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Poster De Conférence Année : 2014

Structure and rheological properties of casein micelles and whey protein aggregates acid gels

Résumé

Milk contains a colloidal particle, called the casein micelle (CAS) and globular proteins, called whey proteins. If a whey protein solution is heated, heat-induced whey proteins denature and form colloidal aggregates, called whey protein aggregates (WPA). These compounds are present in milk when it is heated, as for the manufacture of yoghurts. Indeed, CAS and WPA form particular gels by acidification, either in mixture or even separatly. The aim of this aim was to understand how the gel formed from these 2 colloids. The CAS and WPA were dispersed in a milk permeate at different protein concentrations ranging from ~15 to ~105 g kg-1 separately and in a mixture at 80/20 on a weight ratio, respectively and as in milk. Acidification was performed at 35 °C by addition of glucono- -lactone to achieve a final pH at ~ 4.5 in 6 h. Acid gelation was studied by rheology, namely by small amplitude oscillation, followed by large deformation measurement at pH 4.5. Viscoelastic moduli versus time or pH were compared for the different systems at different concentrations, while the microstructure of the gels at their final pH value was studied by confocal scanning laser microscopy. Results show that increasing the protein concentration for the 3 systems promoted a faster gelation, led to higher moduli and to gels with smaller pore sizes, which is due to the increase in the number of particles and consequently probably in the number of potential bonds between them and to the reduction in the distances between colloids. Replacing 20 % of CAS by WPA increased the moduli of the acid gels as long as the protein concentrations was < 90 g kg-1 and increased their pH of gelation as compared to pure CAS gels. We fitted the model of Shih et al. (1990) on the elastic modulus and the yield strain to determine the fractal dimension (Df) of the gel structure and compared the mixture gel to the 2 other ones. From the strain yield behavior, we concluded that the mixture gel and the CAS gel were of the weak-link regime, i.e. that bonds inside the protein clusters making the gel are stronger than bonds between clusters, with Df > 2.6, and probably built under a reaction-limited mechanism. The WPA gel was of the strong-link regime, with lower Df value around 1.7 and produced by a diffusion-limited mechanism. We suspect that these differences were possibly due to the different surface interactive properties of these 2 colloids, together with their different internal structure that lead to a different mechanism of acid gelation.
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Dates et versions

hal-01209637 , version 1 (02-10-2015)

Identifiants

  • HAL Id : hal-01209637 , version 1
  • PRODINRA : 262526

Citer

Robi Andoyo, Fanny Guyomarc'H, Marie-Hélène Famelart. Structure and rheological properties of casein micelles and whey protein aggregates acid gels. 6. Rencontres de Biologie Physique du Grand Ouest, Jun 2014, Le Mans, France. 2014. ⟨hal-01209637⟩
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