THE PROTEOLYTIC FORMATION OF ESSENTIAL COCOA-SPECIFIC AROMA PRECURSORS DEPENDS ON PARTICULAR CHEMICAL STRUCTURES OF THE VICILIN-CLASS GLOBULIN OF THE COCOA SEEDS LACKING IN THE GLOBULAR STORAGE PROTEINS OF COCONUTS, HAZELNUTS AND SUNFLOWER SEEDS

Cocoa-specific aroma precursors were generated in vitro, when the vicilin-class globulin of cocoa seeds was successively degraded by the aspartic endoprotease and the carboxypeptidase isolated from ungerminated cocoa seeds. To study the significance of the chemical structure of the protein substrate, globular storage proteins were isolated from different crops and subjected to proteolysis by the aspartic endoprotease and the carboxypeptidase of ungerminated cocoa seeds. The obtained proteolysis products were comparatively analysed for their patterns of oligopeptides and free amino acids and were roasted in the presence of reducing sugars and deodorised cocoa butter. Sensory evaluation of the roasting aromas revealed that neither the proteolysis products of the legumin-class globulins from hazelnuts or sunflower seeds, nor those derived from the vicilin-class globulin of coconuts contained the typical pattern of aroma precursors formed by degradation of the vicilin-class globulin of cocoa seeds with the same proteases. Considerable differences were observed between the patterns of free amino acids and oligopeptides generated by proteolysis of the cocoa vicilin and of the globular storage proteins from the other crops. These findings indicate that the formation of the cocoa-specific aroma precursors is determined by the particular chemical structure of the vicilin-class globulin present in the cocoa seeds.