Phenylgalactoside, ti a tun mọ si p-nitrophenyl β-D-galactpyranoside (pNPG), jẹ sobusitireti sintetiki nigbagbogbo ti a lo ninu awọn idanwo biokemika ati awọn adanwo isedale molikula.O jẹ lilo nigbagbogbo lati ṣe awari ati wiwọn iṣẹ ṣiṣe ti henensiamu β-galactosidase.
Nigbati phenylgalactoside ba jẹ hydrolyzed nipasẹ β-galactosidase, o tu p-nitrophenol silẹ, eyiti o jẹ awọ-awọ-ofeefee.Ominira ti p-nitrophenol ni a le ṣe iwọn ni iwọn nipa lilo spectrophotometer, bi gbigba p-nitrophenol le ṣee wa-ri ni igbi ti 405 nm.