R. D. Setiowati, Y. Yenni, F. R. Panjaitan, S. Sujadi, M. Irfan Lubis, and E. Ernayunita, “Preliminary Study of Vitamin E Content in IOPRI’S Oil Palm Varieties”, J. Penelitian Kelapa Sawit, vol. 29, no. 3, pp. 159-166, Dec. 2021.