Ikrawan, Yusep

Selamat, Jinap

Universiti Putra Malaysia Institutional Repository

UPM Research Report 1998: Volume 2PROFILES OF THE AROMA-RELATED PEPTIDES INUNFERMENTED AND UNDERFERMENTED COCOABEANSY. Ikrawan and Jinap SelamatFaculty of Food Science and BiotechnologyUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: carboxypeptidase, cocoa aroma precursors,unfermented, underfermented cocoa beans, oligopep-tides.IntroductionThe development of cocoa aroma requires that cocoa beansare fermented and dried and then roasted (Rohan, 1964 andZiegleder and Biehl, 1988). Fermentation results in the pro-duction of aroma precursors, such as amino acids, reducingsugars and peptides. Cocoa specific aroma precursors areformed during fermentation by proteolytic prosesses (Ziegle-der and Biehl, 1988). The proteolysis of seed proteins andthe formation of aroma precursors are strongly dependent onthe degree and the time of nib acidification during fermenta-tion. Recent studies on the formation of cocoa-specificaroma precursors have shown that they are derived from thevicillin-class globulin of the cocoa seeds by the coordinateaction of an aspartic endoprotease and a carboxypeptidase.In addition to the released (hydrophobic) free amino acids,hydrophilic oligopeptidases were shown to be essential pre-cursors of the typical cocoa aroma. However, up to now, thearoma-related hydrophilic peptides have not been isolatedand characterised. Therefore, this report describes aroma-related peptides in unfermented and underfermented cocoabeans.Materials and MethodsRipe cocoa pods of the PBC 140 variety were obtained fromPerak, Malaysia. The pods were depodded and 45 kg of freshbeans were fermented using shallow wooden boxes (0.78 x0.78 x 0.78 m) for duration of 72 h. The beans were turnedevery 24 h. Representative samples of 2 kg each were takenfrom fermenting box at 0 and 3 days during fermentation.Cocoa powders were prepared from 3 days fermented beans.Samples were defatted and powdered. Unfermented and un-derfermented cocoa powder (2 g each) were suspended in cit-ric-phosphate buffer (pH 3.5 and 5.8). The suspensions wereincubated at 45°C in a shaking water bath for 24 h. After in-cubation, methanol was added to a final concentration of70% (v/v). The suspensions were stirred at room tempera-ture for 1 h and centrifuged at 10 000 x g for 15 min. The178supernatants were collected and the methanol was removedunder pressure at 40°C by rotary evaporator. The aqueoussolution was freeze-dried. Peptide mixtures were analysedby reversed-phase HPLC as recently described of Voigt et al.(1994).Results and DiscussionPeptide patterns from unfermented and undefermented cocoabeans were analysed by reversed phase HPLC. The extractfrom underfermented cocoa beans obtained by autolysis atpH 3.5 revealed very similar HPLC chromatrogram with un-fermented cocoa beans and autolysis at pH 5.8 obtained verysimilar with underfermented cocoa beans without incubation.However, the proportion of hydrophobic component at pH3.5 was considerably increased as compared with autolysis atpH 5.8. Analyses of the peptide patterns revealed that thehydrophobic peptides generated during autolysis at pH 3.5were transformed to considerably more hydrophilic compo-nents. The liberation of hydrophobic amino acids are due tothe cooperative action of the aspartic endoprotease and thecarboxypeptidase present in the ripe cocoa beans (Voigt et al.1993; 1994). Therefore, the optimum fermentation condi-tions are dependent on the optimum pH values of the asparticendoprotease (pH 3.5) and the carboxypeptides (pH 5.8)(Voigt et al. 1994).ConclusionsThe released (hydrophobic) free amino acids, hydrophilicoligopeptides were shown to be essential precursors of thetypical cocoa aroma. Raw cocoa with high aroma potentialswhich are obtained from fermentations with moderate acidi-fication (pH 5.5 - 5.0) contain considerably higher levels ofpredominantly hydrophobic free amino acids than raw cocoabeans from very acidic fermentations (pH 4.5 - 4.0).ReferencesRohan, T. 1964. The precursors of chocolate aroma: a comparativestudy of fermented and unfermented cocoa beans. J. Food Sci.29: 456-459.Voigt, J., Biehl, B. and Kamaruddin, S. 1993. The major seed pro-teins of Theobroma cacao L. Food Chem: 47: 145-151Voigt, J., Biehl, B., Heinrichs, H., Kamaruddin, S., Gaim Marsoner,G. and Hugi, A. 1994. In-vitro formation of cocoa-specific aromaprecursors: aroma-related peptides generated from cocoa seedprotein by co-operation of an aspartic endoprotease and a car-boxypeptidase. Food Chem. 49: 173-180.Ziegleder, G. and Biehl, B. 1988. Analysis of cocoa flavour compo-nents and fl~vour prec~ors. In: Methods in Plant Analysis (Vol8) (new senes), eds Lmskens H & Jackson J F. Springer, NewYork, USA. p.321-393.Supponed by IRPA GrantOl-02-04-OIlI

Profiles of the aroma related peptides in unfermented and underfermented cocoa beans

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Profiles of the aroma related peptides in unfermented and underfermented cocoa beans

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