Structural and antioxidant properties of gamma irradiated hyaluronic acid.

Hyaluronic acid (Hyaluronan, HA) was depolymerised by gamma irradiation and its structural changes and antioxidant activities were investigated. The structural changes of gamma irradiated HA were studied by gel-permeation chromatography (GPC), viscosity, pH, Hunter colour measurement, UV spectrophotometry, and FT-IR spectroscopy. The results demonstrated that gamma irradiation decreased molecular weight size, viscosity and pH of the hyaluronic acid and its colour turned to intense yellow. UV spectra of the irradiated HA showed a change at 265nm, which indicates the formation of double bonds. Differences in the height and shape of certain absorption bonds of FT-IR spectra in the range 1700-1750cm(-1) were also observed, which is associated with the formation of carboxylic acid. From these structural changes of the HA, gamma irradiation may have a role in the formation of pyrancarboxylic acid rings. DPPH radical scavenging ability and the reducing power of gamma irradiated HA were significantly higher than that of non-irradiated HA. However, non-irradiated and irradiated HA did not show significant differences in the Rancimat test.