July 10-14, 2016
Passive microrheology based on Diffusing Wave Spectroscopy (DWS) [1,2] is presented as a straightforward tool for the analysis of milk gel preparation. Diffusing Wave Spectroscopy consists of analysing the interferential images of light, which is backscattered by the sample. This so called speckles images, which are detected by a CCD camera, change in time due to the Brownian motion of the particles that scatter the light. The variation of the images as a function of time can be directly correlated to the viscoelastic properties of the sample. As it is an optical method, it is perfectly adapted to study the weak gels of milk products.
Nowadays, milk gels such as yogurts or chees have attracted lots of interest due to its growing market. The milk properties, such as pH, calcium content and protein content are very important and change significantly the cheese properties. This work shows how passive microrheology can be used to follow up the milk gel formation with exact gel time determination. Gel time was determined by a new rescaling method, namely Time-Cure Superposition (TCS) [3,4]. This data processing determines the gel point according to the Winter-Chambon criterion . Moreover, the viscoelastic properties of the preparation can be compared according to parameters, such as the protein enrichment, calcium ion addition or others. Results were compared to other instruments (texturometers, rheometer, Optigraph®, etc.).
 D. A. Weitz et al., in Dynamic Light Scattering, W. Brown (Ed.) (Oxford Univ. Press, New York (1993), Chap. 16.
 D. J. Pine et al., Phys. Rev. Lett. 1988, 60, 1434.
 T. H. Larsen, E. M. Furst, Phys. Rev. Letters, 2008, 100, 14600
 K. M. Schultz, E. M. Furst, Soft Matter, 2012, 8, 6198
 H. H. Winter, F. Chambon, J. Rheology 1986, 30, 364-382
Roland Ramsch, Giovanni Brambilla, Mathias Fleury, Pascal Bru, and Gérard Meunier, "Passive microrheology as a useful tool for milk gel analyses" in "Colloidal, Macromolecular & Biological Gels: Formulation, Properties & Applications", ECI Symposium Series, (2016). http://dc.engconfintl.org/cmb_gels/28