Thermal and rheological properties of L-polylactide/polyethylene glycol/silicate nanocomposites films

The melt rheology and thermal properties of polylactide (PLA)-based nanocomposite films that were prepared by solvent casting method with L-PLA, polyethylene glycol (PEG), and montmorillonite clay were studied. The neat PLA showed predominantly solid-like behavior (G' > G″) and the complex viscosity (η*) decreased systematically as the temperature increased from 184 to 196 °C. The elastic modulus (G') of PLA/clay blend showed a significant improvement in the magnitude in the melt, while clay concentration was at 6% wt or higher. At similar condition, PEG dramatically reduced dynamic modulii and complex viscosity of PLA/PEG blend as function of concentration. A nanocomposite blend of PLA/PEG/clay (74/20/6) when compared to the neat polymer and PLA/PEG blend exhibited intermediate values of elastic modulus (G') and complex viscosity (η*) with excellent flexibility. Thermal analysis of different clay loading blends indicated that the melting temperature (T(m)) and glass transition temperature (T(g)) remained unaffected irrespective of clay concentration due to immobilization of polymer chain in the clay nanocomposite. PEG incorporation reduced the T(g) and the T(m) of the blends (PLA/PEG and PLA/PEG/clay) significantly, however, crystallinity increased in the similar condition. The transmission electron microscopy (TEM) image of nanocomposite films indicated good compatibility between PLA and PEG, whereas clay was not thoroughly distributed in the PLA matrix and remained as clusters. The percent crystallinity obtained by X-ray was significantly higher than that of differential scanning calorimeter (DSC) data for PLA.     

Dynamic Rheological Properties and Microstructure of Partially lnsolubilized Whey Protein Concentrate Gels

Viscoelasticity and microstructure of gels prepared with four whey protein concentrates (WPC) with solubilities from 27.5 to 98.1% in 0.1M NaCl, pH 7.0 were evaluated. Dynamic moduli were determined while 16% (w/w protein) WPC in 0.6M NaCl, pH 7.0, was heated isothermally at 90°C for 15 min. Storage moduli (G′) increased and tangent δ decreased when 80.0 and 98.1% soluble WPC were heated, whereas G' and tangent δ of 27.5 and 41.0% soluble WPC did not change. The 27.5% soluble WPC had the highest G' throughout the heating period. Rheological measurements suggested that globular aggregates observed in 80.0% and 98.1% soluble WPC were formed during heating, whereas aggregates in 27.5 and 41.0% WPC were present prior to heating.     

Soybean Protein Dispersions at Acid pH. Thermal and Rheological Properties

The influence of pH, protein concentration, and ionic strength, on rheological properties of thermally treated acidic soy protein dispersions, was studied. Structural changes due to pH effect and thermal treatment were analized. DSC-thermograms at pH 3.5 showed a shoulder at 74.11±0.16°C that could be attributed to both β-conglycinin and the hexameric form of glycinin; and a peak at 81.88±0.29°C corresponding to 11S dodecameric form. At pH 2.75 one endotherm corresponded to denaturation of β-conglycinin. The acidic dispersions presented pseudoplastic behavior with_app values higher than those at pH 8.0. At pH 3.50 the ±_app was higher than at pH 2.75.The maximum viscoelasticiy was obtained with addition of 0.1 and 0.25M NaCl in the dispersions of pH 3.50 and 2.75, respectively. The increase in viscoelasticity was enhanced by the formation of 11S native fraction dimers.     

Dynamic Rheological and Thermal Properties of Soft Wheat Flour Dough Containing Structured Lipid

ABSTRACT: The effect of substituting canola oil/caprylic acid structured lipid for shortening (at 0%, 25%, 50%, 75%, and 100% levels) on the viscoelastic and thermal properties of soft wheat flour dough (28.4% total lipid, 43% moisture) was determined using dynamic rheological and differential scanning calorimetry tests. Ambient frequency scans produced higher G" (loss modulus) and G' (storage modulus) values at increasing frequencies. Temperature scans revealed rapid G" and G' increases for dough heated to above 56 °C, apparently because of starch gelatinization. Three differential scanning calorimetry endothermic peaks were observed at 54 °C, 69 °C, and 93 °C, which were attributed to shortening transition and gelatinization of starch granules.     

白鲢鱼糜流变特性的研究

本实验利用ARES-RDA流变仪,通过动态振荡测量,研究了不同温度和浓度下的白鲢鱼糜的流变特性、凝胶过程及动态粘弹性的变化规律。结果表明白鲢鱼糜的粘度随剪切速率增大而减小,存在剪切变稀行为;鱼糜的动态剪切模量(包括弹性模量和损耗模量)在5℃和10℃时几乎与动态频率(f)(2～16Hz)无关,其中G’远高于G’’,20℃时,当动态频率(f)>8Hz,糊状鱼糜的动态剪切模量与动态频率有关,随着频率的增加而增加;温度扫描(温度范围:5～70℃)结果表明鱼糜凝胶过程经历了三个阶段:第一段在30℃之前,第二段出现在38～43℃,第三段出现在46℃之后,蛋白开始形成了最终的凝胶。该结果为进一步扩宽白鲢鱼糜的应用范围有一定的借鉴意义。     

Dynamic Rheological Properties of Mozzarella Cheese During Refrigerated Storage

Storage (G′) and loss (G″) moduli of low-moisture, part-skim Mozzarella cheese were determined at 10 and 20°C during 1 mo of refrigerated aging. At both temperatures, G′ was always greater than G″. Averaged over aging, G′ increased from 90 to 630 and G″ from 44 to 52 kPa at 10°C, and at 20°C G′ increased from 28 to 190 and G″ from 14 to 53 kPa for the frequency range 0.005-20 Hz. Averaged over frequency, both G′ and G″ decreased about 20% at 10°C and 25% at 20°C during aging. Relaxation spectrum, computed from shear relaxation data, was used to calculate the G. The calculated values of G′ were in good agreement with those determined experimentally. These data help predict and compare melting behaviors of such cheeses.     

淀粉糊流变特性研究新进展

对淀粉糊和改性淀粉糊的流变特性研究分别进行了综述,详细介绍了各因素对淀粉糊的流变特性的影响以及不同物理化学改性方法对淀粉糊的流变特性的影响,指出今后应着重于淀粉糊流变特性各个影响因素的研究,获得各个因素对流变性能影响的规律,以开拓淀粉的广阔的应用前景。     

初乳的流变学特性研究

研究了２０～６０℃区间内ｌｎηｒ和总干物质、ｌｎηｒ和１／Ｔ的关系，得出温度在２０～３５℃时，ｌｎηｒ＝０．１４４Ｃ＋２．８１２×１０３１Ｔ－１０．８５及３５～６０℃时，ｌｎηｒ＝０．１４４Ｃ＋２．０５６×１０３１Ｔ－８．４２的关系式。依据上式能够很好地表征２０～６０℃区间内初乳的流变学特征受温度和总干物质的影响情况。     

4种马铃薯淀粉糊流变特性的研究

对4种不同加工方式获得的马铃薯淀粉糊流变特性进行了探讨。静态流变特性测定结果表明,4种淀粉糊的流变模型为幂率模型,均为假塑性流体,每种淀粉糊以相同方式流动需要施加的力不同。在相同流动方式下,淀粉4粘度最大,其次为淀粉2,淀粉1和淀粉3的粘度近似相同。动态流变特性测定结果表明:随着温度的增加,淀粉1、2、4的弹性模量、粘性模量刚开始基本不发生变化,到60℃后,两模量急剧增加到最大值,然后降低到某恒定值。淀粉3的两模量随温度升高逐渐增加到最大值,然后逐渐降低到某恒定值。粘性模量达到最大后,淀粉2的粘性模量最大,其次为淀粉4、淀粉1,淀粉3的最低。弹性模量达到最大后,淀粉4的弹性模量最大,其次为淀粉2、淀粉1,淀粉3最低。     

The Composition,Rheological and Thermal Properties of Tajonal (Viguiera Dentata) Mexican Honey

Samples of Tajonal honey (Viguiera dentata) from Yucatan, Mexico with different moisture contents were studied for their physicochemical, crystallization, rheological, and thermal characteristics. The presence of crystals changed the flow behavior from Newtonian to non-Newtonian. A characteristic glass transition temperature (Tg') was found for each sample, and it was observed to be dependent of the initial moisture content but independent of the storage period. The temperature and latent heat of fusion were not affected by the crystallization phenomenon, while both the moisture content and the glucose/water ratio were useful indexes for crystal growth in honey. Crystallization process can be controlled by harvesting the product with higher moisture contents without exceeding the limits established by international regulations.     

板栗糊饮料流变学特性研究

在保留板栗全营养成分的基础上,研究板栗糊体系的贮藏稳定性。本文利用流变仪考察加入黄原胶、卡拉胶、CMC及复合稳定剂的板栗糊流变学特性与贮藏稳定性的关系。设定剪切速率在2.0~200 s^-1之间,角频率范围在0.1~100 Hz之间,测定其在4℃冷藏和25℃常温条件下静态与动态流变特性。研究表明:在贮藏50 d内,加入复合稳定剂的板栗糊品质最佳,其黏度变化范围为0.2~6.6 Pa·s,剪切应力范围为4~12 Pa。当温度从4℃升至40℃时,板栗糊表观黏度从1.1 Pa·s降到0.45 Pa·s,说明板栗糊具有良好的贮藏稳定性。     

3 种发酵乳制品流变性质的比较与分析

用流变仪分析评价发酵乳制品的流变学特性。分别测定以牛乳和豆乳以及二者的混合乳为原料制备的3种发酵乳制品的流变学特性。结果表明：3种发酵乳制品均是正触变性流体,其滞后环面积之比为1:0.56:0.69。黏丝性指数之比为1:0.63:0.91;恒温恒速下表观黏度初始值之比分别为1:0.99:1.28,发酵豆乳表观黏度下降速率最慢;应变扫描中发现3种发酵乳制品的稳定性从高到低依次为：发酵豆乳、发酵混合乳和发酵牛乳;在温度扫描中发现发酵豆乳耐温度变化的能力最强,发酵混合乳的表观黏度值最高。通过比较三者的流变学特性说明发酵牛乳的稳定性较差,发酵豆乳的表观黏度值较低,但其稳定性较好。发酵混合乳不仅表观黏度值较高,而且其稳定性也高于发酵牛乳。     

Rheological, Thermal and Microstructural Properties of Whey Protein-Cassava Starch Gels

Mixed gels of cassava starch (CS) and a whey protein isolate (WPI), obtained by heating solutions of 10% total solids, pH 5.75 to 85°C, were characterized as a function of the starch fraction, θ_s, by axial compression, small-amplitude oscillatory rheometry, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Gelation did not occur for θ_s > 0.7. In the range 0<θ_s < 0.4 mixed gels showed higher mechanical (E, elastic modulus) and rheological (G′, storage modulus) properties than pure gels, with maximum values for θ_s= 0.2–0.3. Viscoelastic measurements as a function of time showed that gels containing higher levels of WPI developed a larger G. Blends of both biopolymers showed independent thermal transitions in DSC measurements, related to gelatinization and denaturation. Microstructure of a mixed gel formed at θ_s= 0.2 showed a continuous matrix formed by strands of WPI particle aggregates and an independent CS phase.     

驴乳的系统流变学性质研究

目的:研究不同温度对驴乳流变学性质的影响。方法:选取测试温度为4、20、36、50℃,测试其流动性、触变性、动态粘弹性,并采用流变学模型进行拟合分析。结果:驴乳为非牛顿流体,表现出剪切稀化行为;流动曲线服从Carreau模型,随温度升高,其黏度越小,触变测试中形成的滞后环面积变小;并且在粘弹性测试中4℃的储能模量G'表现出最大值,储能模量G'和损耗模量G″对温度的依赖性较大;4~50℃测量温度范围内驴乳黏度随温度增加逐渐减小。结论:驴乳的流变性对温度的依赖性较大。     

猕猴桃果胶的黏度特性与流变性分析

采用冷冻干燥和热风干燥方法制备出猕猴桃果胶(kiwifruit pectin,KP),得到KP1和KP2两种成分,二者的pH值分别为3.16和3.39,主要含有半乳糖醛酸。以羧甲基纤维素钠(carboxy methyl cellulose-Na,CMC-Na)为参照系,采用MCR301旋转流变仪研究4因素(pH值、质量浓度、温度和剪切速率)对KP溶液流变性的影响。结果表明,KP1和KP2溶液黏度较低,在1.0 m Pa·s上下,溶液pH值和质量浓度对其影响有限。研究KP1和KP2溶液黏度与温度倒数1/T间的对数关系并观测到,10~30℃区间内其黏度随温度升高而下降,与CMC-Na溶液黏度变化相似。但40~50℃时其溶液黏度和流动性不完全遵循Arrhenius方程,究其原因,KP1和KP2活化能Ea分别为10.075 kJ/mol和4.510 kJ/mol,它们对温度的敏感性低,而导致其黏度和流动性发生改变。幂律方程对KP1和KP2溶液黏度和剪切速率的关系拟合,二者流动指数n均小于1,符合幂律定律对非牛顿流体特征的解释。因此,KP1和KP2溶液具有较典型的剪切稀化现象和流变性,可归属于非牛顿流体。但KP是一种低黏度果胶,故Arrhenius方程不能有效诠释KP溶液黏度与温度变化的规律。     

Rheological Properties of Chymosin-Induced Skim Milk Gels as Affected by Milk Storage Time and Temperature

Fundamental dynamic rheological tests were used to measure the rigidity (|G*|) and viscoelasticity (tan δ) of gels made from skim milk samples that were (1) never cooled, (2) stored at 4°C, or 3) stored at 4°C and then rewarmed to 25°C. Milk cooled and held at 4°C prior to gel formation produced gels with lower |G*| and higher tan(δ) than fresh milk gels. Chilled milk samples that were rewarmed to 25°C for 16h prior to gel formation produced gels with rheological properties similar to fresh milk gels. The solubilization of β-casein during cold storage was hypothesized to be the cause of observed differences in gel rheology.     

Antimicrobial,Rheological, and Thermal Properties of Plasticized Polylactide Films Incorporated with Essential Oils to Inhibit Staphylococcus aureus and Campylobacter jejuni

Polylactide (PLA) is the most mature biobased and biodegradable polymer. Due to its inherent brittleness, the polymer cannot be used as a packaging material without plasticizer. An attempt was made to develop antimicrobial plasticized PLA film by incorporating polyethylene glycol (PEG) and 3 essential oils (EO), namely cinnamon, garlic, and clove by solvent casting method. Physical, thermal, and rheological properties of those films were evaluated for practical applications whereas the antimicrobial properties were tested against Staphylococcus aureus and Campylobacter jejuni—pathogens related to poultry industry. Both PEG and EOs led to the formation of flexible PLA/PEG/EO films with significant drop in the glass transition temperature (T_g), and mechanical property. Time–temperature superposition (TTS) principle was employed to melt rheology of EO‐based films at selected temperature, and rheological moduli superimposed well in an extended frequency range. Among EOs, cinnamon and clove oil–based films (PLA/PEG/CIN and PLA/PEG/CLO) exhibited a complete zone of inhibition against C. jejuni at the maximum concentration (1.6 mL per 2 g PLA/PEG blend) whereas the garlic oil–based film (PLA/PEG/GAR) had the lowest activity.