Currently, antioxidants are added in the human diet to prevent free
radical-induced cell damage, and there has been an explosive interest in the
use of antioxidant nutritional supplements. The effects of different factors
on the antioxidant activity of phycocyanins (PCs) were studied. The results
showed that PCs generated hydroxyl radicals in the light, while scavenging
them in the dark. When PCs were denatured by sodium dodecyl sulfate,
urea and in alkaline condition, their ability to generate hydroxyl radicals
disappeared and that of scavenging them greatly increased. This showed
that the phycobilin moiety is the main part of PC involved in scavenging
hydroxyl radicals. Trypsin hydrolysis of PCs showed that the apoprotein
portion of the molecule also made a significant contribution to the antioxidant
activity.