Evaluation of different extraction procedures for salivary peptide analysis.

Sample preparation is a critical step for all kind of biological fluids analysis with serious implications in data retrieved. In this sense, efforts have been made to standardize biofluids' management procedures for diagnosis and research purposes. However, no agreement exists regarding saliva preparation. Aiming the delineation of an ideal preparation procedure for salivary peptidome analysis, the commonly used extraction methods such as selective precipitation with organic solvents, acid and addition of chaotropic agents in combination with filtration, were evaluated in the present study. Data concerning protein/peptide content, Tricine-gel electrophoresis and MALDI-TOF/TOF identification suggest that centrifugation, a generally used sample cleanup step, should be critically reconsidered based on the hydrophobic peptides that can be loss by aggregation with high molecular weight (MW) components. Although no individual method per se resulted in the identification of all MS identified peptides, the extraction method with bicarbonate/acetonitrile (ACN) followed by filtration resulted in the higher number of identified peptides.