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.     

Milk protein fractions strongly affect the patterns of coagulation,curd firming,and syneresis

The aim of this study was to assess the role of milk protein fractions in the coagulation, curd firming, and syneresis of bovine milk. Analyses were performed on 1,271 individual milk samples from Brown Swiss cows reared in 85 herds classified into 4 types of farming systems, from the very traditional (tied cows, feed manually distributed, summer highland pasture) to the most modern (loose cows, use of total mixed rations with or without silage). Fractions α_S1-casein (CN), α_S2-CN, β-CN, κ-CN, β-lactoglobulin (LG), and α-lactalbumin (LA) and genotypes at CSN2, CSN3, and BLG were obtained by reversed-phase HPLC. The following milk coagulation properties were measured with a lactodynamograph, with the testing time extended to 60 min: rennet coagulation time (RCT, min), curd firming time (min), and curd firmness at 30 and 45 min (mm). All the curd firmness measures recorded over time (total of 240 observations/sample) were used in a 4-parameter nonlinear model to obtain parameters of coagulation, curd firming, and syneresis: RCT estimated from the equation (min), asymptotic potential curd firmness (mm), the curd firming and syneresis instant rate constants (%/min), and the maximum curd firmness value (CF_max, mm) and the time taken to reach it (min). All the aforementioned traits were analyzed with 2 linear mixed models, which tested the effects of the protein fractions expressed in different ways: in the first, quantitative model, each protein fraction was expressed as content in milk; in the second, qualitative model, each protein fraction was expressed as a percentage of total casein content. Besides proteins, additional nuisance parameters were herd (included as a random effect), daily milk production (only for the quantitative model), casein content (only for the qualitative model), dairy system, parity, days in milk, the pendulum of the lactodynamograph, and the CSN2, CSN3, and BLG genotypes. Both α_S1-CN and β-CN showed a clear and favorable effect on CF_max, where the former effect was almost double the latter. Milk coagulation ability was favorably affected by κ-CN, which reduced both the RCT and RCT estimated from the equation, increased the curd firming and syneresis instant rate constants, and allowed a higher CF_max to be reached. In contrast, α_S2-CN delayed gelation time and β-LG worsened curd firming, both resulting in a low CF_max. The results of this study suggest that modification of the relative contents of specific protein fractions can have an enormous effect on the technological behavior of bovine milk.     

Invited review: Microfiltration-derived casein and whey proteins from milk

Milk, a rich source of nutrients, can be fractionated into a wide range of components for use in foods and beverages. With advancements in filtration technologies, micellar caseins and milk-derived whey proteins are now produced from skim milk using microfiltration. Microfiltered ingredients offer unique functional and nutritional benefits that can be exploited in new product development. Microfiltration offers promise in cheesemaking, where microfiltered milk can be used for protein standardization to improve the yield and consistency of cheese and help with operation throughputs. Micellar casein concentrates and milk whey proteins could offer unique functional and flavor properties in various food applications. Consumer desires for safe, nutritious, and clean-label foods could be potential growth opportunities for these new ingredients. The application of micellar casein concentrates in protein standardization could offer a window of opportunity to US cheese makers by improving yields and throughputs in manufacturing plants.     

The Effect of Inclusion of Naked Oats in the Concentrate Offered to Dairy Cows on Milk Production,Milk Fat Composition and Properties

Dairy cows in early or mid-lactation were offered naked oats- or barley-based concentrates in addition to ad libitum access to grass silage in a continuous design experiment of 10 weeks duration. Concentrates were formulated on an isonitrogenous basis and contained either 500 g barley or 565 g naked oats kg⁻¹ concentrates as the principal energy source in the concentrate. Concentrate type had no effect on silage intake, milk yield or milk protein concentration. However, nitrogen and modified acid detergent fibre digestibility were significantly reduced by inclusion of naked oats and this was reflected in a significant reduction in milk fat concentration. Milk fat from early lactation cows on the naked oats diet contained the highest proportion of unsaturated and the lowest proportion of saturated fatty acids. Sensory and instrumental analyses determined that this milk fat produced the softest, most spreadable butter. This was supported by solid fat content results. The degree of change in milk fat composition due to diet was similar irrespective of stage of lactation but milk fat compositions with the control treatment differed with stage of lactation. Dietary effects were established by the end of the first week of the trial and persisted for the 10-week trial period.     

乳脂肪中的生理活性物质

主要介绍了乳脂肪中的生理活性物质,包括共轭亚油酸,神经鞘磷酯,丁酸和醚脂类等物质,以及它们在免疫调节,防治癌症和心血管,肠胃道疾病方面的功效,并对影响乳脂肪中各成分的因素进行了分析。     

Milk Proteins Affect Yield and Sensory Quality of Cooked Sausages

Sausages were produced with seven different mixtures with skim milk powder, sodium caseinate and whey protein (1.5, 3, 5%) according to a simplex-centroid design, where the proportion of each ingredient varied from 0 to 100%. Principal component analysis (PCA) identified that sausages with 1.5% milk protein were most similar in sensory quality to the controls and had minimum cooking loss. PCA was effective to reduce the number of attributes to five to describe the main variation among the 1.5% milk protein sausages. A mixture of 1:1 blend of skim milk powder and whey protein resulted in the product with lowest cooking loss.     

牛羊乳蛋白组分比较研究

羊乳被国际营养学界誉为"奶中之王",逐渐被人们列为日常生活的营养保健佳品。该文对羊乳和牛乳的蛋白组分(主要是酪蛋白和乳清蛋白)含量、氨基酸组成及变异体等方面的差异进行了综述,并且对两者酪蛋白胶束的差异进行了比较,为羊乳检验和加工提供理论依据。     

Milk proteins for edible films and coatings

Due to the recent increase in ecological consciousness, research has turned toward finding edible materials. Viable edible films and coatings have been produced using milk proteins. These films and coatings may retard moisture loss, are good oxygen barriers, show good tensile strength and moderate elongation, are flexible, and generally have no flavor or taste. Incorporation of lipids in protein films, either in an emulsion or as a coating, improve their properties as barriers to moisture vapor. Interactions between chemical, structural properties, as well as film-forming conditions and functional properties of edible milk films are elucidated. Some potential uses of milk protein packaging, which are hinged on film properties, are described with examples.     

UHT乳贮存期间脂肪变化的研究

在UHT乳贮存期间,对其脂肪酶活力、上层脂肪含量、上层脂肪粒径、游离脂肪酸含量进行测定。结果表明,随着贮存时间的延长,脂肪酶活力、上层脂肪含量、上层脂肪粒径、游离脂肪酸含量变化极显著(P<0.01);贮存时间与脂肪酶活力、上层脂肪含量、上层脂肪粒径、游离脂肪酸含量间均呈极显著正相关(P<0.01)。     

牛乳中脂肪,密度,干物质之间的相关关系测算

根据黑龙江省东部地区黑白花奶牛牛奶中的乳脂率、乳密度和乳干物质含量等１５０多组数据进行测算,得出了乳脂率、乳密度和乳干物质含量之间的相关关系。发现这一地区奶牛牛奶中乳脂率和干物质含量间的相关系数为０．７７２,乳密度和乳脂率之间的相关系数为－０．２１６,乳密度和乳干物质含量间的相关系数为０．４３６。     

干柱法测定牛奶中总脂肪含量

报道了一种测定牛奶中总脂肪含量的快速干柱法.使用7.5cm×27mm i.d玻璃层析柱,以1.5g Celite 545/CaHPO4·     

Physical and Sensory Properties of Milk Chocolate Formulated with Anhydrous Milk Fat Fractions

Maximum additions of milk fat that produced temperable milk chocolates were anhydrous milk fat (AMF), middle-melting fraction (MMF) or low-melting fraction (LMF) up to 40 wt % total fat, and high-melting fraction (HMF) up to 35%. The solid fat content (SFC), melting point, melting enthalpy, instrumental and sensory hardness of milk chocolates decreased with increasing milk fat addition. No differences in sensory attributes sweetness, milk powder, chocolate, butter flavor or thickness of melt were observed. Chocolate with 40% MMF or LMF had greater milk flavor than that with 12.2% HMF. Onset of melt correlated (r = 0.96) with melting enthalpy. No differences between types of milk fat (AMF, HMF, MMF, LMF) were observed for any textural attribute assessed.     

离心除菌UHT乳贮藏期内乳蛋白组成的变化

通过凯氏定氮法、高效液相色谱法和氨基酸分析仪研究了离心预除菌的UHT乳（C-UHT）和常规UHT乳（N-UHT）在常温6个月贮藏过程中乳蛋白和氨基酸成分的变化。热处理和贮藏过程中乳清蛋白质量浓度逐渐降低,非蛋白氮（NPN）质量分数逐渐增加,N-UHT和C-UHT的NPN质量分数从4.2%分别增加到8.7%和7.9%。热处理导致部分酪蛋白胶束解聚和酪蛋白组分进入了乳清相,乳清蛋白聚合进入胶束相,贮藏过程中这种作用持续进行。N-UHT和C-UHT中酪蛋白的解聚量分别为28.6%和22.6%,乳清蛋白的聚合量分别为8.5%和11.3%。热处理导致所有的乳蛋白组分发生了降解,贮藏过程中乳蛋白继续降解。N-UHT和C-UHT中总蛋白由39.81 g/L分别降解到29.57 g/L和31.42 g/L;游离氨基酸总量由原乳的31.4 mg/L增加到35.1～35.7 mg/L。C-UHT乳的乳蛋白降解和乳蛋白相转移程度显著低于N-UHT乳。     

The balance between caseins and whey proteins in cow's milk determines its allergenicity

Cow's milk allergy is quite common in the first years of human life. Protein composition plays an important role in this pathology, particularly the casein/whey protein ratio. It is known that milks from different species have different sensitization capacities although their protein sources are quite similar. Thus, the objective of this work was to compare the allergenicity of native cow's milk and milk with a modified ratio of casein and whey proteins in a murine model of atopy. Twenty-four Balb/c mice were orally sensitized to native cow's milk or modified cow's milk with a casein/whey protein ratio of 40:60. During the sensitization period, the number of mice suffering from diarrhea was significantly higher in the native cow's milk-sensitized group than in the modified milk-sensitized group. Once mice were killed, plasma histamine levels were shown to be significantly higher in native cow's milk-sensitized mice. In addition, cow's milk proteins induced a higher lymphocyte sensitization in the native milk-sensitized mice, with a significant increase in the specific proliferation ratio of these cells.These results suggest that the balance between caseins and whey proteins plays an important role in the sensitization capacity of cow's milk, and its modification might be a way to reduce the allergenicity of cow's milk.     

牛奶脂肪含量对超声波检测参数的影响

探测了不同温度下不同脂肪含量牛奶的超声特性参数———声速与衰减系数,分析了脂肪含量与超声参数间的关系以及温度对此关系的影响。结果表明:在温度10.9～39.1℃内,声速随脂肪含量的变化不大,其在39.1℃表现出来的最大变化率仅为0.164%,声速/温度随脂肪含量的变化稍大,其表现的变化率为4.29%;而衰减随脂肪含量的增加显著,在39.1℃时,衰减随脂肪含量变化的变化率最大,为113.2%,衰减/温度随脂肪含量变化的变化率为40.4%。这表明衰减随脂肪含量的变化趋势最明显,且温度对衰减的影响也相对较小,因此利用衰减系数作为测定牛奶脂肪含量的主要指标比其他参数更易于检测出脂肪含量上的差异。     

超滤在生产浓缩乳蛋白类产品中的应用

超滤技术是一种先进的膜分离技术,其作为一种分离和浓缩的工具已经被广泛应用于乳品工业。本文对超滤技术进行了概述,综述了其在生产乳蛋白浓缩物及浓缩乳清蛋白产品中的研究及应用现状,同时对如何通过超滤过程中条件的选择以提高膜过滤性能进行了阐述,并且对该领域的未来发展趋势做了展望。     

人乳脂脂肪酸组成及其制备方法研究进展

该文介绍人乳脂的脂肪酸组成及吸收特点最新研究进展,并介绍目前几种人乳脂替代品的人 工构造方法。     

Continuous Supercritical Fluid Processing of Anhydrous Milk Fat in a Packed Column

A continuous supercritical carbon dioxide processing system was designed, built and operated to investigate its performance for fractionation of anhydrous milk fat (AMF). Packed columns showed mass transfer efficiencies five times greater than a spray column, Short- and medium-chain fatty acids were concentrated in the extract fractions and their amounts decreased as separation pressure increased. The ratio of unsaturated to saturated fatty acids in the raffinate fraction was 0.68 compared to 0.52 in the original AMF. The proportions of low-melting triglycerides in the range —42 to 15°C were greater in the extract fractions (44–72%) compared to the original AMF (29%).     

驴乳粉蛋白的特性、结构与组成分析

采用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、圆二色谱和基质辅助激光解析电离-飞行时间质谱法研究德州驴乳粉蛋白质的性质、结构和组成,为德州驴乳的深层次开发提供依据。结果表明,驴乳粉蛋白质量分数为16.10%,等电点均匀分布在4.5～6.5之间,分子质量主要集中在10～20 kDa和53～78 kDa的乳清蛋白区域,以及28～36 kDa酪蛋白区域。通过与马科蛋白图库进行对比,检索出386种可识别的蛋白,其中有139种蛋白首次在驴乳中发现,为揭示驴乳的生理功效提供理论基础。