Kinetics of the formation of free amino acids in cocoa seeds during fermentation

Abstract

The predominance of leucine, phenylalanine, alanine and tyrosine among the free amino acids released from proteins during fermentation of cocoa seeds was further studied by following the kinetics of amino acid turnover during fermentation-like seed incubation and acetone dry-powder incubation by HPLC-analyses. Free acidic amino acids of the unfermented seeds disappear before onset of post-mortem proteolysis in a premortem phase of seed incubation. During subsequent post-mortem proteolysis in whole seeds (incubated at 50°C in acetic acid/NaOH (200 m m ; pH 4·5)) leucine, phenylalanine, alanine and tyrosine are predominantly released. The initial high rate of amino acid formation decreases rapidly and their relative proportions change continually. With acetone dry-powder incubations it is shown that a decreasing nib pH affects the amino acid composition but does not explain these changes, especially not the strongly decreasing ratio of (ala + tyr):(leu + phe). Since vacuolar storage proteins are degraded earlier than other seed proteins, it is assumed that this change in substrate proteins is responsible.