转谷氨酰胺酶对牛乳酪蛋白功能性质的影响

采用微生物转谷氨酰胺酶 (TG)对牛乳中的酪蛋白进行了酶法改性 ,并对改性后牛乳中酪蛋白功能性质如溶解性、起泡性、泡沫稳定性和持水性进行了研究 .结果表明 ,牛乳经TG作用后 ,其酪蛋白功能性质发生了较大变化 ,酪蛋白的起泡性、泡沫稳定性和持水性都有不同程度的增加 ,而溶解性略有下降 .实验中考察了TG作用的时间、温度、剂量等因素对酪蛋白功能性质的影响 ,结果显示 ,要获得综合性能优良的酪蛋白 ,TG最佳的作用条件为 :pH 7.0 ,5 0℃ ,6 0min ,酶的添加量0 .1～ 0 .2U/mL .     

牦牛酪蛋白理化及功能特性的研究

研究了不同温度、pH值条件下牦牛酪蛋白的溶解度、表观黏度、疏水性以及乳化、发泡等功能特性.结果表明,在等电点范围之外,牦牛酪蛋白具有较理想的溶解性、乳化性、起泡性,其功能特性受pH值、温度影响较显著.     

谷氨酰胺转氨酶交联对牦牛乳曲拉酪蛋白功能性质的影响

以曲拉和荷斯坦牛乳酪蛋白为原料,利用安全、高效的谷氨酰胺转氨酶对其进行交联修饰,研究谷氨酰胺转氨酶对酪蛋白功能性质的影响,测定交联前后样品的持水性、持油性、热稳定性、黏度、起泡性。结果表明,牦牛乳曲拉酪蛋白和荷斯坦牛乳酪蛋白经过谷氨酰胺转氨酶交联后,两种酪蛋白的交联度分别可达到20.04%(p<0.05)和25.15%(p<0.05),曲拉酪蛋白的持水性、热稳定性、黏度和泡沫稳定性显著增加(p<0.05),荷斯坦酪蛋白的黏度和热稳定性显著增加(p<0.05),其余性质均无显著差异。研究结果能为酶法改性酪蛋白的工业化生产提供理论依据。      

Glycosylation of κ-casein: Genetic and nongenetic variation and effects on rennet coagulation properties of milk

The aims of this study were to investigate genetic and nongenetic variation in the degree of glycosylation of κ-casein (κ-CN) and to estimate the effects of glycosylated (G-κCN) and unglycosylated (U-κCN) κ-CN contents on milk coagulation properties of Simmental cows. Measures of contents of the main casein fractions, G-κCN, and U-κCN, and assessment of genotypes at CSN2, CSN3, and BLG were obtained by reversed-phase HPLC analysis of 2,015 individual milk samples. Content of total κ-CN (κ-CNtot, g/L) was the sum of G-κCN and U-κCN, and the glycosylation degree of κ-CN (GD) was measured as the ratio of G-κCN to κ-CNtot. Rennet coagulation time (RCT) and curd firmness were measured by using a computerized renneting meter. Measures of curd firmness were adjusted for RCT before statistical analysis. Variance components of κ-CNtot, G-κCN, U-κCN, and GD were estimated by Bayesian procedures and univariate linear models that included the class effects of the herd-test-day, parity, days in milk, genotypes at milk protein genes, and animal. These class effects, those of G-κCN, U-κCN, and content of other caseins, and the linear effect of milk pH were accounted for by models investigating the influence of κ-CN glycosylation on coagulation properties. The GD ranged from 22 to 76%, indicating that variation in G-κCN depends on the variation both in κ-CNtot and in the efficiency of κ-CN glycosylation. Genotype CSN3 BB exhibited high G-κCN and U-κCN relative to that of CSN3 AA. Heritability of G-κCN, U-κCN, and GD was high and ranged from 0.46 to 0.56. A large proportion of the additive genetic variation in G-κCN and U-κCN was attributable to influence of CSN and BLG, but these genes did not affect variation in GD, and across-genotypes differences in the trait were small or trivial. Average RCT of the milk class having the highest G-κCN was, on average, 2 min (standard deviation 0.5) shorter than that of the lowest class. Conversely, U-κCN and content of other caseins were not associated with any effect on RCT, except for a slight delay in coagulation when U-κCN was very high. Curd firmness increased when the contents of both κ-CN fractions and other caseins increased. This study provides evidence that the positive association between RCT and κ-CN content is exclusively attributable to the glycosylated fraction of the protein. Because exploitable additive genetic variation in G-κCN exists, improvement of κ-CN composition through selective breeding might be an effective way to enhance milk coagulation properties.     

糖基化方法对于大豆7S球蛋白糖基化产物构象及功能特性的影响

针对传统的两种糖基化接枝方法和一种改进方法从糖基化产物构象和产物功能特性方面对三种糖基化方法进行研究比较,以期进一步揭示不同糖基化方法对于蛋白质糖基化反应及产物的影响机制,结果表明:水相体系比固相体系对于蛋白质空间结构影响更大,二级结构中,湿热法和水热法的制备产物α-螺旋含量均减少,三种糖基化产物二级结构的主要结构与大豆7S球蛋白一样仍以β-结构为主,接入糖链导致蛋白质的二级结构无规则卷曲含量都增加;三级结构中,干热法对于三级结构的变化影响不明显,然而湿热法和水热法对于蛋白质分子的三级结构有显著的影响;三种糖基化产物的主要功能特性溶解性、乳化性和热稳定性均有提高,干热法产物在溶解性和乳化性方面均优于其它两种方法,热稳定性三种方法差异性不大。     

胞壁蛋白酶（CEP）酶解对酪蛋白结构及功能特性的影响

通过纳米粒度分析、傅立叶红外光谱（FTIR）、乳化性、乳化稳定性、蛋白溶解性、抗氧化性及ACE抑制率的测定,分析探讨酪蛋白及其不同水解度（DH 2.4%、4.5%、7.1%、8.3%）的嗜酸乳杆菌胞壁蛋白酶（CEP）酶解产物的结构及功能特性。FTIR分析表明CEP酶解改变了酪蛋白各种构象所占的比例,酪蛋白二级结构发生了不同程度的变化;纳米粒度分析表明酪蛋白颗粒大小随水解的加深先减小后增大,其水解物颗粒在DH 4.5%时最小,乳化稳定性最大;酪蛋白的乳化性随水解的加深先增大后减小,DH 7.1%时增至最大,与其溶解性的变化趋势一致;此外酪蛋白的酶解物具有一定的ACE抑制活性及抗氧化性,且DPPH清除能力在一定范围内随水解度及浓度的增大而增大,当DH为8.3%,浓度为5mg/mL时,DPPH清除能力增大至35.00%。因此CEP酶解可有效改善酪蛋白的结构及功能特性,为乳源性功能多肽的开发提供理论依据。     

Preparation and potential applications of casein–polysaccharide conjugates: a review

Glycation of casein and caseinates with polysaccharides via Maillard reaction is a simple and environmentally safe way to prepare new food ingredients of improved functional properties. Sodium caseinate has been used mainly to prepare conjugates with several polysaccharides particularly maltodextrins and dextrans. The functional properties of these conjugates are influenced by the used polysaccharides and heating conditions. Under optimal heating conditions substantial improvements have been evident in their emulsification and foam properties of these conjugates. Casein–polysaccharide conjugates have several potential applications in food processing and microencapsulation. This article gives an overview on their formation and potential uses. © 2019 Society of Chemical Industry     

小麦面筋蛋白糖基化改性研究进展

小麦面筋蛋白是麦谷蛋白和麦醇溶蛋白与水结合形成的独特产物,具有优良的黏弹性和延伸性,但是由于水溶性差,应用受到较大限制。蛋白质的糖基化修饰,是将糖类物质以共价键连接的方式导入蛋白质分子中,糖基化能改善面筋蛋白溶解性、乳化性和起泡性等性质,使其应用于不同领域。本文从面筋蛋白糖基化的机理、糖的种类、糖基化对面筋蛋白理化性质的影响、糖基化面筋蛋白的应用等方面综述了小麦面筋蛋白糖基化的研究进展。     

鲢鱼肌原纤维蛋白-低聚异麦芽糖的制备及功能特性评价

为改善鲢鱼肌原纤维蛋白的溶解性、热稳定性以及乳化特性等功能特性,本文将不同比例的低聚异麦芽糖与鲢鱼肌原纤维蛋白(Mf)进行糖基化反应制备鲢鱼肌原纤维糖蛋白,并对其功能特性进行测定.结果表明低聚异麦芽糖与Mf质量比为4:1,在55℃,反应12h生成的低聚异麦芽糖蛋白具有较好溶解性,反应48h生成的低聚异麦芽糖蛋白具有较好热稳定性;低聚异麦芽糖与Mf质量比为2:1在55℃经过48h反应后可制备具有较好乳化稳定性.糖基化后的鲢鱼肌原纤维蛋白在0.5 mol/L NaCI溶液中的溶解性、热稳定性和乳化性得到了不同程度的改善.     

冷榨脱脂核桃仁的营养和蛋白质特性分析

为提高核桃蛋白溶解性,对核桃蛋白进行糖基化改性,通过单因素及响应面试验优化核桃分离蛋白-菊粉共轭物的制备工艺,测定核桃分离蛋白-菊粉共轭物的红外光谱、内源荧光光谱、溶解度、乳化特性等结构特性及功能性质。结果表明：当反应温度为89 ℃、反应时间为75 min、蛋白与糖质量比为1:2时,核桃分离蛋白-菊粉共轭物可达到最大溶解度83%,比核桃分离蛋白的溶解度提高了47%。傅里叶红外光谱、扫描电镜分析结果表明,核桃分离蛋白与菊粉通过共价键结合,结构由散落小颗粒状变为片状。功能性结果显示,与核桃分离蛋白相比,核桃分离蛋白-菊粉共轭物起泡性、泡沫稳定性分别提高了49%和23%,乳化性指数增加了17%。说明糖基化改性能够改善产物的结构及性质,本研究为核桃分离蛋白的加工利用提供新的方法途径,拓宽了核桃蛋白加工利用的领域。     

Effect of dietary crude protein degradability and corn processing on lactation performance and milk protein composition and stability

The present study aimed to evaluate the effect of crude protein degradability and corn processing on lactation performance, milk protein composition, milk ethanol stability (MES), heat coagulation time (HCT) at 140°C, and the efficiency of N utilization for dairy cows. Twenty Holstein cows with an average of 162 ± 70 d in milk, 666 ± 7 kg of body weight, and 36 ± 7.8 kg/d of milk yield (MY) were distributed in a Latin square design with 5 contemporaneous balanced squares, 4 periods of 21 d, and 4 treatments (factorial arrangement 2 × 2). Treatment factor 1 was corn processing [ground (GC) or steam-flaked corn (SFC)] and factor 2 was crude protein (CP) degradability (high = 10.7% rumen-degradable protein and 5.1% rumen-undegradable protein; low = 9.5% rumen-degradable protein and 6.3% rumen-undegradable protein; dry matter basis). A significant interaction was observed between CP degradability and corn processing on dry matter intake (DMI). When cows were fed GC with low CP degradability, DMI increased by 1.24 kg/d compared with cows fed GC with high CP degradability; however, CP degradability did not change DMI when cows were fed SFC. Similar interactions were observed for MY, HCT, and lactose content. When cows were fed GC diets, high CP degradability reduced MY by 2.3 kg/d, as well as HCT and lactose content, compared with low CP degradability. However, no effect of CP degradability was observed on those variables when cows were fed SFC diets. The SFC diets increased dry matter and starch total-tract digestibility and reduced β-casein (CN) content (% total milk protein) compared with GC diets. Cows fed low-CP degradability diets had higher glycosylated κ-CN content (% total κ-CN) and MES, as well as milk protein content, 3.5% fat-corrected milk, and efficiency of N for milk production, than cows fed high-CP degradability diets. Therefore, GC and high-CP degradability diets reduced milk production and protein stability. Overall, low CP degradability increased the efficiency of dietary N utilization and MES, probably due to changes in casein micelle composition, as CP degradability or corn processing did not change the milk concentration of ionic calcium. The GC diets increased β-CN content, which could contribute to reducing HTC when cows were fed GC and high-CP degradability diets.     

鱼贝肌肉分离蛋白糖基化功能改性的研究与比较

分别对栉孔扇贝闭壳肌分离蛋白及鲤鱼肌肉分离蛋白进行基于糖基化的改性处理,以此探索分离鱼蛋白的功能改性机制,并比较无脊椎类与脊椎类不同蛋白源之间的差异。用碱溶出法制备分离蛋白,将分离蛋白的改性处理分为直接糖基化和间接糖基化。直接糖基化是将分离蛋白与葡萄糖混合后进行干法糖基化;间接糖基化则是将分离蛋白预先经过胰凝乳蛋白酶修饰,再与葡萄糖混合后的糖基化。二者糖基化反应条件一致,其中蛋白与糖质量比为1∶5,温度为60℃,相对湿度为65%,时间为6 h。以赖氨酸、果糖胺及吸光度为糖基化指标,同时结合十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析来检测糖基化效果;将乳化性和热稳定性作为糖基化产物功能特性的分析指标。研究发现,鲤鱼和扇贝分离蛋白6 h直接糖基化处理均显示了糖基化效果,赖氨酸分别下降59.89%和30.94%,果糖胺浓度分别为3.04 mmol/L和2.99 mmol/L,吸光度分别为0.000和0.084;肌球蛋白重链和肌动蛋白的电泳条带均发生上移;二者功能特性指标中的乳化性分别为14.08 m~2/g和16.44 m~2/g;与对照组26%和50%的下降率相比,糖基化处理组的热稳定性有改善,分别下降14%和28%。扇贝分离蛋白的直接糖基化和间接糖基化处理结果发现,胰凝乳蛋白酶的修饰明显促进糖基化效果,未修饰与修饰的分离蛋白比较,赖氨酸分别下降30.94%和67.64%,果糖胺浓度分别为2.99 mmol/L和5.72 mmol/L,吸光度分别增加265%和500%;蛋白各个组分条带均发生上移;二者功能特性指标中的乳化性分别增加33.11%和37.38%;热稳定性分别下降28%和3%。结果表明,相同条件下鱼类与贝类分离蛋白具有相似的糖基化特性;胰凝乳蛋白酶的修饰能够显著提高分离蛋白的糖基化效果。     

亚麻籽胶糖基化改性核桃蛋白及性质分析

针对核桃蛋白溶解性差,限制其在食品工业中应用的问题,本文采用亲水性多糖亚麻籽胶（LG）糖基化改性核桃分离蛋白（WPI）,通过单因素结合响应面方法优化核桃分离蛋白亚麻籽胶（WPI-LG）偶联物制备工艺,测定WPI-LG及其对照样品的糖基化反应程度、聚丙烯酰胺凝胶电泳、氨基酸含量、傅里叶变换红外光谱、圆二色谱、紫外光谱、溶解度、持水性持油性、起泡性和泡沫稳定性等结构和功能特性。结果表明：糖基化最优工艺为WPI与LG质量比为4.4:1、反应温度 91 °C、反应时间94 min,测得WPI-LG偶联物溶解度为90.35%,较WPI提高了54%。聚丙烯酰胺凝胶电泳、傅里叶变换红外光谱、氨基酸含量、紫外光谱证实WPI与LG共价结合。相较于WPI,持水能力和持油能力提高2.03倍和2.04倍、起泡性和泡沫稳定性提高1.72和1.37倍。通过研究发现LG糖基化改性WPI能够改善其结构和功能特性,为核桃蛋白在食品工业中的应用提供理论依据。     

不同分子质量葡聚糖对玉米醇溶蛋白糖基化产物结构和功能性的影响

采用湿热法将玉米醇溶蛋白（Zein）与不同分子质量（6、20、40、70 kDa）的葡聚糖（dextran,DX）制备成Zein-DX糖基化产物,探讨不同分子质量DX对Zein糖基化产物结构和功能性的影响。随着DX分子质量的增加,Zein-DX糖基化产物的接枝度和褐变强度降低,说明低分子质量DX更容易与Zein发生糖基化反应,且糖基化产物具有更高的溶解度和更低的表面疏水性。糖基化反应能够提高Zein的乳化活性（emulsifying activity index,EAI）和乳化稳定性（emulsifying stability index,ESI）,随着DX分子质量的增加,Zein-DX糖基化产物的EAI逐渐降低,ESI逐渐增加。此外,高分子质量DX的共价结合能够使Zein的二级结构由有序的α-螺旋结构转变为无序的β-折叠和无规则卷曲结构,导致蛋白质构象变得更加灵活和松散。     

Invited review: perspectives on the basis of the rheology and texture properties of cheese

Physical and chemical properties of cheese, such as texture, color, melt, and stretch, are primarily determined by the interaction of casein (CN) molecules. This review will discuss CN chemistry, how it is influenced by the cheese-making process, and how it impinges on the final product, cheese. We attempt to demonstrate that the application of principles governing the molecular interactions of CN can be useful in understanding the many physical and chemical properties of cheese and, in turn, how this can be used by the cheesemaker to produce the desired cheese. The physical properties of cheese (as well as flavor) are influenced by a number of factors including: milk composition; milk quality; temperature; the rate and extent of acidification by the starter bacteria; the pH history of cheese; the concentration of Ca salts (proportions of soluble and insoluble forms); extent and type of proteolysis, and other ripening reactions. Our hypothesis is that these factors also control and modify the nature and strength of CN interactions. The approach behind the recently proposed dual-binding model for the structure and stability of CN micelles is used as a framework to understand the physical and chemical properties of cheese.     

超声处理对山羊奶酪蛋白理化和功能特性的影响

以山羊奶酪蛋白为原料,利用不同强度超声处理山羊奶酪蛋白,探究超声处理对山羊奶酪蛋白的pH和电导率、Zeta电位、浊度等理化指标以及乳化性和起泡性等功能特性的影响。结果表明,与未处理相比,超声处理后山羊奶酪蛋白pH下降,电导率变化不显著（P>0.05）;Zeta电位绝对值在400 W处理2 min时达到最大值27.85±1.55 mV;浊度值与未处理相比显著性降低（P<0.05）;与未处理相比,超声处理可以减小蛋白平均粒径,并在700 W处理6 min时达到最低值,由383.20±13.07 nm减少至176.17±4.28 nm;扫描电镜结果表明超声改变了酪蛋白原有表观形态,导致不规则碎片的产生;超声处理后的酪蛋白乳化性在100 W处理10 min时提高了41.44%。在400 W处理10 min时起泡性和泡沫稳定性显著增加（P<0.05）,分别达到最大值32.88%±0.07%和91.93%±0.19%。综上,超声处理产生的空化效应以及机械作用可以为山羊奶酪蛋白提供更好的理化特性和功能特性。     

牦牛奶中不同酪蛋白的提取及其功能特性研究

本研究以新鲜牦牛乳为原料,添加钙盐后利用其等电点分离提取牦牛奶中的不同酪蛋白,利用单因素实验筛选牦牛奶中α-、β-、κ-酪蛋白的提取分离参数;并利用电泳(SDS-PAGE)分析牦牛乳不同酪蛋白纯度。同时对牦牛乳中α-、β-、κ-酪蛋白的溶解性、乳化性、发泡性进行分析比较。结果表明:牦牛奶不同酪蛋白分离的最佳Ca~(2+)浓度为0.08 mol/L,最佳温度2℃,此时牦牛乳中α-、β-酪蛋白分离效果较好。牦牛乳不同酪蛋白在等电点(p I)附近时,α-、β-、κ-酪蛋白溶解性、乳化性、发泡能力最低,泡沫稳定性最好。等电点附近酪蛋白的溶解度最低,α-、β-酪蛋白pH值在2.1时溶解度最高(分别为60%、80%),而k-酪蛋白在pH值6.22时最高(43%);在40～80℃范围内,κ-酪蛋白溶解度受温度影响显著;当pH值为2.1时,α-、β-、κ-酪蛋白的乳化能力和发泡能力都最大,其乳化稳定性则是远离等电点后逐渐上升;本研究旨在为牦牛乳酪蛋白的利用和深加工提供思路,为云南特色乳制品的开发利用提供科学依据。