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The translational dynamics of poly(ethylene glycol) (PEG) polymers with molecular weights (Mw) varying from 6x10(2) to 5x10(5) were investigated by pulsed field gradient NMR in casein suspensions and in gels induced by acidification, enzyme action, and a combination of both. For molecules with Mw<or=1020, the diffusion was only dependent on the cas...
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In this study, phosphate-solubilizing bacterial strains were isolated and characterized for their solubilization efficiency in Pikovskaya's media amended with tri-calcium phosphate. There are seven bacterial strains were isolated and screened their phosphate solubilization efficiency. Among the seven isolates, only one bacterial strain was dominant...
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... La mesure du coefficient de diffusion de l'eau n'est pas sensible à la taille des molécules de soluté [108], mais uniquement à la concentration massique. Ainsi, nous obtenons la même valeur de coefficient de diffusion pour le glucose, le fructose et le saccharose à la même concentration massique, glucose et fructose étant des isomères, alors que la molécule de saccharose est environ deux fois plus grande. ...
L'objectif de cette thèse était d’améliorer la compréhension des mécanismes impliqués dans la relaxation de tissus végétaux en prenant en compte la composition du contenu cellulaire et la microstructure des tissus. L'effet de la température, du pH et de la teneur en soluté sur les temps de relaxation T2 ont été décrits dans le cas de solutions de sucres simples, en première approximation du contenu vacuolaire de fruits charnus. Cela a permis de mettre en évidence, l'impact non négligeable des effets des échanges chimiques sur la relaxation à 1,5T dans des conditions d'imagerie. Par la suite, les effets combinés des échanges chimiques et de la structure compartimentée sur les paramètres de relaxation des tissus végétaux ont été étudiés en prenant la tomate comme modèle de fruit charnu. Dans le cadre de cette étude, nous nous sommes intéressés aux changements induits par des variations de température dans de gammes de températures où l'intégrité cellulaire est maintenue, la taille des compartiments et la concentration vacuolaire étant supposée constantes au cours de ce processus. Enfin, l'influence de la taille des cellules ainsi que de la teneur en eau a été abordée grâce à l'étude de l'impact de la déshydratation sur des tissus de tomate. Ce travail a permis d'estimer la sensibilité des paramètres de relaxation au cours de ces différents processus, permettant ainsi de proposer une interprétation des variations de T2 observées, prenant en compte les divers mécanismes impliqués.
... Similar approaches have led to comparable findings in the field of food science. Just recently, fluorescence techniques gave the first measurements of inactive pepsin diffusion in dairy gels (Luo et al., 2017;Thévenot et al., 2017), and the results overlapped with previous findings on the diffusion of NPs in dairy gel systems, showing a high dependency on both protein concentration and size ratio between the diffusing particle and the network mesh (Le Feunteun and Mariette, 2007, 2008a, 2008b. ...
Enzymes are essential and ubiquitous biocatalysts involved in various metabolic pathways and used in many industrial processes. Here, we reframe enzymes not just as biocatalysts transforming bioproducts but also as sensitive probes for exploring the structure and composition of complex bioproducts, like meat tissue, dairy products and plant materials, in both food and non-food bioprocesses. This review details the global strategy and presents the most recent investigations to prepare and use enzymes as relevant probes, with a focus on glycoside-hydrolases involved in plant deconstruction and proteases and lipases involved in food digestion. First, to expand the enzyme repertoire to fit bioproduct complexity, novel enzymes are mined from biodiversity and can be artificially engineered. Enzymes are further characterized by exploring sequence/structure/dynamics/function relationships together with the environmental factors influencing enzyme interactions with their substrates. Then the most advanced experimental and theoretical approaches developed for exploring bioproducts at various scales (from nanometer to millimeter) using active and inactive enzymes as probes are illustrated. Overall, combining multimodal and multiscale approaches brings a better understanding of native-form or transformed bioproduct architecture and composition, and paves the way to mainstream the use of enzymes as probes.
... Lucey, Tamehana, Singh, and Munro (1998) reported rheological and microstructural properties using confocal scanning laser microscopy (CSLM) during acid gels formation with bacterial culture or glucono-δ-lactone (GDL) or both GDL and rennet, but mainly for skim milk. These properties were also studied using SEM for combined gel formation with starter cultures and rennet (Le Feunteun & Mariette, 2007), and Cryo-SEM for Mozzarella (Hussain, Bell, & Grandison, 2013) and Cheddar (Ong, Dagastine, Kentish, & Gras, 2011) curd formation. Few studies reported the storage time effect on cheese structure, e.g., Farbod et al. (2013) studied Feta cheese SEM microstructure and Henno, Jõudu, Kaart, Veskioja, and Ots (2017) analysed the rheological properties of Edam-type cheese. ...
Structural (cryo-scanning electron microscopy), and viscoelastic changes (dynamic rheometry), with storage time in Afuega'l Pitu cheese Blancu (B) and Roxu (R) varieties were observed. Biochemical parameters were also measured. pH, fat, and protein content did not change during the storage time for B and R varieties. R micrographs showed large fused-fat particles within the protein matrix, as a consequence of a specific kneading step to mix the partially dehydrated curd with paprika and salt. B samples exhibited more homogeneous microstructures with small fat globules, improving viscoelastic parameters such as conformational stability (stress amplitude, σmax) and network flexibility (strain amplitude, γmax). The longer storage time, the higher total solids (TS) content (lower moisture to protein ratio-MPR) for B and R varieties, evolving into a less porous microstructure, which increased the thickening of the protein strands. These structural changes were shown in the enhanced rigidity (high complex modulus, G*), structural stability (high σmax) and more shear-sensitive or physically structured (lower γmax) cheese network.
... About 80% of the proteins in bovine milk are caseins, and casein has four generic variances: α, β, κ, and γ [1]. Caseins are the building blocks of the network of many dairy gels and contribute to their rheological and structural properties [2]. The gelation of casein can be induced by either acidification or enzymatic hydrolysis, e.g. ...
... chymosin cleavage of the glycomacropeptide. Casein gel structures can be manipulated by using different gelation methods [1] and/or using different gelation conditions (temperature, concentration, pH, sonication) [2][3][4]. ...
... with pH having the biggest impact on C. These results were expected based on previous studies [2,45]. ...
Hydrogels are soft materials with applications in multiple industries, but their fundamental wear behaviors are relatively unknown. Studies on hydrogel wear behaviors generally use empirical measurements. Additionally, it can be difficult to measuring hydrogel wear rates by traditional mass loss measurements because wear debris cannot always be removed without disturbing intact sample. Therefore, the objective of study was to develop a method for more precise calculation of soft material wear rates. The method developed compared creep-recovery and wear-recovery behaviors of casein hydrogels to separate deflection of the material under an applied load from the amount of material removed. Casein hydrogels were prepared at different concentrations (8, 10, and 15% w/w) and pH (2.3, 3.6, 4.8), and tested under a range of normal loads (0.3, 0.4, 0.5 N). Wear-recovery behaviors were fit to an exponential model. Maximum penetration depth during wear and creep, creep-recovery, and wear-recovery increased with lower casein concentration and higher normal force and pH. Exponential models for casein gel wear-recovery behaviors indicated good fit (R2> 0.99). This wear measurement method is useful for developing food products with specific oral and industrial processing behaviors.
... Other studies showed that the PEG diffusion coefficient for PEG molecular weights above 8440 g/mol in a casein gel was strongly dependent on the structure of the casein network [54]. Marked variations in PEG diffusion were obtained between rennet gel, acidic gel, and the gel obtained by a combination of both processes. ...
This chapter focuses on nuclear magnetic resonance relaxation, pulsed field gradients NMR, and magnetic resonance imaging applied to the characterization of dairy products and dairy processes. This chapter is an updated version of a previously published review (Mariette F. Nuclear magnetic resonance: principles. In: Fuquay JW, Fox PF, Mc Sweeney PLH, editors. Encyclopedia of dairy sciences. 2nd ed. San Diego: Academic Press; 2010). This chapter is organized in several parts. The first part provides an overview on the interpretation of water NMR relaxation and its application in dairy systems. It starts with diluted models where the diffusion exchange is fast and only chemical exchange and molecular mobility are considered. Next, the regime of slow diffusion exchange is considered and applications to concentrated and complex systems are discussed. The second part of this chapter focuses on the special case of fat relaxation in the liquid and solid states. The third part includes all the aspects related to the use of the pulsed field gradient NMR technique for water diffusion and molecular probe diffusion. The fourth part provides some insights into applications of magnetic resonance imaging. This chapter is dedicated to Brian Hills for his impressive contribution to NMR science and its application in food. © Springer International Publishing AG, part of Springer Nature 2018.
... Mariette et al. have intensively studied coagulation of milk proteins into casein micelle gels using the nanoparticle diffusometry approach. Their initial work focused on the diffusion of flexible PEG molecules through the networks (Colsenet, Mariette, & Söderman, 2006a;Colsenet, Söderman, & Mariette, 2005a;2005b;Le Feunteun & Mariette, 2007;. More recently, dendrimer particles have been used for the same purpose (Salami et al., 2014;Salami, Rondeau-Mouro, van Duynhoven, & Mariette, 2013b). ...
... In both MF-and UF-suspensions, and in agreement with the work by Colsenet, Soderman, and Mariette (2005) and by Le Feunteun and Mariette (2007), the reduction in the D r value was more pronounced for larger solutes compared with the smaller ones, showing that the solute size influences diffusion behavior in those dairy systems. The smaller D r values in the case of the larger solutes may be explained by the existence of frictional phenomena between solutes and particles. ...
... In both MF-and UF-suspensions, and in agreement with the work by Colsenet, Soderman, and Mariette (2005) and by Le Feunteun and Mariette (2007), the reduction in the D r value was more pronounced for larger solutes compared with the smaller ones, showing that the solute size influences diffusion behavior in those dairy systems. The smaller D r values in the case of the larger solutes may be explained by the existence of frictional phenomena between solutes and particles. ...
... Mariette et al. have intensively studied coagulation of milk proteins into casein micelle gels using the nanoparticle diffusometry approach. Their initial work focused on the diffusion of flexible PEG molecules through the networks Colsenet, S€ oderman, & Mariette, 2005a, 2005bLe Feunteun & Mariette, 2007;2008a). More recently, dendrimer particles have been used for the same purpose (Salami et al., 2014;Salami, Rondeau-Mouro, van Duynhoven, & Mariette, 2013b). ...
At the submicron scale, food biopolymer networks can be visualized by a wide array of microscopic techniques, but these methods are mostly invasive and require careful image analysis in order to quantify network features. ‘Nanoparticle diffusometry’ provides a non-invasive alternative to infer quantitative submicron structural information about biopolymer networks. In this approach, spectroscopy-based methods are used to monitor hindered diffusion of nanoparticles due to network obstructions. Both rigid-spherical and flexible nanoparticles can be used and models are available to derive structural network parameters. A range of applications to polysaccharide and protein sols and gels has been described. The approach offers opportunities to assess (sub-)micron scale network heterogeneity and changes in sub-micron structure under dynamical conditions such as shear or aging.
... Electron microscopy provides a resolution at a nanometer scale, making it possible to observe the organization of the gel protein network itself. Scanning Electron Microscopy (SEM) has already been used for investigating the microstructure of a variety of dairy products (Fallico et al., 2006;Le Feunteun & Mariette, 2007Marchesseau, Gastaldi, Lagaude, & Cuq, 1997;McMahon, Fife, & Oberg, 1999). However, SEM provides only a topographical view of the sample surface, making it difficult to quantify properties from the observed images. ...
