Raj K. P. Patel

A Proteomic-Based Approach for Detection of Chicken in Meat Mixes

A proteomic-based method has been developed for the detection of chicken meat within mixed meat preparations. The procedure is robust and simple, comprising the extraction of myofibrillar proteins, enrichment of target proteins using OFFGEL isoelectric focusing, in-solution trypsin digestion of myosin light chain 3, and analysis of the generated peptides by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Using this approach, it was possible for example to detect 0.5% contaminating chicken in pork meat with high confidence. Quantitative detection of chicken meat was done by using AQUA stable isotope peptides made from the sequence of previously selected species-specific peptide biomarkers. Linearity was observed between the amount of the peptide biomarker and the amount of chicken present in the mixture; further independent replication is required now to validate the method. Apart from its simplicity, this approach has the advantage that it can be used effectively for the detection of both raw and cooked meat. The method is robust, reliable, and sensitive, representing a serious alternative to methods currently in use for these purposes. It is amenable to highly processed foods which can be particularly problematic, as the tertiary protein structure is often affected in processed food precluding immunoassays. In addition, this proteomic analysis will permit the determination of definitive discriminatory sequence, unlike the DNA PCR based methods used presently. The present article also demonstrates the translation of the technology to routine mass spectrometry equipment, making the methodology suitable for public analysts.

Determination of streptomycin residues in honey by liquid chromatography-tandem mass spectrometry.

Streptomycin is an aminoglycoside antibiotic used in apiculture to protect bees against a variety of brood diseases. Brazilian authorities have included it in the National Regulatory Monitoring Program for honey production. A simple and reliable method using liquid chromatography-tandem mass spectrometry has been developed and validated for the determination of streptomycin in honey. The chromatography separation was performed on a Gemini 5 microm C18 (50 mm x 2 mm) column using 5mM heptafluorbutiric acid/acetonitrile (85:15) as the mobile phase at a flow rate of 0.2 mLmin(-1). The detection of the analyte was achieved by positive ionization electrospray in multiple reaction-monitoring modes. Two characteristic transitions were monitored for streptomycin. Some analytical parameters were validated according to the guidelines laid down by European Commission Decision 2002/657/EC: decision limit, detection capability, recovery, precision and ruggedness. The recoveries of streptomycin from honey fortified at 2.5, 10, 15 and 20 microgkg(-1) levels are around 100%. The decision limit and detection capability of streptomycin was 3 microgkg(-1) and 4.7 microgkg(-1) respectively.

Evaluation of stable isotope labelling strategies for the quantitation of CP4 EPSPS in genetically modified soya

The introduction of genetically modified (GM) crops into the market has raised a general alertness relating to the control and safety of foods. The applicability of protein separation hyphenated to mass spectrometry to identify the bacterial enolpyruvylshikimate-3-phosphate synthase (CP4 EPSPS) protein expressed in GM crops has been previously reported [M.F. Ocana, P.D. Fraser, R.K.P. Patel, J.M. Halket, P.M. Bramley, Rapid Commun. Mass Spectrom. 21 (2007) 319.]. Herein, we investigate the suitability of two strategies that employ heavy stable isotopes, i.e. AQUA and iTRAQ, to quantify different levels of CP4 EPSPS in up to four GM preparations. Both quantification strategies showed potential to determine whether the presence of GM material is above the limits established by the European Union. The AQUA quantification procedure involved protein solubilisation/fractionation and subsequent separation using SDS-PAGE. A segment of the gel in which the protein of interest was located was excised, the stable isotope labeled peptide added at a known concentration and proteolytic digestion initiated. Following recovery of the peptides, on-line separation and detection using LC-MS was carried out. A similar approach was used for the iTRAQ workflow with the exception that proteins were digested in solution and generated tryptic peptides were chemically tagged. Both procedures demonstrated the potential for quantitative detection at 0.5% (w/w) GM soya which is a level below the current European Unions threshold for food-labelling. In this context, a comparison between the two procedures is provided within the present study.

Proteome changes in tomato lines transformed with phytoene synthase-1 in the sense and antisense orientations

The commercial cultivation of genetically engineered (GE) crops in Europe has met with considerable consumer resistance, which has led to vigorous safety assessments including the measurement of substantial equivalence between the GE and parent lines. This necessitates the identification and quantification of significant changes to the metabolome and proteome in the GE crop. In this study, the quantitative proteomic analysis of tomato fruit from lines that have been transformed with the carotenogenic gene phytoene synthase-1 (Psy-1), in the sense and antisense orientations, in comparison with a non-transformed, parental line is described. Multidimensional protein identification technology (MudPIT), with tandem mass spectrometry, has been used to identify proteins, while quantification has been carried out with isobaric tags for relative and absolute quantification (iTRAQ). Fruit from the GE plants showed significant alterations to their proteomes compared with the parental line, especially those from the Psy-1 sense transformants. These results demonstrate that MudPIT and iTRAQ are suitable techniques for the verification of substantial equivalence of the proteome in GE crops.

Optimizing the balance between false positive and false negative error probabilities of confirmatory methods for the detection of veterinary drug residues

GC-MS data on veterinary drug residues in bovine urine are used for controlling the illegal practice of fattening cattle. According to current detection criteria, peak patterns of preferably four ions should agree within 10 or 20% from a corresponding standard pattern. These criteria are rigid, rather arbitrary and do not match daily practice. A new model, based on multivariate modeling of log peak abundance ratios, provides a theoretical basis for the identification of analytes and optimizes the balance between the avoidance of false positives and false negatives. The performance of the model is demonstrated on data provided by five laboratories, each supplying GC-MS measurements on the detection of clenbuterol, dienestrol and 19 beta-nortestosterone in urine. The proposed model shows a better performance than confirmation by using the current criteria and provides a statistical basis for inspection criteria in terms of error probabilities.

Determination of tilmicosin in ovine milk using high-performance liquid chromatography

Tilmicosin is a novel macrolide antibiotic with a wide range of therapeutic uses against gram positive (+ve) and gram negative (-ve) bacteria and mycoplasmae causing pneumonia and mastitis and can be used to treat these diseases in sheep. After its use there may be residues present in ovine milk that interfere with cheese making and processing of other milk products. It is important to monitor for the presence of tilmicosin in ovine milk and a method has been optimized and validated for its determination. Tilmicosin is extracted from milk into methanol. The methanol extract is acidified and non-polar co-extractives removed using hexane followed by carbon tetrachloride. The pH is adjusted to 9.0 and the tilmicosin partitioned into chloroform. The chloroform extract is evaporated to dryness and the residue resuspended in high-performance liquid chromatography (HPLC) mobile phase. Tilmicosin is determined using reversed-phase HPLC and ultraviolet (UV) detection at 280 nm. Recovery of tilmicosin from ovine milk fortified over the range 50 to 250 micrograms l-1 is in the range 84.3-104.8%, with a relative standard deviation ranging from 6.6 to 12.9%. The proposed procedure allows the determination of residues of tilmicosin in ovine milk at levels less that 50 micrograms l-1 and satisfies the quality criteria specified in European Commission Decision 93/526/EEC with the exception of reproducibility data from interlaboratory trials.