Rapid monitoring of alkaline phosphatase in raw milk using chemiluminescence detection

A simple biosensor with 1,1'-oxalyldiimidazole chemiluminescence (ODI-CL) detection capable of rapidly quantifying and screening alkaline phosphatase (ALP) in raw and pasteurized milk was developed as an indicator for confirming whether commercial milk is properly pasteurized. Fluorescein was formed when standards containing 1.0% milk with different activities of ALP and samples containing 1.0% raw milk were incubated with fluorescein diphosphate (FDP) for 15 min at room temperature. The relative CL intensity of fluorescein measured with the addition of 80 mM H2O2 and ODI formed from the reaction of 2.0 μM bis(2,4,6-trichlorophenyl) oxalate and 10.0 μM 4-methyl imidazole in ethyl acetate was proportional to the concentration of ALP in milk. The range (39∼2500 mU/L) of linear calibration curve (R2 = 0.998) for the quantification of ALP in milk using ODI-CL detection was wider than those using currently applied fluorescence and 1,2-dioxetane CL detections. Also, the limit of detection (3.7 mU/L) determined using the former detection, which has good precision, was lower than those reported using the latter detections. In conclusion, the cost-effective and highly sensitive biosensor with ODI-CL detection can be applied to monitor whether milk is pasteurized according to acceptable ALP activities threshold level (350 mU/L) for public safety newly adopted by US and EU and the internal investigation level (100 mU/L) proposed by EU.