Determination of peracid and putative enzymatic peracid formation by an easy colorimetric assay Original Research Article

A sensitive and semi-quantitative colorimetric method for the determination of peracids in the presence of hydrogen peroxide in Luria–Bertani (LB) agar is described. For this purpose the redox active azo-dye 2-methylsulfanyl-4-(3-methylsulfanylphenylazo)-aniline for the visual detection of peracids was synthesized. The change in color is based on the exclusive oxidation of methylsulfanyl-groups derived from peracids. Because of the lethal effect of hydrogen peroxide and peracids to microorganisms and the degradation of hydrogen peroxide it was not possible to add the assay substances directly to the medium. Thus, we overlayed the medium with a soft agar. The assay system was validated with peracetic acid, a mixture of tetraacetylethylene diamine (TAED) and hydrogen peroxide, as well as with the lipase from Pseudomonas cepacia (PCL). A semi-quantitative relationship between the size of the halo and the concentration of peracetic acid could be shown. With this assay it should be possible to discover enzymes or enzyme producing microorganisms, which are capable to form peracids in situ.