Structure of skimmed milk during ultrafiltration process probed by in-situ small angle X-ray scattering

TL;DR

This study used in-situ small-angle X-ray scattering to investigate the microstructure and deposit formation of casein micelles during ultrafiltration of skimmed milk, revealing key structural scales and deformation behaviors.

Contribution

It introduces a novel in-situ SAXS method with specially developed filtration cells to analyze microstructural changes during ultrafiltration.

Findings

Identified two characteristic length scales of casein micelles: 100 nm and 5.6 nm.

Showed that permeation flow decrease is due to micelle deformation and compression.

Quantified micelle concentration in deposits using absolute SAXS intensities.

Abstract

The stability and mechanism underlying the formation of deposits of casein micelles during ultrafiltration process were investigated by small-angle (SAXS) and ultra small-angle X-ray scattering(USAXS) which allowed us to probe the structure of skimmed milk on an exceptionally wide range of length scales from 1 to 2000 nm. Frontal filtration cells were specially developed to probe the microstructure of deposits by SAXS during the separation process. The results revealed two characteristic length scales for the equilibrium structure with radius of gyrations Rg, about 100 nm and 5.6 nm, pertaining to the globular micelles and their non-globular internal structure respectively (Pignon et al. 2004). In-situ scattering measurements showed that the decrease of permeation flows is directly related to the deformation and compression of the micelles in the immediate vicinity of the membrane (figure 1). From absolute SAXS intensities, the concentration of the micelles in the deposit can be deduced reliably.