温度对乌鳢鱼皮胶原蛋白肽聚集体结构及理化特性的影响

研究乌鳢鱼皮胶原蛋白肽在20～52 ℃低温诱导下自组装体的结构稳定性与理化性质,比较分析聚集体变化过程中圆二色谱、自组装动力学、微观结构、凝胶强度、粒径、黏度、变性温度和红外光谱的变化。结果表明：在20～30 ℃温度范围内,升温对乌鳢鱼皮胶原蛋白肽自组装速率及聚集体稳定性具有促进作用,组装成核时间缩短13.5 min,形成的三维网络致密性增强,平均粒径增大,凝胶强度从50.23 g/cm2升高至212.55 g/cm2（P＜0.05）,最大剪切黏度增加549.34%,β-折叠相对含量增加45.42%,胶原蛋白肽结构稳定性显著增强;在30～52 ℃温度范围内,升温促使纤维网络结构发生溶解和絮集,凝胶强度降低97.87%（P＜0.05）,粒径降低46.16%,最大剪切黏度和β-折叠相对含量降低;差示量热扫描测定结果表明,聚集体自组装程度越高,其热稳定性越强。因此,适宜的温度可有效改善乌鳢鱼皮胶原蛋白肽纤维网络的结构稳定性及理化性质。     

草鱼皮胶原的体外自组装动力学研究

体外自组装是天然胶原的重要分子行为特征之一,并对胶原基产品性能产生显著影响。以草鱼皮酶溶性胶原蛋白为研究对象,重点开展胶原体外自组装动力学行为、影响因素、组装纤维的微观结构及其热稳定性能研究。浊度实验和自组装程度分析的结果表明,草鱼皮胶原蛋白具备体外自组装能力,其自组装进程受胶原质量浓度、pH值、离子强度、温度等因素的影响。在pH 7～8、胶原质量浓度3～5 mg/mL、体系温度25～30 ℃以及NaCl浓度0～200 mmol/L条件下胶原自组装进程较快、自组装程度较高;组装动力学分析的结果表明,在较高的离子强度（NaCl浓度300 mmol/L）和较低的组装温度（20 ℃）时,胶原组装进程表现为：成核、组装和平衡3 个阶段,而在较高组装温度（25～30 ℃）和较低离子强度时（NaCl浓度0～200 mmol/L）,胶原组装进程表现为：快速组装段、低速组装段和平衡段;胶原纤维形态学观察结果表明,草鱼皮胶原组装纤维具有典型的D周期特征但D周期长度值（64.6 nm）小于哺乳动物胶原纤维（约67 nm）;示差扫描量热法（differential scanning calorimetry,DSC）分析结果表明,经纤维重组后,草鱼皮胶原蛋白的热稳定性得到明显提升。     

阳离子可染聚酯的流变性能

为研究阳离子可染聚酯流变性能，使用毛细管流变仪以及旋转流变仪对特性黏度相近的普通聚酯及阳离子可染聚酯进行对比研究。结果表明：阳离子可染聚酯熔体与普通聚酯熔体一样表现出剪切变稀现象，为假塑性非牛顿流体。强极性磺酸基的引入使得分子间作用力变强且与基质极性的差距会使磺酸基之间聚集形成离子聚集体，所以阳离子可染聚酯熔体的黏度、结构黏度指数更高。可逆的离子聚集现象使得阳离子可染聚酯熔体对于温度、剪切速率的变化更加敏感。同时口模直径的增大使得熔体流动阻力、入口收敛流动、黏性耗散减少，造成阳离子可染聚酯熔体的剪切黏度上升，非牛顿指数增大，黏流活化能下降。旋转流变仪的实验结果说明，阳离子可染聚酯处于高温环境下时，磺酸基发生聚集且随着时间的延长而加剧，引起黏度的明显增大。     

离子强度对煮制前后猪肉胶原蛋白乳化特性的影响

为研究离子强度对煮制前后猪肉胶原蛋白乳化特性的影响,测定煮制前后不同NaCl浓度（0.0、0.2、0.4、0.6 mol/L）猪肉可溶性胶原蛋白和不溶性胶原蛋白的乳化特性,包括乳化活性指数（emulsification activity index,EAI）、乳化稳定性指数（emulsion stability index,ESI）、黏度及乳化液微观结构,同时测定猪肉胶原蛋白溶解度。结果表明：随着介质离子强度的提高,猪肉可溶性胶原蛋白溶解度降低,黏度增大,EAI先升高后降低,ESI先降低后升高;猪肉不溶性胶原蛋白溶解度升高,黏度增大,EAI、ESI均呈先升高后降低趋势。改变胶原蛋白的离子强度或对胶原蛋白进行热处理,均能使猪肉可溶性胶原蛋白和不溶性胶原蛋白的乳化特性发生显著变化。     

热处理温度和离子强度对汉麻蛋白热聚集行为的影响

目的 研究热处理和不同离子强度条件下汉麻蛋白的热聚集行为。方法 以汉麻籽为原料，考察在80、90、100℃热处理下，以及不同离子强度（0、0.2、0.4、0.6、0.8 mol/L NaCl溶液）下汉麻蛋白的ζ-电位、粒径、浊度、二级结构、凝胶电泳、巯基及二硫键等指标。结果 汉麻蛋白随着热处理温度的升高和离子强度的增大，ζ-电位绝对值降低、粒径增大、浊度增加；电泳图中在70 kDa处有聚集条带显示；红外光谱显示随着热处理温度升高，α-螺旋结构显著降低，β-折叠和无规则卷曲结构显著增大，β-转角的相对含量变化不大；随着离子强度增大，α-螺旋和β-转角结构显著降低，β-折叠结构增加，无规则卷曲变化不大；90℃热处理时游离巯基含量低于80℃和100℃，二硫键含量在80℃处理下最少；离子强度对汉麻蛋白总巯基影响不显著。结论 热处理温度的升高及离子强度增大对汉麻蛋白聚集行为具有促进作用，为汉麻蛋白热加工工艺优化和品质调控提供了理论基础。     

大豆球蛋白自组装聚集及凝胶特性

研究了在低pH值、低离子强度下,分别加热诱导不同浓度11S(大豆球蛋白)和7S(大豆伴球蛋白)自组装纤维化聚集体的形成。通过平均粒径和Thioflavin T(硫磺素T)荧光光谱,对自组装纤维化聚集体的性质进行表征,并对其热致凝胶的流变学,硬度和微结构特性进行考察。结果表明:在低pH值、低离子强度的诱导条件下,蛋白浓度对自组装聚集的形成起着关键作用,随着诱导浓度的增大,蛋白的纤维化聚集越明显,7S比11S更容易形成纤维化聚集。在酸性环境下,大豆球蛋白的纤维化聚集程度越高,越有利于热致凝胶网络结构的形成。在相同的预处理条件下,11S自组装凝胶硬度强于7S。扫描电镜结果显示7S自组装凝胶的网络结构较11S致密,但有序性较11S低。     

兔皮胶原蛋白的微观结构及不同因素对其聚集特性的影响

以兔皮胶原蛋白为原料,通过紫外光谱(UV)、红外光谱(FTIR)和扫描电镜(SEM)对兔皮胶原蛋白的微观结构进行了初步研究,在该基础上进一步研究了温度、胶原蛋白浓度、pH值和离子强度对其聚集特性的影响。紫外光谱和红外光谱的峰型及对应波长均符合Ⅰ型胶原蛋白的特征,电镜扫描观察到兔皮胶原蛋白为不规则的致密片状膜,部分表面褶皱;聚集特性研究表明,胶原蛋白浓度与测定温度升高,胶原蛋白的聚集速度和聚集程度均增加;在酸性环境中,胶原蛋白聚集时间较长;pH由7增至8的过程中,胶原蛋白的聚集程度先增加后降低,在pH 7.2时,聚集程度和速度均最高;随着离子浓度的增加,聚集程度和聚集速度先增加后降低,在NaCl浓度为120mmol/L时聚集速度最快,且自组装程度最高。     

糖基化对β-伴大豆球蛋白热聚集行为的影响研究(I)

基于Maillard反应的机理,采用干热法分别制备出7S和不同分子量葡聚糖(67 kD,150 kD、500 kD)的三种糖基化产物,从糖基化产物的热性质分析到热聚集体的浊度、粒径,研究了糖基化对于7S在pH和离子强度诱导下的热聚集行为.结果显示,糖基化具有抑制7s热聚集行为的作用,并且葡聚糖在分子量为67 kD和150 kD时的糖基化产物抑制效果相近且优于分子量为500 kD的葡聚糖糖基化产物.     

不同离子强度大豆分离蛋白热诱导聚集体的研究

目的:研究离子强度对大豆分离蛋白热诱导聚集的影响.方法:采用可见分光光度计,在波长600 nm处测定不同离子强度下的大豆分离蛋白热处理溶液的吸光值,并将其作为溶液的浊度;采用体积排阻色谱(SECHPLC)、动态激光光散射(DLS)及zeta电位仪研究不同离子强度下大豆分离蛋白热诱导聚集体的分子质量分布、粒径分布及zeta电位.结果:随着离子强度的增加,大豆分离蛋白聚集体溶液的浊度增加,体系的聚集体部分及平均流体动力学半径(Rh)大幅增加,zeta电位逐渐降低.结论:电荷屏蔽作用使分子间斥力降低,促进了高离子强度下聚集的产生.     

糖基化对β-伴大豆球蛋白热聚集行为的影响研究(Ⅰ)

基于Maillard反应的机理,采用干热法分别制备出7S和不同分子量葡聚糖(67kDa、150kDa、500kDa)的三种糖基化产物,从糖基化产物的热性质分析到热聚集体的浊度、粒径,研究了糖基化对于7S在pH和离子强度诱导下的热聚集行为。结果显示,糖基化具有抑制7S热聚集行为的作用,并且葡聚糖在分子量为67kDa和150kDa时的糖基化产物抑制效果相近且优于分子量为500kDa的葡聚糖糖基化产物。     

Characterisation of sodium caseinate as a function of ionic strength, pH and temperature using static and dynamic light scattering

Extensive static and dynamic light scattering (DLS) measurements were done on sodium caseinate solutions as a function of the ionic strength (3–500 mM NaCl), pH (5–8) and temperature (10–70 °C). DLS results were analysed in terms of two populations: the caseinate and a small weight fraction of large particles with a hydrodynamic radius (R_h) of about 65 nm that was independent of the ionic strength, pH and temperature. Caseinate was present as individual molecules at low ionic strength (3 mM), but formed small aggregates (R_h=11 nm) at high ionic strength (>100 mM). The aggregation number (N_agg) increased weakly with decreasing pH between pH 8 and 6, but extensive acid-induced aggregation occurred below pH 5.4 at 250 mM and below pH 6.0 at 3 mM. N_agg increased reversibly with increasing temperature.     

Influence of Jet‐Cooking Temperature and Ionic Strength on Size and Structure of Cationic Potato Amylopectin Starch as Measured by Asymmetrical Flow Field‐Flow Fractionation Multi‐Angle Light Scattering

Asymmetrical flow field‐flow fractionation (AsFlFFF) in combination with multi‐angle light scattering (MALS) was applied to cationic potato amylopectin (CPAP) to investigate how molar mass, root‐mean‐square (r.m.s.) radius and shape was influenced by different conditions of jet‐cooking. The effect of different jet‐cooking temperatures in the range 110°C – 140°C was studied in an excess steam jet‐cooker. This equipment is used in the industry for dissolution of starch and starch derivatives before technical application. The effect of different ionic strengths conditions was examined in the range of 10–200 mM. The weight‐average molar mass decreased from about 34×10⁷ g/mol to 2.6×10⁷ g/mol when the jet‐cooking temperature was increased from 110°C to 140°C. Concurrently the root‐mean‐square radius decreased from ca 380 nm to 90 nm. The decrease in size was reflected by a decrease in viscosity with increasing temperature. The root‐mean‐square radius was reduced when increasing the ionic strength. This decrease in size was correlated with a decrease in viscosity. Conformation and Kratky plots showed that at low ionic strength (≤ 10 mM) CPAP behaved as a flexible chain with high degree of branching, close to hyperbranching. Increase of the ionic strength gave a more compact structure and changes in the internal structure were observed as well. Consequently, by using AsFlFFF – MALS the effect of technical processing on the molar mass, molecular radius, conformational structure, and shape could be determined in a size region where standard methodology commonly fails.     

壳聚糖溶液的流变学性质及应用研究

对壳聚糖稀溶液的流变学性质进行了研究,探讨了分子量和脱乙酰度结构参数以及温度、浓度、剪切速率、pH、离子强度等环境因素对壳聚糖稀溶液流变性质的影响。结果表明:壳聚糖溶液的黏度随分子量的增大而增大;随着脱乙酰度的增大和pH的增大,壳聚糖溶液的黏度先减小后增大,分别在脱乙酰度70.8%和pH4.9时黏度达到最小;离子强度的增大导致壳聚糖溶液的黏度降低。壳聚糖溶液是剪切变稀的假塑性流体,其黏度随浓度的增加逐渐增加,随温度的升高而减小,在0~80℃范围内,温度对壳聚糖溶液的黏度的影响符合Arrhenius模型,活化能为32.60kJ/mol。因此当作为食品增稠剂时,应该选用高分子量、高脱乙酰度的壳聚糖,添加到酸性低盐食品体系中。     

猕猴桃糖蛋白及其去糖链蛋白功能特性的研究

本文研究了25~60 ℃范围内温度对猕猴桃糖蛋白(CGP)及其去糖链蛋白(GPP)吸油性、溶解性、起泡性和乳化性的影响,以及CGP、GPP的浓度及其溶液pH3~7.5和0~5 g/100 mL范围的NaCl离子强度对CGP和GPP溶解性、起泡性和乳化性的影响。结果表明:25~60 ℃温度范围内CGP吸油性、溶解度高于GPP,随温度升高,CGP、GPP溶解度下降,两者的起泡性先降低后升高,CGP乳化性先降低后升高,GPP乳化性先升高后降低;不同pH条件下,CGP的溶解度始终高于GPP,pH3~6范围内CGP、GPP溶解度均先下降后升高,pH3~7.5范围内CGP、GPP起泡性和乳化性先下降后升高;随离子强度的升高,CGP、GPP溶解度均下降,且CGP的溶解度始终高于GPP,CGP的起泡性和乳化性下降,GPP起泡性先下降后升高而乳化性则相反;CGP、GPP起泡性和乳化性均随其浓度的增高而增高,1.0 mg/mL时起泡性和乳化性最高,0.2 mg/mL时最低。     

Effect of concentration,ionic strength and freeze-drying on the heat-induced aggregation of soy proteins

The effects of protein concentration, ionic strength, and lyophilization on heat-induced aggregation of soy proteins were analyzed by SDS-PAGE, SEC-HPLC and laser light scattering (LLS). SDS-PAGE profile suggested that the aggregates were formed via non-covalent forces and/or disulfide bonds. At ionic strength of zero, SEC-HPLC revealed that the samples were composed of three major fractions: aggregates, intermediate fractions and non-aggregated molecules. Furthermore, the relative proportion of the aggregate fraction increased as protein concentration increased. Similarly, LLS indicated that the average hydrodynamic radius (R_h) increased at higher protein concentration. In sample with an ionic strength of zero, the intermediate fraction decreased after freeze-drying with a concomitant increase of the aggregate fraction. When the sample was heated at elevated ionic strength, the SEC-HPLC and LLS profiles changed substantially, the intermediate fractions decreased, and lyophilization had effect on the fraction of aggregates. These experiments suggest novel strategies for producing soy protein aggregates with controlled properties.     

Emulsion properties of algae soluble protein isolate from Tetraselmis sp.

To study possible applications of microalgae proteins in foods, a colourless, protein-rich fraction was isolated from Tetraselmis sp. In the present study the emulsion properties of this algae soluble protein isolate (ASPI) were investigated. Droplet size and droplet aggregation of ASPI stabilized oil-in-water emulsions were studied as function of isolate concentration (1.25–10.00 mg/mL), pH (3–7), and ionic strength (NaCl 10–500 mM; CaCl₂ 0–50 mM). Whey protein isolate (WPI) and gum arabic (GA) were used as reference emulsifiers. The lowest isolate concentrations needed to reach d₃₂ ≤ 1 μm in 30% oil-in-water emulsions were comparable for ASPI (6 mg/mL) and WPI (4 mg/mL). In contrast to WPI stabilized emulsions ASPI stabilized emulsions were stable around pH 5 at low ionic strength (I = 10 mM). Flocculation only occurred around pH 3, the pH with the smallest net droplet ζ-potential. Due to the charge contribution of the anionic polysaccharide fraction present in ASPI its droplet ζ-potential remained negative over the whole pH range investigated. An increase in ionic strength (≥100 mM) led to a broadening of the pH range over which the ASPI stabilized emulsions were unstable. GA emulsions are not prone to droplet aggregation upon changes in pH or ionic strength, but much higher concentrations are needed to produce stable emulsions. Since ASPI allows the formation of stable emulsions in the pH range 5–7 at low protein concentrations, it can offer an efficient natural alternative to existing protein–polysaccharide complexes.     

Fabrication of viscous and paste-like materials by controlled heteroaggregation of oppositely charged lipid droplets

This study describes the formation of materials with novel textural characteristics by controlled heteroaggregation of oppositely charged protein-coated lipid droplets. Heteroaggregation was induced by mixing a suspension of β-lactoglobulin (β-Lg)-coated lipid droplets (ζ = −51 mV, d₄₃ ∼ 0.35 μm, 20 wt.%) with a suspension of lactoferrin (LF)-coated lipid droplets (ζ = +32 mV, d₄₃ ∼ 0.35 μm, 20 wt.%) under conditions where the two proteins had opposite charges (pH 7). The mean particle size, flow behaviour, and shear modulus of the materials depended on positive-to-negative particle ratio (0–100%), pH (3–9), ionic strength (0–400 mM), and temperature (30–90 °C). The largest particle sizes, highest viscosities, and largest gel strengths were observed at intermediate particle ratios (40% LF:60% β-Lg), which was attributed to a strong electrostatic attraction between oppositely charged droplets (0 mM NaCl, pH 7, 25 °C). A reduction in particle aggregation, viscosity, and gel strength occurred at intermediate ionic strengths due to screening of the electrostatic attraction between oppositely charged droplets. However, increased aggregation, thickening, and gelation occurred at higher ionic strengths due to screening in electrostatic repulsion between similarly charged droplets. Thermal treatment of the samples (90 °C) promoted a substantial increase in gel strength due to protein denaturation and increased droplet attraction. This study has important implications for the utilisation of controlled particle aggregation to create novel structures in foods, cosmetics, personal care, and other products.     

Thermal aggregation and gelation of kidney bean (Phaseolus vulgaris L.) protein isolate at pH 2.0: Influence of ionic strength

Thermal aggregation and gelation of kidney bean protein isolate (KPI) at pH 2.0 and varying ionic strengths (0–300 mM) were investigated using dynamic light scattering (DLS), atomic force microscopy (AFM), and turbidity and dynamic oscillatory measurements. DLS and AFM analyses showed that the extent of thermal aggregation at pH 2.0, or contour length of the worm-like and fine-stranded aggregates, progressively increased with increasing ionic strength. Turbidity and dynamic rheological analyses indicated that, the turbidity and mechanical moduli of the formed gels also increased with the increase in both ionic strength and protein concentration (c). The c dependence of the elastic modulus G′ could be well described using both fractal and percolation models, though in the case of fractal model applied, two distinct scaling regimes were observed. These results suggest that at pH 2.0, the thermal aggregation and gelation behaviors of the proteins in KPI could be remarkably affected by a change in electrostatic repulsion, and homogenous fine-stranded gels formed at ionic strengths in the 0–300 mM range.