J. H. Tobing, D. R. Ricky, and D. N. Sari, “THE ANTIOXIDANT ACTIVITY OF THE EXTRACT OF AFRICAN LEAVES (VERNONIA AMYGDALINA) USING 1,1-DIPHENYL-2- PICRYLHYDRAZYL (DPPH) METHOD”, isc, vol. 4, no. 1, p. 74, Oct. 2016.