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Rheological Data (rheological + data)
Selected AbstractsEnhanced production of lovastatin in a bubble column by Aspergillus terreus using a two-stage feeding strategyJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2007EM Rodríguez Porcel Abstract A two-stage feeding strategy is shown to improve the rate of production of lovastatin by Aspergillus terreus when compared with conventional batch fermentation. The feeding strategy consisted of an initial batch/fed-batch phase and a semi-continuous culture dilution phase with retention of pelleted biomass in a slurry bubble column reactor. The batch phase served only to build up the biomass for producing lovastatin, a secondary metabolite that inhibits its own synthesis in the producing microfungus. The semi-continuous dilution phase provided nutrients to sustain the fungus, but prevented biomass growth by limiting the supply of essential nitrogen. (Synthesis of lovastatin does not require nitrogen.) The preferred pelleted growth morphology that favors lovastatin synthesis was readily obtained and maintained in the 20 L bubble column used. In contrast, a stirred tank fermentation had a substantially lower production of lovastatin because mechanical agitation damaged the fungal pellets. The two-stage feeding method increased lovastatin production rate by more than 50% in comparison with the conventional batch operation. Rheological data for the fungal broth are presented. Copyright © 2007 Society of Chemical Industry [source] PHYSICO-CHEMICAL AND STORAGE CHARACTERISTICS OF GARLIC PASTEJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2001JASIM AHMED A processed paste with a total solids and pH value of 33% and 4.1, respectively was prepared from fresh garlic by addition of 10% sodium chloride (w/w) and citric acid. Appearance of green pigment (in terms of the Hunter color -a* value) was noticed in the product during preparation. Paste was thermally processed at 70, 80 or 90C, respectively for 15 min. Greening of paste decreased with increase in temperature. Rheological data revealed that garlic paste behaved as a psuedo-plastic fluid with a flow behavior and consistency index of 0.14 and 279 Pa.sn, respectively. The paste was analyzed periodically for color and microbiological counts. The product was found to be shelf stable at 25C for a period of at least 6 months. The green coloration decreased significantly (p<0.05) during storage. [source] Capillary Flow and Rheology Measurements on Chocolate Crumb/Sunflower Oil MixturesJOURNAL OF FOOD SCIENCE, Issue 9 2004S. Carbonell ABSTRACT: Rates of penetration of sunflower oil into beds of 3 types of chocolate crumb have been measured and the results analyzed using the Washburn-Rideal theory. The data show that the rates are a function of both the specific surface area of the crumb particles and their surface composition. Addition of an emulsifier to the oil reduces the penetration rate into the crumb made with full-cream milk powder, whereas for crumbs containing skimmed-milk powder, rates go through a maximum with increase of emulsifier concentration. Rheological data for dispersions of crumb in oil were fitted to the Casson equation. An inverse correlation was found between penetration rates and Casson yield values. [source] LUBRICITY INDEX OF MAYONNAISEJOURNAL OF TEXTURE STUDIES, Issue 1 2003JAMES F. STEFFE ABSTRACT The Lubricity Index (LI) is defined as a new parameter to quantitatively evaluate mouthfeel. Rheological data were collected using a helical ribbon mixer viscometer with commercial mayonnaise products. The LI is calculated from changes in apparent viscosity due to temperature and moisture variations that mirror those found in the mouth during mastication. The rate of change in apparent viscosity with moisture and temperature was much lower with a fat free product than regular products resulting in a low LI value. The LI provides a basis for future efforts to understand, and mathematically model, the complicated process of fluid food mastication. [source] An experimental study of morphology and rheology of ternary Pglass-PS-LDPE hybridsPOLYMER ENGINEERING & SCIENCE, Issue 6 2003Peter C. Guschl Ternary blends of low-density polyethylene (LDPE), polystyrene (PS), and a low Tg tin-based phosphate glass (Pglass) were prepared at compositions ranging from 0,50 vol% Pglass in which either LDPE or PS was the continuous matrix phase. Differential scanning calorimetry was used to investigate the phase behavior of the pure components, PS-LDPE blends and binary Pglass-polymer hybrids. Interesting steady-shear and transient rheology was observed for the hybrids. In particular, the steady shear viscosity curves for the hybrids of ,Pglass , 30% exhibited unusual, four-region flow behavior, similar to that of liquid crystalline polymers. Two Newtonian plateaus at low ( , 0.1 s,1) and moderate (0.4 , , s,1) shear rates connected by two distinct shear-thinning regimes were apparent. This observed rheology is ascribed to a unique composite morphology of these multi-component systems. Rheological data on the binary Pglass-polymer systems suggest that the presence of the Pglass within both PS and LDSE contributes significantly to this unusual behavior, perhaps because of the interfacial behavior between the phases. Micrographs obtained via scanning electron microscopy reveal preferential placement of the Pglass phase dispersed within the PS-phase and surrounding the LDPE phase. Optical shearing data confirmed the evolution of this microstructure under specific shear conditions. [source] Addition of Soluble Soybean Polysaccharides to Dairy Products as a Source of Dietary FiberJOURNAL OF FOOD SCIENCE, Issue 6 2010Wenpu Chen Abstract:, Increasing consumption of dietary fiber in food leads to many important health benefits: for example, reduction in blood cholesterol, reduced risk of diabetes, and improved laxation. Water soluble soybean polysaccharide (SSPS) is a dietary fiber extracted and refined from okara, a byproduct of soy manufacturing. It was incorporated into 3 categories of dairy-based products, thickened milkshake-style beverages, puddings, and low-fat ice cream, to the maximum amount without over-texturing the food. Rheological measurements and sensory tests were used to develop desirable SSPS-fortified products. From the rheological data, 4% SSPS-fortified dairy beverages and 4% SSPS -fortified puddings were in the range of commercial products. From sensory analyses, 4% SSPS-fortified dairy beverage with 0.015%,,carrageenan, 4% SSPS-fortified pudding with 0.1%,,carrageenan, and 2% SSPS-fortified low-fat ice cream gained the highest scores in consumer hedonic rating. Panelists also indicated their willingness to consume those products if they were available commercially. Practical Application:, Since the dietary fiber intake of many people is below their suggested adequate intake values, strategies to successfully fortify foods with fiber may help alleviate this gap. We have developed 3 dairy products, a beverage, a pudding, and a low-fat ice cream, that have been fortified with soluble soybean polysaccharide at levels of 4%, 4%, and 2%, respectively. These products were within acceptable ranges of rheological parameters and other physical stability measurements and were judged to be acceptable by sensory analyses. [source] Phase and Rheological Behavior of High-Concentration Colloidal Hard-Sphere and Protein DispersionsJOURNAL OF FOOD SCIENCE, Issue 7 2007S.M. Loveday ABSTRACT:, Colloidal hard-sphere (HS) particles of narrow-size distribution exhibit crystalline and glassy states beginning at the particle volume fractions ,= 0.494 and ,G= 0.58, respectively. Dynamic rheological data on the dispersions were strongly modified to solid-like behavior as , approached ,G. In addition, cooperative motion in structural relaxation has been observed microscopically in the colloidal dispersions near the glassy state. Very high viscosities and glassy states were also found in high-concentration dispersions of sodium caseinate and the globular proteins: bovine serum albumin and ,-lactoglobulin. Viscosity models developed for HS dispersions predicted accurately the trends but not the absolute values of protein dispersions. Dispersions of food colloidal particles may be employed in studies, in which volume fraction is the thermodynamic variable, for understanding the relaxation and transport processes related to 1st-order and colloidal glass transitions. [source] Synthesis and rheology of biodegradable poly(glycolic acid) prepared by melt ring-opening polymerization of glycolideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2009Estelle Gautier Abstract Ring-opening polymerization (ROP) of glycolide was studied in melt conditions and in the presence of two different initiators: 1-dodecanol and 1,4-butanediol and tin(II) 2-ethylhexanoate as catalyst. Its subsequent polymerization provided poly(glycolic acid) with controlled molar masses ranging from 2000 to 42,000 g/mol with well-defined structures characterized by NMR. Their thermal properties were evaluated by DSC analysis, and a glass transition temperature at infinite molar mass (Tg,) of 44.8 °C was thus calculated. From rheological data, the critical molar mass for entanglement, Mc, was estimated to be near 11,000 g/mol. Furthermore, in situ polymerizations were also performed between the plates of the rheometer within a same temperature range from 210 to 235 °C. The variation of the storage and loss moduli during the polymerization step have been monitored by time sweep oscillatory experiments under an angular frequency , = 10 rad/s. Finally, the development of an inverse rheological method allowed to calculate the bulk polymerization kinetics in the temperature range 200,230 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1440,1449, 2009 [source] Influence of Coupling Agents on Melt Flow Behavior of Natural Fiber CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2007Velichko Hristov Abstract The influence of coupling agents on the melt rheological properties of natural fiber composites has been investigated in this work using capillary and rotational rheometers. Scanning electron microscopy was also employed to supplement the rheological data. It was found that molecular weight and molecular weight distribution of the polymer matrix and coupling agent characteristics influence the filler wetting and the melt flow properties of the filled composites. Generally, low molecular weight and narrow molecular weight distribution polyethylene matrix provides relatively larger increase of the viscosity of the composites. Coupling agents tend to increase the resistance to shearing, but wall slip effects may interfere with the measured values, especially at very high filler loadings. Entrance pressure loss in capillaries is also influenced by polymer matrix and coupling agent used. [source] Sensory and rheological properties of transgenically and chemically modified starch ingredients as evaluated in a food product modelMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 2 2004Tina Ahmt Abstract Starches derived from five genetically modified potato lines, two chemically modified potato starches and two native starches from potato and maize were subjected to physical and chemical analyses and their functionality evaluated in a milk-based food product model. The transgenic starches were specifically modified with respect to amylopectin chain length and phosphorous content by suppression of the starch branching enzyme and overexpression of glycogen branching enzyme. Transgenic starches with long amylopectin chains and high phosphorous content had increased gelatinisation temperatures, produced gels with a higher tendency to retrograde and a low freeze/thaw stability as compared to starches with shorter amylopectin chains and lower phosphorous content. The textural properties of the food product model prepared from genetically and chemically modified starches were characterised by sensory and rheological analyses. To clearly visualise the effects of the modifications, data was evaluated by radar plots and multiple regression analysis (chemometrics). Genetically modified potato starches with longer amylopectin chains and increased phosphorous content gave a more gelled and a shorter texture as compared to starches with shorter amylopectin chains and decreased phosphorous content. Acetylated and hydroxypropylated potato starches gave sticky and stringy textures. Correlations between rheology parameters and sensory parameters were found. The sensory parameter stringy/long could be predicted from the rheological data. [source] Twin-screw extrusion of polypropylene-clay nanocomposites: Influence of masterbatch processing, screw rotation mode, and sequencePOLYMER ENGINEERING & SCIENCE, Issue 6 2007Mark A. Treece This work seeks to optimize the twin-screw compounding of polymer-clay nanocomposites (PCNs). Proportional amounts (3:1) of maleic anhydride functionalized polypropylene compatibilizer (PP- g -MA) and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt% were melt-blended with a polypropylene (PP) homopolymer using a Leistritz Micro 27 twin-screw extruder. Three melt-blending approaches were pursued: (1) a masterbatch of PP- g -MA and organoclay were blended in one pass followed by dilution with the PP resin in a second pass; (2) all three components were processed in a single pass; and (3) uncompatibilized PP and organoclay were processed twice. Both corotation and counterrotation operation were utilized to investigate the effect of screw rotation mode and sequence on organoclay exfoliation and dispersion. X-ray diffraction was employed to characterize basal spacing; however, since rheology is known to be highly sensitive to mesoscale organoclay structure, it is an ideal tool to examine the relationship between the various processing methods and exfoliation and dispersion. A holistic analysis of rheological data demonstrates the efficacy of the masterbatch approach, particularly when compatibilizer and organoclay are blended in counterrotating mode followed by dilution with matrix polymer in corotating mode. POLYM. ENG. SCI., 47:898,911, 2007. © 2007 Society of Plastics Engineers [source] Modification of recycled high-density polyethylene by low-density and linear-low-density polyethylenes,POLYMER ENGINEERING & SCIENCE, Issue 1 2003N. Kukaleva The present study investigated mixed polyolefin compositions with the major component being a post-consumer, milk bottle grade high-density polyethylene (HDPE) for use in large-scale injection moldings. Both rheological and mechanical properties of the developed blends are benchmarked against those shown by a currently used HDPE injection molding grade, in order to find a potential composition for its replacement. Possibility of such replacement via modification of recycled high-density polyethylene (reHDPE) by low-density polyethylene (LDPE) and linear-low-density polyethylene (LLDPE) is discussed. Overall, mechanical and rheological data showed that LDPE is a better modifier for reHDPE than LLDPE. Mechanical properties of reHDPE/LLDPE blends were lower than additive, thus demonstrating the lack of compatibility between the blend components in the solid state. Mechanical properties of reHDPE/LDPE blends were either equal to or higher than calculated from linear additivity. Capillary rheological measurements showed that values of apparent viscosity for LLDPE blends were very similar to those of the more viscous parent in the blend, whereas apparent viscosities of reHDPE/LDPE blends depended neither on concentration nor on type (viscosity) of LDPE. Further rheological and thermal studies on reHDPE/LDPE blends indicated that the blend constituents were partially miscible in the melt and cocrystallized in the solid state. [source] Intercalation and exfoliation behaviour of clay layers in branched polyol and polyurethane/clay nanocompositesPOLYMER INTERNATIONAL, Issue 2 2006Hesheng Xia Abstract The exfoliation of clay layers was realized in a tri-hydroxyl branched polyether polyol by direct mixing and the corresponding exfoliated polyurethane/clay nanocomposite was prepared by further in situ curing. The effects of various surface-modified organoclays and various polyol types on the intercalation and exfoliation behaviour of clay layers were investigated. The interaction between the polyol and clay and the mixing temperature plays an important role in the occurrence of exfoliation and intercalation. The relationship between rheological data of polyol/clay dispersion and the intercalation or exfoliation state of the clay was established. This provides a convenient and efficient way to evaluate the dispersion state of the clay. Based on the experimental results, a possible layer-by-layer exfoliation mechanism is proposed. Copyright © 2006 Society of Chemical Industry [source] | |||||||||||||