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| 2. |
- Funebo, Tomas, et al.
(författare)
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Microwave and convective dehydration of ethanol treated and frozen apple : Physical properties and drying kinetics
- 2002
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Ingår i: International journal of food science & technology. - : Wiley. - 0950-5423 .- 1365-2621. ; 37:6, s. 603-614
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to examine how the drying kinetics and physical properties of apples are affected by pre-treatment with 95% ethanol or freezing at -18 °C before microwave-assisted air dehydration at 50, 60 and 70 °C. Microwave heating was used to obtain these temperatures in the centre of the apple cubes. After dehydration the shrinkage and rehydration capacity were measured. The texture of dehydrated and rehydrated samples was analysed with a puncture test in a texture analyser. Samples were also analysed with confocal laser scanning microscopy to determine the correlation between physical and microstructural properties. Diffusivity in the different dehydration processes was calculated. Ethanol-treated apples showed both high rehydration and high effective rehydration capacity compared with the other samples. Freezing before dehydration increased the diffusivity and reduced the firmness of rehydrated apples compared with no pre-treatment.
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| 3. |
- Funebo, Tomas, et al.
(författare)
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Microwave heat treatment of apple before air dehydration : Effects on physical properties and microstructure
- 2000
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Ingår i: Journal of Food Engineering. - 0260-8774 .- 1873-5770. ; 46:3, s. 173-182
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Tidskriftsartikel (refereegranskat)abstract
- Golden delicious apple cubes were heated with microwave energy of high intensity (20 W/g), as a pre-treatment before air-dehydration at 40 °C, 60 °C and 80 °C. After the microwave treatment extending for 0.75 up to 5 min, the cubes were finish-dried with only forced air at 2 m/s. Dehydrated and rehydrated samples were analyzed with a puncture test using a texture analyzer. The microstructure of the samples was studied with confocal laser scanning microscopy (CLSM). Dried apple pieces were harder and more shrunk when pre-treated with microwaves, compared to only air dehydration. Despite the shrinkage and increased firmness, the rehydration capacity of microwave `blanched' apple cubes was higher than when they were only air-dehydrated. Image analysis of the rehydrated apples showed that large voids (up to 0.5 mm in diameter) had developed, and that these increased with air temperature. Higher magnification of the images revealed cell separation and disruption of cell walls, caused by the microwave heating.
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| 4. |
- Loren, Niklas, et al.
(författare)
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Dendrimer diffusion in ?-carrageenan gel structures
- 2009
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:2, s. 275-284
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the ?-carrageenan concentration on gel microstructure and self-diffusion of polyamideamine dendrimers has been determined by transmission electron microscopy (TEM), image analysis, and nuclear magnetic resonance (NMR) diffusometry. Different salt conditions of KCl, NaCl, and mixtures thereof allowed for formation of significantly different microstructures. The ?-carrageenan concentrations were varied between 0.25 and 3.0 w/w% for a salt mixture containing 20 mM KCl and 200 mM NaCl gels and between 0.5 and 4.0 w/w% for 250 mM NaCl gels. Furthermore, the effect of potassium ion concentration on the gel structure and the dendrimer diffusion rate was determined. The potassium ion concentration was varied between 20 mM KCl and 200 mM KCl. Two different dendrimer generations with significant difference in size were used: G2 and G6. Dendrimers were found to be sensitive probes for determination of the effect of the gel microstructure on molecular diffusion rate. A qualitative comparison between TEM micrographs, NMR diffusometry data and image analysis showed that the gel structure has a large impact on the dendrimers diffusion in ?-carrageenan gels. It was found that diffusion was strongly influenced by the ?-carrageenan concentration and the dendrimer generation. Small voids in the gel network gave strongly reduced diffusion. Image analysis revealed that the interfacial area between the gel network and the surrounding water phase correlated well with the dendrimer diffusion. © 2009 American Chemical Society.
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| 5. |
- Ofstad, R., et al.
(författare)
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Factors influencing liquid-holding capacity and structural changes during heating of comminuted cod (gadus morhua l.) muscle
- 1996
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Ingår i: Lebensmittel-Wissenschaft + Technologie. - 0023-6438 .- 1096-1127. ; 29:42006, s. 173-183
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Tidskriftsartikel (refereegranskat)abstract
- The loss of liquid in cod muscle finely comminuted with salt was studied as a function of heating temperature from 5 to 70 °C. Three different groups of raw material were tested: wild and farmed maturing cod and wild post-spawn cod. The effects of ionic strength, pH and heating temperature upon liquid-holding capacity were examined either individually or simultaneously by using a general linear statistical model. The liquid-holding capacity was measured by a low-speed centrifugation net test. The microscopic changes of the comminuted samples were evaluated by light microscopy. The intact muscle, used as raw material, was investigated with light and transmission electron microscopy. The liquid loss was very low and almost constant between 5 and 30 °C, and increased rapidly thereafter at elevated temperatures. NaCl concentration, pH, heating temperature and interactions among these factors influenced the liquid released according to a first-order interaction linear model. Upon comminution with salt, most of the fibre structure is lost and a homogeneous phase is formed from the depolymerized myofibrils. Pores and gaps appeared in the protein matrix upon heating, enhancing the liquid loss. Melted collagen was seen either as a thin film or as an aggregated network structure, depending on the temperature, in the aqueous phase filling the pores and gaps. Wild, maturing cod possessed better liquid-holding capacity at higher heating temperatures than did both farmed and post-spawn fish, owing to different fibre structure. Post-spawn fish underwent a more severe degradation than did the maturing fish during ice-storage. ©1996 Academic Press Limited.
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| 6. |
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| 7. |
- Ofstad, R., et al.
(författare)
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Liquid-holding capacity and structural changes in comminuted salmon (Salmo salar) muscle as influenced by pH, salt and temperature
- 1995
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Ingår i: Lebensmittel-Wissenschaft + Technologie. - 0023-6438 .- 1096-1127. ; 28:3, s. 329-339
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Tidskriftsartikel (refereegranskat)abstract
- The loss of liquid in salmon muscle comminuted with salt was studied as a function of pH and heating temperature. A factorial experiment was designed to compare the effects of; the raw material, NaCl concentration, pH, degree of comminution and heating temperature in order to evaluate both main effects and interaction effects. The liquid-holding capacity was measured by a low speed centrifugation net test. The changes in microstructure in the samples were investigated by light microscopy using fat- and protein-staining techniques. The heating temperature, pH, NaCl concentration, variation of raw material and degree of comminution influenced liquid loss according to a second-order interaction linear model. The interaction effect between low pH, low salt concentration and high temperature was strongest. Addition of salt extracted the myofibrillar proteins and resulted in a homogeneous protein matrix with few intact fibres and uniformly dispersed fat droplets. Liquid loss was closely related to the microstructure of the comminutions. When heated above 30 °C, enlarged pores and gaps, some of them forming channels, occurred in the protein matrix. In comminutions prepared with a low salt concentration and/or a low pH the more frequent presence of pores and gaps enhanced the liquid loss. © 1995 Academic Press Limited.
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| 8. |
- Ofstad, R., et al.
(författare)
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Liquid loss as effected by post mortem ultrastructural changes in fish muscle : Cod (Gadus morhua L) and salmon (Salmo salar)
- 1996
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Ingår i: Journal of the Science of Food and Agriculture. - 0022-5142 .- 1097-0010. ; 71:3, s. 301-312
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Tidskriftsartikel (refereegranskat)abstract
- This study was performed in order to assess the effect of early post mortem structural changes in the muscle upon the liquid-holding capacity of wild cod, net-pen-fed cod (fed cod) and farmed salmon. The liquid- holding capacity was measured by a low speed centrifugation test. Transmission electron microscopy was used to discover ultrastructural changes both in the connective tissue and in the myofibrils. Differential scanning calorimetric thermograms of the muscle proteins were recorded to elucidate whether fundamental differences did exist between the proteins of the raw material tested. Multivariate statistics were used to explicate the main tendencies of variations in the thermograms. The salmon muscle possessed much better liquid-holding properties than the cod muscle, and wild cod better than fed cod regardless of the storage time. Both fed cod and farmed salmon, underwent the most severe structural alterations, probably caused by the low muscle pH values. The higher liquid-holding capacity of the salmon muscle was related to species specific structural features and better stability of the muscle proteins. The myofibrils of the salmon muscle were denser and intra- and extracellular spaces were filled by fat and a granulated material. The differences in thermograms of muscle from wild and fed cod were largely explained by the variations in pH. The severe liquid loss of fed cod is due to a low pH induced denaturation and shrinkage of the myofibrils. Post mortem degradation of the endomysial layer and the sarcolemma may have further facilitated the release of liquid.
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| 9. |
- Ofstad, R., et al.
(författare)
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Ultramicroscopical structures and liquid loss in heated cod (Gadus morhua L) and salmon (Salmo salar) muscle
- 1996
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Ingår i: Journal of the Science of Food and Agriculture. - 0022-5142 .- 1097-0010. ; 72:3, s. 337-347
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Tidskriftsartikel (refereegranskat)abstract
- This study was performed in order to assess the effect of heating in pre-and post-rigor muscle of fed cod, wild cod and farmed salmon harvested at different times of the year. The structural changes in muscle samples pre- heated from 5 to 60°C were qualitatively evaluated using both light and transmission electron microscopy techniques. The microstructural changes are discussed in relation to the liquid loss measured by a low-speed centrifugation test. The heat-induced structural changes varied between the fish tested, reflecting different degrees of post mortem degradation prior to heating, the muscle-pH and species-specific structural properties. The fed fish, both cod and salmon, underwent the most severe structural degradation. This reflected both the low muscle pH and the more severe post mortem degradation observed in these fish prior to heating, compared with the wild cod. Heating caused extensive shrinkage of the myofibrils and hence, widened intermyofibrillar and extracellular spaces in both the fed cod and the salmon muscle. In the sample of wild cod muscle, the extracellular spaces were narrow and the myofibrils were closely packed. The difference in heat-induced liquid loss of the fed compared with the wild cod muscle coincides with their different structural features, as observed both by LM and TEM. The better liquid-holding properties of the salmon muscle than the cod muscle are attributed to the species-specific ultrastructural features as observed with TEM. In addition to the denser appearance of the salmon myofibres, it is suggested that both fat droplets and aggregated sarcoplasmic proteins filling the intermyofibrillar and extracellular spaces are important in preventing release of liquid upon heating.
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| 10. |
- Prothon, Frederic, et al.
(författare)
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Effects of Combined Osmotic and Microwave Dehydration of Apple on Texture, Microstructure and Rehydration Characteristics
- 2001
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Ingår i: Lebensmittel-Wissenschaft + Technologie. - : Elsevier BV. - 0023-6438 .- 1096-1127. ; 34:2, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- The effect of microwave-assisted air-drying with or without osmotic pre-treatment on apple cubes was evaluated. Osmotic pre-treatment in sucrose solution was followed by microwave-assisted air-dehydration at different temperatures (50, 60 and 70°C). The products were compared to the samples that did not undergo any pre-treatment. A puncture test and confocal laser scanning microscopy (CLSM) were used to analyse the effects of these processes on texture and microstructure. Rehydration in water and in yoghurt were studied and compared. Results showed that osmotic pre-treatment before microwave-assisted air-drying increased the final overall quality of the product. Although the drying time to reach 10% moisture content (wb) was reduced, the presence of infused sucrose in the osmotically dehydrated tissue decreased the drying rate during the microwave finish-drying. The effective moisture diffusivity was slightly lower for the osmosed samples than for the non-treated ones at all the studied temperatures. Osmotic pre-treatment had a beneficial effect on the firmness of the rehydrated samples that had been air-dried at 50°C. Microstructural studies showed a thickening of the cell wall after the osmotic treatment. Structural changes in the cell wall due to the final drying could also be detected. Finally, the rehydration capacity in water was significantly higher for non-treated samples than for the pre-treated ones - although rehydration in yoghurt reduced this difference.
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