Sodium caseinate (NaC) is a water-soluble protein that is produced from casein (αs1-, αs2-, β-, and κ-casein), the most common protein found in milk. Relatively small amounts of NaC are added to food products to achieve desired foamability, emulsification, viscosity, texture, and mouthfeel. Examples of food products containing this protein include baked goods, coffee creamer, cheese, ice cream, whipped topping, and margarine. NaC is an amphiphilic molecule, meaning it possesses both hydrophobic and hydrophilic regions. Because of this, it can self-assemble in aqueous solution into negatively charged spherical aggregates / micelles, whose properties like size and interactions are reflected in the macroscopic and rheological behavior of food products.
Proper intrinsic viscosity measurements and analysis can be used to examine the size and interactions of proteins, polymer coils, micelles, and other colloidal suspensions. The intrinsic viscosity measures a solute’s contribution to viscosity at infinite dilution and can be used to calculate parameters like the hydrodynamic radius and volume fraction. The VROC® initium one plus is a fully automated system that can distinguish small viscosity increments and achieve relatively high throughput for multiple concentrations appropriate for intrinsic viscosity analysis. Our aim is using this instrument to perform intrinsic viscosity measurements and analysis to gain a deeper understanding of the protein-protein and protein-solvent interactions in protein solutions, including those with NaC micelles.
In our application note "Intrinsic Viscosity Analysis – Sodium Caseinate", we use the Huggins and Kraemer equations to calculate the Huggins and Kraemer constants as well as the intrinsic viscosity from measurements of viscosity vs. NaC concentration obtained with the VROC® initium one plus. This allows us to estimate the micelle hydrodynamic radius and volume fraction. Results of intrinsic viscosity and hydrodynamic radius are compared to those of bovine serum albumin (BSA), a small globular protein with many biochemical applications. Our viscosity measurements and intrinsic viscosity analysis for dilute NaC samples provides a robust characterization of protein solutions that are relevant for manufactured food products.
Written by: Chrystian Ochoa, PhD, RheoSense Applications Scientist