Use of a gel iodometric method for the rapid determination of β–lactamase in milk

A rapid, accurate, and low-cost enzyme assay based on the discolouration of a reaction gel is described for the qualitative and semi-quantitative detection of β-lactamase. β-Lactamase is produced by certain antibiotic-resistant bacteria in raw milk and has been detected as an illegal additive in certain dairy products. The strength of this gel iodometric kit lies in its response to many different types of substrate and the easy and direct determination of enzymatic activity. This approach was used to detect β-lactamase in milk. The detection time was as low as 0.5 h, and the detection limit of β-lactamase was 0.1 U mL−1. Furthermore, two β-lactamase-positive raw milk samples (2% of total samples) were detected using this kit. Thus, the gel iodometric kit could offer a practical detection tool for β-lactamase screening in milk.