Impact of proteins on milk gel structure (yogurt, cheese)

Abstract: Protein addition has become a standard procedure in milk gel preparation. On the one hand, proteins can offer interesting structural and textural properties, on the other hand, the nutritive values of dairy products are increasing. Indeed, consumers ask more and more for protein-enriched food. The number and type of proteins are continuously growing, which makes the possibilities practically infinite. Developers of new protein-enriched food need a reliable and fast method to study the viscoelastic properties and reduce the time-to-market.

Passive microrheology has become of utmost interest in recent years due to its non-invasive character. This work will present work done with Rheolaser Master©, which uses Multi Speckle Diffusing Wave Spectroscopy (DWS) [1]. A coherent laser beam is applied to the sample and multiply scattered by the scatterers (particles, droplets, fibers…) present in the sample. The interfering backscattering waves form an interference image (speckle image), which is detected by a multi-pixel detector. The scatterers’ motion is directly related to the spot movement of the speckle image and can be analyzed in the dynamic mode. Determining the Mean Square Displacement (MSD) curve enables us to characterize the sample's viscoelastic properties.

This work is focused on milk gels, such as yogurts and cheese. Rheolaser Master can be used as a non-invasive and non-destructive technique for these delicate products. The quality of yogurt and cheese depends on many factors, such as fat content, protein content and quantity of ferment. We will show how the gel point can be easily determined in an accurate way using the TCS method [2,3]. In addition, we tried to correlate the microrheological data with the texture properties, such as creaminess, ropiness, and brittleness.


[1] Weitz, D. A.; Pine, D. J. Diffusing-Wave Spectroscopy. In Dynamic light scattering; Oxford University Press: New York, 1993; p 652.
[2]T. H. Larsen, E. M. Furst, Physical Review Letters, 2008, 100, 14600
[3] K. M. Schultz, E. M. Furst, Soft Matter, 2012, 8, 6198