乳清分离蛋白凝胶蔗糖释放过程的动力学分析

以蔗糖为食品风味成分,封装于乳清分离蛋白凝胶内,探讨pH值、温度、载药量、释放液离子浓度对乳清分离蛋白凝胶释放蔗糖的动力学机制。结果表明：蔗糖在乳清分离蛋白凝胶中的释放过程符合Korsmeyer-Peppas模型,且拟合相关系数R2在0.95～0.99之间,扩散常数n均小于0.45,符合Fick扩散机理。动力学常数K随pH值、温度、以及释放液离子浓度（0.05～0.10 mol/L）的增加而增大,随载药量的增加而减小。乳清分离蛋白凝胶具有环境应答性,以其为载体的物质释放过程受环境温度、pH值、载药量、释放液离子浓度等因素影响。通过调节释放体系的pH值、温度、载药量、释放液离子浓度可以达到控制载物释放的目的。     

影响猪血浆蛋白热诱导凝胶质构特性及持水性因素的研究

本实验研究在一定的加热条件下猪血浆蛋白质量浓度、加热温度、加热时间、离子种类、离子强度和pH 值对猪血浆蛋白热诱导凝胶的质构、持水性等性质的影响。利用质构仪测定猪血浆蛋白热诱导凝胶的硬度和黏附性,利用离心的方法测定凝胶的持水性。结果表明,在80℃下加热45min,猪血浆蛋白质量浓度超过6g/100mL可以形成凝胶,并且随蛋白质量浓度的增大,凝胶强度和持水性也增大;凝胶强度随pH 值(3～9)增加而增大,pH5 时凝胶的持水性最小,pH3 时最大;NaCl 浓度0.2mol/L,CaCl2 浓度0.6mol/L 时,凝胶硬度最大。实验得出,猪血浆蛋白热诱导凝胶的质构特性及持水性受许多因素影响,在实际生产中应该控制加热条件,以获得高质量的凝胶。     

EGCG与乳清蛋白相互作用的光谱分析

探究表没食子儿茶素没食子酸酯(epigallocatechin gallate,EGCG)与乳清分离蛋白(whey protein isolate,WPI)间的相互作用。测定不同pH值与不同离子浓度条件下WPI的紫外吸收光谱、导数光谱和荧光光谱,利用SternVolmer方程判断荧光猝灭机制,采用位点结合模型公式计算结合常数和结合位点数。结果表明,紫外吸收光谱和导数光谱结果显示EGCG改变了WPI中酪氨酸和色氨酸残基所处的微环境,使WPI的分子构象发生了变化。荧光光谱结果显示EGCG可以有规律地猝灭WPI的内源荧光,猝灭机理为静态猝灭,EGCG与WPI结合常数在pH 2.0~9.0范围内随pH的增大先减小后增大,在离子浓度0.10 mol/L^0.20 mol/L范围内随离子浓度的增大而增大,结合位点数约为1。EGCG与WPI间存在静电相互作用。     

叶黄素-海藻酸钠微球的制备及质量评价

目的:选取海藻酸钠为载体材料,氯化钙为交联剂,采用离子转移乳化凝胶法制备叶黄素-海藻酸钠微球,并对其质量进行评价。方法:通过单因素试验考察海藻酸钠浓度、叶黄素浓度、氯化钙(CaCl_2)溶液浓度对微球的影响,正交试验设计优化微球制备工艺,使用光学显微镜和扫描电子显微镜观察微球表观形态,并对微球的粒度分布、载药量、包封率、体外释药及温度稳定性进行了研究。结果:依据优化处方制得的微球表面较粗糙,有细小微孔,外观圆整、分散性好;平均包封率及平均载药量分别为36.86%和5.24%;平均粒径为145μm,且粒径在110~160μm范围内的微球个数占81.90%;pH 7.4环境下,累积释放率达到74.98%。结论:采用离子转移乳化凝胶法制备微球重现性较好,操作简单易行;通过包封叶黄素的稳定性被明显提高,且微球体外释放过程较缓慢。     

载锌坡缕石的制备及其体内外抗菌性能研究

采用离子交换方法制备栽锌坡缕石,探索和分析了交换液离子浓度、溶液pH值、反应温度、交换时间对锌交换量的影响;通过X射线衍射分析对锌离子与坡缕石的组装体进行了表征;并研究了载锌坡缕石对大肠杆菌、金黄色葡萄球菌的抑制作用和肉鸡肠道菌群的影响.结果表明,载锌坡缕石的最佳制备工艺条件以交换液浓度为1 mol/L、溶液pH值为4、反应时间为3 h、反应温度为60 ℃为宜;载锌坡缕石能明显抑制大肠杆菌的生长,降低肉鸡空肠大肠杆菌数,增加了空肠乳酸杆菌数.     

超高压处理对乳清分离蛋白凝胶特性的影响

研究了超高压处理压力、时间、蛋白质量浓度、pH值、CaCl_2对乳清分离蛋白(whey protein isolated,WPI)凝胶特性的影响。当处理压力≥300 MPa、处理时间≥10 min、蛋白质质量浓度≥12 g/L时,WPI溶液经超高压处理后可以形成凝胶,且随着处理压力增大、处理时间延长和蛋白质浓度的提高,凝胶中二硫键含量明显升高,凝胶网络结构趋于致密,质地逐渐细腻,凝胶强度、得率和保水性呈现增大的趋势;WPI溶液pH在等电点以上且接近中性时,形成凝胶的二硫键含量较高,凝胶网络致密,凝胶品质较好;添加CaCl_2对形成凝胶的二硫键含量不产生影响,但其可以通过键桥作用提高凝胶强度;凝胶得率与CaCl_2浓度呈负相关。当CaCl_2浓度为0.06mol/L时,凝胶具有较大保水能力,之后保水性随Ca~(2+)浓度的升高而下降。     

pH响应性纤维素纳米纤丝/海藻酸钠基水凝胶的制备及其释药性研究

将纤维素纳米纤丝（CNF）和海藻酸钠（SA）共混,然后在CaCl2的交联作用下,制得具有pH响应性的CNF/SA水凝胶,并通过物理包裹的方式将阿司匹林（ASP）、CNF和SA三者混合均匀后,在CaCl2的交联作用下制得ASP/CNF/SA载药水凝胶,研究ASP在不同pH值环境中的缓释行为。结果表明,ASP/CNF/SA载药水凝胶的载药量为194 mg/g,包封率达49.9%,且药物分子和水凝胶都保持了很好的热稳定性。ASP/CNF/SA载药水凝胶的药物释放具有pH响应性,药物分子的释放速率随着环境pH值的升高而加快。在p H值为1.5～11.0的缓释条件下,药物的释放行为均为溶蚀作用。     

k－卡拉胶凝胶特性的研究

本文研究了卡拉胶含量、钾离子浓度、凝胶温度和pH值对卡拉胶水凝胶的强度和粘度的影响。结果表明:胶体含量是影响凝胶强度和粘度的主要因素,凝胶强度随胶体含量的增加线性提高后渐趋平稳、受钾离子的影响出现峰值、在pH值8.0和10.0处出现两个拐点;胶液粘度随卡拉胶含量增加迅速增大、随钾离子浓度提高而减小,中性时的粘度最大。     

壳聚糖／果胶水凝胶的制备及其在药物控制释放中的应用

以戊二醛（GA）为交联剂制备了一系列壳聚糖／果胶（CS-PT）pH值敏感水凝胶。研究了合成条件对CS-PT水凝胶溶胀性能的影响。试验结果表明,交联剂含量、pH值、离子强度对水凝胶溶胀率的影响较大,且在酸性条件下的水凝胶的溶胀率远大于碱性条件下的溶胀率,包埋在此水凝胶中的牛血清蛋白（BSA）释放随载药介质的pH值的变化而显著不同,pH值1．0条件下载药的水凝胶释药率大于pH值7．4和9．18条件下的释药率。     

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pH 2.0和pH 7.0条件下,85 ℃加热12 h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乳液微观结构、盐离子稳定性和热稳定性。结果表明：WPI分别在pH 2.0和pH 7.0且高温加热条件制得2 种微观形貌截然不同的蛋白聚集体（纤维状聚集体和球状聚集体）,并且2 种蛋白聚集体相较于WPI等电点均发生偏移,在不同pH值或盐离子浓度环境下,乳化性能均提高。2 种聚集体所稳定的Pickering乳液对不同pH值、盐离子浓度环境下有更好的稳定性,球状聚集体所稳定的Pickering乳液具有更好的热稳定性。这也为WPI聚集体稳定的Pickering乳液在乳饮料中的应用奠定基础。     

FUNCTIONAL PROPERTIES OF HIGH HYDROSTATIC PRESSURE-TREATED WHEY PROTEIN

Surface hydrophobicity, solubility, gelation and emulsifying properties of high hydrostatic pressure (HHP)‐treated whey protein were evaluated. HHP treatment of whey protein buffer or salt solutions were performed at 690 MPa and initial ambient temperature for 5, 10, 20 or 30 min. Untreated whey protein was used as a control. The surface hydrophobicity of whey protein in 0.1 M phosphate buffers treated at pH 7.0 increased with an increase in HHP treatment time from 10 to 30 min. HHP treatments of whey protein in salt solutions at pH 7.0 for 5, 10, 20 or 30 min decreased the solubility of whey proteins. A significant correlation was observed between the surface hydrophobicity and solubility of untreated and HHP‐treated whey protein with r = ?0.946. Hardness of HHP‐induced 20, 25 or 30% whey protein gels increased with an increase in HHP treatment time from 5 to 30 min. An increase in the hardness of whey protein gels was observed as whey protein concentration increased. Whey proteins treated in phosphate buffer at pH 5.8 and 690 MPa for 5 min exhibited increased emulsifying activity. Whey proteins treated in phosphate buffer at pH 7.0 and 690 MPa for 10, 20 or 30 min exhibited decreased emulsifying activity. HHP‐treated whey proteins in phosphate buffer at pH 5.8 or 7.0 contributed to an increase in emulsion stability of model oil‐in‐water emulsions. This study demonstrates that HHP treatment of whey protein in phosphate buffer or salt solutions leads to whey protein unfolding observed as increased surface hydrophobicity. Whey proteins treated in phosphate buffers at pH 5.8 and 690 MPa for 5 min may potentially be used to enhance emulsion stability in foods such as salad dressings, sausage and processed cheese.     

VC脂质体水凝胶的制备及其消化特性研究

将脂质体和水凝胶结合,以卡拉胶和乳清分离蛋白通过酶和离子交联形成凝胶,将维生素C(VC)脂质体包埋于其中形成VC脂质体水凝胶.通过表征脂质体水凝胶在不同储存时间的磷(Pi)释放量和脂质氧化程度,以及模拟消化过程中的平均粒径及粒度分布,脂质体和乳清分离蛋白的降解,VC的释放量,研究脂质体水凝胶的储存稳定性和体外消化稳定性...     

Microstructure of Whey Protein Isolate Gels Containing Emulsified Butterfat Droplets

The effects of concentration and droplet size of anhydrous butterfat globules on the microstructure of heat-induced whey protein isolate gels (pH 4.60) were studied by scanning and transmission electron microscopy (TEM). All fat globules were emulsified with whey protein isolate and incorporated into the system prior to gelation. Protein aggregates became more closely packed as whey protein concentration was increased from 8 to 15% by weight in gels without added fat. There was no notable change in overall gel microstructure upon addition of fat globules, up to 25% by weight, when viewed by scanning electron microscopy. However, it appeared fat globules were intimately associated with the gel protein matrix. A twofold difference in fat globule size was obvious by TEM. Clusters of droplets became more predominant as butterfat content increased.     

Physical Properties of Mixed Dairy Food Proteins

Foods may contain more than one type of protein, and food formulators sometimes combine different proteins for desired synergistic textural benefits. Egg albumin, fish protein isolate, or soy protein isolate were blended with calcium caseinate or whey protein isolate and mixed in water adjusted to pH 2.5, 6.8, and 9.0 at 25 or 60°C. The effect of pH and temperature on solubility, viscosity, and the structure of the resulting gels were determined. The viscosity at the most soluble concentration at 25°C were: egg albumin (175.2 mPa.s/35 wt%), fish protein isolate (2207.4 mPa.s/30 wt%), soy protein isolate (2531.5 mPa.s/10 wt%), calcium caseinate (1115.8 mPa.s/15 wt%), and whey protein isolate (161.2 mPa.s/35%). In mixed protein systems viscosity values were reduced. The values for calcium caseinate or whey protein isolate with egg albumin, at the protein level of 15 g/100 g were: calcium caseinate/egg albumin (10:5 wt%) 535.1 mPa.s and whey protein isolate/egg albumin (10:5 wt%) 8.7 mPa.s. Microscopy imaging revealed changes in protein aggregation clusters during heating of calcium caseinate, egg albumin, and whey protein isolate. Egg albumin acted synergistically to increase viscosity, while fish protein isolate acted antagonistically to reduce viscosity. This knowledge is useful to manufacturers who may seek to enhance food texture by blending different proteins.     

Viscoelastic Properties of Whey Protein Gels: Mechanical Model and Effects of Protein Concentration on Creep

The creep behavior of gels made using different concentrations of whey protein isolate (WPI, >95% protein) was systematically determined. The creep curves of these gels conformed to a six element mechanical model consisting of one Hookean, two Voigt and one Newtonian component. The concentration and temperature dependence of each viscoelastic constant were examined and the data are discussed in terms of mechanisms involved in gel network structure.     

乳清蛋白菊粉糖基化复合物的褐变特性与抗氧化活性

以褐变程度及抗氧化活性为检测指标,研究湿热反应条件对乳清蛋白菊粉糖基化复合物的褐变特性与抗氧化活性的影响。研究结果表明:反应物浓度越大,反应温度越高,乳清蛋白菊粉糖基化产物的褐变强度越大,抗氧化活性越强;起始反应pH值越大,乳清蛋白菊粉糖基化产物的褐变强度及还原能力越强,而其DPPH.清除能力呈现先升高后降低的趋势。当反应物浓度为6%,温度为100℃,起始反应pH值为9时,所获得的乳清蛋白糖基化产物抗氧化活性较强。     

Formation of Elastic Whey Protein Gels at Low pH by Acid Equilibration

Abstract: Whey protein gels have a weak/brittle texture when formed at pH ≤ 4.5, yet this pH is required to produce a high-protein, shelf-stable product. We investigated if gels could be made under conditions that produced strong/elastic textural properties then adjusted to pH ≤ 4.5 and maintain textural properties. Gels were initially formed at 15% w/w protein (pH 7.5). Equilibration in acid solutions caused gel swelling and lowered pH because of the diffusion of water and H⁺ into the gels. The type and concentration of acid, and presence of other ions, in the equilibrating solutions influenced pH, swelling ratio, and fracture properties of the gels. Swelling of gels decreased fracture stress (because of decreased protein network density) but caused little change to fracture strain, thus maintaining a desirable strong/elastic fracture pattern. We have shown that whey protein isolate gels can be made at pH ≤ 4.5 with a strong/elastic fracture pattern and the magnitude of this pattern can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time. Practical Application: Low-pH shelf-stable whey protein gels having the strong/elastic texture can be made by forming gels at high pH and equilibrating in acid solutions. Acid equilibration causes the gel to swell and lower the gel pH. Moreover, gel properties can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time.     

Rheology of whey protein isolate-xanthan mixed solutions and gels. Effect of pH and xanthan concentration

Flow properties at pH 5.5-7.5 of whey protein isolate (WPI)-xanthan solutions containing 0-0.5 w/w% xanthan were studied by viscosimetry, although rigidity and fracture properties of the corresponding heat-set gels (90°C, 30 min) were determined by uniaxial compression. All the studied solutions displayed generalized shearthinning flow behaviour. Synergistic WPI-xanthan interactions has been revealed by observing that rheological parameters [σ_msf, K, n, η (γ)] characterizing blends were larger than those calculated from the two separated solutions. Such a behaviour was attributed to segregative phase separation of whey proteins and xanthan. Effects of xanthan on WPI-xanthan gel properties both depended on pH and xanthan concentration. Simultaneous increased xanthan concentration and decreased pH inhibited gelation of WPI-xanthan blends. Regarding gel strength, synergistic WPI-xanthan interactions were observed at pH >7.0 and low xanthan concentration (0.05 or 0.1 w/w%). Antagonism between the two macromolecules occurred at low xanthan concentration and pH ≤6.5, and high xanthan concentration (0.2 or 0.5 w/w%) at all pH tested. Low xanthan concentration rendered mixed gels more brittle than protein gels, and high xanthan concentration decreased pH effects on gel stress-strain relationships. The balance between strong thermal aggregation of concentrated whey proteins - in presence of incompatible xanthan -, high viscosity of blends and repulsive surface forces of protein molecules was thought to be at the origin of WPI-xanthan gel mechanical properties.     

Characterization of cold-set gels produced from heated emulsions stabilized by whey protein

This paper reports the cold gelation of preheated emulsions stabilized by whey protein, in contrast to, in previous reports, the cold gelation of emulsions formed with preheated whey protein polymers. Emulsions formed with different concentrations of whey protein isolate (WPI) and milk fat were heated at 90 °C for 30 min at low ionic strength and neutral pH. The stable preheated emulsions formed gels through acidification or the addition of CaCl₂ at room temperature. The storage modulus (G′) of the acid-induced gels increased with increasing preheat temperature, decreasing size of the emulsion droplets and increasing fat content. The adsorbed protein denatures and aggregates at the surface of the emulsion droplets during heat treatment, providing the initial step for subsequent formation of the cold-set emulsion gels, suggesting that these preheated emulsion droplets coated by whey protein constitute the structural units responsible for the three-dimensional gel network.