Creep/Recovery Behavior of Oil-Water Emulsions: Influence of Disperse Phase Concentration

The rheological (creep/compliance) behavior has been studied for a series of soya oil (soybean oil)-water emulsions with the disperse phase (oil) concentration ranging from 20% to 70%. The compliance response was due to three mechanisms: instantaneous elastic, retarded elastic and viscous flow. It was necessary to postulate the presence of two retardation processes to account for the Theological behavior. As the oil concentration was increased, the emulsions became more elastic, with the instantaneous elastic mechanism becoming more dominant. In the non-linear region, the viscous flow was more dominant, with the emulsions becoming less elastic with increasing shear stress. The results are rationalized in terms of the breaking and reforming of bonds in the network like coagulation structure.     

Effects of Constituent Concentration on Rheological Properties of Corn Oil-In-Water Emulsions

Rheological properties were studied with a tube viscometer. Emulsifying agents were soy lecithin and Tween 20. The volume concentration of dispersed phase, φ, ranged from 0.32-0.62. The emulsions behaved as pseudoplastic fluids. The flow behavior index, n, of the lecithin emulsions increased slightly with increasing φ and concentration of emulsifying agent, C_e. However, the n values of Tween 20 emulsions were nearly constant. Apparent viscosity of the emulsions increased with increase of φ and C_e. With φ constant the apparent viscosity was still strongly affected by C_e.     

Concentration and Temperature Dependence of Flow Behavior of Xanthan Gum Dispersions

Apparent viscosities of xanthan gum dispersions over shear rates of 0.5–3000s^?1 were studied at concentrations of 0.05–1.00% (w/w) and temperatures of 5–45°C. All dispersions were shear rate thinning non-Newtonian fluids described accurately by the power-law model. The logarithm of viscosity varied with the logarithm of concentration and the reciprocal of absolute temperature. A combined model was derived to describe the variation of viscosity with shear rate, concentration and temperature for aqueous dispersions of xanthan gum.     

Effect of Xanthan Gum Upon the Rheology and Stability of Oil-Water Emulsions

Soyabean oil-water emulsions were studied. In oil-water emulsions (up to 60% oil) xanthan is essential to prevent creaming. A yield stress arises primarily from the polysaccharide liquid crystalline structure. In concentrated systems where the oil droplets interact strongly there is a significant contribution to the yield stress arising from the need to modify individual droplet shapes when shear is applied to the system. Studies of droplet sizes suggest that the xanthan gum can also modify the equilibrium droplet size by lowering the oil-water interfacial tension.     

乳化剂、油浓度及油滴粒径对乳状液中油脂氧化稳定性的影响

以过氧化值(POV)为指标,研究了乳化剂类型、油浓度及油滴粒径对O/W乳状液中油脂氧化稳定性的影响.以用十二烷基硫酸钠(SDS)和Tween-80为乳化剂制备的含红花籽油的乳状液为研究对象,结果表明,乳化剂类型和油浓度对乳状液体系中油脂氧化有较显著的影响.用阴离子型表面活性剂SDS稳定的乳状液中的油脂氧化速率明显大于用非离子型Tween-80稳定的乳状液;随着油浓度下降,油脂氧化速率增大.油滴粒径和油脂氧化速率没有显著的相关性.     

Correlation of the Rheological Behavior of Egg Albumen to Temperature, pH, and NaCl Concentration

Rheological parameters of viscosity, gel strength, and elasticity were determined on heat-set egg albumen gels over various treatment combinations ranging from 65-90°C, pH 6.4-9.6, and NaCl concentrations of 0.0-0.1M added NaCl. Maximum viscosity was measured at a treatment combination of 77.5°C, pH 8.00, and 0.1M NaCl. Elasticity and gel strength were highest in gels with a treatment combination of 85.2°C, pH 9.0, and 0.08M NaCl. Temperature had the greatest effect on all three rheological parameters. Gels heated above 80°C were of unusual character, exhibiting syneresis and shrinkage.     

肉桂酸基油脂凝胶的制备及其流变特性和结晶特性分析

选择米糠油为溶剂体系,肉桂酸作为凝胶剂制备油脂凝胶,借助流变仪、X-射线衍射仪、荧光显微镜研究其流变特性及结晶特性。结果表明：米糠油凝胶的持油性和熔点随肉桂酸添加量的增加逐渐增加,当肉桂酸添加量超过10%,油脂凝胶的持油性和熔点增加不显著（P＞0.05）;米糠油凝胶的持油性随加热温度升高迅速上升,在85?℃时升高至93.62%,此时的凝胶熔点也相对较高;当冷却温度从0?℃升高至5?℃时,凝胶的持油性和熔点相对较高,当冷却温度进一步升高,凝胶的持油性和熔点显著下降至93%（P＜0.05）。通过对肉桂酸添加量10%、加热温度85?℃、冷却温度5?℃形成的油脂凝胶进行流变学特性分析,发现该油脂凝胶呈现假塑性流体状态,样品的表观黏度-剪切速率的关系符合幂律方程关系;并且在频率扫描范围内,油脂凝胶体系的储能模量（G’）明显大于损耗模量（G”）,样品形成较为紧密的凝胶结构;通过凝胶结晶特性分析发现,米糠油凝胶中的结晶结构细小,分布均匀,存在同质多晶现象,主要含有β和β′?2?种晶体类型。     

共混可润湿聚丙烯的流变性能研究

共混可润湿聚丙烯流体的流动特征与常规聚丙烯相似 ,为典型的假塑性流动 ,其非牛顿指数随剪切速率的增大而减小 ,表观粘度和粘流活化能随共混比的增大而减小     

Rheological Behavior of Comminuted Meat Batters

Good agreement was observed between the shear stress-shear rate results obtained with a capillary extrusion viscometer and the yield stress as determined with a rotational viscometer. The frankfurter batter used in this study was pseudoplastic with a flow behavior index of 0.2–0.4, and a yield stress of approximately 840 Pa at 10°C. To compare the effects of batter composition, an apparent viscosity term was defined. Dilution of the batter resulted in reduced apparent viscosities, while increased fat led to increased apparent viscosities. Although chopping time significantly altered the stability of the batter and the visco-elastic properties of the cooked product, no significant difference in the apparent viscosity was detected. This observation was discussed in light of the apparent insensitivity of viscosity measurements to the degree of fat comminution.     

中国大鲵油脂肪酸组成、抗氧化及流变性研究

分析中国大鲵油的脂肪酸组成,并研究大鲵油抗氧化和流变学行为,提供大鲵油开发利用的基础理论.通过气相色谱/质谱联用技术分析大鲵油的脂肪酸组成;Schaal烘箱法(63±1)℃研究大鲵油的抗氧化特性;流变仪测定大鲵油和花生油不同配比(100:0,75:25,50:50,25:75,0:100)的黏度和剪切应力随剪切速率的变化情况.GC-MS分析结果表明:大鲵油主要含13种脂肪酸(24.2%C18:1,15.4%C16:0,13.7%C16:1,8.2%C18:2,6.7%C20:5,4.5%C18:3,4.3%C22:6,3.0%C14:1,2.8%C18:0,2.6%C22:5,2.2%C20:4,2.0%C17:0,1.9%C17:1),饱和脂肪酸(SFA)为20.2%,单不饱和脂肪酸(MUFA)为42.8%,多不饱和脂肪酸(PUFA)为28.5%,ω-6型PUFA为13.0%,ω-3型PUFA为15.5%.Schaal烘箱法研究结果表明:抗氧化剂二丁基对甲苯酚(BHT)、没食子酸丙酯(PG)、特丁基对苯二酚(TBHQ)对大鲵油均有抗氧化作用,其中特丁基对苯二酚抗氧化效果较佳.流变性分析结果表明:大鲵油及其与花生油75:25、25:75配比的黏度随剪切速率的增加变化不大,二者50:50的配比黏度显著降低,大鲵油及其和花生油不同配比呈牛顿流体特性.     

含有改性纳米CaCO3的纸张涂料的流变行为

以阳离子表面活性剂、偶联剂及脂肪酸为表面改性剂获得表面性能不同的3种纳米CaCO3改性产品。用透射电镜桨相关化学分析方法表征了改性纳米CaCO3的界面行为。将改性纳米CaCO3加入纸张涂料体系中,制得不同配方的纸张涂料,并对涂料的静态流动性能和动态黏弹性进行了研究。结果表明,与加入普通CaCO3的传统涂料相比,含纳米CaCO3的纸张涂料具有较高的表观黏度、动态弹性模量和黏性模量,相位角则较低。表面亲油疏水的纳米CaCO3能够很好地与胶乳、增稠剂等聚合物胶体结合,弹性模量较大;而表面亲水的纳米CaCO3所制得的纸张涂料动态黏弹性较小。     

Effect of Ultra-high-pressure Homogenization on Structure and on Rheological Properties of Soy Protein-stabilized Emulsions

ABSTRACT: An ultra high-pressure homogenizer (20 to 350 MPa) was used to realize fine food emulsions stabilized by soy proteins. The first aim of the work was to understand how dynamic high-pressure processing affects soybean globulin conformation. Then, the effect of homogenizing pressure on the emulsions structure and rheology was investigated. High-pressure homogenization caused denaturation of proteins due to strong mechanical forces and high temperatures encountered in the valve. Droplet sizes of emulsions were greatly reduced with high-pressure homogenization and Newtonian liquid emulsions were converted into shear-thinning emulsion gels by homogenization at pressures above 250 MPa. Hydrophobic interactions between proteins were supposed to cause the gel-like network structure of emulsions.     

不饱和脂肪酸对猪肉蛋白质乳化特性的影响

研究不同饱和程度且不同添加量的脂肪酸对全肉盐溶性蛋白乳化特性、流变特性以及Zeta电位等影响。结果显示：脂肪酸添加量越大,乳化液的乳化活性越强,而乳化液的分层现象越严重;添加油酸和亚油酸可以明显增加乳化液的表面活性巯基;各乳化液粒度分布曲线均呈现“单峰”型,且较空白组的分布均向粒径较小的范围偏移;此外,随着剪切速率的增大,各乳化液黏度均逐渐减小,最后趋于平缓,在同一剪切速率下,添加量越大,乳化液剪切应力越大;Zeta电位值显示,荷电粒子不稳定。总之,C18的脂肪酸饱和程度越大,添加量越多,猪肉盐溶性蛋白质乳化的效果越好,在脂肪酸液滴表面形成蛋白膜的能力就会越强,使得乳化液的乳化特性越好。     

紫苏籽油双层乳状液的制备及其物理化学稳定性评价

采用紫苏籽油为芯材,大豆多糖和壳聚糖为壁材,分别制备紫苏籽油单层与双层乳状液,并且对乳状液的粒径、Zeta电位、物理稳定性以及化学稳定性进行评价。结果显示,单层乳状液粒径随着芯壁比（质量比）的升高而增大,物理稳定性变差,最适的芯壁比（质量比）为2∶1;随着壳聚糖质量分数的增加,双层乳状液的Zeta电位逐渐增大,并且由负值变为正值,壳聚糖质量分数为0.2%时电位绝对值最小为3.6 mV,当壳聚糖质量分数为0.4%时电位为43 mV,电位增加速率变小;随着壳聚糖质量分数的增加,乳状液粒径呈先减小、再增大、再减小的变化,壳聚糖质量分数为0.2%时达到最大粒径为5.21 μm,0.4%时达到最小粒径为1.185 μm;随着壳聚糖质量分数的增加乳状液物理稳定逐渐增强。壳聚糖质量分数对乳状液化学稳定性影响显著（p＜0.05）,抗氧化效果依次为0.4%＞0.6%＞0.2%。     

Rheological Properties of Solutions and Emulsions Stabilized with Xanthan Gum and Propylene Glycol Alginate

The rheological effects of propylene glycol alginate (PGA) added to solutions and model emulsions containing xanthan gum (XG) were studied using controlled stress rheometry with concentrations appropriate for salad dressings. For samples with XG and XG + PGA blends, solutions and emulsions showed a Newtonian plateau at low shear stresses. The Newtonian plateau of a solution accurately predicted (r²= 1.00) the Newtonian plateau for an emulsion of equivalent gum concentration. Addition of PGA to constant levels of XG showed a more than additive increase in the Newtonian plateau viscosity for solutions and emulsions. For XG aqueous solutions, pseudoplasticity decreased upon addition of PGA. Storage and loss moduli increased with addition of PGA to XG for solutions and emulsions, although G’ for solutions of PGA alone were negligible.     

Rheological Behavior of Tomato Juice: Steady-State Shear and Time-Dependent Modeling

Introduction  

The present work has evaluated the time-dependent and steady-state shear rheological properties of tomato juice.     

Refractive Index of the Dispersed Phase in Oil-in-Water Emulsions: Its Dependence on Droplet Size and Aging

A simple method of determining the refractive index of the dispersed phase was applied on different gum-stabilized oil-in-water emulsions, in which this refractive index is taken to be equal to that of the continuous phase at (extrapolated) zero optical density point. Refractive indices of dispersed phases were usually lower than those of the oil part alone. In dilute emulsions, the refractive index of the dispersed phase increased with time, while optical density of emulsion decreased. In aged concentrated emulsions, both refractive index and optical density decreased with time. At a given composition, the refractive index and optical density varied directly with droplet size. The results are interpreted in terms of reasonable physical and chemicl phenomena.     

Effect of Tomato Paste on Rheological Properties and Particle Size Distribution of Model Oil-in-Water Emulsions

The role of tomato paste in stabilizing model o/w salad dressing formulations pre-stabilized with xanthan and propylene glycol alginate was studied at levels of tomato paste ranging from 3 to 12% using creep measurements, steady shear measurements and particle size measurements. The addition of tomato paste shifted the particle size distribution to lower values; this distribution was a function of aging time. Creep and steady shear measurements showed an increase in rheological parameters and an increase in viscosity, respectively, suggesting that at higher or equal levels of 6% tomato paste the stability of the o/w emulsion was enhanced significantly.