Specificity and stability of the carboxypeptidase activity in ripe, ungerminated seeds of Theobroma cacao L.

As previously reported the carboxypeptidase activity present in ripe, ungerminated Theobroma cacao seeds is involved in the proteolytic formation of the cocoa-specific aroma precursors. Therefore, we have investigated the specificity of this particular enzyme activity using crude homogenates of acetone dry powder prepared from unfermented, ripe cocoa seeds. Both oligopeptide mixtures derived from cocoa seed proteins and synthetic peptides have been found to be suitable substrates for this enzyme activity. However, peptides with carboxyterminal arginine, lysine or proline residues are resistant against degradation by the cocoa seed carboxypeptidase. The enzyme preferentially liberates hydrophobic amino acids, whereas acidic amino acids are released very slowly. The rate of hydrolysis is not only determined by the carboxyterminal, but also affected by the neighbouring amino acid residue. Furthermore, the specificity of the enzyme is influenced by the pH-value. The specificity of the cocoa seed carboxypeptidase activity is remarkably similar to the specificity of carboxypeptidase A from porcine pancreas which (in addition to the cocoa aspartic endoprotease) has recently been successfully used for the in vitro formation of the cocoa-specific aroma precursors. These results are discussed in the light of the pH-dependent generation of the cocoa-specific aroma precursors during fermentation of the cocoa seeds.