title: Two-dimensional mapping as a tool for classification of green coffee bean species.
abstract: Two species of the genus Coffea, Coffea arabica (Colombia) and Coffea canephora (Indiano Robusta) were analysed by two-dimensional (2-D) maps in order to obtain fingerprints of the expressed polypeptide chains and to determine which ones would characterize the two species. Green beans were milled under liquid nitrogen. A dry powder was produced by three different extraction protocols aimed at eliminating interfering substances (polyphenols). A reduced powder was produced by two successive extractions performed in acetone. Trichloroacetic acid (TCA; 10% w/v) and beta-mercaptoethanol (0.07% v/v) in acetone were used for the first extraction (a) and 10% w/v TCA in acetone was used for the second extraction (b). Proteins were then solubilized in a solution (40 microL per 1 mg powder) containing 7 M urea, 2 M thiourea, 3% w/v 3-(3-cholamidopropyldimethyl-amino)-1-propanesulfate, 1% v/v carrier ampholytes, 40 mM Tris, 5 mM tributylphosphine and 10 mM acrylamide as alkylating agent. Following incubation at room temperature for 1 hour and centrifugation (7000 rpm for 20 minutes), the supernatant was used for 2-D electrophoresis. The proteins were revealed by Sypro Ruby staining. Master maps of the five replicas of each species were compared by PDQuest analysis. The results of this differential proteome analysis were: sixteen proteins were expressed solely in C. canephora (var. Indiano Robusta) and five proteins were only found in C. arabica (var. Colombia). Another eight proteins were up-regulated in C. canephora (var. Indiano Robusta) in comparison to C. arabica (var. Colombia) and one was down-regulated in the same comparison. A number of these polypeptide chains were further characterized by mass spectrometry in the matrix-assisted laser desorption/ionisation-time of flight mode. Additionally, considering the low number of protein sequences of Coffea present in the databases we also investigated some spots with a more powerful tool, reversed phase-high-performance liquid chromatography-electrospray ionisation-tandem mass spectrometry, thus obtaining an internal peptide sequence. The general properties of the identified proteins are presented and discussed.
authors.affiliation: Area Química Analítica, CCEE, ESTCE, Universitat Jaume I, Castellon, Spain.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Gil-Agusti
authors.forename: Natascia
authors.initials: N
authors.lastname: Campostrini
authors.forename: Lello
authors.initials: L
authors.lastname: Zolla
authors.forename: Corrado
authors.initials: C
authors.lastname: Ciambella
authors.forename: Carlo
authors.initials: C
authors.lastname: Invernizzi
authors.forename: Pier Giorgio
authors.initials: PG
authors.lastname: Righetti
mesh_terms: D002851:Chromatography, High Pressure Liquid; D040503:Coffea / Q000737:chemistry / Q000145:classification*; D015180:Electrophoresis, Gel, Two-Dimensional; D010449:Peptide Mapping; D010936:Plant Extracts / Q000737:chemistry; D010940:Plant Proteins / Q000032:analysis*; D020543:Proteome / Q000032:analysis*; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D010936:Plant Extracts; D010940:Plant Proteins; D020543:Proteome