Filter the 20 ml culture with filter paper Whatman No. 42. Filtrate was centrifugated at 1000 rpm for 15 minutes, 5.0 ml
of supernatan then poured into test tubes, added with 0.5 ml of concentrated reagents P (12 g ammonium molibdat, 0.277 g kaliumantimoltartat) and Reagent dye concentrated (0.53 gascorbic acid), shaked for a few minutes, and let it standed for 30 minutes.