Berlin 2015 – scientific programme

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MI: Fachverband Mikrosonden

MI 10: Poster: Microanalysis and Microscopy

MI 10.9: Poster

Wednesday, March 18, 2015, 15:00–17:30, Poster B

Determination of the refractive index of casein micelles — •Sabrina Kröner, Steffen Nothelfer, Florian Foschum, and Alwin Kienle — Institut für Lasertechnologie in der Medizin und Meßtechnik, 89081 Ulm, Germany

Casein micelles are mostly found in dairy products. These micelles consist of α1-, α2-, β- and κ-casein proteins. The refractive index of casein micelles is not known, but constitutes a key parameter to enable the optical characterization of dairy products, like milk as a frequently used product in everyday life.

We determine the refractive index with three different setups and we use Mie theory for the theoretical description of the light scattering. First, with an optimized goniometer setup, single scattered photons were measured angularly resolved. The size distribution and the refractive index were derived from the experimental scattering phase function of the micelles. Second, a collimated transmission setup was used to obtain the extinction coefficient. Under specification of size distribution and concentration of the micelles we derived the refractive index as fit parameter. Third, with a spatially resolved reflectance setup we determine the reduced scattering coefficient and again fit the refractive index. For the measurements we used skim milk, because the protein in commercially available skim milk is expectedly similar to the protein which will be examined at industrial applications. The derived refractive indices show good agreement for all three independent methods.