Comparison of two new methods for the detection of bacterial proteases

Bioluminescence and fluorimetric fluorescein isothiocyanate-casein based assays were compared for their ability to detect bacterial proteases in buffer and milk. Both assays gave linear relationships with protease concentration. The fluorimetric assay was overall 1000 times more sensitive than the bioluminescence assay. Only the fluorescent assay was capable of detecting protease activity produced in raw milk inoculated with Pseudomonas fluorescens and stored at 6°C. The protease activity was detectable in raw milk before physical changes occurred and was also detectable after a laboratory ultra high temperature treatment. Use of the fluorimetric assay is a promising means of detecting protease activity in raw materials before manufacture