Abstract: The present study aimed to investigate the effect of repeated freeze-thawing treatment on the antioxidant capacity of phycobiliprotein from Nostoc sphaeroides Ku ting. Phycobiliproteins extracted from Nostoc sphaeroides Ku ting with and without repeated freeze-thawing treatment were dissolved separately in double distilled water and pH 7.3, 50 mol/L dipotassium phosphate-sodium hydroxide buffer, resulting in four different samples: RFTPW, RFTPP, NRFTPW and NRFTPP, respectively. The antioxidant activity of the four samples was comparatively assessed by ABTS+ radical scavenging assay, FRAP assay and inhibition assay against erythrocyte hemolysis and lipid peroxidation both induced by H2O2. RFTPP was found to have greater inhibitory effects against ABTS+ radicals, erythrocyte hemolysis and lipid peroxidation than other three samples. Moreover, its ferric reducing activity was stronger. These results may be due to an increase in the dissolved phycobiliprotein caused by repeated freeze-thawing treatment, altering the ratio between phycocyanin and phycoerythrin.

Key words: repeated freeze-thawing treatmen, ABTS+ ·, red blood cell homelysis inhibition, lipid peroxidation inhibition