Effect of Maillard‐based conjugation with dextran on the functional properties of lysozyme and casein

The purpose of this research was to find the best experimental conditions for glycosylation of lysozyme and casein with dextran, and to investigate the effect of glycosylation on the functional properties of these proteins. Glycosylation was performed by allowing proteins to react with dextran under Maillard reaction conditions. The extent of glycosylation was determined by sugar analysis, SDS‐PAGE, gel filtration and cation‐exchange chromatography. Glycosylation of lysozyme with a 1:5 weight ratio of protein to dextran, held at 60 °C for one week under a relative humidity of 79% resulted in coupling of 3.0 mole dextran to one mole lysozyme. In the case of casein, at 60 °C, 48 h and 79% relative humidity, 0.1 and 0.13 mole dextran was attached to one mole of casein when a weight ratio of protein to dextran of 1:5 and 1:7.5 was used, respectively. A decrease in the degree of glycosylation occurred when samples were incubated for 72 h. Enzymatic activity of glycosylated lysozyme was reduced by 20% compared with unmodified lysozyme (P < 0.05). Both proteins exhibited improved solubility at different pH values (3, 7 and 9), different temperatures (25, 40 and 60 °C) and increased heat stability, with a better emulsion activity and emulsion stability than with un‐modified proteins (P < 0.05). These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems. Copyright © 2005 Society of Chemical Industry     

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。      

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.     

酪蛋白磷酸肽-钙络合物对酸乳贮藏特性的影响

为探究酪蛋白磷酸肽-钙（CPP-Ca）络合物对酸乳贮藏特性的影响,研究CPP-Ca络合物不同添加量对酸乳21 d贮藏期内乳酸菌总数、pH值、滴定酸度、乳清析出率及黏度的影响。与对照组比较,当CPP-Ca络合物添加量为0.15 g/100 mL时,酸乳中乳酸菌存活率从32.92%提高至47.15%（P＜0.05）;滴定酸度增长率从9.96%降低至7.06%（P＜0.05）;乳清析出率降低了0.4%（P＜0.05）,黏度比提高了5 729 mPa·s （P＜0.05）。结果表明,CPP-Ca络合物的添加能增加酸乳贮藏期内的乳酸菌总数,延缓酸度积累,降低乳清析出率,增加黏度,改善酸乳贮藏期内的产品品质。     

酪蛋白的转谷氨酰胺酶酶促糖基化交联条件及产物性质

在氨基葡萄糖存在的条件下,利用转谷氨酰胺酶(EC2.3.2.13)对酪蛋白进行糖基化交联修饰。以修饰酪蛋白产物中氨基葡萄糖的导入量为指标,采用单因素试验分别考察反应体系pH值、酶添加量、反应温度和时间对修饰反应的影响。优化后的适宜修饰条件为:酪蛋白底物质量浓度为30g/L,氨基葡萄糖添加量为3mol(每kg酪蛋白中)、pH值为7.5、酶添加量为10kU(每kg酪蛋白中)、反应温度为37℃、时间4h。与酪蛋白和转谷氨酰胺酶促交联的酪蛋白相比,修饰酪蛋白产物的乳化性质和胶凝性质得到显著改善,并且体外消化性能未受到影响,表明转谷氨酰胺酶催化的糖基化交联修饰可以用于改善酪蛋白的这些功能性质。     

酪蛋白胶束结构和理化性质的研究进展

酪蛋白是乳中一大类蛋白质的总称,约占乳蛋白质量分数的80%。牛乳中的酪蛋白不是单独存在的,而是和矿质元素相互缠绕在一起而形成的复合物。牛乳的酸凝、酶凝以及液态乳稳定性的变化,从本质上来说都是酪蛋白胶束发生的一系列变化所导致的。本文概述了组成酪蛋白胶束中四种酪蛋白单体各自的结构和理化特征。综述了胶束的组成、胶束的流体力学直径、容积度、密度、水合性、分子间距等几个重要的特征参数。最后总结了核壳模型、双结合模型、亚单元模型和Holt模型等酪蛋白胶束的理论结构模型的特征及各种的缺陷,以期对乳制品的生产和加工提供一些思路。      

Physicochemical and functional properties of goat milk whey protein and casein obtained during different lactation stages

During lactation, goat milk contains colostrum, transitional milk, mature milk, and end milk. The protein present in goat milk during different lactation periods has different characteristics. This study aimed to characterize the protein profile of goat milk samples obtained at different lactation stages and to identify changes in the physicochemical and functional properties of whey protein and casein from goat milk collected at 1, 3, 15, 100, and 200 d after calving. The results demonstrated that the lactation period had a great influence on the physicochemical and functional properties of goat milk whey protein and casein, especially the protein properties of colostrum on the first day after delivery. The denaturation temperature, hydrophobicity, and turbidity of whey protein were significantly higher on the first day postpartum than at other lactation periods. Correspondingly, the colostrum whey protein also had better functional properties, such as emulsification, oil holding capacity, and foaming properties on the first day postpartum than at other lactation periods. For casein, the turbidity, particle size, water holding capacity, and foaming properties on the first day after delivery were significantly higher than those at other lactation periods, whereas the denaturation temperature, oil holding capacity, and emulsification followed the opposite trend. For both whey protein and casein, the 2 indicators of emulsifying properties, namely, emulsifying activity index and the emulsion stability, also followed an opposite trend relative to lactation stage, whereas the changes in foaming capacity with the lactation period were completely consistent with the change of foaming stability. These findings could provide useful information for the use of goat milk whey protein and casein obtained during different lactation stages in the dairy industry.     

牛奶纤维拉伸性能理论模型的研究

文章探讨了牛奶纤维拉伸性能的理论数学模型,对牛奶纤维的力学性能进行了模拟,利用4元件非线性粘弹模型对其应力应变关系进行了分析和计算,结果表明,理论和实测结果符合得很好.该模型对于预测纤维的拉伸性能具有理论指导意义.另外,文章还对牛奶纤维干湿条件下的断裂强力和断裂伸长率进行了对比,其在干态下的力学性能优于湿态下的力学性能.     

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。     

Progress in micellar casein concentrate: Production and applications

Micellar casein concentrate (MCC) is a novel ingredient with high casein content. Over the past decade, MCC has emerged as one of the most promising dairy ingredients having applications in beverages, yogurt, cheese, and process cheese products. Industrially, MCC is manufactured by microfiltration (MF) of skim milk and is commercially available as a liquid, concentrated, or dried containing ≥9, ≥22, and ≥80% total protein, respectively. As an ingredient, MCC not only imparts a bland flavor but also offers unique functionalities such as foaming, emulsifying, wetting, dispersibility, heat stability, and water-binding ability. The high protein content of MCC represents a valuable source of fortification in a number of food formulations. For the last 20 years, MCC is utilized in many applications due to the unique physiochemical and functional characteristics. It also has promising applications to eliminate the cost of drying by producing concentrated MCC. This work aims at providing a succinct overview of the historical progress of the MCC, a review on the manufacturing methods, a discussion of MCC properties, varieties, and applications.     

酪蛋白与明胶的酶促交联与产物的流变学性质

利用转谷氨酰胺酶对酪蛋白和明胶进行酶促混合交联。在酪蛋白与明胶比例为4︰1(质量比)时,以交联产物中羟脯氨酸质量分数为指标,采用单因素试验研究酶添加量、反应时间和温度对交联反应的影响。优化后的适宜交联条件为:底物质量浓度固定为50 g/L,酶添加量为每克蛋白质20 U,反应时间为4 h,温度为45℃。SDS-聚丙烯酰胺凝胶电泳分析表明产物中含有蛋白质聚合物。与原料酪蛋白、转谷氨酰胺酶促交联的酪蛋白相比,所得到的产物的分散液表观黏度和黏弹性均有显著的改变,表明转谷氨酰胺酶催化的酪蛋白和明胶混合可以用于改善其流变学性质。     

糖基化反应改善蛋白质功能特性的研究进展

糖基化反应是改善蛋白质功能特性的一种有效的方法。主要介绍蛋白质糖基化反应机理,糖基化反应对鱼肉蛋白、β-乳球蛋白、卵清蛋白、酪蛋白、精蛋白以及酶等各类蛋白质功能特性影响的国内外研究进展。     

酪蛋白的转谷氨酰胺酶氨基葡萄糖修饰与功能性变化

在37℃、pH值为7.5和氨基葡萄糖存在下,利用转谷氨酰胺酶(EC 2.3.2.13)对酪蛋白进行交联修饰制备修饰酪蛋白;用十二烷基磺酸钠-聚丙烯酰胺凝胶电泳和高效液相色谱分析证实酪蛋白同时发生交联与糖基结合,且反应4 h时每摩酪蛋白可结合1.2摩葡萄糖.与酪蛋白相比,交联酪蛋白的溶解性质和起泡性质受损,而修饰酪蛋白产品的溶解性质得到改善,起泡性质尤其是泡沫稳定性质显著提高.在蛋白质质量浓度为1 g/L时,修饰酪蛋白的起泡能力和泡沫稳定性分别比酪蛋白提高8.6%和21%;质量浓度为100 g/L的修饰酪蛋白分散液表现出非牛顿流体特性,表观黏度显著高于交联酪蛋白或酪蛋白.     

Effect of germination and dehulling on functional properties of legume flours

The functional properties of flours derived from selected legumes were studied before and after dehulling of the germinated seeds. Ungerminated seeds were used as the control. The chosen legumes were green gram (Phaseolus aureus), cowpea (Vigna catjang), lentil (Lens culinaris) and bengal gram (Cicer arietinum). Dehulled samples had a higher protein solubility compared with germinated and control samples. The bulk densities of germinated and dehulled legume flours were lower compared to control. Germination increased water absorption capacities of legume flours from 1226, 1285, 974 and 1362 g kg^?1 to 1481, 1433, 1448 and 1517 g kg^?1 in green gram, cowpea, lentil and bengal gram, respectively. Fat absorption capacities increased in germinated samples (1130, 1242, 920 and 837 g kg^?1) as against 900, 993, 857 and 788 g kg^?1 at ambient conditions for green gram, cowpea, lentil and bengal gram, respectively. On dehulling, the fat absorption capacities of samples were reduced and the differences were statistically significant. The emulsification capacities of control samples ranged from 55 to 193 ml oil emulsified per gram of sample. On germination and dehulling, the emulsification capacities, activities and stabilities of samples increased significantly. There were increases in foaming capacities and reduction in foam stabilities of all the samples investigated on germination and dehulling. Thus, the study indicated that germination and dehulling improved the functional properties of legumes. Copyright © 2006 Society of Chemical Industry     

The effect of ethanol and heat on the functional hydrophobicity of casein micelles

Milk proteins are very important ingredients to the food industry. As new uses and applications for these proteins are developed, it becomes more important to understand their physicochemical properties when they are subjected to different treatments. It has been reported that casein micelles dissociate when heated in the presence of ethanol. The changes to the hydrophobicity of milk proteins during that process were evaluated by using the fluorescent hydrophobic probe 1-anilinonaphthalene-8-sulfonic acid (ANS). Raw skim milk, pasteurized skim milk, and whey protein isolate samples with ethanol concentrations of 0 to 60% (vol/vol) were heated from 20 to 60°C. The fluorescence of the samples with and without the addition of ANS was measured at an excitation wavelength of 390 nm and an emission wavelength of 400 to 500 nm. The results showed a decrease in the extrinsic fluorescence of the samples as the ethanol concentration and temperature increased, indicating competitive inhibition of the ANS-hydrophobic site interaction by ethanol. This inhibition was further enhanced by the addition of heat. This resulted in a reduction in the functional hydrophobicity of the milk proteins as ethanol rendered the hydrophobic sites unavailable for interaction.     

Effect of succinylation on the functional and physicochemical properties of bovine serum albumin

Bovine serum albumin was modijed with succinic anhydride so that 50 or 82% of lysine residues were acylated. The structural alterations caused by modification were examined by pH titration, electrophoretic patterns, circular dichroism, amino acid analysis, and the measurement of amino, sulphydryl and hydrophobic groups. Changes in these physicochemical properties were related to inferior whipping, emulsification and gelling properties of succinylated bovine serum albumin compared with the native protein.     

Comparative study on the microstructure and functional properties of casein in goat milk processed by different methods

This work compared the thermal stability, microstructure and functional properties of casein (CN) in goat milk processed by different methods, including homogenisation, low-temperature long-time (LTLT), high-temperature short-time (HTST), ultrapasteurisation (UP) and ultrahigh temperature (UHT) treatment. The greatest development of CN-whey protein complexes was observed in LTLT goat milk and the least in HTST goat milk. The CN micelles in LTLT, UP and UHT milk were more obviously changed than the CN micelles in HTST milk, and the random coil content increased significantly after the homogenisation, UP and UHT treatments. The homogenisation had a significant effect on the functional properties of CN. In addition, the most obvious changes in the properties of CN were observed in LTLT and UHT goat milk. The results suggested that homogenisation, pasteurisation and UHT can cause effective changes in the functional properties of CN in goat milk that facilitate its application in the milk industry.     

酪蛋白水解方法及水解产物功能性的研究进展

牛奶是婴幼儿喂养时母乳的主要替代品,酪蛋白是牛奶中的主要蛋白质。由于母乳和牛奶中酪蛋白成分存在差异,使得婴幼儿在使用牛奶时出现病症。本文从酪蛋白水解方法和水解产物的功能性等角度,针对其相关的国内外研究进展进行了综述。