MoLife Research Seminar by:
Prof. Dr. Jürgen Voigt, Friedrich-Schiller-University of Jena, Institute of Microbiology, Jena, Germany
Title of the talk:
The peptide precursors of the cocoa-specific aroma components
Essential peptide precursors of the cocoa-specific aroma notes are generated during fermentation of the cocoa beans by acid-induced proteolysis. These aroma-relevant peptides are derived from the vicilin-class(7S) globulin of the cocoa beans by co-operation of an aspartic protease and a carboxypeptidase. They have been partially purified from fermented cocoa beans and in-vitro proteolysis products by ligand-exchange and subsequent Sephadex LH20 chromatography and characterized by matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) and the determination of their amino acid sequences by electrospray ionization mass spectrometry (ESI-MS/MS). By this way, the aroma-relevant regions of the vicilin-class(7S) globulin of the cocoa beans have been identified. A large number of volatile compounds have been found in both roasted cocoa and in the roasting products of partially purified aroma precursor peptides. Discrimination between cocoa-specific and unspecific roasting products was found to be possible by comparing the volatiles obtained by roasting of the cocoa-specific aroma-precursor peptides without and with post-treatment with pepsin. Pepsin was found to partially destroy the cocoa-specific aroma-relevant peptides. The cleavage specificities of pepsin and of the cocoa aspartic protease have been comparatively analyzed and their cleavage sites localized in the vicilin-class(7S) globulin of the cocoa beans.