| 1. |
- Wendin, Karin, 1963-, et al.
(författare)
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Dynamic analyses of sensory and microstructural properties of cream cheese
- 2000
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 71:3, s. 363-378
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Tidskriftsartikel (refereegranskat)abstract
- Flavour and texture in cream cheese depend on the microstructure. The objective of this work was to study the influence of fat content, salt content and homogenisation pressure on the microstructure and sensory properties of cream cheese. Twelve types of cream cheese were produced according to a full-factorial design, whereby the fat content was set at three levels, the salt content at two levels and the homogenisation pressure at two levels. The cheeses were analysed by a sensory panel, using both quantitative descriptive profiling and time intensity (T1) evaluation, and by using a confocal laser scanning microscope, CLSM, whereby the microstructure of the cheeses was analysed. All the design parameters had a significant influence on the flavour and texture, although fat had the largest effect. Interaction effects between the design parameters were also found to influence the character of cream cheese. The results showed that it is possible to create a cream cheese with lower fat content and with sensory attributes similar to the attributes in cream cheese with high fat content, by modification of production parameters.
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| 2. |
- Olsson, E E M, et al.
(författare)
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Heat transfer from a slot air jet impinging on a circular cylinder
- 2004
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774 .- 1873-5770. ; 63:4, s. 393-401
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Tidskriftsartikel (refereegranskat)abstract
- Heat transfer from a slot air jet impinging on a cylinder shaped food product placed on a solid surface in a semi-confined area as investigated using computational fluid dynamics (CFD). Simulations of a cylinder in cross flow with the k-epsilon, k-omega and SST models in CFX 5.5 were compared with measurements in the literature. The SST model predicts the heat transfer better than the other models and is therefore used in this study. The distribution of the local Nusselt numbers around the cylinder for various Reynolds numbers (23,000-100,000), jet-to-cylinder distances, H/d (2-8), and cylinder curvature, d/D (0.29-1.14) was determined. The results show that the local Nusselt numbers varies around the surface of the cylinder and that the average Nusselt number and the stagnation point Nusselt number increases with increasing Reynolds numbers and surface curvature but has little dependency on the jet-to-cylinder distance. The result is Nu(m) = 0.14Re(0.65)(H/d)(-0.077)(d/D)(0.32) and Nu(s) = 0.46Re(0.59)(H/d)(-0.026)(d/D)(0.32). (C) 2003 Elsevier Ltd. All rights reserved.
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| 3. |
- Kovács, Tamás
(författare)
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Flow and turbulence in the discharge stream of different agitators for stirred tanks
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the fluid dynamic properties of the conventional Rushton turbine and another impeller type, the Scaba Radial flow Gas dispersing Turbine (with six concave blades) are compared. For comparison, point-wise velocity measurements were made in the discharge of the two turbine types using Hot-Wire Anemometry in constant temperature mode (CTA) with a split film probe. For the time-averaged flow and turbulent properties, good agreement was found for the turbines using both a representation of data based on an analogy to a jet, and the power input. These comparisons were not available when a larger 6SRGT was studied, due to the presence of the axial pumping impellers. These turbines lift the radial jet in the 6SRGT discharge, making the tangential velocity in the impeller centreline significantly lower. Because of the effect of the rotating blades, the measured time series is considered to be the superposition of the periodic (pseudo-turbulent) and the random turbulent signal. These two parts were separated by eliminating or retaining the associated frequencies in the Fourier spectrum. Using plane projections of the phase portraits of the deterministic part, the dynamics of pseudo-turbulence were found to be very similar for the 6SRGT turbine regardless of the diameter or agitation rate. Somewhat slightly different projections were obtained for the 6RT turbine. From the profile measurement, the lack of trailing vortices was concluded in the case of the 6SRGT turbines, and the turbulence was found to be characterised by the same integral length scales and Eulerian time scales in both cases at pilot scale.
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| 4. |
- da Cruz Francisco, José
(författare)
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On the Extraction of Essential Oils by Supercritical Carbon Dioxide and its Influence on the Mesomorphic Phase Structures
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A comparison of essential oils from leaves of Eucalyptus camaldulensis Dehn. obtained by hydrodistillation (HD) and supercritical carbon dioxide (SC-CO2) extraction is presented. Selected major components of the oils showed a predominance of higher molecular weight components in the SC-CO2 extracts than in those obtained by HD. Physico chemical properties such as molecular weight, vapour pressure of the components, steric factor as well as in oil composition. Discussions on environmental effects on the quality of the essential oils obtained on the same eucalyptus genotype treated by the same techniques are also presented. The monoterpenes 1,8-cineole, limonene and a-pinene, present in considerable amounts in eucalyptus leaf oils, as well as their mixtures and three eucalyptus oils from different genotypes, namely E. dives, E. polybractea and E. radiata, were also studied with regard to their solubility in dense CO2 (SC-CO2 and LCO2). In general, pure compounds showed a higher solubility in SC-CO2. The composition SC-CO2 at the highest pressure and temperature. Since polar lipids are always present in eucalyptus leaves from which the oil is extracted, the interaction between such lipids, water, SC-CO2 and essential oils is important to study. First, liquid crystalline properties and the extractability of monoolein/water systems by supercritical carbon dioxide are discussed. The most remarkable observation in this study was the loss of the native mesomorphic structure at high temperatures and the low recovery of monoolein in monoolein/water systems within the highest (18wt%) water content at temperatures between 35 and 65°C. These effects are explained by the SC-CO2, water and monoolein interactions which lead to different water and monoolein activities in the phase present. Further, two model systems composed of monoolein/water or soybean lecithin/water, cineole and SC-CO2 are presented for studying the phase behaviour. Generally, it is observed that the liquid crystalline structure remain also in presence of surplus of SC-CO2. Hence, it can be assumed that lipid structures in the plant tissues may remain also during SC-CO2 extraction and contribute to the matrix effects observed in extraction trials.
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| 5. |
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| 6. |
- Olsson, Crister
(författare)
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Characterisation of Food Associated Bacteria by DNA based Methods, with Special Reference to Enterobacteriaceae
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The presence of genes in food, encoding some virulence factors, was studied by PCR, and species of Enterobacteriaceae, associated with food, were studied by the DNA-based methods of TTGE, ribotyping and sequencing. The flora of fresh and chill-stored pork were analysed by a culture-independent approach, using specific amplification of 16S rRNA genes followed by cloning and sequencing. No evidence for the presence of toxin coding genes related to E. coli was found in meat and fish but a strain of Serratia liquefaciens positive for the Yersinia HPI, was isolated from a sample of beef. Up to now, this is the first Serratia found to be HPI positive but the significance, from a food hygiene point of view, is not clear and S. liquefaciens is only occasionally isolated from clinical specimens. For the primary purpose of evaluating the TTGE method for identification of Enterobacteriaceae associated with food, strains isolated from meat, fish and milk and human isolates of Klebsiella, a genus that is frequently found in food, were included in the study. TTGE proved to be a tool for differentiating E. coli, E. vulneris, E. cloacae, E. amylovora, H. alvei, K. terrigena, P. agglomerans, R. aquatilis, and distinguished between the clinically important strains of K. pneumoniae and K. oxytoca. In addition, it was possible to identify R. aquatilis genomospecies (GS) 1 and 2 and presumably one additional GS group of this species using TTGE. The closely related species of K. planticola, K. ornithinolytica and E. aerogens were not separated by TTGE. Furthermore, the C. freundii and Y. ruckeri type strains could not be distinguished from each other and S. liquefaciens and S. proteamaculans could not be identified due to diffuse or lack of band on the gel. Ribotyping was useful to subdivide Rahnella aquatilis into genomic subtypes and for confirmation of the TTGE grouping. The strains of H. alvei and S. liquefaciens were genomically defined by ribotyping. Sequencing of 16S rRNA genes was useful for the verification of the identity of Klebsiella isolates and the different Rahnella genomospecies. In addition a protocol was developed for rapid identification of Klebsiella spp. By picking a colony from an agar plate, preparing the DNA for PCR and running TTGE over night, identification was possible within 24 hours. A culture-independent analysis of the flora of fresh and chill-stored pork gave an overall picture, of the bacterial composition, which was in agreement with cultivation-dependent methods previously used. The initial flora turned out to be diverse in terms of the numbers of genera present, and a change occurred during refrigerated storage into a gram-negative psychrotrophic flora, dominated by Pseudomonas. The method used here also indicated the possibility of detecting bacterial species such as Eperythrozoon, that do not grow on ordinary media.
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| 7. |
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| 8. |
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| 9. |
- Ahrné, Lilia, et al.
(författare)
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Modelling textural changes of vegetables during acidification under isothermal and non-isothermal conditions
- 2001
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Ingår i: Acta Horticulturae. - 0567-7572. ; 566, s. 323-328
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Tidskriftsartikel (refereegranskat)abstract
- Acidification can be used to improve the quality of canned vegetables because it can decrease thermal processing requirements. Moreover, there is some evidence that acidified vegetables retain a better texture than non-acidified ones. Optimisation of the acidification processes requires the knowledge of the relationship between texture and thermal process at low/moderate temperature. The main objective of this work was the modelling of textural changes of vegetables during acidification under isothermal conditions, and the application of the model to predict textural changes in non-isothermal processes. Turnip was the vegetable used in the experiments. The effect of pre-treatments (blanching, freezing/thawing, calcium addition and vacuum infusion of water before acidification) on the kinetics of textural changes during acidification was also studied. Turnips were acidified in acetic acid under isothermal (20, 50, 70, 80, 90 and 100°C) and non-isothermal conditions (20 to 90°C). Texture was modelled by a two subtract first order kinetic model, assuming an Arrhenius-type dependence of the rate constants on temperature. The model parameters were estimated by nonlinear regression. At temperatures lower then 70°C no significant changes in texture were detected. At higher temperatures the model showed a good fit to the data for all the conditions tested. Acidification decreased the percentage of heat labile substrate from 96% to 62%, thus improving firmness retention. The parameters of the kinetic model estimated under isothermal conditions provided an adequate prediction of texture changes under non-isothermal conditions. The methodology developed in this work can be further applied to model the textural changes of vegetables during other thermal processes, such as drying, blanching, and frying.
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| 10. |
- Borch, Elisabeth, et al.
(författare)
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Bacteriological safety issues in red meat and ready-to-eat meat products, as well as control measures
- 2002
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Ingår i: Meat Science. - 0309-1740 .- 1873-4138. ; 62:3, s. 381-390
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Tidskriftsartikel (refereegranskat)abstract
- The importance of Eschericha coli O157, Listeria monocytogenes and Salmonella typhimurium DT104 as meat-borne pathogens is well established. Pathogenic bacteria such as Aeromonas spp., Arcobacter spp., psychrotrophic Bacillus cereus, Campylobacter spp., Clostridium botulinum and non-invasive Listeria monocytogenes can be regarded as rookies, but not yet firmly associated with today's production of red meat and meat products. The development of PCR and other DNA-based techniques will shed new light on so called emerging pathogens. Important safety issues in meat production, such as insufficient cleaning and disinfection (including the stable/lairage, processing environment), carcass decontamination and chilling, and cross contamination are discussed. Furthermore, probability modelling of survival and growth is identified as an important way to achieve a better understanding of how to deal with the complexity of further processing, including heat treatment and storage. © 2002 Elsevier Science Ltd. All rights reserved.
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