LTQ-Orbitrap 液- 质联用技术对水牛奶酪蛋白的鉴定

建立一种快速、高效的分析酪蛋白组分氨基酸序列的LTQ-Orbitrap质谱方法。为了研究水牛奶酪蛋白、乳牛奶酪蛋白和山羊奶酪蛋白的氨基酸序列组成及氨基酸的替换现象,采用LTQ-Orbitrap液-质联用技术分别对乳源酪蛋白的4种主要组分进行分析,搜索数据库获得4种组分的氨基酸全序列。与水牛奶4种酪蛋白组分进行比对。结果表明,乳牛奶的4种酪蛋白发生氨基酸替换的部位和比率明显小于山羊奶。这意味着与水牛奶酪蛋白相比,乳牛奶酪蛋白氨基酸的稳定性优于山羊奶酪蛋白。     

水牛奶营养物质及其制品研究现状

水牛奶中干物质含量较高,其综合营养价值高于普通牛奶,是多种生物活性成分的良好来源。因此,水牛奶及其相关制品受到越来越多的消费者的关注。本文根据水牛奶营养物质及其制品相关研究的前沿成果,介绍了水牛奶中蛋白质、脂肪、碳水化合物及其他营养物质的含量及其理化性质,同时针对水牛奶乳制品,如干酪、奶油、酸奶、冰淇淋等制备和相关研究进行了概述,最后针对水牛奶中的生物活性物质开发功能性食品的可能性提供了见解,为企业研发水牛奶相关产品提供参考。     

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.     

不同热处理对水牛乳酪蛋白结构和加工性质的影响

以未经热处理的水牛乳酪蛋白为对照,探究常见的4种热杀菌处理条件对水牛乳酪蛋白结构的影响,结果表明,加热产生大分子聚合物,大分子聚合物主要由二硫键联接形成;80 ℃时,水牛乳酪蛋白的起泡性和起泡稳定性最高,起泡性为137.33%,起泡稳定性为32.33%;超高温灭菌（135 ℃）条件下,水牛乳酪蛋白的平均粒径显著增加,粒径为516.2 nm;超高温灭菌乳的酪蛋白胶束被破坏,表面结构发生变化;热处理造成酪蛋白的二级结构发生变化,135 ℃条件下,α-螺旋结构和β-折叠含量显著下降,最小分别为13.76%和35.84%;酪蛋白的三级结构和表面疏水性发生改变,其中巴氏杀菌乳（80 ℃）,荧光强度最高为582.44,超高温灭菌乳表面疏水性最大为258.96。基于上述结果,说明巴氏杀菌条件对酪蛋白的影响比较小,超高温条件容易造成蛋白聚集,从而影响产品的稳定性,80 ℃是较佳的热杀菌处理条件。从而为提升生产过程中水牛乳制品的稳定性提供理论基础。     

牛奶过敏原PCR检测方法的建立

牛奶是主要的食品过敏原之一,其中β-乳球蛋白是引起牛奶过敏的主要成分。基于牛奶β-乳球蛋白基因序列设计一对PCR引物,经过反应条件的优化,建立了适合检测牛奶β-乳球蛋白过敏原的PCR方法。实验结果表明,当PCR反应体系中模板DNA量为25ng,引物浓度为4mmol/L时,检测效果最佳。所建立的方法不仅可用于不同保质期、不同来源牛奶β-乳球蛋白过敏原的测定,亦可用于牛、羊奶不同比例混合物中β-乳球蛋白过敏原的检测。     

基于双向电泳和质谱联用技术的水牛乳源酪蛋白的研究

利用双向电泳和基质辅助激光解吸电离飞行时间质谱(MALDI-MS)联用技术对水牛乳酪蛋白与其他乳源蛋白差异性进行了研究。根据Image Master 2D Platinum图像分析软件对不同乳源酪蛋白的双向电泳(2-DE)图谱进行蛋白斑点的匹配分析,获得21个存在于水牛奶中,主要分布在低丰度蛋白区的差异蛋白点,经质谱分析,得到4个属于水牛奶酪蛋白的主要组分,另外发现两个与水牛奶中的蛋白有较高同源性的新组分。     

Proteolysis,protein distribution and stability of UHT milk during storage at room temperature

Proteolytic degradation and distribution of caseins and whey proteins between the soluble and colloidal phases were studied in six batches of commercial UHT milk (three skim and three whole milks) during storage at 25 ± 2 °C. For that purpose, at 30 day intervals, milk samples were ultracentrifuged and the pellets and supernatants analysed by capillary electrophoresis and SDS‐PAGE. Samples were also visually examined for signs of gelation. Extensive proteolytic degradation of the micellar fractions and severe changes in the electrophoretic pattern of the proteins present in the serum fractions were observed in all the batches. A higher proportion of denatured whey proteins not attached to the micelle surface was found in the skim milk samples as compared with the whole milk samples that could provide less resistance against gelation. In addition to β‐Lg, para‐κ‐casein was also found in the serum fraction. A high proteolytic activity against κ‐casein could be responsible for the hydrolysis of serum‐liberated κ‐casein or could have enhanced the liberation of β‐Lg–para‐κ‐casein complexes through proteolysis of micellar κ‐casein. © 1999 Society of Chemical Industry     

酶解水牛奶酪蛋白制备抗氧化活性肽工艺的研究

以水解度、还原能力和DPPH自由基清除率为检测指标,比较筛选碱性蛋白酶、中性蛋白酶、胰蛋白酶、木瓜蛋白酶和胃蛋白酶水解水牛奶酪蛋白制备抗氧化活性肽,筛选出中性蛋白酶是最适用酶。应用单因素和响应面法对酶解工艺进行优化。结果表明:中性蛋白酶酶解酪蛋白的最佳工艺参数:pH为6.9,温度为46℃,酶与底物浓度比为4.6%,酶解时间4.0h,此时10mg/mL酶解物的还原能力为0.457。实测结果与预测值符合性良好。