| 1. |
- Bayod, Elena, et al.
(författare)
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Low shear rheology of concentrated tomato products. Effect of particle size and time
- 2007
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1866 .- 1557-1858. ; 2:4, s. 146-157
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Tidskriftsartikel (refereegranskat)abstract
- Time-dependent rheological properties of three tomato paste suspensions in the concentration range of 200-1,000 g paste/kg suspension have been investigated by using the vane geometry at shear rates gamma < 10 s(-1). Creep tests were conducted to analyze the influence of the level of stress on the rheological behavior of the samples before and after homogenization. The experimental results indicate that the suspensions exhibit an elastic behavior at long times and relatively low stresses, which proves that this type of material can be characterized by a yield stress (sigma(y)). Applying stresses just beyond the yield stress, an initial rheopectic behavior appeared. This increase in viscosity at low deformations was markedly larger after homogenization, and this difference was attributed to changes in the aspect ratio, shape, and orientation of the particles induced by homogenization. These structural changes were also reflected in the transient viscosity when the samples were subjected to larger stresses (sigma >>sigma y): before homogenization the suspensions exhibited a steady-state viscosity at large deformations, whereas after homogenization, the transient viscosity continuously decreased. That behavior was attributed to flocculation of the particles.
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| 2. |
- Chen, Guo, 1969, et al.
(författare)
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A Porosimetric Mapping of Breadcrumb Structures by Differential Scanning Calorimetry and Nuclear Magnetic Resonance
- 2013
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 8:3, s. 209-215
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Tidskriftsartikel (refereegranskat)abstract
- Ice crystals in frozen bread are substantially shaped by the complex pore structures of crumb. In this study we inspected the breadcrumb porosity of ice-filled pores from the profiles of ice crystals mapped by differential scanning calorimetry and nuclear magnetic resonance. Two types of wheat bread containing different amounts of dietary fiber and sugar were studied after frozen storage at -18 A degrees C for 3 weeks. Both pore sizes and pore size distributions were derived via comparing the measurements to those of water-saturated mesoporous silica (MCM-41 C18) with a well-defined pore size distribution. Good consistency was shown for the crumb pore structures obtained using the two techniques. Both bread types featured broad nanometer ranges of pore sizes characterized with largely bimodal size distributions. Besides, the frozen high-fiber bread displayed a higher proportion of large pores and a broader pore size distribution than the high-sugar bread. By comparing such pore size distributions with those obtained previously for the corresponding fresh bread, it can be concluded that structural differences between the two bread types were produced during the frozen storage, manifesting the disparate freezing performances of bread with different formulations.
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| 3. |
- Gillgren, Thomas, et al.
(författare)
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Mechanical and barrier properties of avenin, kafirin, and zein films
- 2008
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 3:3, s. 287-294
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Tidskriftsartikel (refereegranskat)abstract
- Biodegradable and renewable materials can be manufactured from prolamins, which are the major storage protein fraction of cereals. This paper investigates the material properties of oat prolamin (avenin), corn prolamin (zein), and sorghum prolamin (kafirin). Glass transition temperature, dry solid content, stress at break, strain at break, oxygen permeability, and water vapor permeability were analyzed at different plasticizer contents. Avenin was plasticized with glycerol, and kafirin and zein were plasticized with a mixture of polyethylene glycol, glycerol, and lactic acid. Avenin displayed potential, although it did not exhibit the mechanical qualities of gluten, which resembles avenin at the molecular level. Compared to kafirin and zein, avenin was more extensible at low plasticizer contents, while kafirin and especially zein were more extensible at the highest plasticizer content. Avenin was far weaker than the other two at all plasticizer contents. Kafirin and zein displayed similar barrier properties, whereas avenin was notably more permeable. © 2008 Springer Science+Business Media, LLC.
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| 4. |
- Gillgren, T., et al.
(författare)
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Mechanical and Barrier Properties of Films from Millet Protein Pennisetin
- 2011
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 6:4, s. 474-480
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Tidskriftsartikel (refereegranskat)abstract
- Plastics are one of the most commonly used materials today in an immense range of applications. Since plastics originate from petroleum, which is not a renewable resource, we need to find alternatives to achieve environmentally sustainable goals. One of our most abundant renewable resources is cereals; wheat gluten is recognized as a replacement for synthetic plastics. Another cereal protein is pennisetin from pearl millet, which can grow in more arid areas and is therefore an important crop in times of climate change. In contrast to gluten, the material properties of pennisetin have as yet been relatively unexplored. This work evaluated the mechanical and barrier properties of pennisetin films, including three different plasticizers (glycerol only, glycerol/citric acid mixture, and glycerol/lactic acid/polyethylene glycol mixture). The films were cast from ethanol solutions. It was found that all of the three plasticizers resulted in approximately equal thermomechanical properties in the pennisetin films. However, the glycerol/citric acid mixture seemed to give more beneficial tensile and barrier properties. The advantage of this plasticizer mixture was believed to be due to the altered microstructure of the films. The material properties of pennisetin were found to be fully comparable to those of other cereal protein materials.
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| 5. |
- Gomez, Federico, et al.
(författare)
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Exploring metabolic responses of potato tissue induced by electric pulses
- 2008
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1866 .- 1557-1858.
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigated the metabolic responses of potato tissue induced by pulsed electric field (PEF). Potato tissue was subjected to field strengths ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 μs, 100 μs, or 1 ms. Metabolic responses were monitored using isothermal calorimetry, changes on electrical resistance during the delivery of the pulse, as well as impedance measurements. Our results show that the metabolic response involves oxygen consuming pathways as well as other unidentified events that are shown to be insensitive to metabolic inhibitors such as KCN and sodium azide. The metabolic response is strongly dependent on pulsing conditions and is independent of the total permeabilization achieved by the pulse. Evidence shows that calorimetry is a simple and powerful method for exploring conditions for metabolic stimulation, providing information on metabolic responses that can not be obtained from electrical measurements. This study set the basis for further investigations on defense-related consequences of PEF-induced stress.
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| 6. |
- Nygren Babol, Linnea
(författare)
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Binding Interactions Between alpha-glucans from Lactobacillus reuteri and Milk Proteins Characterised by Surface Plasmon Resonance
- 2012
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 7, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between milk proteins and alpha-glucans at pH 4.0-5.5 were investigated by use of surface plasmon resonance. The alpha-glucans were synthesised with glucansucrase enzymes from Lactobacillus reuteri strains ATCC-55730, 180, ML1 and 121. Variations in the molecular characteristics of the alpha-glucans, such as molecular weight, linkage type and degree of branching, influenced the interactions with native and denatured beta-lactoglobulin and kappa-casein. The highest overall binding levels were reached with alpha-(1,4) compared to alpha-(1,3) linked glucans. Glucans with many alpha-(1,6) linkages demonstrated the highest binding levels to kappa-casein, whereas the interaction with native beta-lactoglobulin was suppressed by alpha-(1,6) linkages. Glucans with a higher degree of branching generally displayed lower protein binding levels whereas a higher molecular weight resulted in increased binding to kappa-casein. The interactions with kappa-casein were not pH dependent, whereas binding to denatured beta-lactoglobulin was highest at pH 4.0 and binding to native beta-lactoglobulin was optimal at pH 4.5-5.0. This study shows that molecular weight, linkage type and degree of branching of alpha-glucans highly influence the binding interactions with milk proteins.
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| 7. |
- Pereira, Ricardo N., et al.
(författare)
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Effects of Pulsed Electric Field on the Viscoelastic Properties of Potato Tissue
- 2009
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1866 .- 1557-1858. ; 4:3, s. 229-239
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated whether transient permeabilization caused by the application of pulsed electric field would give rise to transient changes in the potato tissue viscoelastic properties. Potato tissue was subjected to nominal field strengths (E) ranging from 30 to 500 V/cm, with a single rectangular pulse of 10(-5), 10(-4), or 10(-3) s. The changes on the viscoelastic properties of potato tissue during pulsed electric fields (PEF) were monitored through small amplitude oscillatory dynamic rheological measurements. The elastic (G') and viscous moduli (GaEuro(3)) were measured every 30 s after the delivery of the pulse and the loss tangent change (tan-delta) was calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Results show a drastic increase of tan-delta in the first 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by pulsing conditions and is independent of the total permeabilization achieved by the pulse. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of tan-delta to values similar to those before pulsation strongly suggests recovery of cell membrane properties and turgor, pointing at reversible permeabilization of the cells. A slight increase of stiffness traduced by a negative change of tan-delta after application of certain PEF conditions may also give an indication of events occurring on cell wall structure due to stress responses. This study set the basis for further investigations on the complex cell stress physiology involving both cell membrane functional properties and cell wall structure that would influence tissue physical properties upon PEF application.
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| 8. |
- Quiroga, Carla, et al.
(författare)
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Characterization of the microstructure of phase segregated amylopectin and beta-lactoglobulin dry mixtures
- 2007
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1866 .- 1557-1858. ; 2:4, s. 172-182
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of phase-segregated amylopectin (AP) and β-lactoglobulin (βlg) mixtures formed during drying from solutions with different concentrations and different polysaccharide and protein ratios have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM was used as the main technique and TEM was used to confirm the results. Systems with only one of the components, AP or βlg, displayed even structures. When the polysaccharide and the protein were in the same system they phase segregated with a sharp boundary between the phases. According to the type of surface morphology of the phase-segregated samples, they were grouped into: domains wetting the air-water surface and domains appearing to be immersed in the solid film. The size range of the domains varied widely from about some nanometers to about a few micrometers which was determined by kinetic reasons or by restrictions given by the film structure of the sample. The two phase systems were AP-continuous phase at AP to βlg ratios above about 1:3 and βlg-continuous phase at ratios below about 1:6. Between these ratios, the systems appeared more or less bicontinuous. The morphology as well as its position in the phase diagram suggested a spinodal phase separation. Phase separation was also observed in the metastable region (AP to βlg ratio 3:1), although the domains were smaller and less developed and it was interpreted as binodal phase separation.
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| 9. |
- Reis, Pedro, 1978, et al.
(författare)
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The Influence of Surfactants on Lipase Fat Digestion in a Model Gastro Intestinal System
- 2008
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 3:4, s. 370-381
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, we use a model gastro-intestinal system to study the influence of different food-grade surface-active molecules (Sn-2 monopalmitin, beta-lactoglobulin, or lysophosphatodylcholine) on lipase activity. The interfacial activity of lipase and surfactants are assessed with the pendant drop technique, a commonly used tensiometry instrument. A mathematical model is adopted which enables quantitative determination of the composition of the water-oil interface as a function of bulk surfactant concentration in the water-oil mixtures. Our results show a decrease in gastric lipolysis when interfacially active molecules are incorporated into a food matrix. However, only the Sn-2 monopalmitin caused a systematic decrease in triglyceride hydrolysis throughout the gastro-intestinal tract. This effect is most likely due to exclusion of both lipase and triglyceride from the water-oil interface together with a probable saturation of the solubilization capacity of bile with monoglycerides. Addition of beta-lactoglobulin or lysophopholipids increased the hydrolysis of fat after the gastric phase. These results can be attributed to an increasing interfacial area with lipase and substrate present at the interface. Otherwise, beta-lactoglobulin, or lysophopholipids reduced fat hydrolysis in the stomach. From the mathematical modeling of the interface composition, we can conclude that Sn-2 monopalmitin can desorb lipase from the interface, which, together with exclusion of substrate from the interface, explains the gradually decreased triglyceride hydrolysis that occurs during the digestion. Our results provide a biophysics approach on lipolysis that can bring new insights into the problem of fat uptake.
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| 10. |
- Tylewicz, Urszula, et al.
(författare)
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Gas in Scattering Media Absorption Spectroscopy (GASMAS) Detected Persistent Vacuum in Apple Tissue After Vacuum Impregnation
- 2012
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1866 .- 1557-1858. ; 7:1, s. 28-34
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and the capillary pressure of the pore space are important variables for better understanding of the complex phenomena occurring during vacuum impregnation (VI) of plant tissues. In this study, we used GASMAS (Gas in Scattering Media Absorption Spectroscopy) of oxygen to, non-destructively, measure the dynamics of the internal pressure in apple pieces after restoration of the atmospheric pressure. Apple pieces were impregnated with isotonic sucrose solution (18% w/v) at different reduced pressures (15, 30, 45 kPa (abs.)). After restoration of the atmospheric pressure, the pressure of the remaining pore space gas could remain as low as 50 kPa (abs) and rise slowly toward ambient over a time scale of hours. Both the residual vacuum and the timescale of pressure equilibration with ambient varied with applied vacuum level and apple variety. It is proposed that at least a part of the pore space of apples may be hydrophobic, giving rise to a negative Laplace pressure, and thus the convective flow of impregnating solution is arrested at a mechanical equilibrium where internal pressure is lower than external pressure. Further pressure equilibration can then only be achieved either by gas diffusion in gas phase, or by gradual wetting of the pores.
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