| 1. |
- Altskär, Annika, et al.
(författare)
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Some effects of processing on the molecular structure and morphology of thermoplastic starch
- 2008
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 71:4, s. 591-597
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxypropylated and oxidised potato starch (HONPS) was used together with glycerol and water to produce thermoplastic starch. The amount of glycerol was kept constant at 22 parts by weight per 100 parts of dry starch. The thermoplastic starch was converted into films/sheets using three different processing techniques; casting, compression moulding and film blowing. The last two methods represent typical thermoplastic conversion techniques requiring elevated processing temperatures. By means of size-exclusion chromatography, it was found that compression moulding and film blowing led to some degradation of high-molecular weight amylopectin as well as of high-molecular weight amylose-like molecules. The degradation was significantly less pronounced for the cast films. The morphology of the specimens was quite complex and phase separations on different levels were identified. In the cast films and, to a lesser extent, in the compression-moulded specimens, a fine network structure could be distinguished. Such a structure could however not be ascertained in the film-blown material and this is discussed in terms of the thermo-mechanical treatment of the starch materials. © 2007 Elsevier Ltd. All rights reserved.
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| 2. |
- 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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| 4. |
- Ekberg, Olle, et al.
(författare)
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Effect of barium sulfate contrast medium on rheology and sensory texture attributes in a model food
- 2009
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 50:2, s. 131-138
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Tidskriftsartikel (refereegranskat)abstract
- Background: The swallowing process can be visualized using videoradiography, by mixing food with contrast medium, e.g., barium sulfate (BaSO4), making it radiopaque. The sensory properties of foods may be affected by adding this medium. Purpose: To evaluate if and to what extent sensory and rheological characteristics of mango puree were altered by adding barium sulfate to the food. Material and Methods: This study evaluated four food samples based on mango puree, with no or added barium sulfate contrast medium (0%, 12.5%, 25.0%, and 37.5%), by a radiographic method, and measured sensory texture properties and rheological characteristics. The sensory evaluation was performed by an external trained panel using quantitative descriptive analysis. The ease of swallowing the foods was also evaluated. Results: The sensory texture properties of mango puree were significantly affected by the added barium in all evaluated attributes, as was the perception of particles. Moreover, ease of swallowing was significantly higher in the sample without added contrast medium. All samples decreased in extensional viscosity with increasing extension rate, i.e., all samples were tension thinning. Shear viscosity was not as dependent on the concentration of BaSO4 as extensional viscosity. Conclusion: Addition of barium sulfate to a model food of mango puree has a major impact on perceived sensory texture attributes as well as on rheological parameters. © 2009 Informa UK Ltd.
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| 5. |
- Emmambux, M Naushaud, et al.
(författare)
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In situ tensile deformation of zein films with plasticizers and filler materials
- 2007
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 21:8, s. 1245-1255
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Tidskriftsartikel (refereegranskat)abstract
- Material deformation is a dynamic process. Visualisation of this deformation can help to understand the local deformation and fracture behaviour. Zein (the prolamin protein from maize) films with different amount of plasticizers (0-25%) and different filler materials (maize oil, Dimodan (R), Vestosint (R)), at 25% (w/w) to protein) were deformed under tension and observed at micron scale in real time by a confocal laser scanning microscope (CLSM). The addition of plasticizers increased strain and decreased stress of zein films. At low level of plasticizers (6.25% and 12%), zein films deformed and fracture through micro-crack formation and propagation normal the tensile axis. At high Plasticization, only micro-pores were observed during tensile deformation. The filler material oil and Dimodan (R)( increased, but Vestosint (R)) decreased tensile strain in comparison to the control. This shows that the fracture dynamic is affected by the filler materials and is indeed observed by the CLSM. Analysis of local strain by Fluospheres (R) as particle tracking showed a good linear correlation with the tensile strain of the plasticized zein films. The local strains of filler materials and zein matrix in the films were different from the overall tensile strain. The combination of CLSM with a fluospheres (R) as particle tracking is a good method to study local deformation in biomaterials to understand the deformation and fracture behaviour of biomaterials. (C) 2006 Elsevier Ltd. All rights reserved.
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| 6. |
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| 7. |
- Gao, C., et al.
(författare)
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Plasticization of a protein-based film by glycerol : A spectroscopic, mechanical, and thermal study
- 2006
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 54:13, s. 4611-4616
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Tidskriftsartikel (refereegranskat)abstract
- Kafirin, the seed storage protein of the cereal sorghum, is highly homologous with the maize storage protein zein. The effects of plasticisation of a kafirin film by glycerol in the absence of water were examined by a combination of spectroscopic (NMR and infrared), rheological, and calorimetric methods. The results suggest that at low glycerol levels the glycerol is absorbed onto and possibly into the protein. Increasing the level of glycerol increases the motion of the protein and changes the protein conformation. There are corresponding changes of the mechanical properties of protein films. At 40% (w/w) of glycerol, two glass transition temperatures were observed, one of which corresponded to the glass transition temperature of pure glycerol. This result indicates that at this level of plasticizer there are sufficient glycerol/glycerol interactions occurring to allow a separate glass formation process for glycerol. © 2006 American Chemical Society.
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