Suitability of the enzyme treatment and ammonium sulfate precipitation method for detection of staphylococcal enterotoxin from different foods

Summary

An enzyme treatment and ammonium sulfate precipitation procedure was adapted to the detection of staphylococcal enterotoxin from high-protein foods. The enterotoxin is extracted from food with distilled water, after which soluble proteins are acid-precipitated (pH 4.5) and the supernatant washed with chloroform (pH 7.5). The extract is then treated with trypsin andPseudomonas peptidase for 2 h at +37°C. Residual unhydrolyzed material is precipitated with 60% ammonium sulfate for 15 min at +4°C. The precipitate is redissolved in phosphate buffer and concentrated by dialysis against polyethyleneglycol. The concentrate is washed with chloroform and lyophilized. The dry material is dissolved in 0.2 ml distilled water and enterotoxin detected by the micro-slide method with 24 h incubation at +37°C. Using this method, it has been possible within three days to detect 0.2–1.0 μg staphylococcal enterotoxin A added to minced meat, dry sausage, smoked fish, cheese and milk.