To determine peroxidase presence, add 50 μl of sample to 50 μl of ELISA kit
substrate reagent in an untreated microtiter plate (no antibody to staphylococcal enterotoxin) and let stand 10 min. If
color changes to blue (or bluish-green), the sample contains intrinsic peroxidase, which must be inactivated. If sample
remains colorless (or original color), analyze it for enterotoxin by ELISA.