3种乳源酪蛋白粒径及胶束结构的差异性

通过纳米粒度分析仪和扫描电子显微镜,分别对水牛乳、牛乳及羊乳中的酪蛋白颗粒直径大小分布情况及酪蛋白胶束结构进行研究。结果表明：水牛乳、牛乳及羊乳中酪蛋白的粒径分布及胶束结构方面存在明显的差异。水牛乳酪蛋白平均颗粒直径为182.3nm,酪蛋白颗粒互相连接成较细长的胶束,胶束之间交联成网络状;牛乳酪蛋白平均颗粒直径为207.4nm,酪蛋白颗粒聚集成直径较大的胶束;羊乳酪蛋白平均颗粒直径为173.8nm,酪蛋白颗粒仅能够形成较短的胶束,也不能交联成网络状。     

牛羊乳酪蛋白制备及电泳分析比较

采采用新鲜和复原的牛羊乳为原料,等电点沉淀,通过洗涤、干燥等步骤分别制得牛乳和羊乳酪蛋白,用凯氏定氮法对其进行定量检测,应用十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS—PAGE）分析比较牛羊乳酪蛋白组分差异。结果表明：牛乳酪蛋白得率为86．75％,羊乳酪蛋白得率为90．55％,高含量的酪蛋白主要集中在电泳图谱的中分子量组,可分为ds,CN、as2-CN、β-CN和K—CN,牛羊乳as2-CN分子量羊乳大于牛乳,牛乳a-CN含量比较多,羊乳β—CN含量比较多,鲜乳与复原乳全蛋白主要组分在电泳图谱中除酪蛋白差别外,上端的高分子量组清蛋白区羊乳IgG重链的分子量比牛乳小。应用蛋白质电泳分析技术可以区分羊乳和牛乳的蛋白质组分,等电点沉淀法制备酪蛋白的方法简单,易于操作。     

热处理羊乳酪蛋白结构与抗原性的变化规律

热加工处理羊乳 α-酪蛋白(α-casein,α-CN)和 β-酪蛋白(β-casein,β-CN),通过圆二色谱、荧光光谱等方法探索不同热加工条件下羊乳的蛋白结构变化与抗原性的关系.结果表明:随着对蛋白热处理温度的升高,会破坏羊α-CN和β-CN的天然结构,使得分子内部发生交联或聚集,导致分子量发生改变,分子内游离羰...     

谷氨酰胺转胺酶对酪蛋白的改性效应

羊乳中的酪蛋白经商品级谷氨酰胺转胺酶作用后,产物经SDS-PAGE检测,发现生成了相对分子量较大的聚合物。聚合的最佳条件为:酶量/酪蛋白=15U/g;最适pH:6.0～8.0;最适反应温度:50℃;反应时间:120min。其中β-酪蛋白最易被催化,其次为αs-1酷蛋白,αs-2酷蛋白,k-酪蛋类白不易被催化。经谷氨酰胺转胺酶改性后的酪蛋白溶液,其粘度增加,乳化能力提高,起泡性下降。     

低温诱导羊乳中β-酪蛋白从胶束中解离的研究

在羊乳酪蛋白胶束结构中,部分β-酪蛋白通过疏水作用结合到胶束骨架上,在低温条件下,蛋白质疏水作用减弱,部分β-酪蛋白从胶束中解离。以脱脂羊乳为原料,采用HPLC、SDSPAGE、ICP-MS进行检测,研究温度、平衡时间、pH、NaCl、柠檬酸钠、CaCl2对β-酪蛋白从胶束中解离的影响。低温诱导β-酪蛋白从胶束中的解离在120 min达到平衡。降低温度、降低pH、添加柠檬酸钠诱导胶束钙的解离,使胶束中通过疏水作用结合的β-酪蛋白含量增加,进一步促使低温条件下β-酪蛋白从胶束中解离。温度4℃、pH 6.0条件下平衡120 min,β-酪蛋白从胶束中的选择性解离效果较好,β-酪蛋白、κ-酪蛋白、α-酪蛋白的解离率分别达41.8%、19.9%、15.2%,3种酪蛋白解离部分的占比分别为68.2%、24.4%、7.4%。上述结果可应用于羊乳β-酪蛋白低温微滤分离的工艺优化。     

热处理对牛乳酪蛋白胶束结构影响的研究进展

概述了热处理过程中对牛乳中酪蛋白内部作用力、酪蛋白各个单体以及胶束结构的影响。指出热处理的温度和处理时间的不同,导致酪蛋白的疏水作用及二硫键的变化、组成酪蛋白胶束的各个单体(αs-酪蛋白、β-酪蛋白、κ-酪蛋白)离解程度及结构的差异、酪蛋白胶束尺寸及胶束间作用力的改变。这对于牛乳酪蛋白的应用和整个胶束结构在热处理过程中的研究具有指导意义。     

预热处理对谷氨酰胺转氨酶催化羊乳热稳定性的影响

研究了羊乳经预热处理后谷氨酰胺转氨酶(transglutaminase,TGase)诱导催化羊乳热稳定性的影响。结果表明,随着预热处理温度的提高和处理时间的延长,羊乳热凝固时间(heat coagulation time,HCT)显著增加(P 0. 05);羊乳经60～70℃/60 min或80～90℃/30 min预热处理可使羊乳中天然TGase抑制剂完全灭活;预热处理可使羊乳中乳清蛋白变性,且随着处理温度的升高,乳清蛋白变性程度增大,这有利于TGase对乳蛋白的交联;十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE)进一步证实了羊乳中存在天然TGase抑制剂,预热处理可使羊乳中κ-酪蛋白在TGase作用下交联度提高,防止κ-酪蛋白从酪蛋白胶束中解离,进一步提高羊乳的热稳定性。     

牛乳蛋白与钙磷结合特性的研究进展

对牛乳中酪蛋白与钙磷、乳清蛋白与钙的结合特性进行了综述,详细介绍了酪蛋白的结构、p H、压力、温度、凝乳酶、氯化钙等因素对酪蛋白与钙磷结合特性的影响。旨在为牛乳蛋白与钙磷结合的研究提供理论依据。     

低温微滤处理对牛乳组成、胶束结构及凝乳性质的影响

β-酪蛋白具有低温溶出的特性。本文通过低温微滤处理制备了β-酪蛋白脱除率为10、20、30%的牛乳,运用HPLC、场发射扫描电镜、流变仪以及激光共聚焦研究了这些牛乳的蛋白组分、酪蛋白胶束结构及凝乳性质变化。结果表明：脱脂乳与低温微滤处理得到的牛乳样品的脂肪含量,总钙含量及pH值无显著性差异,但总蛋白含量有显著性差异,其中κ-酪蛋白和αs2-酪蛋白浓度无差异,αs1-酪蛋白浓度有显著差异,但低温处理样品间αs1-酪蛋白浓度则无差异,β-酪蛋白及乳清蛋白浓度差异极显著,其浓度随处理时间增加显著减小。脱脂乳与牛乳样品均可形成致密的具有空隙的凝胶结构,且其酸凝乳及酶凝乳所表现的流变学变化趋势相似,但随着β-酪蛋白脱除率升高,表征凝乳块硬度的最大G''逐渐下降,凝胶结构逐渐变疏松,出现的孔隙则更大更多。     

酪蛋白水解物替代乳清蛋白的加工性能评价研究

利用复合蛋白酶水解酪蛋白制备适度及深度水解酪蛋白产品,测定酪蛋白水解物的加工性能。结果表明,经过酶解后,适度水解酪蛋白溶解度接近90%,深度水解酪蛋白溶解度接近100%,显著高于酪蛋白和乳清蛋白。此外,适度水解酪蛋白吸油性、起泡性分别约为乳清蛋白的3倍和1.5倍。深度水解酪蛋白在起泡性和乳化性上也显著高于乳清蛋白。可见,两款酪蛋白水解物在起泡性、乳化性、吸油性、溶解性等方面均在一定程度上优于乳清蛋白,可广泛替代乳清蛋白在食品工业中大规模应用。     

不同泌乳期羊乳和牛乳的高通量定量乳清蛋白质组学

利用高分辨质谱技术获取牛初乳、牛常乳、羊初乳和羊常乳的乳清蛋白组轮廓,基于其非标记定量强度建立偏最小二乘判别分析模型。结果发现牛初乳和牛常乳在蛋白质组成方面较羊初乳和羊常乳更相似,同时筛选出羊乳中丰度较高的9 种蛋白用作标志物区分这4 组乳样。生物信息学分析发现羊乳中的高丰度蛋白大部分与免疫应答和代谢过程有关,说明羊乳更有助于新生儿建立抗微生物感染的免疫系统。该研究可加深对羊乳蛋白的认识,对牛乳及其制品的营养改良和母乳替代品的生产具有重要意义。     

The effect of formulated goats' milk on calcium bioavailability in male growing rats

BACKGROUND: There are two main proteins in milk; whey and casein. Casein contains casein phosphopeptides (CPP), which are released on digestion of the milk. These may increase calcium solubility by binding calcium in the small intestine. Thus increasing casein in the diet may help to stimulate bioavailability of calcium and increase bone density. The present study tested this hypothesis in growing male rats fed diets containing three different concentrations of casein from goat milk. RESULTS: Rats fed the diet containing no casein had significantly lower calcium absorption when compared to rats fed the diets that contained 80% and 57% of goat milk protein as casein; however, no significant difference was observed between rats fed diets with 80% and 57% casein. The varying amounts of casein had no effect on mineral uptake or retention in the femur. Biomechanical testing and mineral analysis of the femurs showed no differences between diet groups. The mechanism to explain this lack of retention remains unclear. CONCLUSION: The diets containing 80% and 57% of goat milk protein as casein delivered increased calcium absorption compared to the diet containing no casein, suggesting a minimum level of casein is needed to optimize calcium absorption from goat milk. Copyright © 2009 Society of Chemical Industry     

Comparative analysis of caseins in Saanen goat milk from 3 different regions of China using quantitative proteomics

A quantitative proteomic technique based on data-independent acquisition (DIA) was used to analyze differentially expressed caseins of Saanen goat milk samples collected from 3 regions in China (Guangdong, GD; Inner Mongolia, IM; Shaanxi, SX). A total of 345 proteins were quantified in each sample. Gene Ontology (GO) analysis showed that proteins were mainly involved in cellular process and cell and binding functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that proteins were mainly involved in metabolic pathways. Differentially expressed proteins (DEP) between goat milk from 3 comparison groups composed of paired regions were compared and analyzed. The number of DEP was 114, 69, and 79 for GD versus IM, GD versus SX, and IM versus SX, respectively. The GO enrichment analysis of the 3 comparison groups showed that differences were mainly related to the regulation of biological quality, biological regulation, and response to stimulus in terms of biological process; extracellular region for cellular component; and binding function for molecular function. Pathways in which DEP of GD versus IM, GD versus SX, and IM versus SX were mostly protein processing in endoplasmic reticulum for the first 2 groups and metabolic pathways for the last. Protein-protein interaction network analysis demonstrated that the most prominent DEP was heat shock protein 90 β family member 1 for both the GD versus IM and the GD versus SX groups, and haptoglobin for the IM versus SX group. Data from this study may offer useful information for further investigation of the protein composition of Saanen goat milk and its application in the dairy industry.     

羊乳乳清蛋白组成和功能及其与人乳、牛乳的对比分析

本研究将羊乳、牛乳、人乳中乳清蛋白进行分离并结合液质联用技术鉴定,在羊乳、牛乳、人乳乳清蛋白中分别鉴定出156、278、454种蛋白质。与牛乳与人乳乳清蛋白对比显示,羊乳含有99种特异性表达蛋白质,与牛乳和人乳分别有31种和15种相同表达蛋白质。通过分析基因本体(gene ontology,GO)功能注释发现,羊乳乳清蛋白在生物过程中主要发挥生物调节作用;在分子功能上,主要体现在结合作用方面;在细胞组成上,参与的细胞组成主要为细胞器区和胞外区。羊乳乳清蛋白在以上三种功能上与人乳有较大差距,但与牛乳相近。通过分析京都基因与基因组百科全书系统(Kyoto Encyclopedia of Genes and Genomes,KEGG)代谢通路可知,羊乳主要参与补体和凝血级联反应以及吞噬作用,对人体免疫能力有积极影响。对羊乳与人乳、牛乳乳清蛋白组成及功能区别的研究,为羊乳的进一步研究和开发提供一定的理论参考。     

Developmental changes in proteins of casein micelles in goat milk using data-independent acquisition-based proteomics methods during the lactation cycle

Casein micelles (CM) play an important role in milk secretion, stability, and processing. The composition and content of milk proteins are affected by physiological factors, which have been widely investigated. However, the variation in CM proteins in goat milk throughout the lactation cycle has yet to be fully clarified. In the current study, milk samples were collected at d 1, 3, 30, 90, 150, and 240 of lactation from 15 dairy goats. The size of CM was determined using laser light scattering, and CM proteins were separated, digested, and identified using data-independent acquisition (DIA) and data-dependent acquisition (DDA)-based proteomics approaches. According to clustering and principal component analysis, protein profiles identified using DIA were similar to those identified using the DDA approach. Significant differences in the abundance of 115 proteins during the lactation cycle were identified using the DIA approach. Developmental changes in the CM proteome corresponding to lactation stages were revealed: levels of lecithin cholesterol acyltransferase, folate receptor α, and prominin 2 increased from 1 to 240 d, whereas levels of growth/differentiation factor 8, peptidoglycan-recognition protein, and 45 kDa calcium-binding protein decreased in the same period. In addition, lipoprotein lipase, glycoprotein IIIb, and α-lactalbumin levels increased from 1 to 90 d and then decreased to 240 d, which is consistent with the change in CM size. Protein–protein interaction analysis showed that fibronectin, albumin, and apolipoprotein E interacted more with other proteins at the central node. These findings indicate that changes in the CM proteome during lactation could be related to requirements of newborn development, as well as mammary gland development, and may thus contribute to elucidating the physical and chemical properties of CM.     

Grazing season and forage type influence goat milk composition and rennet coagulation properties

Two different types of pasture (cultivated and rangeland) and 2 different hay qualities (high and low quality) were examined for their effects on goat milk composition and rennet coagulation properties. Furthermore, the effect of dietary treatments in both the early and late grazing season was studied. As lactation stage is known to influence milk composition, the goats in the early and late grazing season were in the same lactation stage at the start of the experiment. The milk composition was influenced both by dietary treatment and season. Milk from goats on pasture was superior to those on hay by containing a higher content of protein and casein, and the goats on cultivated pasture had the highest milk yield. Casein composition was significantly influenced by forage treatment. Goats grazing on cultivated pasture had higher contents of α_s1-casein and also of κ-casein compared with the other treatments, whereas goats grazing on rangeland had the highest content of β-casein. Factors such as milk yield, casein micelle size, α_s2-casein, and calcium content were reduced in late compared with early season. More favorable rennet coagulation properties were achieved in milk from the early grazing season, with shorter firming time and higher curd firmness compared with milk from the late grazing season, but the firming time and curd firmness were not prominently influenced by forage treatment. The content of α_s2-casein and calcium in the milk affected the firming time and the curd firmness positively. The influence of season and forage treatment on especially milk yield, casein content, and rennet coagulation properties is of economic importance for both the dairy industry and goat milk farmers.     

Major proteins of the goat milk fat globule membrane

Fat is present in milk as droplets of triglycerides surrounded by a complex membrane derived from the mammary epithelial cell called milk fat globule membrane (MFGM). Although numerous studies have been published on human or bovine MFGM proteins, to date few studies exist on MFGM proteins from goat milk. The objective of this study was thus to investigate the protein composition of the goat MFGM. Milk fat globule membrane proteins from goat milk were separated by 6% and 10% sodium dodecyl sulfate-PAGE and were Coomassie or periodic acid-Schiff stained. Most of MFGM proteins [mucin-1, fatty acid synthase, xanthine oxidase, butyrophilin, lactadherin (MFG EGF-8, MFG-E8), and adipophilin] already described in cow milk were identified in goat milk using peptide mass fingerprinting. In addition, lectin staining provided a preliminary characterization of carbohydrate structures occurring on MFGM proteins from goat milk depending on α_S1-casein genotype and lactation stage. We provide here first evidence of the presence of O-glycans on fatty acid synthase and xanthine oxidase from goat milk. A prominent difference between the cow and the goat species was demonstrated for lactadherin. Indeed, whereas 2 polypeptide chains were easily identified by peptide mass fingerprinting matrix-assisted laser desorption/ionization-time of flight analysis within bovine MFGM proteins, lactadherin from goat milk consisted of a single polypeptide chain. Another striking observation was the presence of caseins associated with MFGM preparations from goat milk, whereas virtually no caseins were found in MFGM extracts from bovine milk. Taken together, these observations strongly support the existence of a singular secretion mode previously hypothesized in the goat.     

掺假羊乳及其制品中牛乳的检测技术研究进展

羊乳具有营养价值高、蛋白质组成更接近人乳、脂肪球直径小及致敏性低等优点, 更利于人体消化吸收, 受到消费者和乳品企业的青睐。近年来我国羊乳产业发展迅速且潜力巨大, 但由于受羊乳产量和养殖规模的限制, 羊乳价格昂贵, 市场中存在羊乳及其制品掺假牛乳的现象, 且掺假手段多样, 难以辨别。为了保证消费者的健康和权益, 保障羊乳市场良性发展, 羊乳及其制品的纯正性、真实性检测已经成为热点研究方向。本文通过分析基于乳中蛋白质、脂肪和核酸差异的羊乳中牛乳掺假检测技术的研究现状, 介绍和探讨了各检测技术的基本原理及其在应用中的优缺点, 同时展望羊乳掺假检测技术的发展方向, 旨在为牛羊乳混合掺假检测技术的进一步发展提供资料参考和思路。     

基于陶瓷膜技术的羊乳酪蛋白和其他组分的高效分级分离

为量化0.05 μm陶瓷膜脱除羊乳中乳清蛋白、乳糖、灰分、钙和磷的能力,在50 ℃条件下,脱脂乳进行3 倍浓缩,之后2 次间歇补水至原体积进行清洗过滤,最终得到1 份截留液、3 份透过液,并计算各组分总脱除率。结果表明：乳清蛋白脱除率为96.17%,乳糖脱除率为86.42%,灰分脱除率为73.39%,钙脱除率为34.90%,磷脱除率为55%。稀释过滤完毕后膜的纯水膜通量衰减系数为55.57%,使用质量分数为2%氢氧化钠和1%的硝酸溶液进行清洗,膜通量的恢复系数为99.21%。0.05 μm陶瓷膜可以实现羊乳酪蛋白和其他组分的有效分离,该技术适合在没有干酪乳清的条件下,以生鲜乳为原料加工酪蛋白胶束粉、乳清蛋白粉、乳糖等乳基配料产品。