| 1. |
- Brink, J., et al.
(författare)
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Simultaneous analysis of the structural and mechanical changes during large deformation of whey protein isolate/gelatin gels at the macro and micro levels
- 2007
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 21:3, s. 409-419
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Tidskriftsartikel (refereegranskat)abstract
- The effect of microstructure on the fracture properties of whey protein isolate (WPI) gels with varying amounts of gelatin was analysed on the macro (mm scale) and micro (?m scale) levels. Eight percent WPI particulate gels with 0-6% gelatin were prepared at a pH near the isoelectric point of whey protein. The tensile stage was placed directly under the confocal laser-scanning microscope (CLSM). The structural changes of the gel during the deformation are visualized in series of micrographs with simultaneous recording of stress and strain data with the tensile stage. The pure whey protein gel exhibited uneven failure at the macro level, where the crack propagated between the whey protein clusters, whereas the crack propagated smoothly through the gelatin phase in the whey/gelatin gel system. At higher magnification the pure WPI protein gel showed porous failure behaviour and gradually ruptured. The WPI gel with high gelatin concentration followed the rheological response of the gelatin phase, resulting in stretched failure behaviour with rapid rupture. The micro strain was calculated directly from micrographs, with the pure WPI gel reaching a seven times higher micro strain than the macro strain. The difference between micro and macro strain decreases with increasing gelatin concentration. Threshold crack propagation values were identified at both the macro and micro levels, and the start of structural failure was observed long before any mechanical response. The fracture dynamics of mixed biopolymer gels can be analysed with this approach both structurally and rheologically at different length scales, contributing to a more comprehensive understanding of the failure behaviour. © 2006 Elsevier Ltd. All rights reserved.
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| 2. |
- Fransson, S., et al.
(författare)
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Effect of confinement and kinetics on the morphology of phase separating gelatin-maltodextrin droplets
- 2009
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:6, s. 1446-1453
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Tidskriftsartikel (refereegranskat)abstract
- The effect of confinement on the structure evolution and final morphology during phase separation and gelation of gelatin and maltodextrin was investigated and compared to the structures seen in bulk phase. Emulsion droplets with diameters from 4 to 300 ?m were analyzed using confocal laser scanning microscopy and image analysis. With the confocal laser scanning microscope it was possible to follow the entire phase separating process inside the droplets in real-time. The samples were either quenched directly from 70°C down to 20°C or exposed to holding times at 40°C. Different cooling procedures were studied to examine the structure evolution both before and after gelation in the restricted geometries. The concentration of the biopolymer mixture was kept constant at 4 w/w% gelatin and 6 w/w% maltodextrin. The results revealed that the size of the confinement had a great effect on both the initiation of phase separation and the final morphology of the microstructure inside the emulsion droplets. The phase separation in small droplets was observed to occur at a temperature above the phase separating temperature for bulk. Small droplets had either a microstructure with a shell of maltodextrin and core of gelatin or a microstructure where the two biopolymers had formed two separate bicontinuous halves. The initiation of phase separation in large droplets was similar to what was seen in bulk. The microstructure in large droplets was discontinuous, resembling the morphology in bulk phase. The kinetics had an effect on the character of the maltodextrin inclusions, as the cooling procedure of a direct quench gave spherical inclusions with an even size distribution, while a holding time at 40°C resulted in asymmetrical and elongated inclusions. © 2009 American Chemical Society.
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| 3. |
- Gatenholm, P., et al.
(författare)
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Hygiene: Jellyfish are blueprint for new absorbent materials
- 2007
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Ingår i: Medical Textiles. - 0266-2078. ; :FEB., s. 9-
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Tidskriftsartikel (refereegranskat)abstract
- Four years ago, scientists from the Chalmers University of Technology and the Swedish Institute for Food and Biotechnology initiated a project aimed at examining the little-known mechanisms of jellyfish. The group found out that the jellyfish's structure is made of interacting proteins and polysaccharides that are built up in a highly hierarchic fashion. Ions were also found to play a key role in the mechanism.
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| 4. |
- Hermansson, Ann-Marie
(författare)
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Structuring water by gelation
- 2008
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Ingår i: Food Materials Science: Principles and Practice. - New York, NY : Springer New York. ; , s. 255-280
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Tidskriftsartikel (refereegranskat)abstract
- Gels are of central importance for most semisolid food products. A gel can contain more than 99% water and still retain the characteristics of a solid. The network structure will determine whether the water will be firmly held or whether the gel will behave more like a sponge, where water is easily squeezed out. The gel structure will also have a major impact on the texture as well as diffusion of water and soluble compounds. Many food matrixes are based on colloidal gels such as yoghurts, cheeses, many desserts, sausages etc (see also Chapters 19 and 20). In whole foods, there is often a combination of colloidal structures and fragments of biological tissues or gel structures in combination with particles, emulsion and foam structures. This level of complexity of composite food structures will not be dealt with here. © 2008 Springer Science+Business Media, LLC.
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| 5. |
- Lofgren, C., et al.
(författare)
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Microstructure and kinetic rheological behavior of amidated and nonamidated LM pectin gels
- 2006
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 7:1, s. 114-121
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure, kinetics of gelation, and rheological properties have been investigated for gels of nonamidated pectin (C30), amidated pectin (G), and saponified pectin (sG) at different pH values, both with and without sucrose. The low-methoxyl (LM) pectin gels were characterized in the presence of Ca2+ by oscillatory measurements and transmission electron microscopy (TEM). The appearance of the gel microstructure varied with the pH, the gel structure being sparse and aggregated at pH 3 but dense and somewhat entangled at pH 7. During gel formation of pectins G and C30 at pH 3 there was a rapid increase in G? initially followed by a small increase with time. At pH 7 G? increased very rapidly at first but then remained constant. The presence of sucrose influenced neither the kinetic behavior nor the microstructure of the gels but strongly increased the storage modulus. Pectins G and C30 showed large variations in G? at pH values 3, 4, 5, and 7 in the presence of sucrose, and the maximum in G? in the samples occurred at different pH values. Due to its high Ca2+ sensitivity, pectin sG had a storage modulus that was about 50 times higher than that of its mother pectin G at pH 7. © 2006 American Chemical Society.
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| 6. |
- Lofgren, C., et al.
(författare)
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Synergistic rheological behaviour of mixed HM/LM pectin gels
- 2007
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 21:3, s. 480-486
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the rheological behaviour of mixed gels of high methoxyl (HM) and low methoxyl (LM) pectins with the purpose of designing gels with reduced sucrose content but unaltered rheological properties. The gelation behaviour of mixed HM/LM pectin gels was compared to that of HM and LM pectin gels in the presence of 30%, 45% and 60% sucrose. The gels were investigated in the presence of 0.1% CaCl2·2H2O and pH 3.5, conditions that favour the gel formation of both HM and LM pectins. Strong synergistic effects occurred in the rheological behaviour for three mixed 0.8% HM/0.4% LM pectin gels under conditions where LM pectin formed microgels instead of coherent gels. The addition of LM pectin strongly increased the storage modulus in mixed HM/LM pectin gels based on 60% and 45% sucrose compared to HM pectin gels of the same sucrose concentration. The kinetic behaviour of the mixed HM/LM pectin gels during gel formation varied depending on the kinetic behaviour of the HM pectins differing in degrees of blockiness. Transmission electron microscopy (TEM) showed that the gel microstructure of the mixed gel with 60% sucrose was inhomogeneous. The addition of HM pectin in mixed gels with only 30% sucrose increased the storage modulus two to five times compared to that of 0.4% LM pectin gels under the same conditions. The phase angle for the mixed gel with 30% sucrose was also higher than for the corresponding 0.4% LM pectin gel. © 2006 Elsevier Ltd. All rights reserved.
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| 7. |
- Loren, Niklas, et al.
(författare)
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Confocal fluorescence microscopy (CLSM) for food structure characterisation
- 2007
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Ingår i: Understanding and Controlling the Microstructure of Complex Foods. - : Elsevier. ; , s. 232-260
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Tidskriftsartikel (refereegranskat)abstract
- * Introduction * Principles of modern CLSM * CLSM and the study of food structure * Application of CLSM to food systems * Measuring and modelling using CLSM images * Conclusions and future trends * References. © 2007 Woodhead Publishing Limited. All rights reserved.
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| 8. |
- Loren, Niklas, et al.
(författare)
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Measuring shapes for application in complex food structures
- 2006
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 20:5, s. 712-722
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Tidskriftsartikel (refereegranskat)abstract
- The image analysis method of Fourier shape description is implemented to analyse shaped food microstructural entities, independent of their complexity, because entity shape is an important and nearly unexploited possibility for designing food material properties. The method is described in four steps: the accuracy of image acquisition, representation of the object outline, calculation of components and interpretation of the components, all focusing on colloidal food system applications. Three different common food systems are used to emphasise the possibilities that Fourier shape description offers for food structure design and food processing. Fourier shape measurements make it possible to quantify, present a typical shape and determine the distribution of shape independently of size of model food suspension consisting of complex shaped entities. This was done in an automatic and replicable way. The time evolution of entities structured in a flow field during model processing is analysed using Fourier shape descriptors. Graphs of time-dependent, low order single Fourier components allow control of the entity shape during processing. Differences in the shape of water domains in heterogeneous emulsions are quantified and classified on different length scales using a multivariate hypothesis test. © 2005 Elsevier Ltd. All rights reserved.
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| 9. |
- Loren, Niklas, et al.
(författare)
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Water mobility in heterogeneous emulsions determined by a new combination of confocal laser scanning microscopy, image analysis, nuclear magnetic resonance diffusometry, and finite element method simulation
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:2, s. 24716-
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear magnetic resonance (NMR) diffusometry and confocal laser scanning microscopy (CLSM) were combined in a quantitative way in finite element calculations of water propagation in CLSM images obtained from a very heterogeneous emulsion. The propagators calculated on the basis of microstructure were Fourier transformed and subsequently compared with the echo decays obtained by the NMR diffusometry method. The results showed very good agreement between microstructure based calculations and experiments, indicating that the short gradient pulse approximation in the NMR diffusometry experiment holds for a certain q range. Furthermore, the CLSM was able to achieve a relevant two-dimensional microstructure although some discrepancy at low q values was noted. This effect is attributed to the inherent three-dimensional connectivity between the water domains in this type of structures, making the calculations slightly underestimate the water diffusion at longer distances. © 2005 American Institute of Physics.
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| 10. |
- Lundell, C., et al.
(författare)
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Effects of confined geometry on phase-separated dextran/gelatine mixtures exposed to shear
- 2005
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 288:1, s. 222-229
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Tidskriftsartikel (refereegranskat)abstract
- The effect of shear on aqueous phase-separated dextran/fish gelatine mixtures with a total concentration of 5 and 10% was studied in a confined geometry. It was measured as a function of composition, strain rate and gap size. This was done by using both small-angle light scattering and a shear cell combined with a confocal laser scanning microscope. At a total polymer concentration of 5%, small-angle light scattering results showed that up to 100 s-1 the deformation of the domains increases with the strain rate. At strain rates less than 100 s-1, the response of the system to strain is dominated by strain rate-dependent deformation. At a higher strain rate there might be balance between break-up and re-coalescence. At a total concentration of 10%, small effects of the gap size were found. In confined geometry, the coalescence rate was faster than expected from viscous hydrodynamic growth. The microscope images showed that the gelatine-enriched phase forms a wetting layer on the surface of the glass wall. The degree of wetting appears to increase with increasing the strain rate up to 60 s -1 and decreases again at higher strain rates. © 2005 Elsevier Inc. All rights reserved.
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