To investigate the β-Lactamases activities in pasteurized milk in China based on an enzyme thermistor (ET) biosensor.MethodsCertain amount of penicillin G was incubated with the milk sample for 3 h, then an aliquot of the mixture was directly injected into the ET system to give a signal corresponding to penicillin G remained. The amount of β-lactamase was calculated by the penicillin G consumed during incubation. 106 pasteurized milk samples collected from 13 provinces were tested. ResultsThe linear range of this method was 4-20 U/ml with LOQ and LOD of 2 and 4 U/ml, respectively. The total detection rate was 3.8%. 47 pasteurized milk products collected in Beijing showed negative results containing β-lactamase lower than 2 U/ml (LOD). 59 products collected from 12 other provinces contained β-lactamase lower than 4 U/ml, among which 4 products were within the range of 2 to 4 U/ml.ConclusionLow levels of β-lactamase were detected in 106 milk samples collected from 13 provinces in China, and it was suggested that the illegal use of β-lactamase was almost eliminated in China.