Degradation and antioxidant activity of κ‐carrageenans

Abstract κ‐Carrageenan was degraded by an oxidative method involving hydrogen peroxide (H2O2). The molecular weight was measured by gel permeation chromatography. The effects of the concentration of H2O2 and initial κ‐carrageenan, pH value, and degradation time on the molecular weights of the degraded products were studied. The structural change of the degraded κ‐carrageenans was characterized by Fourier transform infrared spectroscopy and determination of the sulfate content. The antioxidant activity of the degraded κ‐carrageenans was evaluated as scavengers of superoxide anions and hydroxyl radicals by application of flow injection chemiluminescence technology. The values of the 50% inhibition concentration (IC50) against the superoxide anion of degraded κ‐carrageenans labeled A, B, C, and D (with weight‐average molecular weights of 3250, 5820, 15,080, and 209,000, respectively) were 2.65, 3.22, 6.66, and 8.13 mg/mL, respectively. As for hydroxyl radical scavenging, the IC50 values of κ‐carrageenans A, B, C, and D were 0.014, 0.049, 0.062, and 0.110 mg/mL, respectively. The results indicated that the κ‐carrageenans with lower molecular weights had better antioxidant activity.