IN-VITRO FORMATION OF COCOA-SPECIFIC AROMA PRECURSORS - AROMA-RELATEDPEPTIDES GENERATED FROM COCOA-SEED PROTEIN BY COOPERATION OF AN ASPARTIC ENDOPROTEASE AND A CARBOXYPEPTIDASE

Cocoa-specific aroma precursors were obtained when acetone-drv powder prepared from unfermented cocoa seeds was subjected to autolysis at pH 5.2. Hydrophobic free amino acids and hydrophilic peptides were prefe rentially generated under these conditions. When this mixture or prote olysis products was formulated and roasted in the presence of reducing sugars, cocoa and/or chocolate aroma was detected by two independent panels. Aroma precursors extracted and partially purified from ferment ed cocoa seeds also consisted predominantly of hydrophilic peptides an d hydrophobic free amino acids. No cocoa-specific aroma precursors wer e obtained when the acetone-dry powdcr from unfermented cocoa seeds wa s incubated at pH 3.5. Few free amino acids were released under these conditions, but a large number of hydrophobic peptides were formed. Wh en these hydrophobic peptides were digested with carboxypeptidase A fr om porcine pancreas, mixtures of hydrophilic peptides and hydrophobic free amino acids were generated, which were shown to contain cocoa-spe cific aroma precursors. No typical cocoa aroma was, however, obtained when synthetic mixtures of amino acids adapted to the spectrum of free amino acids present in fermented cocoa seeds (or aroma-precursor extr acts) were roasted in the presence of reducing sugars. Our findings th erefore indicate that the essential cocoa-specific aroma precursors ar e aniong the hydrophilic oligopeptides. Ungerminated cocoa seeds conta in one predoniminant endoprotease (an aspartic endoprotease with a pH optimum at pH 3.5) and a carboxy-peptidase activity (pH optimum: 5.8). Our findings indicate that the co-operative action of these two enzym es on cocoa-seed protein is required for the generation of the cocoa-s pecific aroma precursors.