| 1. |
- Anker, M., et al.
(författare)
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Aging of whey protein films and the effect on mechanical and barrier properties
- 2001
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 49:2, s. 989-995
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the aging of whey protein isolate (WPI) films plasticized with glycerol (G) and sorbitol (S). The films were cast from heated aqueous solutions at pH 7 and dried at 23 °C and 50% relative humidity (RH) for 16 h. They were stored in a climate room (23 °C, 50% RH) for 120 days, and the film properties were measured at regular intervals. The moisture content (MC) of the WPI/G films decreased from 22% (2 days) to 15% (45 days) and was thereafter constant at 15% (up to 120 days). This affected the mechanical properties and caused an increased stress at break (from 2.7 to 8.3 MPa), a decreased strain at break (from 33 to 4%), and an increased glass transition temperature (T g) (from -56 to -45 °C). The barrier properties were, however, unaffected, with constant water vapor permeability and a uniform film thickness. The MC of the WPI/S films was constant at ?9%, which gave no change in film properties.
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| 2. |
- 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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| 3. |
- Anker, M., et al.
(författare)
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Improved water vapor barrier of whey protein films by addition of an acetylated monoglyceride
- 2002
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Ingår i: Innovative Food Science & Emerging Technologies. - 1466-8564 .- 1878-5522. ; 3:1, s. 81-92
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to determine to what extent the water-vapor barrier of whey protein isolate (WPI) films could be improved by adding a lipid and make laminate and emulsion films. The laminate whey protein-lipid film decreased the water vapor permeability (WVP) 70 times compared with the WPI film. The WVP of the emulsion films was half the value of the WPI film and was not affected by changes in lipid concentration, whereas an increased homogenization led to a slight reduction in WVP. The mechanical properties showed that the lipid functioned as an apparent plasticizer by enhancing the fracture properties of the emulsion films. This effect increased with homogenization. The maximum strain at break was 117% compared with 50% for the less-homogenized emulsion films and 20% for the pure WPI films. Phase-separated emulsion films were produced with a concentration gradient of fat through the films, but pure bilayer films were not formed. © 2002 Elsevier Science Ltd. All rights reserved.
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| 4. |
- 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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| 5. |
- Anker, M., et al.
(författare)
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Relationship between the microstructure and the mechanical and barrier properties of whey protein films
- 2000
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 48:9, s. 3806-3816
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Tidskriftsartikel (refereegranskat)abstract
- This work was focused on the relationship between the microstructure and the mechanical and barrier properties of whey protein isolate (WPI) films. Sorbitol (S) and glycerol (G) were used as plasticizers and the pH was varied between 7 and 9. The films were cast from heated aqueous solutions and dried in a climate room at 23 °C and 50% relative humidity for 16 h. The microstructure of the films was found to be dependent on the concentration, the plasticizers, and the pH. When the concentration increased, a more aggregated structure was formed, with a denser protein network and larger pores. This resulted in increased water vapor permeability (WVP) and decreased oxygen permeability (OP). When G was used as a plasticizer instead of S, the microstructure was different, and the moisture content and WVP approximately doubled. When the pH increased from 7 to 9, a denser protein structure was formed, the strain at break increased, and the OP decreased.
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| 6. |
- Anthonsen, M.W., et al.
(författare)
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Aggregates in acidic solutions of chitosans detected by static laser light scattering
- 1994
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 25:1, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- Chitosans having degrees of N-acetylation, FA, ranging from 0 to 0·6, were randomly degraded to different molecular weights and studied by multi angle static laser light scattering (LLS). Under the given experimental conditions, negative second virial coefficients of the solutions, A?2, revealed the presence of concentration dependent aggregates. Attempts to remove the aggregates, or to influence the aggregation behavior, were made by ultracentrifugation and extensive filtering of the solutions. Modification of the solvent conditions such as pH, ionic strength and temperature were carried out, and chitosan solutions were digested with an acidic proteinase. Non-degraded samples and chitosans prepared by both heterogeneous and homogeneous N-deacetylation of chitin were also studied. In all cases, the negative A?2 remained. However, it was observed that ultracentrifugation and filtering of the solutions decreased the measured molecular weights and radii of gyration, indicating that some of the material of high molecular weight and size could be removed by ultracentrifugation and filtration. The chemical nature of the physical basis of the molecular association was not revealed. Nevertheless, by the use of gel permeation chromatography coupled to an on-line low angle laser light scattering instrument and a differential refractive index concentration detector (HPSEC-LALLS-RI), a bimodal molecular weight distribution was observed in which about 5% of the sample had a very high molecular weight. These results coupled with the positive virial coefficients obtained earlier from osmotic pressure measurements suggest that a small fraction of the chitosan is aggregated to high molecular weight material, probably following a closed association model. Electron microscopy revealed the presence of some supramolecular structures. The positive second virial coefficients obtained earlier from osmometry are in harmony with these findings. The results demonstrate the occurrence of reversible aggregation in chitosan solutions. Static laser light scattering therefore cannot readily be used to determine molecular weights and sizes of chitosans under these conditions. It was not possible to correlate the extent of aggregation with the chemical composition of the chitosans. © 1994.
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| 7. |
- 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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