Antioxidant activities of trypsin inhibitor, a 33 KDa root storage proteinof sweet potato (Ipomoea batatas (L.) Lam cv. Tainong 57)

Trypsin inhibitors (TIs), root storage proteins, were purified from sweet p otato (Ipomoea batatas [L.] Lam cv. Tainong 57) roots by trypsin affinity c olumn according to the methods of Hou and Lin (Plant Sci. 1997, 126, 11-19 and Plant Sci. 1997, 128, 151-158). A single band of 33 kDa TI was obtained by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis ( SDS-PAGE) gels; This purified 33 kDa TI had scavenging activity against 1,1 -diphenyl-2-picrylhydrazyl (DPPH) radical. There was positive correlation b etween scavenging effects against DPPH (2 to 22%) and amounts of 33 kDa TI (1.92 to 46 pmol). The scavenging activities of 33 kDa TI against DPPH were calculated from linear regression to be about one-third of those of glutat hione between 5 and 80 pmol. Using electron paramagnetic resonance (EPR) sp ectrometry for hydroxyl radical detection, it was found that 33 kDa TI coul d capture hydroxyl radical, and the intensities of EPR signal were signific antly decreased from 1.5 to 6 pmol of 33 kDa TI compared to those of the co ntrols. It is suggested that 33 kDa TI, one of the sweet potato root storag e proteins, may play a role as an antioxidant in roots and may be beneficia l to health when it is consumed.