Rangées de graines.. © INRA, Elena Schweitzer © Fotolia

Our results

Contents
  1. Introduction
  2. Human milk digestion in the preterm infant: impact of technological treatments
  3. Research & Innovation 2017 - For Food and Biobased Products
  4. The way in which proteins aggregate when heated may change their sensitising potency
  5. Enhancing the viability of spray-dried probiotic bacteria by stimulating their stress tolerance
  6. To stick or not to stick? Pulling pili sheds new light on biofilm formation
  7. When biopolymers selfassemble: a balance between energy and entropy.
  8. Mimicking the gastrointestinal digestion in a lab-on-a-chip:the microdigester
  9. How a milk droplet becomes a powder grain
  10. Research & Innovation 2016 - For Food and Bioproducts
  11. A new process for the biorefining of plants
  12. Under the UV light : the bacterial membrane
  13. Reverse engineering or how to rebuild ... bread!
  14. Green Chemistry: a step towards lipid production in yeast
  15. Individually designed neo-enzymes for antibacterial vaccines
  16. Multi-scale mechanical modelling: from the nanometric scale to the macroscopic properties of bread crumb
  17. Minimill: 500 g to assess the milling value of soft wheats
  18. Microbial production of lipids for energy or chemical purposes
  19. The discrete role of ferulic acid in the assembly of lignified cell wall
  20. Eco-design of composites made from wood co-products
  21. Analysis of volatile compounds enables the authentication of a poultry production system
  22. Nanoparticles as capping agents for biopolymers microscopy
  23. Pasteurisation, UHT, microfiltration...All the processes don't affect the nutritional quality of milk in the same way
  24. Integration of expert knowledge applied to cheese ripening
  25. Controlling cheese mass loss during ripening
  26. The shape memory of starch
  27. Research & Innovation 2015 - For Food & Biobased Products
  28. Behaviour of casein micelles during milk filtering operations
  29. Overaccumulation of lipids by the yeast S. cerevisiae for the production of biokerosine
  30. Sequential ventilation in cheese ripening rooms: 50% electrical energy savings
  31. An innovative process to extract bioactive compounds from wheat
  32. Diffusion weighted MRI: a generic tool for the microimaging of lipids in food matrices
  33. Characterization of a major gene of anthocyanin biosynthesis in grape berry
  34. New enzyme activity detectors made from semi-reflective biopolymer nanolayers
  35. Improving our knowledge about the structure of the casein micelle
  36. Heating milk seems to favour the development of allergy in infants
  37. Fun with Shape
  38. Using volatile metabolites in meat products to detect livestock contamination by environmental micropollutants
  39. SensinMouth, when taste makes sense
  40. A decision support system for the fresh fruit and vegetable chain based on a knowledge engineering approach
  41. SOLEIL casts light on the 3D structure of proteins responsible for the stabilisation of storage lipids in oilseed plants
  42. A close-up view of the multi-scale protein assembly process
  43. Controlling the drying of infant dairy products by taking water-constituent interactions into account
  44. Polysccharide nanocrystals to stabilise pickering emulsions
  45. Discovery of new degradative enzymes of plant polysaccharides in the human intestinal microbiome
  46. A durum wheat flour adapted for the production of traditional baguettes
  47. Virtual modelling to guide the construction of « tailored-made » enzymes
  48. How far can we reduce the salt content of cooked meat products?
  49. Diffusion of organic substances in polymer materials: beyond existing scaling laws
  50. Smart Foams : various ways to destroy foams on demand !
  51. Dates, rich in tannins and yet neither bitter nor astringent
  52. Sodium content reduction in food
  53. Research & Innovation 2014

Behaviour of casein micelles during milk filtering operations

During the transformation of milk into cheese or another dairy product, concentration stages are often necessary. Their major aim is to increase the content of casein, proteins organised in the form of “casein micelles”, quasi-spherical aggregates measuring approximately 100 nanometers in diameter. Understanding how casein micelles behave during the concentration process is essential to a more effective control of operations currently in use and to the development of new processes. Physical chemists working with soft matter physicists demonstrated that the casein micelle, depending on the level of concentration, acts first as a “hard” colloid, then as a “sticky” colloid and, finally, as a “soft and compressible” colloid. In addition to being useful from the technological point of view, these results suggest that the casein micelle may be a true model object for colloid physics.

Micelles de caséine présentes naturellement dans le lait de vache (vues par cryoMET).,. © INRA, GAILLARD Cédric

Understanding how casein micelles behave during the concentration process

During the transformation of milk into cheese or another dairy product, concentration stages are often necessary and sometimes indispensable.  Different technologies such as membrane filtration, evaporation and drying are used and can be broken down according to the level of concentration to be reached. The aim of our research is to understand how casein micelles, which account for the majority of protein content in cow's milk, behave during the concentration process.  This research is essential to control operations currently used in the sector, often managed empirically, and to promote the development of new processes.  Using x-ray scattering, an initial approach consisted of observing how casein micelles concentrate themselves at the surface of a filtration membrane. This research, based on an in situ and unequilibrated approach, has since been supplemented by observations of casein micelle model dispersions ex situ and at a thermodynamic balance, submitted to an osmotic stress.  From the scientific point of view, this research is at the core of an issue of major importance today, that of the phase behaviour of colloidal objects in dense environments and of their interactions.  

Different physical behaviour depending on the concentration regime  

Casein micelle dispersions were "compressed" by osmotic stress, a technique already tested on other colloidal objects and that makes it possible to reach a wide range of concentration levels.  The osmotic pressure of these dispersions, as well as their rheological properties were then determined. The evolution of these physical parameters with the concentration allowed us to identify three major types of behaviour:
 
•     Dilute regime (< 150 g/L of caseins)
In this regime, dispersions have properties totally comparable to those of a relatively unconcentrated "hard-sphere" liquid.  The casein micelles are still sufficiently distant from each other so that they do not directly interact with each other.  The dispersions are liquid and have a moderate viscosity compared to that of water.  They are also white and cloudy, like milk.
•     Transition regime (150-180 g/L of caseins)
In this second regime, the distance between the micelles is sufficiently short at that moment for them to directly interact with each other and get in each other's way.  Just like in a concentrated "hard-sphere" liquid, dispersions show a divergence of the viscosity and the osmotic stress at the approach of a critical concentration that corresponds to a zero distance between micelles (= compact packing). Dispersions also begin to develop an elastic resistance at the approach of this critical concentration.
•     Dense regime (> 180 g/L of caseins)
Beyond the critical concentration, dispersions behave more and more like a gel.  The micelles are in contact and weak energy bonds develop between them (like "adhesive" spheres).  Just like emulsion droplets, their shape changes and "deflates" as the concentration increases.  Overall, dispersions behave like a homogeneous material that no longer diffracts visible light and appears to be quasi-transparent.

As the concentration increases, micelles reveal a succession of behaviours typical of certain colloids: hard-sphere, adhesive sphere, soft and deformable colloid.

These results could be notably extended to the behaviour of microgels (or particles of a hydrogel), objects increasingly under the scrutiny of physicists because they are more complex than "simple" colloids whose properties are well known at this time.

Dispersions de micelles de caséine avant et après compression osmotique : Avant compression, les micelles sont éloignées les unes des autres et diffractent la lumière visible. La dispersion apparait blanche et turbide, comme un lait. Après compression, les micelles sont au contact et comprimées. Elles forment un matériau homogène (un gel), qui ne diffracte plus la lumière visible et apparait comme quasi-transparent. (∏= pression osmotique). © INRA, A. bouchoux
Dispersions de micelles de caséine avant et après compression osmotique : Avant compression, les micelles sont éloignées les unes des autres et diffractent la lumière visible. La dispersion apparait blanche et turbide, comme un lait. Après compression, les micelles sont au contact et comprimées. Elles forment un matériau homogène (un gel), qui ne diffracte plus la lumière visible et apparait comme quasi-transparent. (∏= pression osmotique) © INRA, A. bouchoux
Casein micelle dispersions before and after osmotic pressure:
Before compression, the micelles are far from each other and diffract visible light. The dispersion appears to be white and cloudy, like milk.  After compression, micelles are in contact with each other and compact. They form a homogeneous material (a gel) that no longer diffracts visible light and appears to be quasi-transparent (π= osmotic pressure).

Pursuing the study of dense dispersions to improve and model concentration operations such as milk filtration or spray drying

This research is the first step towards the complete characterisation of the behaviour of casein micelles in dense environments. It will be supplemented in the near future by a fine study of the structural properties of dense dispersions. Another important prospect is the possibility of extending these results to the industrial scale by proposing improvements to concentration processes that already exist. This could be done by combining these results with those already obtained (in situ approach) in order to develop coherent models from the theoretical point of view and that would make it possible to predict the performances of milk filtration or its spray drying.  

En savoir plus

  • C. David, F. Pignon, T. Narayanan, M. Sztucki, G. Gésan-guiziou, A. Magnin, Langmuir 24 (2008) 4523-4529
  • A. Bouchoux, P.E. Cayemitte, J. Jardin, G. Gésan-Guiziou, B. Cabane, Biophysical Journal 96 (2009) 693-706
  • A. Bouchoux, B. Debbou, G. Gésan-Guiziou, M.H. Famelart, J.L. Doublier, B. Cabane, Journal of Chemical Physics 131 (2009) 165106