Abstract
Cocoa bean fermentation relies on the sequential activation of several microbial populations, triggering a temporal pattern of biochemical transformations. Understanding this complex process is of tremendous importance as it is known to form the precursors of the resulting chocolate’s flavour and taste. At the same time, cocoa bean fermentation is one of the least controlled processes in the food industry. Here, a quantitative model of cocoa bean fermentation is constructed based on available microbiological and biochemical knowledge. The model is formulated as a system of coupled ordinary differential equations with two distinct types of state variables: (i) metabolite concentrations of glucose, fructose, ethanol, lactic acid and acetic acid and (ii) population sizes of yeast, lactic acid bacteria and acetic acid bacteria. We demonstrate that the model can quantitatively describe existing fermentation time series and that the estimated parameters, obtained by a Bayesian framework, can be used to extract and interpret differences in environmental conditions. The proposed model is a valuable tool towards a mechanistic understanding of this complex biochemical process, and can serve as a starting point for hypothesis testing of new systemic adjustments. In addition to providing the first quantitative mathematical model of cocoa bean fermentation, the purpose of our investigation is to show how differences in estimated parameter values for two experiments allow us to deduce differences in experimental conditions.
Highlights
The fermentation of cocoa beans is recognized as a key step in cocoa processing in terms of the development of chocolate’s flavour and aroma [1,2]
Metabolite time series measured both in pulp and bean are available for glucose (Glc), fructose (Fru), sucrose, lactic acid (LA), acetic acid (Ac), ethanol (EtOH), mannitol, citric acid and succinic acid
The calculated R^ statistic was 1 for all three cases, showing that convergence of the Markov chain Monte Carlo (MCMC) sampler was accomplished. Such a behaviour is noticeable in the obtained traceplots, that show the typical ‘caterpillar’ shape as probe of a good mixing of the MCMC sampler along the exploration of the parameter space
Summary
The fermentation of cocoa beans is recognized as a key step in cocoa processing in terms of the development of chocolate’s flavour and aroma [1,2]. It occurs mainly in the pulp, i.e. a white mucilagenous mass that surrounds the bean, where three major microbial groups drive mostly the whole process whose main activity occurs in a consecutively way (figure 1a), being metabolically dominated in earlier stages by yeast (Y) and. As a result of the fermentation, a series of biochemical reactions are triggered in the raw material, the qualitative characteristics of which have been exhaustively described in terms of the microbial groups involved and the associated metabolic alterations [9,11,12]
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