Structural modifications of β-lactoglobulin subjected to gamma radiation

It was demonstrated in a previous study that gamma irradiation of solutions of native β-lactoglobulin (β-LG) results in ordered oligomers and aggregates, whereas the protein irradiated in the solid state is not affected. The structural features associated with oligomerization and aggregation were investigated here, using fluorescence and circular dichroism (CD). Bovine β-LG, in solid state or in solution, was irradiated at a dose level of 10, 25 or 50 kGy using a Cobalt-60 radiation source. The effect of doses up to 10 kGy on the tertiary and secondary structure of β-LG irradiated in solid state was not important, and slight changes were observed at 50 kGy. β-LG irradiated in solution showed alterations in fluorescence spectra and decreasing dichroism signal in near-UV CD spectra, suggesting changes in the tertiary structure. However, quantification of the secondary structure showed little overall change in content, despite changes in the spectra noted. The greatest structural changes were observed when protein was irradiated at low concentration (3 mg mL−1) and at high dose (50 kGy), and were similar to those observed in thermal-treated β-LG at mild conditions as reported by other authors.