Scattering is what makes the milk white – but what else can we use it for?

by Dr Norbert Raak (Department of Food Science, University of Copenhagen, Denmark)

Monday 15 Jan 2024, 14:30 → 15:30 Europe/Berlin

PH HS 3 (Physics Department)

Milk is a quite unique colloidal dispersion composed of an aqueous serum phase containing lactose, proteins, and minerals with dispersed milk fat globules and highly hydrated, supramolecular protein assemblies, which are historically denoted as “casein micelles”. The multiple scattering of visible light at the casein micelles and fat globules is causing the pale white to slightly yellow colour of milk, and the aggregation and network formation of especially the casein micelles is essential for making dairy products such as yoghurt and cheese.

The structure of the casein micelle and its changes during processing has therefore been a research topic for several decades, and many different models describing the internal organisation of the casein micelle have been proposed, with the overall agreement that the micelles are stabilised internally through electrostatic interactions with inorganic calcium phosphate and externally through static repulsion caused by a layer of glycosylated κ-casein molecules on the surface.

Unlike other methods, small-angle scattering techniques (SAXS and SANS) can be used at conditions that are relevant for processing of milk and dairy products and can therefore provide valuable insights into modifications of the internal structure of the casein micelle during processing. However, to obtain quantitative results, the scattering data has to be fitted to appropriate mathematical models that describe the potential structure based on physically reasonable assumptions.

In this talk, I will briefly present the casein micelle model that was recently developed by Pedersen [1] and discuss the results we obtained from applying it to milks with different processing histories and enzymatic modifications.

 

[1] Pedersen JS, Møller TL, Raak N, Corredig M (2022) Soft Matter 18, 8613–8625. https://doi.org/10.1039/d2sm00724j