Abstract
Amino acids (AA) composition in cocoa beans can predict the synthesis of compounds which affect cocoa flavor. Thus, their determination is of great interest for the community implied in the commercialization and production of cocoa. In consequence, in this work, the analysis of AA produced during cocoa beans fermentation and roasting was carried out. A high-performance liquid chromatographic method with DAD detection at 254 nm was optimized and validated for their selective determination in six varieties of cocoa beans with different genotypes, all of them grown in Venezuela. AA were extracted by defatted milled cocoa powder ultrasonication using purified water at 70 ºC. Then, they were derivatized with phenyl isothiocyanate, and their derivatives were separated, using a reversed-phase column with gradient elution, achieving a satisfactory resolution among the peaks (greater than 1.0) in less than 29 min. 110 cocoa samples were analyzed. Results showed a significant content of free AA, ranging from 3.87 to 5.97 g/kg in absence of fermentation with a predominance of acidic AA. Moreover, there is a progressive increase in the AA content while fermentation process occurs, with a predominance of hydrophobic AA such as alanine, valine, isoleucine, leucine, phenylalanine, and tyrosine. On the other hand, all cocoa types showed a partial degradation of free AA during the roasting step, especially the hydrophobic ones.
Highlights
Cocoa beans are originated as seeds in fruit pods of the tropical crop Theobroma cacao L., that is cultivated in the humid lowland tropics generally by small-scale producers
The cocoa beans of IMC-67 1st season, 1st year (Forastero) had an acid:hydrophobic:others amino acid ratio of 43:49:8 in unfermented beans and 9:63:28 in the fermented ones (Figure 6 b). This trend agrees with the results reported by other researchers [4, 11], which reported total free amino acid amounts within the range of 2.4 - 5.1 g kg-1 for unfermented cocoa beans with an acidic:hydrophopic:other ratio of 18:30:52, and 9.4 - 14.5 g kg-1 (6:46:48 and 58:16:26) for fermented cocoa beans from Malaysia and Ghana
The obtained results have proved that the developed reversed-phase HPLC method with PTC-Amino acids (AA) diode array detector (DAD) is a useful tool for primary and secondary amino acids determination in cocoa samples
Summary
Cocoa beans are originated as seeds in fruit pods of the tropical crop Theobroma cacao L., that is cultivated in the humid lowland tropics generally by small-scale producers. Fermentation plays a major role in the development of aroma precursors like free amino acids, peptides, and reducing sugars, due to the microbial activity and endogenous enzymes of cocoa beans. Free amino acids and peptides are formed by proteolytic reactions induced by endogenous proteases (aspartic proteinase and carboxypeptidase) during cocoa beans storage [2, 3]. Reducing sugars such as fructose and glucose are products of the hydrolysis of sucrose [4, 5]. Afoakwa et al [1] observed that the nature of the amino components is critical for cocoa flavor due to their influence in the formation of heterocyclic compounds which affect the resulting aroma
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