| 1. |
- Gutierrez, G., et al.
(författare)
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Production of vegetable oil in milk emulsions using membrane emulsification
- 2009
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Ingår i: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 245:1-3, s. 631-638
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Konferensbidrag (refereegranskat)abstract
- The production of emulsions using milk as the continuous phase has a number of applications of interest from the food industry's point of view. In addition, producing an emulsion with a narrow drop size distribution is interesting since their increased stability could avoid Oswald ripening and creaming. Membrane emulsification is a novel technique which helps to obtain a narrower distribution compared to other emulsification techniques such as homogenizers or ultrasound. Moreover the use of membrane emulsification may reduce the energy cost. The food industry is interested in reducing the use of food additives, both to save money and increase consumer acceptance. Therefore the aim of this work was to investigate the use of the intrinsic emulsifying capacity of milk proteins to act as stabilizers for oil droplets produced by membrane emulsification. Using tubular SPG membrane (4.8 mu m pore diameter) in recirculation mode, at dispersed phase fluxes of either 5 L/hm(2) or 50 L/hm(2), a stable final emulsion of 30% w/w oil was obtained. The fat globule size distribution was more bimodal at higher oil concentrations and at the higher flux.
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| 2. |
- Helstad, Kristina, et al.
(författare)
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Liquid droplet-like behaviour of whole casein aggregates adsorbed on graphite studied by nanoindentation with AFM
- 2007
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X. ; 21:5-6, s. 726-738
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Tidskriftsartikel (refereegranskat)abstract
- AFM measurements in the force volume mode were performed over the total penetration depth for different positions on casein aggregates adsorbed to a graphite surface in a liquid cell. The stiffness of the force curves was correlated to indentation depths, layer depth and lateral position within the aggregates with the aim of arriving at a credible explanation for the shapes of the force curves. The commonly used Hertz-based models did not fit the experimental data. The ratio between the height and diameter of the adsorbed casein aggregates was found to be linear, suggesting surface energy dominated liquid droplet behaviour. To investigate the possibility, numerical simulations were performed using the Surface Evolver, an interactive finite element program for the study of surfaces shaped by surface tension and other energies. Simulated force curves were in good agreement with experimental findings, both with respect to slope as a function of indentation as well as describing the variation with indentation position on the aggregate due to interfacial and geometric effects. By comparing the simulated force curves to the measurement data it was found that there would have been an interfacial energy equivalent to 10 mJ/m2.
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| 3. |
- Köhnke, Rickard, et al.
(författare)
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Thylakoids promote release of the satiety hormone cholecystokinin while reducing insulin in healthy humans.
- 2009
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Ingår i: Scandinavian Journal of Gastroenterology. - : Informa UK Limited. - 1502-7708 .- 0036-5521. ; 44:6, s. 712-719
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Tidskriftsartikel (refereegranskat)abstract
- Objective. The effects of a promising new appetite suppressor named "thylakoids" (membrane proteins derived from spinach leaves) were examined in a single meal in man. Thylakoids inhibit the lipase/colipase hydrolysis of triacylglycerols in vitro and suppress food intake, decrease body-weight gain and raise the satiety hormone cholecystokinin (CCK) in rats, but their effects in man remain unclear. The aim of this study was to investigate whether thylakoids, when added to a test meal, affect appetite regulation and blood parameters in healthy individuals. Material and methods. In an intervention crossover study, healthy individuals of normal weight (n=11) were offered a high-fat meal with and without the addition of thylakoids. Blood samples were taken 0 (prior to meal), 30, 60, 120, 180, 240, 300 and 360 min after the start of the meal. Blood samples were analysed for satiety and hunger hormones (CCK, leptin and ghrelin), insulin and blood metabolites (glucose and free fatty acids). Results. The CCK level increased, in particular between the 120 min time-point and onwards, the ghrelin level was reduced at 120 min and leptin level increased at 360 min after intake of the thylakoid-enriched meal. The insulin level was reduced, whereas glucose concentrations were unchanged. Free fatty acids were reduced between time-point 120 min and onwards after the thylakoid meal. Conclusions. The addition of thylakoids to energy-dense food promotes satiety signals and reduces insulin response during a single meal in man.
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| 4. |
- Rayner, Marilyn
(författare)
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Membrane emulsification: modelling interfacial and geometric effects on droplet size
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emulsification is an important unit operation used in the pharmaceutical, food, and cosmetic industry. Membrane emulsification is a relatively new membrane technology which allows the production of emulsion droplets under controlled conditions with a narrow droplet size distribution. The continuous phase flows tangentially to the membrane surface and sweeps away dispersed phase droplets forming from pore openings. Both oil-in-water and water-in-oil emulsions are possible depending on the type of membrane used, as is the ability to form double emulsions, however, this work will focus on oil-in-water emulsions. The key feature of the membrane emulsification process which sets it apart from conventional emulsification technologies is that the size distribution of the resulting droplets is primarily governed by the choice of membrane and not by the development of turbulent or extensional droplet break up. This work reviews current developments and deficiencies in modelling membrane emulsification processes and proposes an innovative model developed to the quantify droplet formation mechanism from the point of view of Gibbs free energy. The droplet's shape as it grows is modelled in terms of interfacial energy and thermodynamic work with the help of an interactive finite element program, the Surface Evolver. A program to test the model was written and run which allows the user to identify the point of instability due to free energy, and thus the maximum stable volume attached to the pore, and predicts the radius of the final detached droplet. The inputs of the program are pore geometry, interfacial tension, and contact angle. The model reasonably predicted droplet sizes using pores of a known geometry under quiescent conditions where the force balance approach is not applicable. The model was extended to include the effects of droplet expansion rate and surfactant mass transfer on the interfacial tension. This allowed the increased droplet size to be determined for a given set of operating conditions and prediction of the onset of jetting as a function of dispersed phase flux. By analysing the results from the Surface Evolver, a general relationship between pore shape, contact angle and droplet size was found. This equation can be used independently of the Surface Evolver to predict droplet diameters for cases where either the pore geometry is defined using Ddroplet=8*Area/(cos theta *Perimeter) or alternatively for cases when the critical pressure in the membrane is known Ddroplet=8*gamma/Pcritical. These equations were tested against literature data for straight-through microchannels, SPG membranes, and ISOPORE polycarbonate membranes. The average relative errors of the predictions were on the order of 8% to 9%. These general equations can significantly aid in the design of membranes through optimising pore size, shape, length and spacing and thereby improving the production capacity of membrane emulsification processes.
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| 5. |
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| 6. |
- Rayner, Marilyn, et al.
(författare)
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Simulation of a design of a lab scale Radio frequency heating unit of hamburgers
- 2006
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Ingår i: Proceecing of the 52nd International Congress of Meat Science and Technology. ; 86-TU, s. 467-469
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Konferensbidrag (refereegranskat)abstract
- With regard to efficient food processing and cost effective production lines, Radio Frequency (RF) heating is a prime example. Thermal processing of food has gained an ever growing importance as food manufactures strive after increasing the number and quality of value added products on the market. Solid food, such as meat and vegetables, is more difficult to heat efficiently since it cannot be pumped or stirred. This is an area where RF cooking can provide significant benefits due to the volumetric nature of dielectric heating. Since heat is generated internally in the product, by inducing an electric field through the food, which acts as a dielectric material, and does not rely on conduction, convection or radiation, heating takes place evenly in the product without temperature gradients. RF is also superior to micro-wave heating in this respect as the wave can penetrate food items up to several meters in diameter whereas the penetration is limited to a few centimeters at micro-wave frequencies. This means that there are no hot-spots, cold-spots or overcooking of surfaces and the total time is significantly reduced and losses are minimized.
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| 7. |
- Rayner, Marilyn, et al.
(författare)
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The impact of mass transfer and interfacial expansion rate on droplet size in membrane emulsification processes
- 2005
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 266:1-3, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- In membrane emulsification, especially under conditions where droplets are forming with a narrow droplet size distribution, it is conjectured that the interfacial phenomena are determining the emulsification result. The process parameters of continuous phase flow and dispersed phase flux were analysed from the perspective of how they could be affecting the interfacial tension of the growing droplet. This work first reviews the applicability of current droplet formation models (force balance and spontaneous transformation based (STB)), describes the interfacial transport of surfactant molecules to an expanding oil-water interface, and models the flow of dispersed phase through a pore using MATLAB. The data from these calculations are then applied in a model to predict the final size of the droplets, which includes dynamic effects of mass transfer and expansion rate. The droplet detachment mechanism in membrane emulsification was modelled from the point of view of Gibbs free energy. An interactive finite element program called the surface evolver was used to test the model. A program was written and run in the surface evolver, which allows the user to track the droplet shape as it grows, to identify the point of instability due to free energy, and thus predict the maximum stable volume (MSV) attached to the pore. The final droplet size was found by applying a pressure pinch constraint (PPC), which is based on the division of the surface into two volumes, a droplet and a segment, which remains attached to the pore mouth. The relative size of these two volumes is such that the resulting radii of curvature of the droplet will maintain an equal Laplace pressure across the surface of both volumes. Predicted droplet sizes were compared to experimental data from the literature. It was found that changes in surfactant coverage caused by mass transfer coupled to the expansion rate of the oil-water interface have a significant and predictable effect on the final droplet size in membrane emulsification. The extent of the influence of the dispersed phase flux on dynamic interfacial tension was quantified using a dimensionless parameter, the mass transfer expansion ratio (MER). The MER can be used to predict the effect of increasing the depletion of surfactant on the relative final droplet size in membrane emulsification. This new insight into the role mass transfer and surface expansion play in membrane emulsification allows us to now predict a priori the final droplet size that would form for a particular set of conditions, and can lead to better process design methods in the future.
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