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91.
Elucidating the relationship between the spreading coefficient, surface-mediated partial coalescence and the whipping time of artificial cream 总被引:1,自引:0,他引:1
Natalie E. Hotrum Martien A. Cohen Stuart Ton van Vliet Serena F. Avino George A. van Aken 《Colloids and surfaces. A, Physicochemical and engineering aspects》2005,260(1-3):71-78
We studied the whipping of artificial creams composed of a blend of sunflower oil and hydrogenated palm fat stabilized by protein or a mixture or protein and low molecular weight (lmw) surfactant. It was found that an increased whipping speed, decreased protein concentration, and the addition of lmw surfactant leads to shorter whipping times. Further, shorter whipping times were observed for WPI-stabilized cream compared to cream stabilized by sodium caseinate. In all cases, the decrease in whipping time was due to a decrease in the length of the second stage of whipping, the stage characterized by the adhesion of fat droplets to the air bubble surface. The decrease in whipping time could be accounted for by considering the influence of the experimental variables on the fraction of bubble surface area at which fat droplet spreading is possible. The same changes in parameters that promote droplet spreading at the air/water interface cause a decrease in the whipping time of our model creams. Correlating the whipping time of cream with the spreading behavior of fat droplets at the air/water interface represents a new insight into the mechanisms involved in the whipping of cream. 相似文献
92.
93.
催化荧光光度法测定砷的研究 总被引:5,自引:0,他引:5
在硫酸介质中,痕量砷对碘酸钾与罗丹明6G的氧化还原反应有催化作用,使罗丹明6G的荧光减弱,据此建立了催化荧光法测定痕量砷的新方法。方法检出限为0.26ng/mL,测定范围4.12ng/mL-82.4ng/mL。已用于环境和生物样品测定。 相似文献
94.
95.
The combination of optical coherence tomography and spectroscopy may allow for highly localized, quantitative measurements of tissue spectral properties. We present, for the first time to our knowledge, quantitative measurements of the absorption coefficients of phantoms and of hemoglobin and oxygenated hemoglobin with spectroscopic optical coherence tomography (SOCT). Our results suggest that SOCT will be able to provide localized, quantitative oxygenation measurements. 相似文献
96.
Ton Daorong 《数学学报(英文版)》1990,6(1):47-56
In this paper we discuss the completions (,
) of a commutativel-groupG with respect to the intrinsic topologies . We give some conditions under which
is the intrinsic topology of the same type on as
and give the relations between these completions. 相似文献
97.
Ganzevles RA Fokkink R van Vliet T Cohen Stuart MA de Jongh HH 《Journal of colloid and interface science》2008,317(1):137-147
Based on earlier reported surface rheological behaviour two factors appeared to be important for the functional behaviour of mixed protein/polysaccharide adsorbed layers at air/water interfaces: (1) protein/polysaccharide mixing ratio and (2) formation history of the layers. In this study complexes of beta-lactoglobulin (positively charged at pH 4.5) and low methoxyl pectin (negatively charged) were formed at two mixing ratios, resulting in negatively charged and nearly neutral complexes. Neutron reflection showed that adsorption of negative complexes leads to more diffuse layers at the air/water interface than adsorption of neutral complexes. Besides (simultaneous) adsorption of protein/polysaccharide complexes, a mixed layer can also be formed by adsorption of (protein/)polysaccharide (complexes) to a pre-formed protein layer (sequential adsorption). Despite similar bulk concentrations, adsorbed layer density profiles of simultaneously and sequentially formed layers were persistently different, as illustrated by neutron reflection analysis. Time resolved fluorescence anisotropy showed that the mobility of protein molecules at an air/water interface is hampered by the presence of pectin. This hampered mobility of protein through a complex layer could account for differences observed in density profiles of simultaneously and sequentially formed layers. These insights substantiated the previously proposed organisations of the different adsorbed layers based on surface rheological data. 相似文献
98.
Ganzevles RA Zinoviadou K van Vliet T Cohen MA de Jongh HH 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10089-10096
There is a large interest in mixed protein/polysaccharide layers at air-water and oil-water interfaces because of their ability to stabilize foams and emulsions. Mixed protein/polysaccharide adsorbed layers at air-water interfaces can be prepared either by adsorption of soluble protein/polysaccharide complexes or by sequential adsorption of complexes or polysaccharides to a previously formed protein layer. Even though the final protein and polysaccharide bulk concentrations are the same, the behavior of the adsorbed layers can be very different, depending on the method of preparation. The surface shear modulus of a sequentially formed beta-lactoglobulin/pectin layer can be up to a factor of 6 higher than that of a layer made by simultaneous adsorption. Furthermore, the surface dilatational modulus and surface shear modulus strongly (up to factors of 2 and 7, respectively) depend on the bulk -lactoglobulin/pectin mixing ratio. On the basis of the surface rheological behavior, a mechanistic understanding of how the structure of the adsorbed layers depends on the protein/polysaccharide interaction in bulk solution, mixing ratio, ionic strength, and order of adsorption to the interface (simultaneous or sequential) is derived. Insight into the effect of protein/polysaccharide interactions on the properties of adsorbed layers provides a solid basis to modulate surface rheological behavior. 相似文献
99.
Natalie E. Hotrum Martien A. Cohen Stuart Ton van Vliet George A. van Aken 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,240(1-3):83-92
The influence of crystalline fat on the amount and rate of oil spreading out of emulsion droplets onto either a clean or a protein-covered air/water interface was measured for β-lactoglobulin stabilized emulsions prepared with either anhydrous milk fat or a blend of hydrogenated palm fat and sunflower oil. At a clean interface, liquid oil present in the emulsion droplets was observed to completely spread out of the droplets unimpeded by the presence of a fat crystal network. Further, the presence of a fat crystal network in the emulsion droplets had no effect on the rate of oil spreading out of the droplets. At a protein-covered interface, the spreading behavior of emulsion droplets containing crystalline fat was evaluated in terms of the value of the surface pressure (ΠAW) at the point of spreading; ΠAW at spreading was unaffected by the presence of crystalline fat. We conclude it is unlikely that the role of crystalline fat in stabilizing aerated emulsions such as whipped cream is to reduce oil spreading at the air/water interface. However, the temperature of the system did have an effect: spontaneous spreading of emulsion droplets at clean air/water interfaces occurred for systems measured at 5 °C, but not for those measured at 22 or 37 °C. Thus, temperature may play a more important role in the whipping process than commonly thought: the entering and spreading of emulsion droplets was favored at lower temperatures because the surface pressure exerted by protein adsorbed at the air/water interface was reduced. This effect may facilitate the whipping process. 相似文献
100.
Dr. Craig S. Day Stephanie J. Ton Clemens Kaussler Daniel Vrønning Hoffmann Prof. Troels Skrydstrup 《Angewandte Chemie (International ed. in English)》2023,62(35):e202308238
Herein, we report a methodology to access isotopically labeled esters and amides from carbonates and carbamates employing an oxygen deletion strategy. This methodology utilizes a decarboxylative carbonylation approach for isotope labeling with near stoichiometric, ex situ generated 12C, or 13C carbon monoxide. This reaction is characterized by its broad scope, functional group tolerance, and high yields, which is showcased with the synthesis of structurally complex molecules. A complementary method that operates by the catalytic in situ generation of CO via the reduction of CO2 liberated during decarboxylation has also been developed as a proof-of-concept approach that CO2-derived compounds can be converted to CO-containing frameworks. Mechanistic studies provide insight into the catalytic steps which highlight the impact of ligand choice to overcome challenges associated with low-pressure carbonylation methodologies, along with rational for the development of future methodologies. 相似文献