The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform
J Mellema - One of the best experts on this subject based on the ideXlab platform.
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steady shear viscosity of stirred yogurts with varying Ropiness
Journal of Rheology, 1999Co-Authors: M E Van Marle, D Van Den Ende, C G De Kruif, J MellemaAbstract:Stirred yogurt was viewed as a concentrated dispersion of aggregates consisting of protein particles. The steady-shear behavior of three types of stirred yogurt with varying Ropiness was investigated experimentally. To describe the shear-dependent viscosity, a microrheological model was used which was developed for weakly aggregating dispersions. This model was capable of successfully describing the steady-state viscosity as a function of shear rate of the stirred yogurts, the protein concentration of which ranged between 2.0% and 3.9%. The value of the fractal dimensionality df, following from the model for the aggregates is about 2.24, which was similar to the value of df found with other methods. Moreover, realistic values were found for the interaction forces (energies) describing interaction between the aggregates. The calculated size of the aggregates was close to the size found before by applying different experimental techniques. Using this model, the interpretation of the measured curves suggests that the exopolysaccharides, produced by the lactic acid bacteria in yogurt, play a significant role in the rheology of stirred yogurt.
Richard Ipsen - One of the best experts on this subject based on the ideXlab platform.
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sensory and rheological screening of exopolysaccharide producing strains of bacterial yoghurt cultures
International Dairy Journal, 2006Co-Authors: Ditte Marie Folkenberg, Petr Dejmek, Anne Skriver, Helle Skov Guldager, Richard IpsenAbstract:Yoghurts were produced with 24 different cultures differing in their ability to produce exopolysaccharides (EPS). Rheological and sensory analyses showed large differences in texture properties in the yoghurt samples. EPS production was found to have a major effect oil the texture properties, but varying textures within the EPS +/- groups were also found. Yoghurts fermented with EPS-producing cultures showed increased mouth thickness and Ropiness and tended to be creamier than yoghurts without these cultures; in contrast, these yoghurts had the lowest syneresis and highest gel firmness (initial gel strength before the yoghurt was subjected to shear). Correlations between rheological parameters and sensory texture attributes included G* correlating with gel firmness, while viscosity measured at 241 s(-1) correlated with mouth thickness. An interesting viscometry relationship was found between Ropiness and hysteresis loop area. (Less)
M E Van Marle - One of the best experts on this subject based on the ideXlab platform.
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steady shear viscosity of stirred yogurts with varying Ropiness
Journal of Rheology, 1999Co-Authors: M E Van Marle, D Van Den Ende, C G De Kruif, J MellemaAbstract:Stirred yogurt was viewed as a concentrated dispersion of aggregates consisting of protein particles. The steady-shear behavior of three types of stirred yogurt with varying Ropiness was investigated experimentally. To describe the shear-dependent viscosity, a microrheological model was used which was developed for weakly aggregating dispersions. This model was capable of successfully describing the steady-state viscosity as a function of shear rate of the stirred yogurts, the protein concentration of which ranged between 2.0% and 3.9%. The value of the fractal dimensionality df, following from the model for the aggregates is about 2.24, which was similar to the value of df found with other methods. Moreover, realistic values were found for the interaction forces (energies) describing interaction between the aggregates. The calculated size of the aggregates was close to the size found before by applying different experimental techniques. Using this model, the interpretation of the measured curves suggests that the exopolysaccharides, produced by the lactic acid bacteria in yogurt, play a significant role in the rheology of stirred yogurt.
Aline Lonvaud-funel - One of the best experts on this subject based on the ideXlab platform.
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Evidence for exopolysaccharide production by Oenococcus oeni strains isolated from non-ropy wines
Journal of Applied Microbiology, 2009Co-Authors: G. Ciezack, Aline Lonvaud-funel, L. Hazo, Gérard Chambat, Alain Heyraud, Marguerite Dols-lafargueAbstract:Aims: The aim of this study was to assess the exopolysaccharide (EPS) production capacities of various strains of Oenococcus oeni, including malolactic starters and strains recently isolated from wine. Methods and Results: Fourteen O. oeni strains displaying or not (PCR check on genomic DNA) the gtf gene generally associated with β-glucan formation and Ropiness were grown on grape juice medium, dialysed MRS-derived medium or synthetic medium. The soluble polysaccharides (PS) remaining in the culture supernatant were alcohol precipitated, and their concentration was quantified by the phenol-sulfuric method. Most of the O. oeni strains studied produced significant amounts of EPS, independently of their genotype (gtf+ or gtf−). The EPS production was not directly connected with growth and could be stimulated by changing the growth medium composition. The molecular weight distribution analysis and attempts to determine the PS chemical structure suggested that most strains produce a mixture of EPS. Conclusion: Oenococcus oeni strains recently isolated from wine or cultivated for many generations as a malolactic starter are able to produce EPS other than β-glucan. Significance and Impact of the Study: These EPS may enhance the bacteria survival in wine (advantage for malolactic starters) and may contribute to the wine colloidal equilibrium.
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rpoB gene: A target for identification of LAB cocci by PCR-DGGE and melting curves analyses in real time PCR
Journal of Microbiological Methods, 2006Co-Authors: Vincent Renouf, Olivier Claisse, Aline Lonvaud-funelAbstract:Lactic acid bacteria (LAB) are essential in the quality of many fermented beverages like beer, cider and wine. In the two later cases, they convert malic acid into lactic acid during the malolactic fermentation. After fermentation, microbial stabilization is needed to prevent the development of spoilage bacteria species. Among them, cocci lead to different alterations: Pediococcus sp., and some strains of Leuconostoc mesenteroides and Oenococcus oeni can produce exopolysaccharides which modify wine viscosity and lead to Ropiness. They also can produce acetic acid, biogenic amine, ethyl carbamate and volatile phenols. Therefore detection and identification are crucial. Results of phenotypic tests and DNA-DNA probes are not accurate enough. 16S RNA gene which is currently used for bacterial species identification presents intraspecies heterogeneity. The rpoB gene is an alternative to this limitation. However previous PCR targeting partial sequence of rpoB gene could not delimit cocci species. Therefore we compared the rpoB gene sequence of the six main cocci species found in fermented beverages: P. damnosus, P. dextrinicus, P. parvulus, P. pentosaceus, L. mesenteroides and O. oeni. The most discriminating partial sequence of the rpoB gene was chosen for designing primers. By PCR-DGGE the reliability of these primers was verified. It was controlled in a mixture of several cocci and other lactic acid bacteria (Lactobacillus sp.). Then we adapted the primers and the PCR conditions in order to achieve the identification of cocci species by real time PCR program including the fluorescent dye SYBR Green I, which gives faster results. PCR melt curves were established and a specific Tm was attributed to each species. © 2006 Elsevier B.V. All rights reserved.
Daniel Wefers - One of the best experts on this subject based on the ideXlab platform.
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Exopolysaccharides from Lactococcus lactis affect manufacture, texture and sensory properties of concentrated acid milk gel suspensions (fresh cheese)
International Dairy Journal, 2020Co-Authors: Georg Surber, Daniel Wefers, Harald Rohm, Carolin Schäper, Doris JarosAbstract:ABSTRACT Two exopolysaccharide (EPS) producing Lactococcus lactis strains that differed largely in their technofunctional properties (gel stiffness, Ropiness) were used to relate their functionality in concentrated acid milk gel suspensions to the structural and macromolecular properties of the EPS. LL-1+ produced ropy and cell-bound EPS that contributed to acid milk gels with a higher gel stiffness, improved serum retention, and resulted in concentrated acid milk gel suspensions with smaller particles and a more ‘creamy’ texture compared with the non-ropy EPS from LL-2. From the basic structural and macromolecular analysis of the EPS it is concluded that mainly the higher hydrodynamic radius of the ropy EPS from LL-1+ is responsible for these features. The use of ropy and cell-bound EPS producing strains has, therefore, potential for the manufacture of low-fat fresh cheese with tailored functionality.
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Characterization of β-glucan formation by Lactobacillus brevis TMW 1.2112 isolated from slimy spoiled beer
International Journal of Biological Macromolecules, 2018Co-Authors: Marion E. Fraunhofer, Andreas J. Geissler, Frank Jakob, Daniel Wefers, Mirko Bunzel, Rudi F VogelAbstract:Despite several hurdles, which hinder bacterial growth in beer, certain bacteria are still able to spoil beer. One type of spoilage is characterized by an increased viscosity and slimy texture caused by exopolysaccharide (EPS) formation of lactic acid bacteria (LAB). In this study, we characterize for the first time EPS production in a beer-spoiling strain (TMW 1.2112) of Lactobacillus brevis, a species commonly involved in beer spoilage. The strain's growth dynamics were assessed and we found an increased viscosity or Ropiness in liquid or on solid media, respectively. Capsular polysaccharides (CPS) and released EPS from the cells or supernatant, respectively, were analyzed via NMR spectroscopy and methylation analysis. Both are identical β-(1 → 3)-glucans, which are ramified with β-glucose residues at position O2. Therefore, we assume that this EPS is mainly produced as CPS and partially released into the surrounding medium, causing viscosity of e.g. beer. CPS formation was confirmed via an agglutination test. A plasmid-located glycosyltransferase-2 was found as responsible for excess β-glucan formation, chromosomal glucanases were proposed for its degradation. The glycosyltransferase-2 gene could also be specifically identified in beer-spoiling, slime-producing Lactobacillus rossiae and Lactobacillus parabuchneri strains, suggesting it as promising marker gene for the early detection of β-glucan-producing Lactobacilli in breweries.
