Surface-bound water in protein solutions has been identified with a reduction in its freezing point. We studied the presence of such nonfreezing water (NFW) in various protein-polyelectrolyte, micelle-polyelectrolyte, and protein-protein (heteroprotein) coacervates, along with appropriate concentrated solutions of macromolecules alone, finding up to 15% w/w NFW for the heteroprotein coacervate of lactoferrin (LF) and â-lactoglobulin (BLG). The level of NFW is always higher in coacervates than in the control (single macromolecule) systems, particularly for protein-containing coacervates: a coacervate of bovine serum albumin (BSA) and poly(dimethyldiallylammonium chloride) (PDADMAC) showed a ratio of NFW/protein twice that of BSA alone (0.6 vs 0.3), with a similarly high ratio for LF-BLG coacervate. These results are attributed to the maximization of water-protein contacts, structural features that reflect the mode of sample assembly, as they are not seen in a noncoacervated LF-BLG solution with identical concentrations of all species.
Animals Cattle