLA)-induced milk fat depression (MFD), and other studies have reported that some MFGM proteins play a central role in regulating mammary cellular lipid droplet size. However, little is known about the relationship between MFD, MFG size, and MFGM proteins in bovine milk. The aim of this study was to investigate the profile of MFGM proteins during MFD induced by CLA. Sixteen mid-lactating Holstein cows (145 ± 24 d in milk) with similar body condition and parity were divided into control and CLA groups over a 10-d period. Cows were fed a basal diet (control, n = 8) or control plus 15 g/kg of dry matter (DM) CLA (n = 8) to induce MFD. Cow performance, milk composition, and MFG size were measured daily. On d 10, MFGM proteins were extracted and identified by quantitative proteomic analysis, and western blotting was used to verify a subset of the identified MFGM proteins. Compared with controls, supplemental CLA did not affect milk production, DM intake, or milk protein and lactose contents. However, CLA reduced milk fat content (3.73 g/100 mL vs. 2.47 g/100 mL) and the size parameters volume-related diameter D_[4,3] (3.72 μm vs. 3.35 μm) and surface area-related diameter D_[3,2] (3.13 μm vs. 2.80 μm), but increased specific surface area of MFG (1,905 m²/kg vs. 2,188 m²/kg). In total, 177 differentially expressed proteins were detected in milk from cows with CLA-induced MFD, 60 of which were upregulated and 117 downregulated. Correlation analysis showed that MFG size was negatively correlated with various proteins, including XDH and FABP3, and positively correlated with MFG-E8, RAB19, and APOA1. The results provide evidence for an important role of MFGM proteins in regulating MFG diameter, and they facilitate a mechanistic understanding of diet-induced MFD.     

乳脂肪球膜的特性、开发及在模拟母乳脂肪球结构中的应用

乳脂肪球膜（milk fat globule membrane,MFGM）是包裹在天然乳脂肪球外部的3 层膜状结构,然而牛乳基和大豆基婴儿配方奶粉缺少MFGM,脂肪球结构与母乳存在较大差异,因此添加外源MFGM以及制备与母乳脂肪球结构接近的婴儿配方奶粉成为了近期的研究焦点。本文综述了MFGM的相关特性和生产开发途径,以及牛乳MFGM在仿母乳脂肪球结构乳液和婴儿配方奶粉中的应用。体外模拟婴儿胃肠道消化实验以及啮齿动物体内实验结果表明,仿母乳脂肪球结构乳液和婴儿配方奶粉能够促进婴儿脂肪消化并且改善脂质代谢过程。     

Heat Denaturation and Emulsifying Properties of Egg Yolk Phosvitin

Phosvitin in water at pH 7 had a denaturation temperature (T_d) of 79.7 ± 1.4°C when heated at 10°C/min. When dissolved in 0.1M and 1.0M NaCl, the T_d decreased to 77.7 ± 1.2°C and 77.2 ± 1.3°C, resoectivelv. and in 10 and 20% sucrose there was no change in T_d. Heat treatment of phosvitin solutions at ≥65°C led to decreased emulsifying activity (EA). The emulsion stability (ES) decreased when phosvitim solutioni were heated at 70, 80 or 96°C for up to 60 min. The ES was not affected (p < 0.05) for phosvitin solutions after heating at ≤67.5°C for up to 60 min.     

Effect of heating whey proteins in the presence of milk fat globule membrane extract or phospholipids from buttermilk

The objective of this study was to determine the contribution of phospholipids from buttermilk as a nucleus in the heat-induced aggregation of whey proteins. Solutions of whey proteins (5%, w/v) were adjusted to pH 4.6 or 6.8 and then heated at 65 or 80 °C for 25 min with or without 1% (w/v) of milk fat globule membrane (MFGM) extract or phospholipid powder. The aggregation mechanisms were characterised using analysis with Ellman's reagent, one-dimensional gel electrophoresis, thin-layer chromatography, and three-dimensional confocal laser-scanning microscopy. Three-dimensional images showed protein/phospholipid interactions in the presence of MFGM extract or phospholipids, and thin-layer chromatography plates showed no trace of free phospholipids after 20 min at pH 4.6. Overall, the results demonstrate that phospholipids from buttermilk were involved in the formation of protein aggregates through the MFGM fragments at a low temperature, whereas phospholipids could interact directly with the proteins at a higher temperature (80 °C).     

High Hydrostatic Pressure Effects on Color and Milk-Fat Globule of Ewe's Milk

ABSTRACT: The influence of high hydrostatic pressure treatments on lipolysis, color, and size distribution of milk fat globule (MFG) on ewe's milk was studied. Treatments consisted of combinations of pressure (100 to 500 MPa) and temperature (4, 25, and 50 °C) for 10 min. Pressurized samples showed FFA levels lower than control. Pressurizations at 25 and 50 °C showed a tendency to increase MFG in the range 1-2 μm and to decrease MFG between the range 2 to 10 μm, whereas at 4 °C the effect was the reverse. A decrease of lightness (L*)value, and an increase of (−a*) and (+b*) values occurred in color with pressure increase.     

Interactive Effects of Milk Fat Globule and Casein Micelle Size on the Renneting Properties of Milk

The size of the casein micelles (CM) and the milk fat globules (MFG) vary depending on farming factors, such as seasonal variation and stage of lactation, and cow genetics. The MFG and CM size of milk can influence the renneting behavior and texture of manufactured dairy products. In this work, we investigated the combined effects of MFG and CM size on the onset of gelation, the maximum rate of gelation, the value for G′_60 min (the final storage modulus) and G″_60 min (the final loss modulus), and tan δ upon renneting. Fractionation of MFG on the basis of size was carried out using laboratory-based centrifugation, whereas milk of predominantly large (184–218 nm) or small (147–159 nm) CM was selected naturally on-farm. Casein micelle size had the dominant effect on curd firmness and gelation rates of milk, where small CM milk formed rennet gels earlier and resulted in a firmer gel than milk with large CM. However, MFG size also influenced the renneting properties. The strongest rennet gels were obtained when large MFG (3.88–5.78 μm) was combined with small CM (153–159 nm). Selecting milk on the basis of the microstructure of key milk components could be achieved by natural selection of dairy cows or via fractionation technologies. Selection may provide a useful tool for efficient manufacturing of different dairy products based on the desirable characteristics specific to each.     

驴初乳与常乳乳脂球膜蛋白质组的对比分析

为阐明驴初乳与常乳中乳脂球膜蛋白的差异,利用蛋白质组学技术对二者进行蛋白质组差异分析。在驴初乳和驴常乳中分别鉴定到216 种和215 种乳脂球膜蛋白,并在其中筛选出40 种差异蛋白,包括15 种差异表达蛋白和25 种特异表达蛋白。将驴初乳与常乳中的差异蛋白进行生物信息学分析发现,差异蛋白主要参与的细胞组成为细胞外泌体、胞外囊泡、胞外细胞器等;主要参与的生物过程为对外部刺激的反应过程、细胞增殖过程、血管形态生成过程等;主要参与的分子功能为金属离子结合、阳离子结合、钙离子结合等。此外,这些差异蛋白主要参与补体和凝血级联,为生成IgA而形成的肠道免疫网络等代谢通路。利用蛋白质网络互作分析发现,差异蛋白中存在具有高连接度的关键乳脂球膜蛋白因子。本研究有助了解驴乳脂球膜蛋白的生物学特性,并为驴乳中乳脂球膜蛋白的营养学研究及相关配方乳粉的研发提供理论基础。     

Effect of Olein Fractions of Milk Fat on Oxidative Stability of Ice Cream

The effect of low melting fractions of milk fat on oxidative stability of ice cream was investigated. Cream was fractionated at three different temperatures (25, 15, and 10°C), designated as LF-25, LF-15, and LF-10. All the low melting fractions were individually incorporated into ice cream and compared with a control, unmodified milk fat. The other ingredients were the same as in the control. Ice creams were stored at –18°C for six months and sampled every 30 days. Fractionation induced major changes in the fatty acid composition of all fractions. Concentration of short-chain and long chain unsaturated fatty acids increased in the low melting fractions. Peroxide value and anisidine value of LF-10 increased from 0.23 to 3.95 (meq/kg O₂) and 3.87 to 8.04. Conjugated dienes of control and LF-10 after six months were 1.39 and 4.72 at the same storage period. The flavor score of LF-10 was more than the control and remained indifferent from the control until two months of storage. After six months, the flavor score of LF-10 dropped by 3.6 points as compared to the control, 1.2 points. Low melting fractions of milk fat can be added in the formulation of ice cream to improve its nutritional value with acceptable sensory attributes. However, storage of ice cream formulated from low melting fractions is not recommended for over 60 days at –18°C.     

The Effect of Minor Components on Milk Fat Microstructure and Mechanical Properties

ABSTRACT: Although minor polar components affected the kinetics of milk fat crystallization, its structure and mechanical properties remained unchanged. At 5 °C, a granular microstructure was observed, while at 20 °C, a combination of granular and spherulitic microstructures were observed. By 27.5 °C, only spherulites were present after 24 h. There were no differences observed in the fractal dimension (D) determined by microscopy or rheology for anhydrous milk fat, milk fat triacylglycerols and MF‐TAGs with added diacylglycerols at 5 °C. There was, however, a strong temperature effect on D, increasing from 1.87 at 5 °C to 1.98 at 22.5 °C. The yield force and storage modulus were unaffected by removal of minor components.     

母乳和牛乳中乳脂肪球膜蛋白质的差异分析

为比较乳脂肪球膜（milk fat globule membrane,MFGM）蛋白在母乳和牛乳中的差异,采用有机试剂提取法,从母乳和牛乳中提取分离出MFGM蛋白,经皮尔斯TM去垢小柱去除十二烷基硫酸钠后,通过液相色谱-质谱联用技术检测分析,检测结果根据特异性肽段匹配数不小于1筛选后,在母乳和牛乳中分别检测到863 种和454 种蛋白,其中二者共有175 种,分别独有688 种和279 种。将母乳中差异表达的688 种蛋白质按PANTHER数据库进行蛋白质的Gene Ontology（GO）功能注释,这些蛋白主要是细胞部分、细胞器、细胞膜等组分,参与的生物途径有新陈代谢过程、生物调节、刺激性反应、免疫系统过程、再生作用等,具有催化、黏合、转运、酶调节等多种分子功能。另外,母乳中的这些差异蛋白参与氨酰tRNA生物合成、致病性大肠杆菌感染、脂肪酸代谢、丙酸代谢、甾体合成、酸降解等都是牛乳中的乳脂肪球膜蛋白不具有的功能。通过分析得出母乳和牛乳中的MFGM蛋白具有明显差异,虽然有部分组成和功能的重叠,但在丰度和代谢路径上,牛乳MFGM蛋白不能替代母乳MFGM蛋白。     

Milk fat globule membrane – a source of polar lipids for colon health? A review

The milk fat globule membrane (MFGM) surrounds fat globules, protects them against lipolysis and disperses the milk fat in the milk plasma. Besides their structural and emulsifying roles, in vivo and in vitro studies have demonstrated that phospholipids and sphingolipids of MFGM possess cancer risk‐reducing properties. Several reports attribute its chemopreventive activity to products of sphingomyelin hydrolysis, which affect multiple cellular targets that control cell growth, differentiation and apoptosis. With knowledge on the potential health benefits of MFGM lipids and proteins, dairy industries could in the future address their research in developing new functional dairy products enriched in beneficial MFGM components.     

Effect of Lenient Steam Injection (LSI) heat treatment of bovine milk on the activities of some enzymes,the milk fat globule and pH

This study investigated the effects of Lenient Steam Injection (LSI) treatment at temperatures 70–150 °C on the enzymatic activities of the indigenous milk enzymes alkaline phosphatase, lactoperoxidase (LPO), xanthine oxidase (XO), lipoprotein lipase (LPL) and plasmin in comparison with two reference heat treatments of 63 °C for 30 s and of 72 °C for 15 s by indirect heating. Milk fat globule (MFG) size distributions and pH were also monitored. Alkaline phosphatase, LPO, XO and LPL activities decreased with increasing LSI temperature. Plasmin activity was increased at temperatures <80 °C and decreased at temperatures above 90 °C. Milk fat globule homogenisation was observed at temperatures above 110–130 °C.     

Emulsifying Capacity and Emulsion Stability of Milk Proteins and Corn Germ Protein Flour

Comparative studies of emulsifying capacity (EC) and emulsion stability (ES) of corn germ protein flour (CGPF), nonfat dry milk (NFDM), whey protein concentrates (WPC), and sodium caseinate (SC) were carried out using response surface methodology. CGPF was an effective stabilizer of fat-protein-water emulsions. Tested proteins showed the following trend in EC and ES: SC > WPC = NFDM > CGPF. EC and ES increased with increased concentration of protein. No effect of incubation temperature on EC and ES of these proteins was detected. All protein samples showed a maximum EC at high pH (near 8.0) and 1.0% concentration under test conditions, except NFDM (about pH 7.0). Minimal pH effect on ES was found.     

Fat Content of Milk and Cream and Effects on Fat Globule Stability

Milk fat globules with crystalline fat content were sheared in defined flow conditions in order to ascertain the critical strain rate, which led to destabilization of the fat globules. Based on a fluid-mechanical model which considered the influence of the dispersed phase, a critical shear rate was defined. The model predicted a linear decrease in destabilization shear rate coupled with an increase in fat volume concentration. This interrelationship was confirmed in experiments. Fat globule stability, as related to shear strain rate, increased at decreasing temperatures. Critical shear rates for milk and cream should be calculated at a fat content not exceeding 45% for temperatures between 5 and 20°C. Any motion at higher fat content had a destabilizing effect on fat globules.     

Milk Fat Globule Membrane Substances Inhibit Mouse Intestinal β-Glucuronidase

The β-glucuronidase inhibitory action of milk fat globule membrane (MFGM) was studied. By increasing the MFGM concentration to 0.2%, nearly 90% of the β-glucuronidase activity was inhibited. The trypsin-derived digests of MFGM inhibited β-glucuronidase activity by ～ 42%. The inhibitory effect of MFGM on intestinal β-glucuronidase of mouse was studied. We administered MFGM (groups I: 5%; group II: 10%; group III: 20%) to mice and investigated the time course of changes in fecal β-glucuronidase activity. In group I and II, enzyme activity had decreased 15–20% on the 5th day of treatment, but in group III, a decrease in enzyme activity was seen with an inhibition rate of 50%, showing a marked intracolonic efficacy of MFGM. Thus MFGM may have potential in explaining, treating or preventing intestinal cancers.     

pH and Sodium Chloride Effects on Emulsifying Properties of Egg Yolk Phosvitin

The emulsifying properties of phosvitin dissolved in water and 0.1, 0.5 and 1.0 M NaCl were determined from pH 3 to 10. The change in its emulsifying activity (EA) with pH was slight but significant (p<0.05) and emulsion stability (ES) was relatively high (68-73%), except at pH 5 (17%) and 10 (48%). The EA of phosvitin was higher than that of bovine serum albumin (BSA) at pH 3 or 8 and ES was higher than BSA at all pH levels except at pH 5 and 10. Added NaCl decreased in the EA of phosvitin at pH 3 and 10 and decreased the ES between pH 3 and 9. Increased instability of emulsions resulted mainly in coalescence of oil droplets at NaCl ≥ 0.5M. Salt increased the viscosity of phosvitin emulsion only at pH 3 but not at pH > 5. The viscosities of BSA emulsions were higher than those of phosvitin at pH 3, 5 or 8.