Structural characterization and antioxidant activities of κ-carrageenan oligosaccharides degraded by different methods

In the present study, four kinds of κ-carrageenan oligosaccharides were obtained by the degradation of parent κ-carrageenan using free radical depolymerization, mild acid hydrolysis, κ-carrageenase digestion and partial reductive hydrolysis, respectively. Their structure types were accurately and comparatively elucidated by ESI-MS and CID MS/MS. The antioxidant activities of different degraded products were investigated by four different antioxidant assays, including superoxide radical scavenging activity, hydroxyl radical scavenging activity, reducing power and DPPH radical scavenging activity. The methods of depolymerization had an influence on the antioxidant activities of κ-carrageenan oligosaccharides obtained from κ-carrageenan. These results indicated that the antioxidant activities of κ-carrageenan oligosaccharides could be related to the degree of polymerization, the content of reducing sugar and sulfate groups, and the structure of reducing terminus.