| 1. |
- Anker, M., et al.
(författare)
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Effects of pH and the gel state on the mechanical properties, moisture contents, and glass transition temperatures of whey protein films
- 1999
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 47:5, s. 1878-1886
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties, moisture contents (MC), and glass transition temperature (T(g)) of whey protein isolate (WPI) films were studied at various pH values using sorbitol (S) as a plasticizer. The films were cast from heated aqueous solutions and dried in a climate chamber at 23 °C and 50% relative humidity (RH) for 16 h. The critical gel concentrations (c(g)) for the cooled aqueous solutions were found to be 11.7, 12.1, and 11.3% (w/w) WPI for pH 7, 8, and 9, respectively. The cooling rate influenced the c(g), in that a lower amount of WPI was needed for gelation when a slower cooling rate was applied. Both cooling rates used in this study showed a maximum in the c(g) at pH 8. The influence of the polymer network on the film properties was elucidated by varying the concentration of WPI over and under the c(g). Strain at break (?(b)) showed a maximum at the c(g) for all pH values, thus implying that the most favorable structure regarding the ability of the films to stretch is formed at this concentration. Young's modulus (E) and stress at break (?(b)) showed a maximum at c(g) for pH 7 and 8. The MC and ?(b) increased when pH increased from 7 to 9, whereas T(g) decreased. Hence, T(g) values were -17, -18, and -21 °C for pH 7, 8, and 9, respectively. E and ?(b) decreased and ?(b) and thickness increased when the surrounding RH increased. The thickness of the WPI films also increased with the concentration of WPI.
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| 2. |
- Anker, M., et al.
(författare)
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Mechanical Properties, Water Vapor Permeability, and Moisture Contents of ?-Lactoglobulin and Whey Protein Films Using Multivariate Analysis
- 1998
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Ingår i: Journal of Agricultural and Food Chemistry. - 0021-8561 .- 1520-5118. ; 46:5, s. 1820-1829
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical and barrier properties of ?-lactoglobulin (?-Lg) and whey protein isolate (WPI) films were studied using sorbitol (S) as a plasticizer. The films were cast from heated aqueous solutions and dried in a climate chamber at 23 °C and 50% relative humidity for 16 h. The multivariate analysis used has proved to be a valuable tool for evaluating and quantifying the influences of the variables in the specified experimental domain. Two identical factorial designs were applied to evaluate the influence of the concentration of ?-Lg and WPI, the concentration of S, and the pH. The two materials, ?-Lg and WPI, show similar results, which can be attributed to the dominating protein ?-lactoglobulin. At pH 9, Young's modulus and stress at break are not affected when the concentration of ?-Lg, WPI, or S varies. At pH 7 and 8, Young's modulus and stress at break increase when the concentration of ?-Lg and WPI increases, and they decrease when the concentration of S increases. Strain at break increases when pH increases from 7 to 9, a more pronounced effect being observed for the WPI films. Water vapor permeability (WVP) decreases and increases for pH 7 and 9, respectively, as the concentration of ?-Lg and WPI increases. This contrast in behavior at different pH values is probably due to a structural difference that occurs above pH 8. Moisture content and WVP increase when S increases. Here a clear distinction can be observed between the two film materials: the ?-Lg films show higher values for both moisture content and WVP measurements.
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| 3. |
- Hermansson, Ann-Marie, et al.
(författare)
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Developments in the understanding of starch functionality
- 1996
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Ingår i: Trends in Food Science & Technology. - 0924-2244 .- 1879-3053. ; 7:11, s. 345-353
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we describe how starch functionality can be explained in terms of structure. The behaviour of different types of starches is demonstrated by showing how the microstructure of potato and wheat starch is related to their rheological properties. The results illustrate the structural importance of amylose and amylopectin. The microstructure of a completely new type of genetically engineered potato amylopectin starch is presented for the first time.
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| 4. |
- Langton, Maud, et al.
(författare)
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Image analysis of particulate whey protein gels
- 1996
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Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 10:2, s. 179-191
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Tidskriftsartikel (refereegranskat)abstract
- Two different methods of image analysis have been used to characterize particulate gel networks quantitatively. The methods have been used to analyse the effect of different preparation conditions on the microstructure of whey protein gels. The microstructure has been characterized at different structural levels by light microscopy, transmission electron microscopy and scanning electron microscopy. The structural parameters have been quantified by digital image analysis and by using a group of experienced microscopists evaluating SEM-micrographs. A stereological approach was used to quantify pore size, particle size and amount of threads within the pores in volume weighted mean volumes. The mode of aggregation was determined by the expert microstructural panel. A 2-level fully factorial experimental design has been used, with heating rate (1-5°C/min), pH (4.6-5.4) and salt addition (0-0.1 mol/dm3) as design parameters. The results showed that the heating rate and the pH had main effects on both the particle size and the pore size. The faster heating rate produced both pores and particles of smaller volume. The mean volume of the particles varied between 0.3 and 1.4 ?3, which could be compared to diameters between 0.8 and 1.4 ?3 if a spherical shape is assumed. The size of pores and particles increased by an increase in pH. Pore volume was found to be affected by an interaction between heating rate and pH. The change in pH had a pronounced effect when the slower heating rate was used. If the voids were approximated with a spherical shape, the diameters varied between 10 and 40 ?, compared with the volumes between 1200 and 29 100 ?3. The interaction effects showed that the heating rate influenced the mode of aggregation at the higher pH 5.4, whereas the salt addition affected the mode of aggregation at the lower pH 4.6. © Oxford University Press.
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| 5. |
- Langton, Maud, et al.
(författare)
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Influence of the microstructure on the sensory quality of whey protein gels
- 1997
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Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 11:2, s. 217-230
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Tidskriftsartikel (refereegranskat)abstract
- A full two-level factorial experimental design was used to study particulate whey protein gels. The processing conditions, pH, heating rate and the addition of salt were used as design factors. The results were evaluated by using a response surface model, and analysis of variance, M(ANOVA), was performed. The microstructure of particulate whey protein gels has been characterized previously, and the two-dimensional images from light microscopy and transmission electron microscopy were quantified by a stereological approach, while the more three-dimensional scanning electron micrographs were quantified by an expert panel of microscopists. In this study the texture of the same gels was analysed by a sensory panel. Correlations were made between the microstructure and sensory descriptors, and the panellists were able to detect differences between very small particles <1 ?m3 in volume. The sensory descriptors grainy appearance, gritty texture, creamy texture and tendency to fall apart had a logarithmic dependence on the microstructural parameters, particle size, and size of small and large pores. Multivariate techniques were used to create models to describe groups of the sensory descriptors by some of the microstructural parameters. A model with good correlation (r ? 0.8-0.9) was found for grainy appearance, gritty texture, creamy texture and falling apart. They were all dependent on the star volume of particles and small and large pores. The soft and springy textures were influenced by combinations of microstructural parameters, where the formation of strands into strings of beads or in clusters and conglomerates seemed to play an important role. The sticky texture was negatively correlated to the proportion of threads within the pores. © Oxford University Press.
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| 6. |
- Langton, Maud, et al.
(författare)
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Microstructure and image analysis of mayonnaises
- 1999
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Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 13:2, s. 113-125
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of full-fat mayonnaise was characterised at different structural levels by using confocal laser scanning microscopy, CLSM, and transmission electron microscopy on freeze-etched samples. The size of droplets varied, and in 80% mayonnaise many very small droplets were found between larger droplets. The colloidal structural parameters were quantified on CLSM images. A stereological approach was used to estimate the droplet size, the interfacial surface area between the fat phase and water phase, and the size of the egg yolk aggregates. The mayonnaise samples were produced by a cold process line in a pilot plant equipment. A two-level fully factorial experimental design was used, with the processing parameters, (speed of the emulsification cylinder, the speed of the visco-rotor and the out-temperature) as design variables. The results showed that the speed of the emulsification cylinder had a main effect on the size of the droplets. No other effects were found when the speed of the emulsification cylinder was high. When the speed was slow, however, an interaction effect was found on the size of the droplets. The distribution of egg yolk was affected by the processing conditions and by the quality of the egg yolk. The storage modulus G? had higher values when the mayonnaise was formed of smaller droplets at a high emulsification cylinder speed. Lower values of G? were found when the mayonnaise was formed of larger droplets produced by a slower emulsification cylinder speed. © 1999 Elsevier Science Ltd.
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| 7. |
- Langton, Maud, et al.
(författare)
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Texture as a reflection of microstructure
- 1996
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Ingår i: Food Quality and Preference. - 0950-3293 .- 1873-6343. ; 7:42067, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- The perception of texture has been correlated to the micro-structure of particulate whey protein gels. A full, two-level, factorial experimental design was used in which the processing conditions, pH, heating rate and addition of salt were used as design factors. The texture of the gels was analyzed by a sensory panel, and the microstructure was analysed by light and electron microscopy. The microstructure was quantified by using different types of image analysis. In this study of particulate whey protein gels, the test principles of analysing texture were divided into two groups: destructive tests and non-destructive tests. The micro-structural parameters can also be divided into two groups: overall network dimensions (pore size and particle size) and strand characteristics. The texture as measured with destructive methods was sensitive to overall network dimensions, whereas texture as measured with non-destructive methods was sensitive to the strand characteristics of particulate protein gels.
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| 8. |
- Loren, Niklas, et al.
(författare)
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Confocal laser scanning microscopy and image analysis of kinetically trapped phase-separated gelatin/maltodextrin gels
- 1999
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Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 13:2, s. 185-198
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Tidskriftsartikel (refereegranskat)abstract
- The effect of phase separation on the gelatin/maltodextrin systems has been studied using confocal laser scanning microscopy and image analysis. Stereological image analysis has been used to analyse the effect of different cooling rates, holding times, holding temperatures and gelatin types on the microstructure at pH 5.3. The quantified microstructural parameters were the volume-weighted mean volume, the interfacial area and the area fraction. A factorial experimental design was used, with cooling rate (0.2°C/min, 1°C/min, 10°C/min), holding time (0 min, 10 min, 20 min), holding temperature (20°C, 25°C, 30°C), and two different gelatin types (LH, PS) as design parameters. Gelatin lime hide (LH) has an isoelectric point of pH 4.7, and gelatin pig skin (PS), has an isoelectric point of pH 9.1. The composition was kept constant at 4% gelatin and 5% maltodextrin. The results showed that the phase-separated system was gelatin continuous. The size of the maltodextrin inclusions decreases with increasing cooling rate and was largest at the lowest cooling rate (0.2°C/min). Gelatin PS has larger maltodextrin inclusions and a smaller interfacial area than gelatin LH. The size of the maltodextrin inclusions varied in diameter between 3 and 10 ?m for gelatin LH and between 3 and 18 ?m for gelatin PS. The size of the maltodextrin inclusions increases with increasing holding time and was largest at 20 min. The interfacial area increases with increasing cooling rates and was largest at 10°C/min. A region was found where the phase separation and the gel formation competed with each other in connection with mobility. The residence time in that region and how fast the sample proceeds through it, are important for the morphology of the resulting microstructure. © 1999 Elsevier Science Ltd.
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| 9. |
- Lundin, Leif, et al.
(författare)
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Influence of locust bean gum on the rheological behaviour and microstructure of K-?-carrageenan
- 1995
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Ingår i: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 28:2, s. 91-99
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of ?-carrageenan-locust bean gum (LBG) were analysed by transmission electron microscopy and dynamic viscoelastic measurements. The effect of two different mannose:galactose (M:G) ratios of LBG on the rheology and microstructure of ?-carrageenan in KCl was studied. The rheological differences observed in the mixed gel as LBGs were added were found to be dependent on M:G ratio, salt concentration and LBG content. Monolayers of dilute samples of ?-carrageenan mixed with LBGs in varying ratios in 0.10 M KCl were visualised by low-angle rotary metal shadowing for transmission electron microscopy. The results obtained showed that LBG hindered the self-association of ?-carrageenan, and that the effect was enhanced at a higher M:G ratio and as the LBG contents were increased. Small deformation viscoelastic measurements were performed on ?-carrageenan-LBG mixtures in 0.050 and 0.10 M KCl at constant temperatures of 38 and 48 °C, respectively. Increased rheological stability was observed for mixtures containing a relatively high LBG content. Mixtures with a relatively low LBG content showed a maximum in storage modulus and an increase in phase angle. The stabilising effect of LBG on the rheology of the blends was more effective for the LBG with high M:G and as the LBG content was increased. © 1996.
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| 10. |
- Lundin, Leif, et al.
(författare)
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Influence of locust bean gum on the rheological behaviour and microstructure of K - ?-carrageenan
- 1998
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Ingår i: Carbohydrates polymer. - 0346-718X. ; 28:2, s. 91-9
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of ?-carrageenan-locust bean gum (LBG) were analysed by transmission electron microscopy and dynamic viscoelastic measurements. The effect of two different mannose:galactose (M:G) ratios of LBG on the rheology and microstructure of ?-carrageenan in KCl was studied. The rheological differences observed in the mixed gel as LBGs were added were found to be dependent on M:G ratio, salt concentration and LBG content. Monolayers of dilute samples of ?-carrageenan mixed with LBGs in varying ratios in 0.10 M KCl were visualised by low-angle rotary metal shadowing for transmission electron microscopy. The results obtained showed that LBG hindered the self-association of ?-carrageenan, and that the effect was enhanced at a higher M:G ratio and as the LBG contents were increased. Small deformation viscoelastic measurements were performed on ?-carrageenan-LBG mixtures in 0.050 and 0.10 M KCl at constant temperatures of 38 and 48°C, respectively. Increased rheological stability was observed for mixtures containing a relatively high LBG content. Mixtures with a relatively low LBG content showed a maximum in storage modulus and an increase in phase angle. The stabilising effect of LBG on the rheology of the blends was more effective for the LBG with high M:G and as the LBG content was increased.
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