Ko te Phenylgalactoside, e mohiotia ana ko p-nitrophenyl β-D-galactopyranoside (pNPG), he tïpako waihanga e whakamahia ana i roto i nga whakamatautau koiora matū me te koiora.Ka whakamahia noa ki te kimi me te ine i te mahi o te enzyme β-galactosidase.
Ina whakamarohia te phenylgalactoside e te β-galactosidase, ka tukuna e ia te p-nitrophenol, he puhui tae kowhai.Ko te whakaputanga o te p-nitrophenol ka taea te ine ine ma te whakamahi i te spectrophotometer, i te mea ka kitea te urunga o te p-nitrophenol i te roangaru o te 405 nm.