Exploring Metabolomic Flux and Achieving Prediction Capability in Cocoa Bean Fermentation using Model Systems

Cocoa bean fermentation encompasses the successive growth of microbial populations on the bean which results in the diffusion of microbial metabolites into the bean, as well as dramatic increases in temperature. A combination of all these events affect the bean structurally and biochemically and lead to the formation of pleasant flavour and aroma precursors. Cocoa bean fermentation still remains an uncontrolled and spontaneously-driven process. This means that there is tremendous variety in the quality of fermented beans. A lack of markers makes it difficult to distinguish between good and bad trials of fermentation. Consequently, Western conglomerates that buy fermented beans from farmers can end up shipping large quantities of beans only to discover that they are not suitable for chocolate manufacture. The experiments described herein were done in order to more accurately study the reactions that underlie the process of fermentation, in order to find biochemical markers defining good-quality fermentations. This was done using chemical-driven and microbial-driven model systems. Cocoa bean fermentation, assessed through bean pH, microbial dynamics and the secretions of microbial metabolites, was successfully reproduced in lab-scale quantities using starter cultures, temperature regimes and submerged incubations. The main findings of this research were that changes in bean pH led to dramatic changes in terms of protein and polyphenol content and that an optimum pH needed to be reached in order to allow correct proteolysis and flavanol degradation for the formation of cocoa aroma and flavour. Acid influx into the bean also exhibited a preservation effect upon flavanols, which could be beneficial in preserving the health properties of cocoa. A comprehensive understanding of the factors contributing to fermentation through design of experiments also enabled the prediction of outcomes of fermentation trials.