复合酶法改性制备乳清分离蛋白可溶性聚合物的性质

为探究胰凝乳蛋白酶与谷氨酰胺转氨酶(transglutaminase,TGase)复合酶法改性制备乳清分离蛋白(whey protein isolate,WPI)可溶性聚合物的性质,本实验利用电泳、荧光分光光度计和旋转流变仪等对可溶性聚合物的性质进行对比分析。结果表明:复合酶改性制得的聚合物与单一TGase改性相比,黏度增大,游离巯基含量显著降低,但表面疏水性和ζ-电位无显著变化。复合酶改性聚合物平均粒径是(153.66±9.15)μm,而TGase改性聚合物平均粒径是(157.92±10.91)μm,没有显著差异。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和非变性聚丙烯酰胺凝胶电泳对比分析得出,单独的TGase改性聚合物分子质量较大,被截留在凝胶加样口,而复合酶改性聚合物分子质量更多的集中在65 k D附近,即聚合物分子大小适中,这与粒径的结果相呼应。胰凝乳蛋白酶和TGase复合改性聚合物表面呈波纹片状,结构均一紧致。与未改性的WPI相比,复合酶改性WPI聚合物pH值溶解性曲线在pH 2.0~7.0范围变化较平缓,且在pH 4.0~5.0时溶解性提高。此研究结果为复合酶法改性WPI在酸乳或酸性乳饮料方面的应用提供了理论依据与技术参考。     

完全热变性、可溶性大豆蛋白聚集物的溶解性质研究

大豆分离蛋白在完全或部分热变性下仍可以保持较高的溶解性,这种类型的大豆蛋白在世界大豆蛋白工业中占据了重要地位.本研究发现:该类型的大豆分离蛋白的亚基之间是以共价键和非共价键相结合.其溶解性质与传统的低变性大豆分离相比:在饱和湿度加热条件下更容易丧失水溶性,在湿度为18%和50%下二者的变化趋势基本相同,盐溶性相对较差,含水乙醇对其溶解度的降低作用相对较弱,在65%乙醇溶液中加热溶解性非但不降低而且还大幅度升高.该研究成果对于大豆分离蛋白产品的开发以及大豆蛋白的基础研究都具有重要的借鉴意义.     

Thermal Aggregation of Whey Proteins in Model Solutions as Affected by Casein/Whey Protein Ratios

Model solutions (32.5 g protein/L) prepared from milk, ultrafiltration permeate, and whey protein isolate were adjusted at pH 6.7 to casein:whey protein (C:W) ratios of 80:20, 60:40, 40:60,20:80, and 0:100. Heating was performed in test tubes at 95 °C for 5 min. Observations of the heated suspensions revealed the occurrence of heterogeneous particulates from the existing casein micelles complexed with denatured whey proteins and from aggregates essentially consisting of denatured whey proteins. The proportion of whey protein aggregates increased as C:W was changed from 80:20 to 20:80. The results from this study confirmed that heat-induced aggregates were formed not only from casein micelles but also from heat-denatured whey proteins.     

Turbidity and Protein Aggregation in Whey Protein Beverages

ABSTRACT:  During storage of heat-treated acidic (pH ≤ 4.6) whey protein beverages, formation of protein aggregates can create undesirable turbidity and sedimentation. In this study, we found that a slow protein aggregation process controlled the rate of formation of sediment and turbidity. A heat-treated model beverage containing 12.5 g/L whey protein at a pH of 4 was stored for 6 wk at 3 different storage temperatures and analyzed for turbidity, soluble protein, and protein aggregates. One sample was stored without further treatment and the other sample was filtered to remove protein aggregates formed during heating. This was done to test the hypothesis that aggregates formed during heat treatment served as nuclei for deposition of soluble protein. Turbidity increased and soluble protein decreased as protein aggregates formed during storage. Increasing the storage temperature accelerated this process. The loss of soluble protein during storage was fit to first- and second-order kinetic equations, allowing the prediction of the effect of protein concentration, storage time, and storage temperature on the formation of protein aggregates.     

乳清蛋白在无添加剂酸奶中的应用

本实验采用乳清蛋白制备了一种不添加稳定剂的酸奶,为制作无添加剂酸奶提供理论依据。通过分析不同添加量的乳清蛋白对酸奶发酵终点,以及后熟和保质期内酸奶的酸度、粘度、脱水收缩作用敏感性（STS）、持水率（WHC）的影响,结果发现：乳清蛋白对发酵终点的影响不大;随着乳清蛋白添加量的增加,在后熟时酸奶的酸度变化加快;乳清蛋白可以提高酸奶在保质期内的稳定性,对STS和WHC都有促进作用,可保证产品最终质量。此外,结合感官测评,乳清蛋白添加量在3~4%时,产品口感及稳定性较佳,通过使用乳清蛋白可以使无添加剂的酸奶在保质期内稳定。     

乳清蛋白及与其它乳成分的热聚合作用机制研究进展

乳蛋白决定奶类品质,而热加工会影响乳清蛋白尤其是β-乳球蛋白的稳定性。热处理时,乳清蛋白不仅自身发生不同程度的聚合,而且通过巯基-二硫键分别与酪蛋白胶束和乳脂球膜蛋白发生结合。乳清蛋白亦可与其它乳成分如乳糖、钙盐、乳脂发生热聚合作用。本文根据乳品受热温度的不同,针对乳清蛋白间及其与其它乳成分的相互作用途径进行分析,阐明热聚合作用过程及机理,对改善乳制品的热稳定性、凝胶性等功能性质具有重要的理论意义,拓宽乳清蛋白作为配料在相关食品体系中的应用。     

Surface Properties of Heat‐Induced Soluble Soy Protein Aggregates of Different Molecular Masses

Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large‐size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium‐size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications.     

乳清分离蛋白聚集体乳化性能及其Pickering乳液稳定性

以乳清分离蛋白(whey protein isolate,WPI)为原料,分别在pH2.0和pH7.0条件下,85℃加热12h制备2种不同形态的蛋白质聚集体,研究2种聚集体微观形貌的特征以及不同pH值和盐离子浓度下的乳化性能;采用透射电镜、动态光散射、光学显微镜等技术手段,探究WPI与2种聚集体稳定的Pickering...     

Ingredients and pH are Key to Clear Beverages that Contain Whey Protein

ABSTRACT:  A challenge of shelf stable beverages that contain whey protein is that a small portion of protein can be denatured and aggregated during thermal processing, resulting in a turbid solution or white precipitate that consumers perceive as a defect. In this study, 3 approaches were taken to reduce turbidity in heat-treated beverages that contain whey protein: (1) centrifugation to remove insoluble protein aggregates, (2) addition of ingredients, and (3) alteration of pH in the range from 3.0 to 4.0. At pH 3.6 and below, all samples were essentially clear both before and after heating for all ingredients. At a pH of 3.8 and above, ingredient selection was crucial to solution clarity after heat treatment. At a pH of 4.0, addition of salts at both 10 and 50 mM increased the turbidity significantly compared to the control, which contained only whey protein in water. Neither addition of sugars at 25, 50, and 100 g/L, nor addition of sugar alcohols at 25 g/L significantly affected turbidity after heat treatment compared to the control. However, sugar alcohols added at 50 or 100 g/L significantly reduced turbidity after heat treatment compared to the control. Removal of insoluble protein aggregates by centrifugation prior to heat treatment resulted in a statistically significant decrease in turbidity after heat treatment. Understanding these results at the molecular level will assist food scientists in selecting processing treatments, ingredients, and pH in the development of shelf stable clear beverages that contain whey protein.     

Development of an Orange-flavored Barley β-Glucan Beverage with Added Whey Protein Isolate

ABSTRACT: Whey protein isolate (WPI) frommilkand (l→3), (l→4)-β-D-glucan (β-glucan), a soluble fiber component found in barley, were used together to formulate a functional beverage product. Formulations tested included 0.5% (w/w) β-glucan with 0%, 0.5%, 1.0%, and 1.5% (w/w) WPI. Trained and consumer panels evaluated beverage quality and acceptability. Shelf stability of products was assessed. Trained panelists found beverages to be similar in sweetness intensity ( P > 0.05). Sourness and orange-flavor intensity decreased ( P 0.05) as WPI concentration increased, whereas beverage cloudiness and viscosity increased ( P 0.05). The consumer panel found no difference (P > 0.05) in the degree of liking for all the attributes studied. Beverages were found to be stable throughout the 8-wk storage period. Barley β-glucan shows great potential as a functional beverage ingredient.     

商用大豆分离蛋白可溶絮凝物的制备及其性能研究

本文报道了超声处理制备可溶的商用大豆分离蛋白(SPI)絮凝物。经SDS-PAGE及SE-HPLC分析确认,超声处理可使不溶的SPI组份形成一种可溶的絮凝物,后者包含了原先不溶的大豆球蛋白的碱性亚基及大部分的β-伴大豆球蛋白。与未经超声处理的SPI分散液相比,经超声处理的分散液具有更高的热稳定性及凝胶性能。该研究结果可为商用SPI在食品中的应用提供一定的指导。     

乳清浓缩蛋白对松仁蛋白溶解度及其乳液稳定性的影响

为研究蛋白质-蛋白质相互作用对松仁蛋白(PKP)溶解度、结构和乳液性质的影响,以PKP和乳清浓缩蛋白(WPC)为研究对象,采用pH循环法制备PKP-WPC复合蛋白,利用SDS-PAGE、内源性荧光光谱、紫外-可见光谱、圆二色谱、荧光探针和ζ-电位等方法分析了复合蛋白结构特性和表面特性,再以PKP-WPC复合蛋白为原料,分别制备了油相体积分数为3%、10%和50%的乳液,并对制备的乳液性质进行了检测。结果表明:当WPC与PKP的质量比为1.0∶1.0,且体系pH值经历由7.0到12.0再回到7.0时的1次pH循环后,PKP的水溶性可从48.53%提高到92.43%。SDS-PAGE结果显示,PKP-WPC复合蛋白完整保留了PKP和WPC的亚基。内源性荧光光谱、紫外-可见光谱和圆二色谱结果表明,静电相互作用、疏水相互作用和氢键是驱动PKP和WPC相互作用的主要作用力,PKP与WPC相互作用使复合蛋白具有较高的结构韧性,抵抗酸诱导的构象折叠;WPC的加入改变了PKP的二级结构,α-螺旋、β-转角和无规卷曲结构的含量增加,而β-折叠结构相对含量降低。PKP-WPC复合蛋白具有较高的表面电荷(-34.74mV)来抵抗蛋白质的聚集。与由PKP制备的乳液相比,由PKP-WPC制备的乳液平均粒径和乳层析指数减小,ζ-电位绝对值增大,稳定性显著提高。乳液的性质因油相体积分数的不同而有较大的差异。油相体积分数为3%的复合乳液液滴小且分布均匀,稳定性好于油相体积分数为10%和50%的复合乳液。通过pH循环法,通过添加WPC,提高了PKP的溶解度,获得了稳定性较佳的PKP乳液,研究可为新型蛋白产品的研发提供理论基础,拓宽松仁蛋白在加工食品中的应用范围,推动PKP-WPC双蛋白乳液研究的发展。     

Water Solubility, Mechanical, Barrier, and Thermal Properties of Cross-linked Whey Protein Isolate-based Films

Water solubility, hermal properties, tensile strength, percent elongation, oxygen permeability (OP), water‐vapor permeability (WVP) of cross‐linked glycerol plasticized whey protein isolate films were studied to determine the effect of cross‐linkers (glutaraldehyde, formaldehyde, dialdehyde starch, carbonyldiimidazole, and UV irradiation) on film properties. With the exception of UV treatment, solubility of the films decreased (P>0.05) upon treatment of the film‐forming solutions with chemical cross‐linkers. Tensile strength increased (P>0.05), whereas percent elongation was not affected by cross‐linking. Chemical cross‐linking increased (P>0.05) WVP and decreased (P>0.05) OP of the films. UV treatment had no effect on WVP and O P. With the exception of UV‐treated films, both onset temperature and degradation temperatures, as determined by differential scanning calorimetry, were increased upon cross‐linking.     

乳清蛋白与老年肌肉衰减征研究进展

肌肉衰减征(Sarcopenia)是伴随衰老而出现的一种以肌肉质明显减少、肌肉力量下降为特点的常见病征,同时伴随功能下降和多种慢性病发生。摄入充足的膳食蛋白质和能量,以及加强抗阻力运动和有氧运动是防治老年人肌肉衰减征的重要措施。乳清蛋白富含亮氨酸等支链氨基酸和谷氨酰胺,在防治老年肌肉衰减征中具有独特而重要的作用。     

Foaming Properties of Whey Protein Isolate and λ‐Carrageenan Mixed Systems

Heating protein with polysaccharide under neutral or near neutral pH can induce the formation of soluble complex with improved functional properties. The objective of our research was to investigate the effects of λ‐carrageenan (λC) concentrations and pH on foaming properties of heated whey protein isolate (WPI) and λC soluble complex (h‐cpx) in comparison to heated WPI with added λC (pWPI‐λC), and unheated WPI with λC (WPI‐λC). In all 3 WPI‐λC systems at pH 7, increasing λC concentration led to improved foamability until a certain concentration before it decreased. Despite their higher viscosity, both heated systems (pWPI‐λC and h‐cpx) showed significantly better foamability and foam stability compared to WPI‐λC. Rheological results of foams with 0.25% λC suggested that higher elasticity and viscous films were produced in h‐cpx and pWPI‐λC systems corresponding to better foam stability. Foam microstructure images indicated that foams produced from h‐cpx had thicker film and consisted of smaller initial bubble area and more uniform bubble size. Results from the effect of pH (6.2, 6.5, and 7.0) further confirmed that stronger interactions between WPI and λC during heating contributed to the improved foaming properties. Foam stability was higher in h‐cpx system at all 3 pH levels, especially under pH 6.2 where there were strongest interactions between the biopolymers.     

乳清分离蛋白-可溶性淀粉接枝物的制备及其理化性质

研究了干热法处理条件下乳清分离蛋白-可溶性淀粉接枝物的制备及其二级结构分析,为蛋白质-淀粉接枝物的研究提供参考。A294、褐变、游离氨基含量变化、电泳图谱等证实乳清分离蛋白与可溶性淀粉在干热处理下确实发生了以美拉德反应为基础的接枝反应,且反应天数的延长能够显著促进乳清分离蛋白-可溶性淀粉接枝物的生成。由于大分子淀粉的共价接入,乳清分离蛋白的二级结构遭到破坏;蛋白质表面疏水性指数降低。     

酶解乳清浓缩蛋白WPC80制备乳清肽的研究

用乳清浓缩蛋白WPC80 为原料,在复合酶A 的作用下,研究乳清肽的制备工艺。复合酶A 的反应条件为[S]12g/100mL、温度50℃、[E]/[S]3%、pH9.0。选用截留分子质量10kD 的磺化聚砜膜,常温并在工作压差0.25MPa 下对水解液进行超滤处理后,选用树脂HZ00x 对水解液进行脱苦,得到的处理液无明显的苦涩味,只有轻微的蛋腥味,最后肽得率36.54%。产品中肽的分子质量分布以二、三和四肽为主,分别占峰面积的27.45%、34.88% 和26.65%。     

乳清蛋白的组成及其主要保健功能

乳清蛋白氨基酸组成合理、消化吸收率高,同时在消化过程中产生多种生物活性多肽,具有增强体质、提高免疫力、抗疲劳、抗氧化、抑菌抗病毒、降血脂、降血压、降血糖、抗癌等多种保健功能。本文就乳清蛋白的组成成分及其保健功能进行了综述。     

乳清蛋白在食品工业中的应用

对乳清蛋白在食品中的应用进行了简要的介绍,其中对乳清蛋白的主要组分(α- 乳白蛋白、β- 乳球蛋白、乳铁蛋白等)、功能特性(成胶性,涂层性和成膜性等)、生产技术(膜分离技术、吸附分离法、亲和色谱提纯法等)及改性方法(物理改性及酶改性)做了详细的介绍,并对我国乳清蛋白的应用前景进行了展望。