Studi kinetika pengaruh penambahan senyawa PMSF terhadap aktivitas bromelain hasil pemurnian bonggol nanas (ananas comosus [l.] merr) dengan kromatografi kolom penukar ion = Kinetic study influences the addition of PMSF compounds to the purified bromelain activity of the pineapple cobs ananas (comosus [l.] merr) by ion exchange column chromatography