Alginate is a naturally occurring polysaccharide, composed of (1→4) linked b-D-mannuronate residues and its C-5 epimer a-L-guluronate residues. There has been increasing interests in utilizing alginate as an effective encapsulation material for the delivery of biopharmaceutical compounds. Therefore, the understanding of protein-polysaccharide interactions and the investigation of protein stability in sodium alginate solution have been important issues in this application.

In this study, the physiochemical property changes of model protein, Bovine Serum Albumin (BSA) during the interaction with sodium alginate in water solution, were monitored by Dynamic Light Scattering (DLS), Fourier Transform Infrared Spectrometer (FT-IR) equipped with Attenuated Total Reflectance (ATR) and Ultraviolet-Visible Spectrometer (UV-Vis). Parallel experiments were conducted for both native BSA-alginate and heat-denatured BSA-alginate mixture. DLS results showed that the hydrodynamic radius size of alginate did not change significantly after mixing with native BSA over 5 days of observation, indicating a thermodynamically stable system. However, the heat-denatured BSA alginate mixture had greater particle sizes than that of alginate only. A consistent turbidimetric analysis showed a sharp increase in turbidity of the heat-denatured BSA alginate mixture which was due to the formation of protein-polysaccharide complexes but a constant trend for the native BSA-alginate mixture. The reduction and addition of characteristic peaks absorbance of native BSA after mixing with alginate solution in FT-IR spectra indicated its secondary structures were changed by the electrostatic interactions between alginate chains and protein coils. Much more intense effects on the peak intensity were observed for the heat-denatured BSA. UV-Vis spectroscopy results confirmed with FT-IR. The increasing absorbance with increasing alginate concentration was caused by the formation of complexes due to interchain hydrophobic association between alginate and native/heat-denatured BSA. Our results showed that intermolecular chain associations were easily formed between BSA and alginate solution by electrostatic interactions. Not very significant conformational changes of native BSA entrapped in alginate solution suggested the potential pharmaceutical application of alginate as a carrier for protein drug delivery.