Xanthones Analysis and Antioxidant Activity Analysis (Applying ESR) of Six Different Maturity Levels of Mangosteen Rind Extract (Garcinia mangostana Linn.), Gondokesumo, Marisca Evalina, Pardjianto Bambang, Sumitro Sutiman Bambang, and Widowati Wahyu , Pharmacognosy Journal, March 2019, Volume 11, Issue 2, p.369-373, (2019)