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Etude structurale et rhéologique des systèmes mixtes caséinates/carraghénanes

Abstract : The carrageenan is a sulphated polysaccharide extracted from red algae. In a acqueous solution carrageenan change its conformation when we cool from a coil to a helix, this coil-helix transition is thermoreversible. In generally, Helical carrageenan aggregates and can form a gel. Rheology shows that carrageenan forms gel during cooling at a critical gelation temperature Tc and that upon heating, the gel melts at a critical melting temperature Th. These critical temperatures depend on the nature and the concentration of kations that are present in the solution, but not on the carrageenan concentration. The shear modulus depends both on nature and concentration of salt and on the carrageenan concentration. Casein is the major milk protein component and consist of 4 kinds of casein molecules: alpha s1, alpha s2, beta and kappa casein. In milk, the caseins form a large complex with a size of about 200nm. This complex is stabilized by colloidal calcium phosphate. SC (sodium caséinate) can be prepare by precipitation of casein micelles at pH 4, washing the precipitate to remove the colloidal calcium phosphate and returning to pH 7 by adding NaOH. The SC is present in water in the form of small particles with a radius of about 11 nm that contain approximately 15 casein molecules. The objective of this work is to study the structure and mechanical properties of SC/carrageenan (kappa carrageenan (KC) and iota carrageenan (IC)) mixtures and to better understand the nature of the interaction between them. mixtures of KC and SC show a segregative phase separation at high concentrations of either. Cluster containing mostly SC and little KC are formed by association between KC and SC. With time, the clusters flocculate and precipitate, but they can be redisperse in solution by heating and shaking. The fraction of protein in the clusters depends on the pH, the ionic strength and the KC concentration, but very little on the protein concentration. During cooling, SC associates with helical KC and forms a mixed network. These mixed gels have two types of crosslinks: links between protein free KC chain sections and links involving of proteins. The break up of these two types of bonds can be seen during the melting process depending on the relative amounts of SC and KC. The gel strength depends on the KC and SC concentration and also the type and the concentration of salt. Mixtures of τ-carrageenan (IC) and sodium caseinate (SC) were investigated and the results are compared with a similar study of mixture of κ-carrageenan (KC) and SC. Segregative phase separation was observed at high biopolymer concentrations and the binodal was determined. At low IC concentrations SC formed aggregates involving a very small amount of IC that were characterized with light scattering. The influence of adding SC on the gelation of IC during cooling and the shear modulus of the gels, was studied in the presence of NaCl or KCl. The main conclusion of this work is that SC binds to both IC and KC, in the coil conformation as well as in the helix conformation, but that its effect on the rheology is much weaker for IC than for KC.
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Submitted on : Wednesday, December 14, 2011 - 6:02:22 PM
Last modification on : Tuesday, March 31, 2020 - 3:22:43 PM
Long-term archiving on: : Thursday, March 15, 2012 - 2:46:46 AM


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  • HAL Id : tel-00652071, version 1


Merveille Clay Nono Djamen. Etude structurale et rhéologique des systèmes mixtes caséinates/carraghénanes. Autre. Université du Maine, 2011. Français. ⟨NNT : 2011LEMA1012⟩. ⟨tel-00652071⟩



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