Surface enhanced laser desorptions ionization-time of flight-mass spectrometry analysis in complex food and biological systems

Effect of NaCl and sucrose tastants on protein composition of oral fluid analysed by SELDI-TOF-MS

During eating, human saliva is secreted into the oral cavity by salivary glands. The relative contribution of different glands to total salivary flow rate depends, among other factors, on the tastants in the food. Few reports indicated that also the salivary protein composition depends on the tastant make-up of the food. We studied the influence of sodium-chloride- and sucrose solutions on the presence of proteins in the M(r) range 2-20kDa in whole saliva. Upon oral stimulation with a sodium chloride solution, a sucrose solution or water, we collected whole saliva from 14 volunteers after t=1 min, t=11 min and t=20 min. Saliva protein profiles were analysed by SELDI-TOF-MS. SELDI-TOF-MS intensities of m/z values representing different protein masses were compared between subjects, tastants and time conditions. For subsets of the 33 detected masses, significant effects were observed for all factors, with most masses involved in the Subjects effect: m/z(Subjects)>m/z(Time×Stimulus)>m/z(Stimulus)>m/z(Time). Most effects on saliva protein composition were observed at t=1 min, whilst almost no effects were observed at t=11 min and t=20 min. When considering the Stimulus×Time interaction, we identified four different stimulus-response patterns. Proteins identified in the present study, and attributed to specific glands or tissues in literature, were used to associate stimulus-response patterns with tissue provenances. Observed stimulus-response patterns were not uniquely associated to particular glands and tissues. Hence, there was no evidence of the involvement of particular tissues or glands in tastant-specific protein responses. In conclusion, oral stimulation with different tastants affects salivary protein composition in a protein- and stimuli dependent way, which seems not be associated with any specific tissues or glands of origin.

Liquid chromatography and mass spectrometry in food allergen detection

Food allergy is an important issue in the field of food safety because of the hazards for affected persons and the hygiene requirements and legal regulations imposed on the food industry. Consumer protection and law enforcement require suitable analytical techniques for the detection of allergens in foods. Immunological methods are currently preferred; however, confirmatory alternatives are needed. The determination of allergenic proteins by liquid chromatography and mass spectrometry has greatly advanced in recent years, and gel-free allergenomics is becoming a routinely used approach for the identification and quantitation of food allergens. The present review provides a brief overview of the principles of proteomic procedures, various chromatographic set ups, and mass spectrometry instrumentation used in allergenomics. A compendium of published liquid chromatography methods, proteomic analyses, typical marker peptides, and quantitative assays for 14 main allergy-causing foods is also included.

SALDI-MS signal enhancement using oxidized graphitized carbon black nanoparticles

The signal intensity of low-molecular-weight compounds analyzed using surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) was significantly enhanced when oxidized graphitized carbon black (GCB) particles were used as the desorption/ionization surface. The surface of oxidized GCB contains more carboxylic acid groups than non-oxidized GCB. Carboxylic acid groups enhance the efficiency of the ionization process and the desorption of more hydrophobic compounds. A common pharmaceutical compound, propranolol, was successfully extracted from Baltic Sea blue mussels and quantified using oxidized GCB as the SALDI surface, whereas deuterated propranolol was used as the internal standard. The calibration curve showed a wide linear dynamic range of response (0.1-20 microg/mL) and good reproducibility (RSD < 10%). It was not possible to detect propranolol in Baltic Sea blue mussels when non-oxidized GCB was used as the SALDI surface.

Nutritional Proteomics: Methods and Concepts for Research in Nutritional Science

Nutritional proteomics or nutriproteomics is the application of proteomics methodology to nutrition-related research but also represents the interaction of bioactive food ingredients with proteins, whereby the interaction with proteins occurs in two basically specific ways. Firstly, the effect of nutrients on protein expression, which can be monitored by protein mapping, and secondly, the interaction of nutrients with proteins by post-translational modifications or small-molecule protein interactions. These interactions result in changes to the three-dimensional structure of such effected proteins. As a consequence, their original functions are modulated, resulting for example in reduced activity in the case of enzymes or changes in ability of recognition between molecules such as protein-protein interactions and ligand-receptor interactions. The characterization of such modifications together with functional data from established biochemical and physiological methods will result in a better understanding of the interplay between bioactive dietary components and diet-related diseases such as cancer, diabetes or neurodegenerative diseases. The occurrence of such modifications can possibly be additionally used as biomarkers in the diagnosis and therapy of these diseases as well as biomarkers for the efficacy or safety of selected nutrients.

SELDI-TOF-MS of saliva: Methodology and pre-treatment effects

Interest in saliva as a diagnostic fluid for monitoring general health and for early diagnosis of disease has increased in the last few years. In particular, efforts have focused on the generation of protein maps of saliva using advanced proteomics technology. Surface-enhanced laser-desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) is a novel high throughput and extremely sensitive proteomic approach that allows protein expression profiling of large sets of complex biological specimens. In this study, large scale profiling of salivary proteins and peptides, ranging from 2 to 100kDa was demonstrated using SELDI-TOF-MS. Various methodological aspects and pre-analytical variables were analysed with respect to their effects on saliva SELDI-TOF-MS profiling. Results show that chip surface type and sample type (unstimulated versus stimulated) critically affect the amount and composition of detected salivary proteins. Factors that influenced normal saliva protein profiling were matrix composition, sample dilution and binding buffer properties. Delayed processing time experiments show certain new peptides evolving 3h post-saliva donation, and quantitative analyses indicate relative intensity of other proteins and peptides changing with time. The addition of protease inhibitors partly counteracted the destabilization of certain protein/peptide mass spectra over time suggesting that some proteins in saliva are subject to digestion by intrinsic salivary proteases. SELDI-TOF-MS profiles also changed by varying storage time and storage temperature whereas centrifugation speed and freeze-thaw cycles had minimal impact. In conclusion, SELDI-TOF-MS offers a high throughput platform for saliva protein and peptide profiling, however, (pre-)analytical conditions must be taken into account for valid interpretation of the acquired data.

Simultaneous Mass Analysis of Positive and Negative Ions Using a Dual-Polarity Time-of-Flight Mass Spectrometer

Positive and negative ions produced from matrix-assisted laser desorption/ionization (MALDI) were simultaneously measured using a newly developed dual-polarity time-of-flight mass spectrometer. This instrument is effective not only for express and comprehensive mass analysis but also for studying the ionization mechanisms of biomolecules. It comprises two identical time-of-flight mass analyzers located symmetrically about a MALDI ion source. The ion optics are arranged to be able to extract positive and negative ions synchronously with equal efficiency to each corresponding mass analyzer. Mass spectra of various proteins with molecular weights as large as that of myoglobin monomer and dimer were obtained. The spectral patterns obtained in this work are approximately mirror images with opposite polarities.