| 1. |
- Georgopoulos, Theofanis, et al.
(author)
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A comparison of the rheological properties of wheat flour dough and its gluten prepared by ultracentrifugation
- 2004
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In: Food Hydrocolloids. - 0268-005X. ; 18:1, s. 143-151
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Journal article (peer-reviewed)abstract
- Ultracentrifugation has been used as a tool for separating dough into different phases and as dough can be described as a bicontinuous system, gluten forms one phase, and starch another. The aim of this study is to investigate the possibility of using ultracentrifugation to extract gluten from dough. By using this method disadvantages such as excess washing, drying and reconstitution of dried gluten (involving a second mixing) were avoided. Gluten samples were obtained by this method (doughs differing in water content from 42.6 to 47.1%) and the rheological properties of dough and the corresponding gluten were studied in frequency sweep. The gluten coming from dough after ultracentrifugation had water contents in the range of 54.2–58.8%. An increase in water content reduced the storage modulus to a greater extent than the loss modulus for the studied dough. The gluten was not affected to the same extent by an increase in water content, as was the dough. The ratios of G′dough/G′gluten and G″dough/G″gluten approached the value of 1 when the amount of dough water increased. The slope of log G″ versus log for gluten (n″gluten) were always higher than n′gluten. For dough the slope of log G″ versus log (n″dough) were on the same level or higher than (n′dough). It was concluded that both the frequency dependency and the values of G′ and G″ were more or less independent of water content for gluten. On the contrary dough showed a strong dependency of water content in particular for the value of G′ and the frequency dependency of G′.
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| 2. |
- Landström, K, et al.
(author)
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Competitive protein adsorption between ß-casein and ß-lactoglobulin during spray-drying: effect of calcium induced association
- 2003
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In: Food Hydrocolloids. - : Fairleigh Dickinson University Press. - 0268-005X .- 1873-7137. ; 17, s. 103-116
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Journal article (peer-reviewed)abstract
- Competitive adsorption between ß-casein and ß-lactoglobulin (ß-Lg) during spray-drying was studied by the new surface sensitive technique using fluorescence quenching of pyrene labelled protein at the powder surface. The difference in competitiveness of -casein when present as monomers and as associated into micellar like structures were studied. Results were compared with the adsorption of single proteins at the powder surface. The adsorption of monomeric ß-casein alone gave an apparent surface load of ≈1 mg/m2 at a protein concentration of 0.3% dry weight and then remained constant with an increasing protein concentration. In the presence of Ca2+, associated ß-casein gave a lower affinity adsorption than monomeric ß-casein and did not reach a plateau value, instead it continued to increase with an increasing protein concentration. ß-Lg showed a low-affinity adsorption during spray-drying compared to monomeric ß-casein, although not as low as associated ß-casein. Competitive adsorption between monomeric ß-casein and ß-Lg resulted in a higher apparent surface load of ß-casein than ß-Lg at both protein concentrations studied (total 0.3 and 3.3% dry weight). However, in an associated form ß-casein was less competitive than ß-Lg. At a low bulk protein concentration (0.3% dry weight) ß-Lg dominated the powder surface, whereas at a higher concentration (3.3% dry weight) there was little difference between the proteins. The results indicate that the competitiveness of a protein during spray-drying is highly influenced by the ability of the protein to attach and rearrange at the droplet's air–water interface during the spray-drying process
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| 3. |
- Howcroft, Debra, et al.
(author)
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Participation : 'Bounded freedom' or hidden constraints on user involvement
- 2003
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In: New technology, work and employment. - 0268-1072 .- 1468-005X. ; 18:1, s. 2-19
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Journal article (peer-reviewed)abstract
- User participation in information systems development is often surrounded by assumptions that the resultant system will be a success, will reflect user needs, and that the process results in an empowered workforce. This paper argues that underlying these foreground rational assumptions are instrumental, politically motivated justifications driving the need to involve users.
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| 4. |
- Girhammar, Ulf Arne, et al.
(author)
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Certain physical properties of water-soluble nonstarch polysaccharide from wheat, rye, triticale, barley and oats
- 1992
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In: Food Hydrocolloids. - : Oxford University Press. - 0268-005X .- 1873-7137. ; 6:4, s. 329-343
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Journal article (peer-reviewed)abstract
- The yield of water soluble non-starch polysaccharides (WSNSP) prepared from whole grains of wheat, rye, triticale, barley and oats was 0.6, 1.8, 0.7, 1.2 and 1.0% respectively of the dry matter. The WSNSP from wheat, rye and triticale contained mainly pentoses (74, 86 and 81% respectively of the total monosaccharides), while in the WSNSP of barley and oats glucose (74 and 69% respectively of the total monosaccharides) was the main monosaccharide. All the WSNSP samples contained some amount of protein (7% in rye-WSNSP to 18% in triticale-WSNSP) attached to their low molecular weight fractions as observed in the gel permeation chromatographic separation. The major amino acids in these samples were aspartic and glutamic acids. No hydroxyproline was found in these samples. Their water binding capacity determined as the amount of unfreezable water using differential scanning calorimetry showed that the WSNSP of wheat, rye, triticale, barley and oats was 0.41, 0.47, 0.42, 0.49 and 0.44 g/g dry matter respectively. The WSNSP of wheat and barley showed higher emulsifying capacities determined as the amount of oil emulsified by one gram of the sample in water. The intrinsic viscosity of the water solutions of these non-starch polysaccharides shows a direct relation to their molecular weight and their simha shape factors indicated that all the samples were of an extended shape. However, the intrinsic viscosity of the water solution of rye-WSNSP was significantly higher than that of wheat, triticale, barley and oats.
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| 5. |
- Girhammar, Ulf Arne, et al.
(author)
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Isolation, separation and characterization of water soluble non-starch polysaccharides from wheat and rye
- 1992
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In: Food Hydrocolloids. - : Oxford University Press. - 0268-005X .- 1873-7137. ; 6:3, s. 285-299
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Journal article (peer-reviewed)abstract
- The water holding capacity of the dough and the freshness of the bread made of rye and wheat are much dependent upon their content of non-starch polysaccharides (NSP), most of which are polymers of xylose and arabinose, i.e. pentosans. The yield of water soluble pentosans from rye flour (1.76%) was higher than that of wheat flour (0.59%), and the xylose to arabinose ratio of rye pentosans was 1:36 while it was 1:16 for wheat pentosans. The galactose content in wheat pentosans was 17% of the total monosaccharides. In rye pentosans the content of galactose was lower (3.5% of the total monosaccharides). The total content of monosaccharides in wheat pentosans (65%) was slightly lower than that in the rye pentosans (71.7%). The weight average molecular weight of rye pentosans (770 000) was higher than that of the wheat pentosans (255 000). The number average molecular weight of the pentosans from rye was 90 000 while the corresponding figure for wheat was 61 000. The rye pentosans showed a higher degree of polydispersity in solution than the wheat pentosans. The separation of the pentosans on a DEAE-Sephadex column resulted in five fractions. The first two fractions contained mainly arabinose and xylose and the protein content in these fractions was approximately 1%. The protein content of the fractions increased with the increased concentration of the borate. The Xyl:Ara ratio was 2:23 and 2:39 in fractions I and II of wheat and 1:63 and 2:32 in fractions I and II of rye. Galactose appeared in fractions IV and V in wheat and fractions IV, V-A and V-B in rye along with some arabinose which suggests the presence of arabinogalactans in these fractions.
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| 6. |
- Hamberg, Lars, et al.
(author)
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Aggregation, viscosity measurements and direct observation of protein coated latex particles under shear
- 2001
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In: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 15:2, s. 139-151
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Journal article (peer-reviewed)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.
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| 7. |
- Hamberg, Lars, et al.
(author)
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Shapes and shaping of biopolymer drops in a hyperbolic flow
- 2003
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In: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 17:5, s. 641-652
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Journal article (peer-reviewed)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.
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| 8. |
- Olsson, C., et al.
(author)
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Dynamic measurements of ?-lactoglobulin structures during aggregation, gel formation and gel break-up in mixed biopolymer systems
- 2002
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In: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 16:5, s. 477-488
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Journal article (peer-reviewed)abstract
- The kinetics of aggregation and gelation of ?-lactoglobulin/amylopectin microstructures have been studied by using confocal laser scanning microscopy (CLSM) equipped with a temperature stage, transmission electron microscopy (TEM) and dynamic mechanical analysis in shear. The behaviour of the final gels was studied during fracture deformations using a tensile stage adapted to the CLSM. The different types of particulate ?-lactoglobulin (?-1g) network structures were generated by adding non-gelling amylopectin of varying concentration and viscosity. The results showed that the higher the concentration and the higher the viscosity of the amylopectin, the lower the temperature required for ?-1g to aggregate into particle aggregates and clusters visible in the CLSM. The gelling temperature of the ?-1g, determined by small deformation rheological measurements, was also found to decrease with increase in amylopectin concentration. However, although an increased concentration of amylopectin accelerated the particle aggregation of ?-1g, amylopectin with a higher viscosity was found to restrict the aggregated protein aggregates and clusters to form a connected protein network. The result of the difference in connectivity was shown when the gel structures were studied during fracture deformations in tension. In the weaker gel type, where the continued aggregation to a connected network had been obstructed, the fracture was extended more deeply inside the structure than in the stronger gel type with good connectivity, when exposed to the same deformation. The distribution of the protein and the amylopectin in the aggregated structure was visualized by TEM. Amylopectin was found inside the ?-1g aggregates in the gels containing a lower viscosity of the amylopectin. In gels containing amylopectin with higher viscosity, the amylopectin was found in the pores between the protein networks, separated from the protein phase. © 2002 Elsevier Science Ltd. All rights reserved.
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| 9. |
- Olsson, C., et al.
(author)
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Microstructures of ?-lactoglobulin/amylopectin gels on different length scales and their significance for rheological properties
- 2002
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In: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 16:2, s. 111-126
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Journal article (peer-reviewed)abstract
- Different microstructures of ?-lactoglobulin gels, generated by adding non-gelling potato amylopectin of varying concentrations and rheological behaviour, were characterised by microscopic techniques on several length scales. The overall network microstructure of the ?-lactoglobulin gels was analysed by using light microscopy (LM) and confocal laser scanning microscopy (CLSM), while the construction of the separate strands was investigated by using transmission electron microscopy (TEM). At an overall level of structure, increased concentration of amylopectin resulted in a more open network with larger pores and coarser clusters of aggregated protein. Examination of the microstructure of one cluster showed that increased concentration of amylopectin resulted in a more close-packed structure of aggregated protein particles. Thus, the results of the studies on different length scales showed that gels with an open protein network structure at an overall level were constructed of close-packed clusters, while gels which were dense at an overall level of structure were constructed of open and porous clusters. By using TEM at high magnifications it was possible to observe the particles forming the aggregates building up the clusters. The particles had about the same diameter, perceived to be 100-200 nm in all the types of gels studied. By studying thick sections of the microstructure in the light microscope, differences in connectivity of the protein network strands were possible to detect. The results from the microstructural investigations were analysed together with the rheological properties of the gels. It was found that the cluster size and the pore size between the strands of clusters were related to storage modulus and stress at fracture as long as the connectivity of the network strands was good. © 2002 Elsevier Science Ltd. All rights reserved.
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| 10. |
- Olsson, C., et al.
(author)
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Rheological influence of non-gelling amylopectins on ?-lactoglobulin gel structures
- 2000
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In: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 14:5, s. 473-483
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Journal article (peer-reviewed)abstract
- The effect of non-gelling potato amylopectin on the gel properties of a particulate ?-lactoglobulin gel was studied by small and large deformation rheology and by light microscopy. Two different techniques using small deformations, one measuring the modulus in shear and the other measuring the modulus in compression, have been compared. The fracture tests of the gels were performed in tension. The concentration of ?-lactoglobulin was kept constant at 6 wt%, and the amount of potato amylopectin was varied from 0 to 2 wt%. Two preparations of potato amylopectin, with different rheological behaviour, were used. The results illustrate the importance of a full theological characterisation, since small and large deformation tests responded different to the structure. Both the viscoelastic and the failure properties of ?-lactoglobulin gels changed on addition of potato amylopectin even at low concentrations. The effect of the potato amylopectin concentration on the rheological properties of the mixed system varied with the properties of the potato amylopectin. The higher viscosity (HV) potato amylopectin had a shear-thinning behaviour and a small yield stress, while the lower viscosity (LV) potato amylopectin had a lower viscosity with a Newtonian behaviour. The gels containing the LV potato amylopectin increased in the modulus of small deformations with increasing potato amylopectin concentration, while the stress at fracture was constant up to a concentration of 0.5 wt% potato amylopectin and then increased with increasing potato amylopectin concentration. For the gels containing the HV potato amylopectin the modulus of small deformations reached a maximum at 0.25 wt% potato amylopectin and then decreased with increasing potato amylopectin concentration. The stress at fracture was constant up to 0.5 wt% potato amylopectin and decreased at higher concentrations. The state of aggregation of ?-lactoglobulin was influenced both by concentration and properties of potato amylopectin. The higher the potato amylopectin concentration the larger the pores in the ?-lactoglobulin gel. (C) 2000 Elsevier Science Ltd.
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