| 1. |
- Hamberg, Lars, et al.
(författare)
-
Aggregation, viscosity measurements and direct observation of protein coated latex particles under shear
- 2001
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 15:2, s. 139-151
-
Tidskriftsartikel (refereegranskat)abstract
- The aggregation under shear, of latex particles coated with whey protein isolate was monitored, in a continuous phase with a complex behaviour in relation to temperature dependence and shear thinning. The monitoring was done with viscosity measurements and microscopy. An aggregating dispersion of whey coated polystyrene latex particles, salt, sucrose and gelatine was sheared in a rheometer at shear rates between 0.05 and 5 s-1. The viscosity was monitored as a function of time during a temperature increase from 30 to 60°C. The viscosity curves were interpreted with the aid of additional information from light microscopy micrographs. The aggregation was clearly visible as an increase in viscosity. Aggregation was observed to initiate at a temperature between 40 and 50°C. Unbound protein, i.e. protein not a part of particle coating, was found to be essential for the aggregation of latex particles. After aggregation, a shear thinning behaviour was detected. This was due to two phenomena: structural changes of the aggregates and shear thinning behaviour of the dispersion. The build-up of the aggregates was followed by direct observation in a confocal laser scanning microscope. A sequence of micrographs was taken, in an unstopped 3-D flow field generated in a four-roll mill, which showed the evolution of the size of the aggregates. The micrographs were in good agreement with the viscosity measurements. This showed that the four-roll mill and a confocal laser scanning microscope is a useful tool for studying aggregation in an undisturbed 3-D flow. © 2001 Elsevier Science Ltd.
|
|
| 2. |
- Hamberg, Lars, et al.
(författare)
-
Shapes and shaping of biopolymer drops in a hyperbolic flow
- 2003
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 17:5, s. 641-652
-
Tidskriftsartikel (refereegranskat)abstract
- The shaping of drops in a model system based on ? -carrageenan-emulsion drops in the millimetre range in silicon oil has been studied. The drops were shaped by exposing them to drag forces in a hyperbolic flow, while their shape was fixed simultaneously by introducing gel formation of the biopolymer in the drop. The shape and the shaping process were studied and evaluated with image analysis of macrograph sequences of the shaping. The effect of process conditions, flow speed and cooling temperature on the final shape and shape progress was investigated as well as the effect of different ?-carrageenan drop characteristics, such as drop viscosity and gel strength. Drop viscosity was altered by addition of locust bean gum, LBG, and the gel strength was altered by addition of ions. The ?-carrageenan solutions in the drop were characterised by rheological investigations. With the same type of flow, different shapes could be achieved with small process changes and with high reproducibility. The fixation of the characteristic drop features, perimeter, area, Feret's X and Y, does not occur at the same time and position. For the different process parameters investigated, a change in speed affected the process in a similar way to a change in the viscosity ratio. This applies if the viscosity ratio is changed at a constant temperature, but if the change in the viscosity ratio is temperature-induced, the effect is different. The final shape of the produced drops could be graded into three classes, correlated to the position in the flow field where the drops were fixed. A shape map of the different drop shapes obtained was presented. © 2003 Elsevier Science Ltd. All rights reserved.
|
|
| 3. |
- Hamberg, Lars, et al.
(författare)
-
Shaping of gelling biopolymer drops in an elongation flow
- 2002
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 252:2, s. 297-308
-
Tidskriftsartikel (refereegranskat)abstract
- Shaping, defined as deformation in combination with gel formation of gelatine and ?-carrageenan drops in an elongation flow, was studied. The focus was to investigate the possibility of shaping and fixating small drops in the diameter range 20 to 229 ?m. In the shaping progress and the influence of experimental properties, the viscosity, temperature, and flow of the deforming fluid were examined on the final drop shape. In the experiments a hot emulsion of an aqueous biopolymer solution in silicone oil was injected into cold silicone oil where a deforming elongation flow field existed. After injection, a temperature decrease in the drops resulted in a gel formation of the biopolymer and a fixation of the deformed drop in the flow. The shape was measured and the effect on the drop aspect ratio was determined by image analysis. Over the total drop diameter range, ?-carrageenan was more ellipsoid-shaped than gelatine, with a maximum aspect ratio of 6 compared to 4 for gelatine. For small drops, around 22 ?m, it is possible to shape ?-carrageenan, but for gelatine small drops tend to be unaffected. An increase in viscosity, temperature, and flow resulted in an increase in the final fixated shape of the drops. The differences in drop deformation between the biopolymers were explained by drop-viscosity/oil differences and differences in the kinetics of gel formation. The different gel formation kinetics resulted in a short, well-defined, shaping process for ?-carrageenan, while for gelatine the process was more complex, with both deformation and relaxation present at different stages. © 2002 Elsevier Science (USA).
|
|
| 4. |
- Lofgren, C., et al.
(författare)
-
Microstructure and rheological behavior of pure and mixed pectin gels
- 2002
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 3:6, s. 1144-1153
-
Tidskriftsartikel (refereegranskat)abstract
- The microstructure and the rheological properties of pure HM (high methoxyl) and LM (low methoxyl) pectin gels and of mixed HM/LM pectin gels have been investigated. Gel formation of either the HM or LM pectin, or both, was initiated in the mixed gels by varying the sucrose and Ca 2+ content. The microstructure was characterized by transmission electron microscopy, light microscopy, and confocal laser scanning microscopy. HM and LM pectin gels showed aggregated networks with large pores around 500 nm and network strands of similar character. Small differences could be found, such as a more inhomogeneous LM pectin network with shorter and more branched strands of flexible appearance. LM pectin also formed a weak gel in 60% sucrose in the absence of calcium. A highly inhomogeneous mixed gel structure was formed in the presence of 60% sucrose and Ca 2+ ions, which showed large synergistic effects in rheological properties. Its formation was explained by the behavior of the corresponding pure gels. In the presence of 60% sucrose alone, a homogeneous, fine-stranded mixed network was formed, which showed weak synergistic effects. It is suggested that LM pectin interacts with HM pectin during gel formation, thereby hindering secondary aggregation leading to the aggregated networks observed for the pure gels.
|
|
| 5. |
- Lundell, C., et al.
(författare)
-
Influence of elongational flow on phase separated inclusions within gelling biopolymer drops
- 2004
-
Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 18:5, s. 805-815
-
Tidskriftsartikel (refereegranskat)abstract
- Drops of an immiscible biopolymer mixture containing maltodextrin/gelatine were shaped and set in an elongational flow in a flow cell called 4-RM. The kinetics of phase separation as well as the kinetics of gel formation were governed by the temperature differences which appear as the 60°C maltodextrin/gelatine mixture reaches the 10°C silicon oil in the 4-RM. The shape and inner structure of the drops were visualized with the help of a confocal laser scanning microscope (CLSM). The result showed that the solution phase separated into gelatine-rich and a maltodextrin-rich phase during the short time it takes to gel the particle, i.e. in approximately 2 s. It was found that the shape of the phase separated inclusions was affected by the elongational flow. Mixtures of a 10% constant gelatine concentration and a 2-15% maltodextrin concentration were evaluated. The size of the inclusions within the phase separated drops increases as the maltodextrin concentration increases. At a maltodextrin concentration of 12%, the phase inversion has occurred. Shape transfer between the drop and its inclusions was investigated. The length to width ratios of the drops and its inclusions were compared and it was found that for the gelatine-continuous drop created at a flow rate of 10 rpm the ratio responds well. A comparison of the Taylor parameter calculated from viscosity data before gel formation and image analysis of experimental results showed that deformation takes place within the critical stage of gel formation. © 2004 Elsevier Ltd. All rights reserved.
|
|
| 6. |
- Walkenström, Pernilla, et al.
(författare)
-
Microstructure and rheological behaviour of alginate/pectin mixed gels
- 2003
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 17:5, s. 593-603
-
Tidskriftsartikel (refereegranskat)abstract
- The synergistic interaction between alginate and pectin was systematically investigated using samples of different chemical compositions. Pectin samples with high and low degrees of esterification (DE) and amidated pectin (LA) were mixed with alginate of high and low M/G (mannuronic acid/guluronic acid) ratio. The microstructure of the gels was characterised by TEM (transmission electron microscopy) and the rheological properties by dynamic oscillatory measurements. The TEM images of the mixed gels revealed a coarse, strand-like network with pores in the range of microns, independent of the ratio and the composition of the samples. A comparison with the microstructure of a pure pectin gel showed that the pectin network was composed of thinner strands and smaller pore sizes than the mixed network. The strongest synergism was found between alginate with low M/G ratio and pectin with a high DE. These gels show the highest G? (storage modulus) and the fastest kinetics of gel formation. Lower G? and slower kinetics were found for gels based on alginate with a high M/G ratio and pectin with a low DE, or LA pectin. The nature of the pectin sample affected the network density and the strand characteristics. In contrast, no influence was found of the alginate sample. Gels based on pectin with a high DE showed a dense network composed of highly branched strands, whereas the LA-pectin based gels showed a sparse, open network, composed of long, straight strands. A relation close to 1:1 for low-G alginate and pectin with a high DE resulted in gels with the highest G?. In contrast, for LA-pectin based gels, the highest G? was found for mixtures of alginate dominant ratios. For the overall network properties, the homogeneity in the microstructure decreased with alginate content, independent of the pectin sample. © 2003 Elsevier Science Ltd. All rights reserved.
|
|
| 7. |
- Walkenström, Pernilla, et al.
(författare)
-
Microstructure in relation to flow processing
- 2002
-
Ingår i: Current Opinion in Colloid & Interface Science. - 1359-0294 .- 1879-0399. ; 7:42130, s. 413-418
-
Tidskriftsartikel (refereegranskat)abstract
- The art of structure formation by process flow control is a growing field of research. The central issue is the understanding that the rheological properties of a food substance are intimately linked to its microstructure. By carefully controlling the flow process environment, the microstructure, and thus the rheological properties, can be crafted to produce new products desired by the consumer market. © 2002 Elsevier Science Ltd. All rights reserved.
|
|
| 8. |
- Walther, Bernhard, et al.
(författare)
-
Flow processing and gel formation : A promising combination for the design of the shape of gelatin drops
- 2002
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 16:6, s. 633-643
-
Tidskriftsartikel (refereegranskat)abstract
- This investigation is a model study on how drops can be structured by a combination of flow processing and gel formation. Different drop shapes were created by subjecting gelatin drops to various flow conditions. At the same time, temperature induced gel formation of the drops fixed the shape. Elongated drops and drops of complex form were created. The flow to shape the gelatin drops was generated in a 4-Roll Mill (4RM) and silicon oil was used as the continuous phase. During processing in the 4RM, the drops were allowed to follow two different streamlines and thereby being subjected to purely elongational and a mixture of shear and elongational flow. The drop size varied between 1.5 and 2.8 mm. The gelatin drops were temperature conditioned before the experiment to 60 °C and the silicon oil to 5 °C. The drops were cooled via the cold oil phase during the flow process, and gel formation was induced. A gel strength strong enough to resist further deformation was achieved at different fixation zones in the 4RM, and this depended on the process parameters of flow type, flow rate, drop size and gelatin concentration. The shape created was directly related to the fixation zone. There was a broad freedom to combine different parameter values to fix a drop in a certain fixation zone. The mechanism behind the various drop shapes is explained in terms of elongation, relaxation, pinching and gel formation in relation to flow pattern and time in the 4RM. Elongation is a major contribution to the mechanism in the case of elongated shapes, while elongation followed by relaxation and pinching are the dominant determinants in the creation of complex shapes. © 2002 Elsevier Science Ltd. All rights reserved.
|
|
| 9. |
- Walther, Bernhard, et al.
(författare)
-
Formation of shaped drops in a fast continuous flow process
- 2004
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 270:1, s. 195-204
-
Tidskriftsartikel (refereegranskat)abstract
- Drop shaping, i.e., flow-induced deformation and fixation by gel formation, was studied under dynamic conditions in a fast continuous process for a water-in-oil system. The system consisted of sunflower oil with different surfactant concentrations (0.1-2% Admul Wol) and a 1.5% ?-carrageenan solution with different Na+ and K+ concentrations. The continuous phase flowed in a 10-mm-wide straight channel into which the dispersed phase was injected via a thin needle. A subsequent shaping channel with a width of 1 or 2 mm deformed the drops. Gel formation was induced by a temperature gradient between the continuous and dispersed phase. Drop sizes in the range 220-roughly 1000 ?m were produced at the needle tip by varying the ratio between the oil and carrageenan flow rate. A diffusion zone before the narrow channel allowed the surfactant to adsorb at the interface. In the elongation flow at the entrance of the shaping geometry, drops underwent initial elongation. In the narrow channel, the drops developed a parabolic shape within a residence time of 0.03-0.15 s. Choosing the correct parameter combinations made it possible to fix the deformation by gel formation within this time period. Shaped drops were shown to be functional. At a concentration of 25% in an emulsion, they increased the viscosity by about 15-20% compared to spherical drops even though 45% of the shaped drops had an aspect ratio of less than 1.2. © 2003 Elsevier Inc. All rights reserved.
|
|
