Ronald Gebhardt - Academia.edu (original) (raw)
Papers by Ronald Gebhardt
Biophysical Journal, 2007
The structure of thin casein films prepared with spin-coating is investigated as a function of th... more The structure of thin casein films prepared with spin-coating is investigated as a function of the calcium concentration. Grazing incidence small-angle x-ray scattering and atomic force microscopy are used to probe the micelle structure. For comparison, the corresponding casein solutions are investigated with dynamic light-scattering experiments. In the thin films with added calcium three types of casein structures, aggregates, micelles, and mini-micelles, are observed in coexistence with atomic force microscopy and grazing incidence small-angle x-ray scattering. With increasing calcium concentration, the size of the aggregates strongly increases, while the size of micelles slightly decreases and the size of the mini-micelles increases. This effect is explained in the framework of the particle-stabilizing properties of the hairy layer of k-casein surrounding the casein micelles.
Food Hydrocolloids for Health, 2021
Film drying is used for the gentle production of casein microparticles. These result from aggrega... more Film drying is used for the gentle production of casein microparticles. These result from aggregates that have previously formed in solution from micellar caseins in the presence of pectin under neutral pH conditions. The particles are stabilized by hydrophobic interactions and have a spherical shape. Their swelling behavior, which is enhanced with increasing pH, could be of interest for future applications in the field of drug encapsulation and release. The swelling of the microparticles occurs within minutes at pH 11, making it possible to perform a total of 46 consecutive individual tests. The analysis of the results showed that the microparticles keep their spherical shape during swelling. Furthermore, the swelling process proceeds in two steps, the rates of which are independent of the initial size of the casein microparticles. The values of the five parameters of the dynamic swelling model, which is used for the analysis of the kinetics, are examined with the Bravais-Pearson coefficient for pairwise linear correlations. Both swelling steps can be clearly distinguished with regard to rate and characteristic time, whereby the second swelling step at pH 11 consequently has a larger characteristic initial time but also a larger rate. For the first swelling step, the characteristic time and the rate coefficient are uncorrelated, while the rate for swelling step 2, which ends with the disintegration of the casein microparticles, is smaller the later it begins. Since there is a positive correlation between the characteristic times of the two swelling steps, it can be concluded that those particles are most stable for which the swelling process starts the latest. It seems plausible that a different degree of hydration of the microparticles after preparation is the cause of the observed stability differences.
International Journal of Biological Macromolecules, 2017
Static and dynamic light scattering was applied to milk proteins Radii of hydration and gyrat... more Static and dynamic light scattering was applied to milk proteins Radii of hydration and gyration, molecular weights and second virial coefficients were estimated Casein micelles show deviation from a hard sphere under native conditions Hard spheres resulted at elevated calcium chloride concentrations or after removal of -Lactoglobulin
Metalloproteins are essential components of cells, namely in redox processes, e.g. in electron tr... more Metalloproteins are essential components of cells, namely in redox processes, e.g. in electron transfer reactions in respiration and photosynthesis, and in oxygen transport and storage functions. Most metallo-proteins exhibit several structural states, which may occur as substates during function, e.g. redox catalysis or ligand binding, or in the molecular regulation (allosteric conformational changes). The accompanied metal ligand and distance changes can be estimated by XANES, EXAFS and ASAXS of protein solutions. The dispersive estimation of the metal environment structure is difficult with metal protein solutions because of two reasons: i) a protein solution consists mainly of water (>80%) and ii) the specific metal content in the protein entity is low because of the high molecular mass of the protein, e.g. n*70,000 in case of oligomeric Hemocyanin oxygen transport proteins. Thus the metal content is below 20 mM/l, i.e. 0.03%. This makes the usual background correction by fit...
Journal of Membrane Science, 2015
ABSTRACT
Procedia Food Science, 2011
Casein micelles form deposit layers on silicon micro-sieves during dead-end filtration. The pore ... more Casein micelles form deposit layers on silicon micro-sieves during dead-end filtration. The pore size of the used micro-sieves was 0.8 μm. Sequential centrifugation was applied to prepare size-fractionated casein micelles. Dynamic light scattering (DLS) led to mono-exponential correlation functions indicating one prominent micelle size and a sharp size distribution. The hydrodynamic radius was R H = 75 nm. Atomic force microscopy (AFM) showed that casein micelles were distributed homogenously on the micro-sieve. Most of the micelles appeared as compact, spherical objects. Some of them got deformed due to aggregation. The sizes estimated from the AFM images were between 140-160 nm and in accordance with light scattering measurements. The filtration process was monitored by static light scattering (SLS) in the permeate. Scattering functions of casein micelles showed angle dependences, since their sizes exceeded /20 of the wavelength of the used laser light. To adjust for the angle-dependence, scattering data were extrapolated to zero using a form-factor fit of a sphere. During filtration, the resulting intensity decreased to 65% of the original value. As for the flux, two processes could be separated by fitting a double exponential function to the intensity data. The first process was fast with a characteristic time of 18 s and led to an intensity decrease by more than a half. The second process decayed with a characteristic time of 6 min. In the fast process retention of larger micelles takes place while smaller micelles pass through the pores of the micro-sieve. A participation of all micelle sizes and their migration through the formed cake explains the slow process.
Soft Matter, 2014
Tobacco mosaic virus particles can be rapidly assembled into 3D-domains by capillary flow-driven ... more Tobacco mosaic virus particles can be rapidly assembled into 3D-domains by capillary flow-driven alignment at the triple contact-line of an evaporating droplet.
Macromolecules, 2009
Investigating the thickness dependence of ordered structure of thin films of electrically conduct... more Investigating the thickness dependence of ordered structure of thin films of electrically conducting conjugated polymers with nano-ordered morphologies is essential for optimizing their applications in advanced electrooptic devices. We demonstrate here that by spin-coating a small drop of a conjugated-coil diblock copolymer, a thickness gradient varying between tens of nanometers to a few micrometers is formed at the drop rim. Compared to other widely used solution casting methods for the preparation of thickness gradients, the spin-coated drop technique produces film gradients with thickness in the interesting range for most applications in an extremely short preparation time. Using a submicrometersized X-ray beam and a scanning technique, spatial mappings of the gradient area are obtained with submicrometer grazing incidence small-angle X-ray scattering (sub-μGISAXS) for the first time. Investigating the thickness gradient with sub-μGISAXS has the advantage of saving the preparations and investigations of many samples each with a certain thickness under identical conditions. As a model system, we use the diblock copolymer polystyrene-block-poly(p-phenylene) with a thickness gradient ranging between 80 and 2280 nm. Detailed analysis of the scattering patterns at selected positions along the gradient identifies a regime of lateral order within a thickness range of 80-210 nm.
Macromolecular Chemistry and Physics, 2009
Macromolecular Bioscience, 2008
Calcium gradients are prepared by piling a micropipette with casein solutions of varying calcium ... more Calcium gradients are prepared by piling a micropipette with casein solutions of varying calcium concentration and spreading them on glass slides. The casein film is formed by solution casting process which results in a macroscopically rough surface. We used microbeam grazing incidence small-angle X-ray scattering to investigate the lateral size distribution of three main components in casein films: casein micelles, casein mini-micelles and micellar calcium phosphate. At length scales within the beam size the film surface is flat and detection of size distribution in a macroscopic casein gradient becomes accessible. The model used to analyze the data is based on a set of three log-normal distributed particle sizes. Increasing calcium concentration causes a decrease in casein micelle diameter while the size of casein mini-micelles increases and micellar calcium phosphate particles remain unchanged.
Journal of Physics: Condensed Matter, 2011
The objective of this study was to determine the effect of size-fractionation by centrifugation o... more The objective of this study was to determine the effect of size-fractionation by centrifugation on the film structure of casein micelles. Fractionated casein micelles in solution were asymmetrically distributed with a small distribution width as measured by dynamic light scattering. Films prepared from the size-fractionated samples showed a smooth surface in optical microscopy images and a homogeneous microstructure in atomic force micrographs. The nano- and microstructure of casein films was probed by micro-beam grazing incidence small angle x-ray scattering (μGISAXS). Compared to the solution measurements, the sizes determined in the film were larger and broadly distributed. The measured GISAXS patterns clearly deviate from those simulated for a sphere and suggest a deformation of the casein micelles in the film.
Journal of Applied Crystallography, 2013
Pressure-driven membrane filtration is a widely used method to separate casein micelles (CM) from... more Pressure-driven membrane filtration is a widely used method to separate casein micelles (CM) from smaller components in milk. The structure of CM attached on the membrane has been investigated because in such a deposited state they reduce the performance of the filtration process. Scattering experiments with nano- and micrometre sized X-ray beams and a filtration setup with silicon micro-sieves as membranes were used. Grazing-incidence small-angle X-ray scattering (GISAXS) experiments above porous regions of the micro-sieves show that spherical CM become stretched in the direction of the filtration flow. The one-dimensional scattering functions extracted from the two-dimensional GISAXS patterns were analyzed by a single ellipsoidal form factor fit. According to the model, CM assume a prolate ellipsoidal shape at a trans-membrane pressure of Δp= 400 mbar (1 mbar = 100 Pa). With increasing trans-membrane pressure, the shape of the CM undergoes a transition towards an oblate structure ...
International Dairy Journal, 2010
The effect of rennin on the micelle structure and microstructure of casein films was investigated... more The effect of rennin on the micelle structure and microstructure of casein films was investigated with micro-beam grazing incidence small angle X-ray scattering and optical microscopy. Size distributions of casein micelles and colloidal calcium phosphate particles were determined as a function of rennin concentration within a rennin gradient film. While the size of the casein micelles decreased with increasing rennin concentration, the size of the colloidal calcium phosphate clusters remained constant. In accordance with a first-order enzyme reaction mechanism, the rennin-induced decay of the micellar sizes could be well described by an exponential function. Two distinct film morphologies at high and low rennin concentration were observed. At intermediate rennin concentration a two-phase surface structure was found, in which both film morphologies coexisted. The conclusions drawn on the behaviour of casein micelles in films can generally be applied to the rennin-induced changes in casein micelles in bulk solutions.
Dairy Science & Technology, 2009
Micro-beam grazing incidence small angle X-ray scattering (μGISAXS) scans were performed to inves... more Micro-beam grazing incidence small angle X-ray scattering (μGISAXS) scans were performed to investigate structural changes that occur after deposition of a droplet of rennin on a casein film. The subsequent diffusion of the droplet into the film led to a lateral and vertical concentration gradient of rennin. As a result of the enzyme action, the film surface became roughened and the formation of islandsevident. The altered surface morphology led to a variation in the μGISAXS pattern, more precisely to the occurrence of a second so-called Yoneda peak. As for the untreated casein film, the mean size of the micelle components (casein micelles, substructure and colloidal calcium phosphate) remained constant within the rennin droplet area. In contrast, a broadening of their corresponding size distributions could be detected. Finally, we discuss the potential of GISAXS scanning experiments with micrometer-sized X-ray beams in view of problems with the interpretation of the data obtained from imaging techniques such as atomic force microscopy. casein micelle / rennin enzyme / casein film / μGISAXS / synchrotron radiation 摘要-微束掠入射小角 X-射线散射法探测凝乳酶表面改性后的酪蛋白膜○ 利用微束掠入 射小角 X-射线散射法 (μGISAXS) 研究了凝乳酶液覆盖酪蛋白膜表面的结构变化○ 凝乳酶的 扩散使其在横向和纵向均形成浓度梯度○ 由于酶的作用，薄膜表面变粗糙，并形成岛屿形状，从 而改变了表面形态，导致 μGISAXS 模式发生变化，出现了所谓的第二 Yoneda 峰○ 与未经 处理的酪蛋白膜一样，在凝乳酶液分布范围内，胶束组分 (包括酪蛋白胶束、亚胶束和胶体磷酸 钙)的平均粒径保持恒定，但是，能检测到的粒径分布范围扩大○ 最后我们用毫米级 X-射线 GISAXS 扫描实验解释了原子力显微镜 (AFM) 成像技术获得的数据所存在的问题○ 酪蛋白胶束 / 凝乳酶 / 酪蛋白膜 / μGISAXS / 同步辐射 Résumé-Modification de la surface de films de caséine par l'action enzymatique de la chymosine mise en évidence par diffusion aux petits angles en incidence rasante de rayons X de taille micrométrique (μGISAXS). Des mesures de diffusion aux petits angles
Colloids and Surfaces B: Biointerfaces, 2011
The paper reports on the structure and formation of casein micelle deposits on silicon nitride mi... more The paper reports on the structure and formation of casein micelle deposits on silicon nitride microsieves during the frontal filtration. The most frequent radius of the fractionated casein micelles we use is R = 60 nm as detected by static light scattering (SLS) and atomic force microscopy (AFM). We estimate the size and size distribution of the casein micelles which pass through the micro-sieve during the filtration process. A sharpening of the size distribution at the beginning of the filtration process (t = 40 s) is followed by a broadening and a shift of the most frequent radii towards smaller sizes at later times (t = 840 s). The size distribution of the micelles deposited on the micro-sieve during filtration is bimodal and consists of the largest and smallest micelles. At larger filtration times, we observe a shift of both deposited size classes towards smaller sizes. The atomic force micrographs of the reference sample reveal a tendency of the casein micelles to order in a hexagonal lattice when deposited on the micro-sieves by solution casting. The deposition of two size classes can be explained by a formation of a mixed hexagonal lattice with large micelles building up the basis lattice and smaller sizes filling octahedral and tetrahedral holes of the lattice. The accompanied compression with increasing thickness of the casein layer could result from preferential deposition of smaller sizes in the course of the filtration.
Brazilian Journal of Medical and Biological Research, 2005
Pressure-induced dissociation of a turbid solution of casein micelles was studied in situ in stat... more Pressure-induced dissociation of a turbid solution of casein micelles was studied in situ in static and dynamic light scattering experiments. We show that at high pressure casein micelles decompose into small fragments comparable in size to casein monomers. At intermediate pressure we observe particles measuring 15 to 20 nm in diameter. The stability against pressure dissociation increased with temperature, suggesting enhanced hydrophobic contacts. The pressure transition curves are biphasic, compatible with a temperature (but not pressure)dependent conformational equilibrium of two micelle species. Our thermodynamic model predicts an increase in structural entropy with temperature.
Brazilian Journal of Medical and Biological Research, 2005
The pressure sensitivities of the near infrared spectra of the lightharvesting (LH2) complex and ... more The pressure sensitivities of the near infrared spectra of the lightharvesting (LH2) complex and a mutant complex with a simplified BChl-B850 binding pocket were compared. In the mutant an abrupt change in the spectral properties occurred at 250 MPa, which was not observed with the native sample. Increased disorder due to collapse of the chromophore pocket is suggested.
Biophysical Journal, 2010
In this study, we used microbeam grazing-incidence small-angle x-ray scattering (mGISAXS) to inve... more In this study, we used microbeam grazing-incidence small-angle x-ray scattering (mGISAXS) to investigate in situ protein nucleation and crystal growth assisted by a protein nanotemplate, and introduced certain innovations to improve the method. Our aim was to understand the protein nanotemplate method in detail, as this method has been shown to be capable of accelerating and increasing crystal size and quality, as well as inducing crystallization of proteins that are not crystallizable by classical methods. The nanotemplate experimental setup was used for drops containing growing protein crystals at different stages of nucleation and growth. Two model proteins, lysozyme and thaumatin, were used under unique flow conditions to differentially probe protein crystal nucleation and growth.
Biophysical Journal, 2007
The structure of thin casein films prepared with spin-coating is investigated as a function of th... more The structure of thin casein films prepared with spin-coating is investigated as a function of the calcium concentration. Grazing incidence small-angle x-ray scattering and atomic force microscopy are used to probe the micelle structure. For comparison, the corresponding casein solutions are investigated with dynamic light-scattering experiments. In the thin films with added calcium three types of casein structures, aggregates, micelles, and mini-micelles, are observed in coexistence with atomic force microscopy and grazing incidence small-angle x-ray scattering. With increasing calcium concentration, the size of the aggregates strongly increases, while the size of micelles slightly decreases and the size of the mini-micelles increases. This effect is explained in the framework of the particle-stabilizing properties of the hairy layer of k-casein surrounding the casein micelles.
Food Hydrocolloids for Health, 2021
Film drying is used for the gentle production of casein microparticles. These result from aggrega... more Film drying is used for the gentle production of casein microparticles. These result from aggregates that have previously formed in solution from micellar caseins in the presence of pectin under neutral pH conditions. The particles are stabilized by hydrophobic interactions and have a spherical shape. Their swelling behavior, which is enhanced with increasing pH, could be of interest for future applications in the field of drug encapsulation and release. The swelling of the microparticles occurs within minutes at pH 11, making it possible to perform a total of 46 consecutive individual tests. The analysis of the results showed that the microparticles keep their spherical shape during swelling. Furthermore, the swelling process proceeds in two steps, the rates of which are independent of the initial size of the casein microparticles. The values of the five parameters of the dynamic swelling model, which is used for the analysis of the kinetics, are examined with the Bravais-Pearson coefficient for pairwise linear correlations. Both swelling steps can be clearly distinguished with regard to rate and characteristic time, whereby the second swelling step at pH 11 consequently has a larger characteristic initial time but also a larger rate. For the first swelling step, the characteristic time and the rate coefficient are uncorrelated, while the rate for swelling step 2, which ends with the disintegration of the casein microparticles, is smaller the later it begins. Since there is a positive correlation between the characteristic times of the two swelling steps, it can be concluded that those particles are most stable for which the swelling process starts the latest. It seems plausible that a different degree of hydration of the microparticles after preparation is the cause of the observed stability differences.
International Journal of Biological Macromolecules, 2017
Static and dynamic light scattering was applied to milk proteins Radii of hydration and gyrat... more Static and dynamic light scattering was applied to milk proteins Radii of hydration and gyration, molecular weights and second virial coefficients were estimated Casein micelles show deviation from a hard sphere under native conditions Hard spheres resulted at elevated calcium chloride concentrations or after removal of -Lactoglobulin
Metalloproteins are essential components of cells, namely in redox processes, e.g. in electron tr... more Metalloproteins are essential components of cells, namely in redox processes, e.g. in electron transfer reactions in respiration and photosynthesis, and in oxygen transport and storage functions. Most metallo-proteins exhibit several structural states, which may occur as substates during function, e.g. redox catalysis or ligand binding, or in the molecular regulation (allosteric conformational changes). The accompanied metal ligand and distance changes can be estimated by XANES, EXAFS and ASAXS of protein solutions. The dispersive estimation of the metal environment structure is difficult with metal protein solutions because of two reasons: i) a protein solution consists mainly of water (>80%) and ii) the specific metal content in the protein entity is low because of the high molecular mass of the protein, e.g. n*70,000 in case of oligomeric Hemocyanin oxygen transport proteins. Thus the metal content is below 20 mM/l, i.e. 0.03%. This makes the usual background correction by fit...
Journal of Membrane Science, 2015
ABSTRACT
Procedia Food Science, 2011
Casein micelles form deposit layers on silicon micro-sieves during dead-end filtration. The pore ... more Casein micelles form deposit layers on silicon micro-sieves during dead-end filtration. The pore size of the used micro-sieves was 0.8 μm. Sequential centrifugation was applied to prepare size-fractionated casein micelles. Dynamic light scattering (DLS) led to mono-exponential correlation functions indicating one prominent micelle size and a sharp size distribution. The hydrodynamic radius was R H = 75 nm. Atomic force microscopy (AFM) showed that casein micelles were distributed homogenously on the micro-sieve. Most of the micelles appeared as compact, spherical objects. Some of them got deformed due to aggregation. The sizes estimated from the AFM images were between 140-160 nm and in accordance with light scattering measurements. The filtration process was monitored by static light scattering (SLS) in the permeate. Scattering functions of casein micelles showed angle dependences, since their sizes exceeded /20 of the wavelength of the used laser light. To adjust for the angle-dependence, scattering data were extrapolated to zero using a form-factor fit of a sphere. During filtration, the resulting intensity decreased to 65% of the original value. As for the flux, two processes could be separated by fitting a double exponential function to the intensity data. The first process was fast with a characteristic time of 18 s and led to an intensity decrease by more than a half. The second process decayed with a characteristic time of 6 min. In the fast process retention of larger micelles takes place while smaller micelles pass through the pores of the micro-sieve. A participation of all micelle sizes and their migration through the formed cake explains the slow process.
Soft Matter, 2014
Tobacco mosaic virus particles can be rapidly assembled into 3D-domains by capillary flow-driven ... more Tobacco mosaic virus particles can be rapidly assembled into 3D-domains by capillary flow-driven alignment at the triple contact-line of an evaporating droplet.
Macromolecules, 2009
Investigating the thickness dependence of ordered structure of thin films of electrically conduct... more Investigating the thickness dependence of ordered structure of thin films of electrically conducting conjugated polymers with nano-ordered morphologies is essential for optimizing their applications in advanced electrooptic devices. We demonstrate here that by spin-coating a small drop of a conjugated-coil diblock copolymer, a thickness gradient varying between tens of nanometers to a few micrometers is formed at the drop rim. Compared to other widely used solution casting methods for the preparation of thickness gradients, the spin-coated drop technique produces film gradients with thickness in the interesting range for most applications in an extremely short preparation time. Using a submicrometersized X-ray beam and a scanning technique, spatial mappings of the gradient area are obtained with submicrometer grazing incidence small-angle X-ray scattering (sub-μGISAXS) for the first time. Investigating the thickness gradient with sub-μGISAXS has the advantage of saving the preparations and investigations of many samples each with a certain thickness under identical conditions. As a model system, we use the diblock copolymer polystyrene-block-poly(p-phenylene) with a thickness gradient ranging between 80 and 2280 nm. Detailed analysis of the scattering patterns at selected positions along the gradient identifies a regime of lateral order within a thickness range of 80-210 nm.
Macromolecular Chemistry and Physics, 2009
Macromolecular Bioscience, 2008
Calcium gradients are prepared by piling a micropipette with casein solutions of varying calcium ... more Calcium gradients are prepared by piling a micropipette with casein solutions of varying calcium concentration and spreading them on glass slides. The casein film is formed by solution casting process which results in a macroscopically rough surface. We used microbeam grazing incidence small-angle X-ray scattering to investigate the lateral size distribution of three main components in casein films: casein micelles, casein mini-micelles and micellar calcium phosphate. At length scales within the beam size the film surface is flat and detection of size distribution in a macroscopic casein gradient becomes accessible. The model used to analyze the data is based on a set of three log-normal distributed particle sizes. Increasing calcium concentration causes a decrease in casein micelle diameter while the size of casein mini-micelles increases and micellar calcium phosphate particles remain unchanged.
Journal of Physics: Condensed Matter, 2011
The objective of this study was to determine the effect of size-fractionation by centrifugation o... more The objective of this study was to determine the effect of size-fractionation by centrifugation on the film structure of casein micelles. Fractionated casein micelles in solution were asymmetrically distributed with a small distribution width as measured by dynamic light scattering. Films prepared from the size-fractionated samples showed a smooth surface in optical microscopy images and a homogeneous microstructure in atomic force micrographs. The nano- and microstructure of casein films was probed by micro-beam grazing incidence small angle x-ray scattering (μGISAXS). Compared to the solution measurements, the sizes determined in the film were larger and broadly distributed. The measured GISAXS patterns clearly deviate from those simulated for a sphere and suggest a deformation of the casein micelles in the film.
Journal of Applied Crystallography, 2013
Pressure-driven membrane filtration is a widely used method to separate casein micelles (CM) from... more Pressure-driven membrane filtration is a widely used method to separate casein micelles (CM) from smaller components in milk. The structure of CM attached on the membrane has been investigated because in such a deposited state they reduce the performance of the filtration process. Scattering experiments with nano- and micrometre sized X-ray beams and a filtration setup with silicon micro-sieves as membranes were used. Grazing-incidence small-angle X-ray scattering (GISAXS) experiments above porous regions of the micro-sieves show that spherical CM become stretched in the direction of the filtration flow. The one-dimensional scattering functions extracted from the two-dimensional GISAXS patterns were analyzed by a single ellipsoidal form factor fit. According to the model, CM assume a prolate ellipsoidal shape at a trans-membrane pressure of Δp= 400 mbar (1 mbar = 100 Pa). With increasing trans-membrane pressure, the shape of the CM undergoes a transition towards an oblate structure ...
International Dairy Journal, 2010
The effect of rennin on the micelle structure and microstructure of casein films was investigated... more The effect of rennin on the micelle structure and microstructure of casein films was investigated with micro-beam grazing incidence small angle X-ray scattering and optical microscopy. Size distributions of casein micelles and colloidal calcium phosphate particles were determined as a function of rennin concentration within a rennin gradient film. While the size of the casein micelles decreased with increasing rennin concentration, the size of the colloidal calcium phosphate clusters remained constant. In accordance with a first-order enzyme reaction mechanism, the rennin-induced decay of the micellar sizes could be well described by an exponential function. Two distinct film morphologies at high and low rennin concentration were observed. At intermediate rennin concentration a two-phase surface structure was found, in which both film morphologies coexisted. The conclusions drawn on the behaviour of casein micelles in films can generally be applied to the rennin-induced changes in casein micelles in bulk solutions.
Dairy Science & Technology, 2009
Micro-beam grazing incidence small angle X-ray scattering (μGISAXS) scans were performed to inves... more Micro-beam grazing incidence small angle X-ray scattering (μGISAXS) scans were performed to investigate structural changes that occur after deposition of a droplet of rennin on a casein film. The subsequent diffusion of the droplet into the film led to a lateral and vertical concentration gradient of rennin. As a result of the enzyme action, the film surface became roughened and the formation of islandsevident. The altered surface morphology led to a variation in the μGISAXS pattern, more precisely to the occurrence of a second so-called Yoneda peak. As for the untreated casein film, the mean size of the micelle components (casein micelles, substructure and colloidal calcium phosphate) remained constant within the rennin droplet area. In contrast, a broadening of their corresponding size distributions could be detected. Finally, we discuss the potential of GISAXS scanning experiments with micrometer-sized X-ray beams in view of problems with the interpretation of the data obtained from imaging techniques such as atomic force microscopy. casein micelle / rennin enzyme / casein film / μGISAXS / synchrotron radiation 摘要-微束掠入射小角 X-射线散射法探测凝乳酶表面改性后的酪蛋白膜○ 利用微束掠入 射小角 X-射线散射法 (μGISAXS) 研究了凝乳酶液覆盖酪蛋白膜表面的结构变化○ 凝乳酶的 扩散使其在横向和纵向均形成浓度梯度○ 由于酶的作用，薄膜表面变粗糙，并形成岛屿形状，从 而改变了表面形态，导致 μGISAXS 模式发生变化，出现了所谓的第二 Yoneda 峰○ 与未经 处理的酪蛋白膜一样，在凝乳酶液分布范围内，胶束组分 (包括酪蛋白胶束、亚胶束和胶体磷酸 钙)的平均粒径保持恒定，但是，能检测到的粒径分布范围扩大○ 最后我们用毫米级 X-射线 GISAXS 扫描实验解释了原子力显微镜 (AFM) 成像技术获得的数据所存在的问题○ 酪蛋白胶束 / 凝乳酶 / 酪蛋白膜 / μGISAXS / 同步辐射 Résumé-Modification de la surface de films de caséine par l'action enzymatique de la chymosine mise en évidence par diffusion aux petits angles en incidence rasante de rayons X de taille micrométrique (μGISAXS). Des mesures de diffusion aux petits angles
Colloids and Surfaces B: Biointerfaces, 2011
The paper reports on the structure and formation of casein micelle deposits on silicon nitride mi... more The paper reports on the structure and formation of casein micelle deposits on silicon nitride microsieves during the frontal filtration. The most frequent radius of the fractionated casein micelles we use is R = 60 nm as detected by static light scattering (SLS) and atomic force microscopy (AFM). We estimate the size and size distribution of the casein micelles which pass through the micro-sieve during the filtration process. A sharpening of the size distribution at the beginning of the filtration process (t = 40 s) is followed by a broadening and a shift of the most frequent radii towards smaller sizes at later times (t = 840 s). The size distribution of the micelles deposited on the micro-sieve during filtration is bimodal and consists of the largest and smallest micelles. At larger filtration times, we observe a shift of both deposited size classes towards smaller sizes. The atomic force micrographs of the reference sample reveal a tendency of the casein micelles to order in a hexagonal lattice when deposited on the micro-sieves by solution casting. The deposition of two size classes can be explained by a formation of a mixed hexagonal lattice with large micelles building up the basis lattice and smaller sizes filling octahedral and tetrahedral holes of the lattice. The accompanied compression with increasing thickness of the casein layer could result from preferential deposition of smaller sizes in the course of the filtration.
Brazilian Journal of Medical and Biological Research, 2005
Pressure-induced dissociation of a turbid solution of casein micelles was studied in situ in stat... more Pressure-induced dissociation of a turbid solution of casein micelles was studied in situ in static and dynamic light scattering experiments. We show that at high pressure casein micelles decompose into small fragments comparable in size to casein monomers. At intermediate pressure we observe particles measuring 15 to 20 nm in diameter. The stability against pressure dissociation increased with temperature, suggesting enhanced hydrophobic contacts. The pressure transition curves are biphasic, compatible with a temperature (but not pressure)dependent conformational equilibrium of two micelle species. Our thermodynamic model predicts an increase in structural entropy with temperature.
Brazilian Journal of Medical and Biological Research, 2005
The pressure sensitivities of the near infrared spectra of the lightharvesting (LH2) complex and ... more The pressure sensitivities of the near infrared spectra of the lightharvesting (LH2) complex and a mutant complex with a simplified BChl-B850 binding pocket were compared. In the mutant an abrupt change in the spectral properties occurred at 250 MPa, which was not observed with the native sample. Increased disorder due to collapse of the chromophore pocket is suggested.
Biophysical Journal, 2010
In this study, we used microbeam grazing-incidence small-angle x-ray scattering (mGISAXS) to inve... more In this study, we used microbeam grazing-incidence small-angle x-ray scattering (mGISAXS) to investigate in situ protein nucleation and crystal growth assisted by a protein nanotemplate, and introduced certain innovations to improve the method. Our aim was to understand the protein nanotemplate method in detail, as this method has been shown to be capable of accelerating and increasing crystal size and quality, as well as inducing crystallization of proteins that are not crystallizable by classical methods. The nanotemplate experimental setup was used for drops containing growing protein crystals at different stages of nucleation and growth. Two model proteins, lysozyme and thaumatin, were used under unique flow conditions to differentially probe protein crystal nucleation and growth.