(181j) The Phase Behavior and Rheology of a Concentrated Protein System (Lysozyme) with Long-Range Repulsion and Short-Range Attraction

The industrial processing of protein solutions in engineered food materials, pharmaceutical manufacturing and bio-processing applications occurs on a world-wide scale. A key aspect to production optimization is maximizing output with concentrated feedstock while maintaining quality and integrity. On a crude scale this is accomplished by empirical adjustment of the disperse phase concentrations with respect to the volumetric through put. However, the use of rheology as a link between a bulk measurable property and the dispersion structure and interactions on the molecular scale is becoming a rapidly growing area of research.

Lysozyme is a protein abundantly found in many biological processes, but can be found in large concentrations in egg whites. As such it has been a focus of protein research for over a century, and has proven to be a model system to understand protein structure and interactions, which in most cases is complex. In this work we use Lysozyme without salt as a model protein that has a short-range attraction and long-range repulsion to make connections between protein interactions and the hierarchy of structures that define the macroscopic stability, phase behavior, and rheology. We use an experimental platform that includes scattering techniques (DLS, SANS), microscopy, and rheology. The strength of attraction and repulsion are temperature dependent, and we determine the potential by fitting small-angle neutron scattering (SANS) measurement utilizing the Ornstein-Zernike equation with a double-Yukawa interaction potential. The rheology is analyzed and interpreted in connection to the interparticle potential and we show a connection between gelation and the SANS scattering profiles.