| Abstract
| - Although immunoassay-based methods are sensitive andwidely used for measuring protein toxins in food matrixes,there is a need for methods that can directly confirm themolecular identity of the toxin in situations where immunoassay tests yield a positive result. A method has beendeveloped that uses mass spectrometry to identify aprotein toxin, staphylococcal enterotoxin B (SEB), in amodel food matrix, apple juice. The approach employsultrafiltration to remove low molecular weight componentsfrom the sample, after which the remaining high molecular weight fraction, containing the protein, is digestedwith trypsin. The tryptic fragments are separated fromresidual biopolymers and analyzed by liquid chromatography−electrospray mass spectrometry. The backgroundis still sufficiently complex that tandem mass spectrometry(MS/MS) is used to confirm the identity of target peptides.Limits of detection are 80 ng of SEB for MS and 100 ngfor full scan MS/MS, using a tryptic fragment as theanalytical target. Lower detection limits can be obtainedusing selected ion monitoring and multiple reactionmonitoring. The presence of SEB can be confirmed atconcentrations as low as 5 parts-per-billion by increasingthe size of the sample to 10 mL. The method is applicableto the detection of SEB in other water-soluble foodmatrixes.
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