Preparation of κ-carrageenan derived oligosaccharides by bacterial carrageenase and their in vitro anti-oxidative activities

A marine carrageenan-decomposing bacterium, Cytophaga sp. MCA-2, was isolated from a specimen of red alga Eucheuma gelatinae. Depolymerization of kappa-carrageenan was performed using carrageenase isolated from the cell-free medium of strain MCA-2. The low-molecular-weight carrageenans after ultrafiltration and lyophilization were sulfonated with fonnamide-chlorosuffonic acid. Three fractions K-I, K-II and its sulfated derivative SII-L were obtained and applied for the analysis of anti-oxidative activities in scavenging hydrogen peroxide, scavenging hydroxyl free radical, scavenging superoxide anion radical and inhibiting lipid peroxidation. All three samples showed a dose-response relation and presented the highest anti-oxidative activity at the highest test dose. The fraction with higher sulfate group content showed stronger anti-oxidative activities than that with lower sulfate group content. Fractions K-I and SII-L showed significant scavenging hydroxyl free radical ability, reaching 88.1% and 87.4% respectively at the concentration of 6.4 mg/ml. SII-L also showed the highest anti-oxidative activities in inhibiting lipid peroxidation and scavenging hydrogen peroxide. The inhibition rate of SII-L against superoxide anion radical production reached 62.5% at the concentration of 6.4 mg/ml whereas K-I and K-II showed no significant inhibition ability. The results indicated that the sulfated oligosaccharides prepared by carrageenan hydrolysis and chemical modification possess anti-oxidative activities, which are closely related to the sulfur content of oligosaccharides.