Ovalbumin thermal Gelation Prediction by Application of Temperature-Time History

A model for characterizing changes in viscosity of soy protein during extrusion was adapted to predict apparent viscosity ratio of gelling ovalbumin. For ovalbumin (87% purity) the temperature time histories of 3,5, and 7% gel formation were determined at 85, 90 and 95°C. A back-extrusion method was used to determine apparent viscosity ratios during gelation. Activation energy for denaturation/gelation was estimated at 159 kJ/mol. The model parameter a (degree of molecular entanglement) was 0.75, 0.75, and 1.0 for 3, 5, and 7% gels, respectively. Reaction rate constants were similar for samples with different protein concentrations. Maximum apparent viscosity ratio increased as protein concentrations increased. The mathematical model was verified by determining apparent viscosity ratios at 86 and 93°C and water holding at 90°C, resulting in R²-0.93. This model may be useful in predicting ovalbumin thermal gelation apparent viscosity ratios.     

Small‐angle neutron scattering of poly(styrene)/poly(acrylic acid–ethyl acrylate) copolymers: The effect of the degree of hydrolysis of the poly(acrylic acid–ethyl acrylate) block

We report the results of systems based on polystyrene‐poly(ethyl acrylate) (PEA) diblocks, which self‐assemble in aqueous solutions to form spherical micelles. Previous work has shown that the rheological properties of these solutions, in particular the gel–liquid transition, can be tuned through the use of a simple hydrolysis reaction to convert PEA to poly(acrylic acid) (PAA). We studied the effect of the extent of hydrolysis on the self‐assembly and micellar interactions. Small‐angle neutron scattering (SANS) spectra were fit with a variety of models to determine the micelle structure. As more PEA was converted to PAA (i.e., as the corona became more charged and more hydrophilic), the micellar aggregation number decreased, analogous to observations of other polymeric micelles. This effect could impact the gel–liquid transition and rheology in this system and in similar micellar block copolymer gels. Finally, our SANS spectra qualitatively agreed with predictions for attractive colloidal glasses, confirming the idea that the elasticity of these gels arises from the jamming of micelles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 490–497, 2004     

Effects of solvent adsorption on solution properties of poly(vinyl alcohol)/dimethylsulfoxide/water ternary systems

In this study, the solvent adsorption phenomena of poly(vinyl alcohol) (PVA) in cosolvent mixtures of dimethylsulfoxide (DMSO; solvent 1) and water (solvent 2) were investigated. Typically, this cosolvent mixture could form hydrogen‐bonded DMSO/(water)₂ complexes, involving one DMSO and two water molecules. Because of the complex formation in the cosolvent mixtures, PVA chains preferentially adsorb water molecules at DMSO mole fraction X₁ < 0.33, but preferentially adsorb DMSO molecules at X₁ > 0.33. The preferential adsorption of DMSO (a good solvent for PVA) could cause the relatively extended conformation of PVA chains in solutions because of the increase in excluded volume effect. Because of various interactions between PVA chains and cosolvent mixtures, the aggregation and gelation behaviors of PVA solutions were significantly affected by the composition of cosolvent mixture. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3211–3217, 2004     

Viscoelastic behavior of thermosetting epoxy mixtures modified with syndiotactic polystyrene during network formation

The rheological behavior of thermosetting epoxy mixtures modified with thermoplastic syndiotactic polystyrene (sPS) was monitored during the curing of the epoxy resin. The selected thermosetting system was diglycidyl ether of bisphenol A cured with 4,4′‐methylene bis(3‐chloro‐2,6‐diethylaniline) in the presence of various compositions of sPS (from 2.5 to 12.5 wt %). The storage and loss shear moduli of the systems were monitored during network formation. The validity of the Winter–Chambon criterion for the accurate determination at the gelation point from rheological data was demonstrated. The influence of the sPS concentration on the dynamic rheological properties of the samples was investigated. The experimental data showed that at sPS concentrations lower than 7.5 wt %, phase separation induced a quick increase in the viscosity, which was related to a crystallization‐induced phase separation of sPS. For sPS concentrations higher than 7.5 wt %, near the phase‐inversion composition, the rheological behavior of the mixtures was characteristic of a cocontinuous structure. After the viscosity jumped at the onset of phase separation, a decrease in the viscosity was found, and later on, the viscosity increased again because of gelation. Additionally, the influence of the cure temperature on the rheological properties was studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2348–2355, 2006     

Effect of milk solids concentration on the gels formed by the acidification of heated pH-adjusted skim milk

Reconstituted skim milk of 10–25% total solids was adjusted to pH values between about 6.2 and 7.1 and heated at 80 °C for 30 min. Gels were formed from the heated milks by slow acidification to pH 4.2 and the gelation process and final gels were analyzed for their rheological properties. At each milk concentration, the final acid gel firmness (final G′) and breaking stress could be changed markedly by manipulation of the pH during heating. The final gel firmness and breaking stress could also be modified by changing the concentration of the milk solids prior to heating and acidification. The results indicated that similar gel firmness and breaking stress could be achieved over a range of milk concentrations by control of the pH of the milk during heating. When expressed as a percentage change in final G′ or breaking stress relative to that obtained at the natural pH, plots of the change in final G′ or breaking stress versus pH fell close to a single curve, indicating that the same mechanism may influence the gelation properties at all milk concentrations. The final G′ and breaking stress were related to the denaturation and interaction of the whey proteins with the casein micelles, and the formation of non-sedimentable casein when the milk was heated.     

煤系高岭岩成矿机理

在阐述研究区高岭岩矿床地质特征的基础上，利用高倍偏光显微镜、X-射线衍射、红外吸收光谱、扫描电镜结合能谱、探针和X-荧光光谱等多种分析测试方法，对研究区高岭岩的矿物成分、化学成分、显微结构、地化特征进行了全面分析，建立了研究区高岭岩矿石宏观-微观综合分类，对该矿床的成矿机理进行了深入探讨.研究表明：研究区煤系高岭岩成矿母质主要来源于酸性岩石，包括源区花岗岩类和酸性火山灰；陆源高岭石黏粒的絮凝作用、陆源氧化铝-氧化硅溶胶的胶凝作用和陆源碎屑的转变作用是研究区高岭岩成矿的主要机理；在煤层顶底板夹矸高岭岩中，生物成矿作用占有重要地位.     

Synthesis and evaluation of ciprofloxacin-loaded carboxymethyl tamarind kernel polysaccharide nanoparticles

Nanotechnology is currently employed as a tool to fight more efficiently against human pathogens. Nanoparticles can be prepared from a variety of materials such as protein, biodegradable polymers and synthetic polymers. Tamarindus indica Linn. or tamarind is one of the most important biodegradable polymer. In the present study, chemically modified polymer of tamarind ‘carboxymethyl tamarind kernel polysaccharide’ (CMTKP) is used for the synthesis of nanoparticulate formulation. Antibacterial activity of CMTKP was analysed which was then enhanced by incorporating a flouroquinolone antibiotic, ciprofloxacin to it. Ciprofloxacin-loaded CMTKP nanoparticles were synthesised via ionotropic gelation technique. Nanosuspension so formed was lyophilised by addition of a cryoprotectant. Nanoparticles obtained were characterised for its particle size, morphology and stability. Interaction studies were confirmed by Fourier transform infrared spectroscopy (FT-IR). Antibacterial activities of ciprofloxacin, CMTKP and ciprofloxacin-loaded CMTKP nanoparticles were tested against two Gram negative and positive bacteria. The antibacterial assay results revealed greatest zone of inhibition by ciprofloxacin-loaded CMTKP nanoparticles in Micrococcus luteus. Toxicity analysis of the prepared formulation was carried out on vero cell lines via resazurin assay which revealed its minimum toxicity.     

Raman spectroscopic study of heat-induced gelation of pork myofibrillar proteins and its relationship with textural characteristic

Structural changes, textural properties and their relationships in pork myofibrillar proteins (PMP) were studied by Raman spectroscopy, texture profile analysis (TPA) and principal component analysis (PCA). Raman spectroscopy analysis revealed the occurrence of secondary structural changes in myofibrillar proteins. Modifications in the amide I (1600-1700 cm(-1)) and amide III (1200-1300 cm(-1)) regions indicated a significant (p<0.05) decrease in α-helix content, accompanied by a significant (p<0.05) increase in β-sheets, β-turns and random coil content. Texture property changes were also determined by TPA. All these features contributed to the formation of strong, irreversible heat-induced gels. The application of a dimensionality reducing technique such as PCA proved to be useful to determine the most influential properties of heat-induced gel. Significant (p<0.05) correlations were found between these structural changes and the textural characteristic (hardness) in the pork myofibrillar proteins system by PCA.     

不同柔性链丙烯酸松香环氧树脂性能比较

以丙烯酸松香二缩水甘油酯(ARE)、丙烯酸松香乙二醇二缩水甘油醚(AR-EDGE)和丙烯酸松香丁二醇二缩水甘油醚(AR-BDGE)为研究对象,通过测定固化反应的凝胶时间、固化产物的耐热性、力学性能及耐溶剂性,研究了不同柔性链对松香基环氧树脂性能的影响。结果表明,松香基的稠环结构有着优异的耐热性,然而也会带来较大的脆性,需引入合适长度的柔性链。三种体系中,AR-EDGE综合性能最好,虽耐热性不及ARE,但其力学性能强于另两种体系;柔性链稍短的ARE因脆性大力学性能不好;柔性链稍长的AR-BDGE耐热性及耐丙酮性不佳,力学性能一般。     

NiY2O3Al2O3 aerogel catalysts with high coke deposition resistance for syngas production by biogas reforming

The control of coke deposition is one of the most important challenges during reforming processes using Ni/Al₂O₃ catalysts. To minimize the effects of coke deactivation and increase the catalytic performance, NiY₂O₃Al₂O₃ aerogel catalysts were synthesized by the epoxide-initiated gelation method and dried with supercritical CO₂. The catalysts with yttria added were evaluated in terms of syngas production and coke formation in biogas reforming reactions in the temperature range of 500–800 °C. The techniques used to characterize the catalysts were nitrogen adsorption tests, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, thermogravimetric analysis, scanning and transmission electron microscopy. Nanoscale and mesoporous catalysts with high specific surface area were obtained. The catalysts maintained an amorphous structure with high metal dispersion and homogeneous distribution. Yttria insertion promoted higher interaction between the active phase and the support in the catalysts. For the first time, profiles for the coke deposition and syngas production were determined simultaneously during reforming reactions. Hydrogen production increased with yttria addition on the catalysts. The syngas production was highest at 800 °C. However, the hydrogen production was highest at 600 and 700 °C. The coke-resistance of the catalysts decreased in the following order: NiY2.5Al > NiY5Al > NiAl > NiY10Al. The yttria promoter showed a decrease in the coke formation of 58 wt% compared to NiAl at 700 °C. NiY₂O₃Al₂O₃ aerogel catalysts are a promising alternative in the search for high-coke-resistance catalysts and for increasing the syngas production in biogas reforming reactions.