Developing a Library for Mass Spectrometry Identification of Gulf Shrimp.

Publication Salla et al., 2013. Anal Chim Acta 794, 55, DOI: 10.1016/j.aca.2013.07.014. A mass spectrometry library for shrimp identification was developed with the goal of developing mass spectrometry methods for identifying contaminated seafood using mass spectrometry fingerprinting. Matrix-assisted laser desorption ionization (MALDI) time of flight mass spectrometry was used to identify shrimp at the species level using commercial mass spectral fingerprint matching software (Bruker Biotyper). In the first step, a mass spectrum reference database was constructed from the analysis of six commercially important shrimp species: L. setiferus, F. azticus, S. brevirostris, P. robustus, P. dispar and P. platyceros. In the second step, the reference database was tested using 74 unknown shrimp samples from these six species. Specimens were collected by extractive fishing in the Gulf of Mexico, North Pacific Coast, and North Atlantic Coast and shipped to our location on ice or, for Louisiana shrimp, obtained locally. Correct identification was achieved for 72 of the 74 samples (97%): 72 samples were identified at the species level and 2 samples were identified at the genus level using the manufacturer’s log score specifications. Samples of 1 g of shrimp skeletal muscle were obtained by dissecting a shrimp and then homogenizing at room temperature in 2 mL of nanopure water using a mortar and pestle. The homogenate was then centrifuged at 13,000 rpm for 20 min. The supernatant was removed and further purified using desalting pipette tips. A 4 µl volume of the desalted sample was directly pipetted into 4 µl of 30 mg/ml 2, 5-dihydroxy benzoic acid matrix solution in 1:1 (v/v) ethanol/0.1 % TFA. A 1 µl aliquot of the analyte/matrix mixed solution was spotted onto a stainless steel MALDI target and allowed to dry at room temperature. MALDI-TOF MS measurements were performed on a commercial instrument in positive ion reflectron mode with an accelerating voltage of 25 kV and analyzed in the mass range of 1,000 – 5,000 Da. A minimum of 500 laser shots per sample was used to generate each mass spectrum. MALDI BioTyper 2.0 software (Bruker) was used for the mass spectra fingerprinting [46]. Unknown spectra are identified by comparing their individual peak lists to the mass spectrum database and a matching score based on identified masses and their intensity is used for ranking of the results. The MALDI fingerprinting method for the identification of shrimp species was found to be reproducible and accurate with rapid analysis. Data was collected between October 2011 and May 2012 in the Department of Chemistry at Louisiana State University in Baton Rouge.