Browsing by Author "Bruckner, H."

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    Gas chromatographic determination and mechanism of formation of D-amino acids occurring in fermented and roasted cocoa beans, cocoa powder, chocolate and cocoa shell
    (Springer-Verlag, 2006) Patzold, R.; Bruckner, H.
    Fermented cocoa beans of various countries of origin (Ivory Coast, Ghana, Sulawesi), cocoa beans roasted under defined conditions (100–150 C; 30–120 min), low and high fat cocoa powder, various brands of chocolate, and cocoa shells were analyzed for their contents of free L- and D-amino acids. Amino acids were isolated from defatted products using a cation exchanger and converted into volatile N(O)-pentafluoropropionyl amino acid 2-propyl esters which were analyzed by enantioselective gas chromatography mass spectrometry on a Chirasil+-L-Val capillary column. Besides common protein L-amino acids low amounts of D-amino acids were detected in fermented cocoa beans. Quantities of D-amino acids increased on heating. On roasting cocoa beans of the Forastero type from the Ivory Coast at 150 C for 2 h, relative quantities of D-amino acids approached 17.0% D-Ala, 11.7% D-Ile, 11.1% D-Asx (AspþAsn), 7.9% D-Tyr, 5.8% D-Ser, 4.8% D-Leu, 4.3% D-Phe, 37.0% D-Pro, and 1.2% D-Val. In cocoa powder and chocolate relative quantities amounted to 14.5% D-Ala, 10.6% D-Tyr, 9.8% D-Phe, 8.1% L-Asx, and 7.2% D-Ile. Lower quantities of other D-amino acids were also detected. In order to corroborate our hypothesis that D-amino acids are generated from Amadori compounds (fructose amino acids) formed in the course of the Maillard reaction, fructose-L-phenylalanine and fructose-D-phenylalanine were synthesized and heated at 200 C for 5–60 min. Already after 5min release of 11.7% D-Phe and 11.8% L-Phe in the free form could be analyzed. Based on the data a racemization mechanism is presented founded on the intermediate and reversible formation of an amino acid carbanion in the Amadori compounds.