| 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. |
- Bayod, Elena, et al.
(författare)
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Microstructure of highly concentrated tomato suspensions on homogenisation and subsequent shearing
- 2011
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Ingår i: Food Research International. - : Elsevier BV. - 0963-9969. ; 44:3, s. 755-764
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Tidskriftsartikel (refereegranskat)abstract
- The changes in the microstructure of tomato paste suspensions have been investigated during homogenisation and subsequent shearing in suspensions with similar composition, at three tomato paste concentrations 10, 30 and 40%. The suspensions were characterised by the particle size distribution (PSD), volume fraction (empty set), and dynamic theological properties (G`, G ''). All suspensions exhibit a solid-like behaviour with G`> G ''. Micrographs indicate that the process of homogenisation creates a smooth network of finer particles, that is easily disrupted by prolonged shearing, giving rise to the formation of densely packed flocs that become clearly oriented in the direction of the shearing. At high concentrations, these changes in the microstructure on homogenisation and subsequent shearing were better reflected by differences in empty set than in G`. The rheological behaviour of the suspensions exhibits a power-law dependence on empty set, over a large range of PSD and for 0.05 < empty set < 0.55. Finally, an experimental equation, including empty set and the size of the coarse particles in the surface-weighted PSD, is found to accurately estimate G` (R-2 > 99.3%, p < 0.001). (c) 2011 Elsevier Ltd. All rights reserved.
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| 3. |
- Bayod, Elena
(författare)
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Mircostructure and rheological properties of concentrated tomato suspensions during processing
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Food processing comprises operations such as dilution (changing the concentration), homogenisation (changing the particle size), and subsequent pumping (shearing), among others. It is thus of great interest to gain a better understanding of the mechanisms governing the creation and disruption of structures during these engineering operations, and the way in which they are related to the textural and rheological properties of the material. The influence of processing on the microstructure and the rheological properties of tomato paste suspensions has been studied. The microstructure was characterised using light microscopy and particle size distribution analysis. The way in which particles of varying size are packed in a specified volume at different concentrations was estimated in terms of the compressive volume fraction. The rheological properties were studied using small-amplitude oscillatory tests, giving the elastic (G') and viscous (G'') moduli, as well as steady shear measurements, giving the viscosity (etha). In the latter case both a rotational and a tube viscometer were used. The results indicate that tomato suspensions consist of a collection of whole cells and cell wall material forming a network (G'>G''). During the process of homogenisation, the particles are broken down, resulting in a smoother and more evenly distributed network of finer particles. The effectiveness of homogenisation in decreasing particle size seemed to be governed by the inherent susceptibility of the particles to breakage (i.e. the type of paste), the viscosity of the suspending medium, and the concentration of particles. Higher viscosities and concentrations were found to prevent breakage to some extent. The presence of larger amounts of fine particles in the homogenised suspensions had a considerable effect on the rheological properties. The yield stress was found to increase, and time-dependent effects became more apparent. At low deformations (gamma < 20), the system consisting of finer particles exhibited rheopectic behaviour (increasing viscosity with time), which was suggested to be caused partly by the rotation of the particles induced by the flow, and partly by the remaining elastic behaviour at stresses close to the yield stress. At larger deformations (gamma<1000), the non-homogenised system exhibited steady-state viscosity, while in the homogenised system it continued to decrease. The unstable behaviour observed in homogenised systems at large deformations gave an indication of particle rearrangement under flow conditions. Micrographs of homogenised suspensions subjected to shearing showed the formation of flocs consisting of densely packed particles that could easily orient in the shearing direction. At high concentrations, the changes in the microstructure caused by homogenisation and shearing were better reflected by the compressive volume fraction than by the elastic modulus. Tube viscometer measurements showed the presence of wall slip in highly concentrated tomato suspensions, which tended to disappear at lower concentrations. The wall slip, which could be as high as 70% of the flow rate, was estimated using both the classical Mooney approach and an inverse numerical method, and the performance of these two methods was compared. The performance of the methods was complicated by the relatively poor reproducibility of the data. Steady shear rheological measurements obtained using a rotational rheometer with different geometries (concentric cylinders, vane, vane-vane) and tube viscometer measurements agreed when no slip was present, and the vane and vane-vane geometries were found to be free of wall slip effects. Finally, the applicability of the Cox-Merz rule (superposition of oscillatory and steady shear data) seemed to be limited to systems that do not form a network (G'G''. However, the dynamic and steady shear data obtained for tomato suspensions coincided when using a shifting factor of about 0.1 on the frequency , which was fairly constant for a large range of tomato paste concentrations (from 100 to 30%, all with G'>G'').
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| 4. |
- Bayod, Elena, et al.
(författare)
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Rheological and structural characterization of tomato paste and its influence on the quality of ketchup
- 2008
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Ingår i: LWT - Food Science and Technology. - : Elsevier BV. - 0023-6438. ; 41:7, s. 1289-1300
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Tidskriftsartikel (refereegranskat)abstract
- Three hot break tomato pastes were investigated to determine the effect of their characteristics on the properties of tomato ketchup, processed in an industrial-scale facility (i.e. diluted, heated, homogenized and cooled). Pastes and ketchups were characterized by particle size distribution, volume fraction, and rheological behavior in steady and dynamic shear. The ketchups were also subjected to sensory assessment. The processing of pastes into ketchups induced large structural changes, which were reflected in all parameters studied. The volume fraction of solids (φ) accurately reflected the changes that the paste suspensions underwent during processing and it appeared to be a good predictor of the flow behavior of both the pastes and the ketchups. The corresponding flow curves were found to be well described by the Carreau model in a large range of shear rates and concentrations. However, the rheological characteristics of the commercial pastes studied did not directly correlate to those of the corresponding ketchups. Instead, our results suggest that the change in structure induced by processing might be governed by other properties of the paste, such as the fraction of small and large particles and their sensitivity to breakage, together with the viscosity of the aqueous phase.
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| 5. |
- Kovácsné Oroszvári, Bea, et al.
(författare)
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The mechanisms controlling heat and mass transfer on frying of beefburgers. III. Mass transfer evolution during frying
- 2006
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774. ; 76:2, s. 169-178
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Tidskriftsartikel (refereegranskat)abstract
- The effects of five different meat raw materials used for making beefburgers on the evolution of mass transfer (total, water and fat losses), patty diameter shrinkage and porosity were studied during frying from the frozen state (-20 degrees C) to a centre temperature of 72 degrees C in a double-sided pan fryer. The normalised water losses increased linearly with increasing average temperature at a degree of 0.4% degrees C-1 during cooking, which suggests that the availability of water is not a restricting factor. The fat content governs both the amount and the initial time of the fat release during frying. Apart from the fattiest beefburger, having a shrinkage of 22%, the shrinkage increased linearly from 0 to 10-12% for all types of meats during the frying. High porosity with a maximum value of about 35% was achieved in the heat treated burgers and was especially evident after crust formation and with high water and fat losses. As a result of the thermal denaturation and contraction of the meat proteins, a flow of water and fat is created moving towards the centre of the patty, which in turn speeds up the heat transfer. The water and fat drip leaves the patty through the circumference of the burger. (c) 2005 Elsevier Ltd. All rights reserved.
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| 6. |
- Kovácsné Oroszvári, Bea, et al.
(författare)
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The mechanisms controlling heat and mass transfer on frying of beefburgers in a double-sided pan fryer
- 2006
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Ingår i: Industries alimentaires et agricoles (Ind. aliment. agric.). - 0019-9311. ; 123:4-5, s. 18-21
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Tidskriftsartikel (refereegranskat)abstract
- La structure de la viande hachée évolue au cours de la cuisson, ce qui a une influence sur les transferts de chaleur et de matière. L'étude a porté sur la friture de steaks hachés de 10 mm d'épaisseur et de 3 à 10 cm de diamètre, provenant de 4 sortes de viande. La cuisson avait lieu entre deux plaques chauffées à 100, 150 ou 175 °C. Elle faisait passer le produit depuis l'état congelé à -20°C jusqu'à 72°C au centre. Ont été mesurés la température au centre et à 2 mm de la surface, la perte d'eau et de matière grasse ainsi que des paramètres de structure tels que le rétrécissement en diamètre et la porosité. Les mesures ont montré une corrélation entre le rétrécissement (variant de 10 à 25%) et les pertes totales et de matière grasse. Ces pertes, qui s'effectuent surtout par les bords, sont à leur tour corrélées avec la quantité de tissus connectifs. L'eau sort sous forme liquide ou vapeur, alors que la matière grasses ne sort qu'à l'état liquide. La température des plaques joue un rôle important sur la quantité d'eau évaporée et sur la durés de cuisson. A 100°C, la formation de croûte est minimale, peu d'eau est évaporée, mais elle sort à l'état liquide. Pour des plaques à 175°C, la perte d'eau est double du cas précédent et se fait par évaporation. La croûte non déformable formée dans ce cas conduit à une porosité plus élevée.
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| 7. |
- Kovácsné Oroszvári, Bea, et al.
(författare)
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The mechanisms controlling heat and mass transfer on frying of beefburgers. Part 2: The influence of the pan temperature and patty diameter
- 2005
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774. ; 71:1, s. 18-27
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Tidskriftsartikel (refereegranskat)abstract
- The effects of varying pan temperature and meat patty diameter on heat (temperature at the centre (5 mm) and 2 mm below the surface) and mass transfer (total, water and fat loss) of beefburgers prepared by double-sided frying were studied, The porosity of the fried beefburgers was determined based on the volume shrinkage and density measurements. The thawing time measured at the centre of the beefburger, total frying time and the final temperature 2mm below the surface were significantly influenced by pan temperature, whereas the choice of meat raw material was of less importance than the pan temperature for the heat transfer. The characteristics of heat transfer, i.e. thawing and total frying time, were significantly influenced by the original patty diameter, with faster temperature increase in the smaller beefburgers. The most determinant factor for the water flux is the temperature gradient, and for the fat flux. the fat content. The water loss based on the initial water content in the form of drip was about 80% of the water loss even at a pan temperature of 175 degrees C. This means that the pressure-driven water loss is the main mechanism governing the water loss in the frying of beefburgers. The higher the heat penetration by using beefburgers of the smaller diameter and the higher the cooking temperature that induces higher water losses, the faster is the crust formation, which ill turn results ill less shrinkage and higher porosity of the heat-processed meat. When beefburgers of different diameters were studied the porosity was dependent both on the rate of heat transfer and on the amount of water and fat flux and was higher with increasing water and fat flux.
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