A mathematical model of cocoa bean fermentation

Salmonella prevalence in raw cocoa beans and a microbiological risk assessment to evaluate the impact of cocoa liquor processing on the reduction of Salmonella

Salmonella in raw cocoa beans (n= 870) from main sourcing areas over nine months was analyzed. It was detected in 71 (ca. 8.2%) samples, with a contamination level of 0.3-46 MPN/g except for one sample (4.1×104 CFU/g). Using prevalence and concentration data as input, the impact of thermal treatment in cocoa processing on the risk estimate of acquiring salmonellosis by a random Belgian chocolate consumer was calculated by a quantitative microbiological risk assessment (QMRA) approach. A modular process risk model from raw cocoa beans to cocoa liquor up to a hypothetical final product (70-90% dark chocolate tablet), was set up to understand changes of Salmonella concentrations following the production process. Different thermal treatments during bean or nib steam, nib roasting or liquor sterilization (achieving a 0-6 log reduction of Salmonella) were simulated. Based on the generic FAO/WHO Salmonella dose-response model and the chocolate consumption data in Belgium, salmonellosis risk per serving and cases per year at population level were estimated. When a 5 log reduction of Salmonella was achieved, the estimated mean risk per serving was 3.35×10-8 (95% CI: 3.27×10-10-1.59×10-7), and estimated salmonellosis cases per year (11.7 million population) was 88 (95% CI: <1-418). The estimated mean risk per serving was 3.35×10-9 (95% CI: 3.27×10-11-1.59×10-8), and the estimated salmonellosis cases per year was 9 (95% CI: <1-42), for a 6 log reduction. The current QMRA model solely considered Salmonella reduction in a single-step thermal treatment in the cocoa process. Inactivation obtained during other process steps (e.g. grinding) might occur but was not considered. As the purpose was to use QMRA as a tool to evaluate the log reduction in the cocoa processing, no post-contamination from the processing environment and ingredients was included. A minimum of 5 log reduction of Salmonella in the single-step thermal treatment of cocoa process, was considered to be adequate.

Electromagnetic fields effects on microbial growth in cocoa fermentation: A controlled experimental approach using established growth models

Understanding the effects of electromagnetic fields is crucial in the fermentation of cocoa beans, since through precise control of fermentation conditions the sensory and nutritional properties of cocoa beans could be improved. This study aimed to evaluate the effect of oscillating magnetic fields (OMF) on the kinetic growth of the core microbial communities of the Collections Castro Naranjal (CCN 51) cocoa bean. The data was obtained by three different models: Gompertz, Baranyi, and Logistic. The cocoa beans were subjected to different OMF strengths ranging from 0 mT to 80 mT for 1 h using the Helmholtz coil electromagnetic device. The viable microbial populations of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast (Y) were quantified using the colony-forming unit (CFU) counting method. The logistic model appropriately described the growth of LAB and Y under magnetic field exposure. Whereas the Baranyi model was suitable for describing AAB growth. The microbial populations in cocoa beans exposed to magnetic fields showed lower (maximum specific growth rate (μmax), values than untreated controls, with AAB exhibiting the highest average growth rate value at 5 mT and Y having the lowest average maximum growth rate value at 80 mT. The lower maximum specific growth rates and longer lag phases when exposed to magnetic fields compared to controls demonstrate the influence of magnetic fields on microbial growth kinetics.

The optimization of sequential fermentation in the dealcoholized apple juice for reducing lipids

Yeast and lactic acid bacteria are widely used in fermented foods and the nutrients and metabolites produced by fermentation have cholesterol degrading effects. This study utilized Xinjiang Aksu apples as the material to optimize the sequential fermentation process of different strains and construct a fermentation kinetic model to develop a functional fermentation product with low-sugar, probiotics-rich and lipid-lowering properties. The sequential fermentation of dealcoholized apple juice with Saccharomyces cerevisiae and Lactobacillus plantarum was optimized by response surface design, based on which a sequential fermentation kinetic model was constructed. The changes of short-chain fatty acids, cholesterol elimination rate and hydrophobic properties during the fermentation process were studied. The results showed that the kinetic model established under the optimal conditions could effectively predict the dynamic changes of the basic indexes during the fermentation process. After fermentation, the viable number of L. plantarum was 4.96 × 108 CFU/mL, short-chain fatty acids increased, the cholesterol elimination rate reached 45.06%, and the hydrophobicity was 51.37%, which had favorable lipid-lowering properties and hydrophobic effect. This research will provide a theoretical basis and technical support for the monitoring of microbial dynamics and functionalization development of sequentially fermented apple juice with different strains.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05741-z.

Metabolomics during the spontaneous fermentation in cocoa (Theobroma cacao L.): An exploraty review

Spontaneous fermentation is a process that depends on substrates' physical characteristics, crop variety, and postharvest practices; it induces variations in the metabolites that are responsible for the taste, aroma, and quality. Metabolomics makes it possible to detect key metabolites using chemometrics and makes it possible to establish patterns or identify biomarker behaviors under certain conditions at a given time. Therefore, sensitive and highly efficient analytical techniques allow for studying the metabolomic fingerprint changes during fermentation; which identify and quantify metabolites related to taste and aroma formation of an adequate processing time. This review shows that studying metabolomics in spontaneous fermentation permits the characterization of spontaneous fermentation in different stages. Also, it demonstrates the possibility of modulating the quality of cocoa by improving the spontaneous fermentation time (because of volatile aromatic compounds formation), thus standardizing the process to obtain attributes and quality that will later impact the chocolate quality.

Exploring cocoa bean fermentation mechanisms by kinetic modelling

Compared with other fermentation processes in food industry, cocoa bean fermentation is uncontrolled and not standardized. A detailed mechanistic understanding can therefore be relevant for cocoa bean quality control. Starting from an existing mathematical model of cocoa bean fermentation we analyse five additional biochemical mechanisms derived from the literature. These mechanisms, when added to the baseline model either in isolation or in combination, were evaluated in terms of their capacity to describe experimental data. In total, we evaluated 32 model variants on 23 fermentation datasets. We interpret the results from two perspectives: (1) success of the potential mechanism, (2) discrimination of fermentation protocols based on estimated parameters. The former provides insight in the fermentation process itself. The latter opens an avenue towards reverse-engineering empirical conditions from model parameters. We find support for two mechanisms debated in the literature: consumption of fructose by lactic acid bacteria and production of acetic acid by yeast. Furthermore, we provide evidence that model parameters are sensitive to differences in the cultivar, temperature control and usage of steel tanks compared with wooden boxes. Our results show that mathematical modelling can provide an alternative to standard chemical fingerprinting in the interpretation of fermentation data.

Dissecting fine-flavor cocoa bean fermentation through metabolomics analysis to break down the current metabolic paradigm

Cocoa fermentation plays a crucial role in producing flavor and bioactive compounds of high demand for food and nutraceutical industries. Such fermentations are frequently described as a succession of three main groups of microorganisms (i.e., yeast, lactic acid, and acetic acid bacteria), each producing a relevant metabolite (i.e., ethanol, lactic acid, and acetic acid). Nevertheless, this view of fermentation overlooks two critical observations: the role of minor groups of microorganisms to produce valuable compounds and the influence of environmental factors (other than oxygen availability) on their biosynthesis. Dissecting the metabolome during spontaneous cocoa fermentation is a current challenge for the rational design of controlled fermentations. This study evaluates variations in the metabolic fingerprint during spontaneous fermentation of fine flavor cocoa through a multiplatform metabolomics approach. Our data suggested the presence of two phases of differential metabolic activity that correlate with the observed variations on temperature over fermentations: an exothermic and an isothermic phase. We observed a continuous increase in temperature from day 0 to day 4 of fermentation and a significant variation in flavonoids and peptides between phases. While the second phase, from day four on, was characterized for lower metabolic activity, concomitant with small upward and downward fluctuations in temperature. Our work is the first to reveal two phases of metabolic activity concomitant with two temperature phases during spontaneous cocoa fermentation. Here, we proposed a new paradigm of cocoa fermentation that considers the changes in the global metabolic activity over fermentation, thus changing the current paradigm based only on three main groups of microorganism and their primary metabolic products.

Two classes of functional connectivity in dynamical processes in networks

The relationship between network structure and dynamics is one of the most extensively investigated problems in the theory of complex systems of recent years. Understanding this relationship is of relevance to a range of disciplines-from neuroscience to geomorphology. A major strategy of investigating this relationship is the quantitative comparison of a representation of network architecture (structural connectivity, SC) with a (network) representation of the dynamics (functional connectivity, FC). Here, we show that one can distinguish two classes of functional connectivity-one based on simultaneous activity (co-activity) of nodes, the other based on sequential activity of nodes. We delineate these two classes in different categories of dynamical processes-excitations, regular and chaotic oscillators-and provide examples for SC/FC correlations of both classes in each of these models. We expand the theoretical view of the SC/FC relationships, with conceptual instances of the SC and the two classes of FC for various application scenarios in geomorphology, ecology, systems biology, neuroscience and socio-ecological systems. Seeing the organisation of dynamical processes in a network either as governed by co-activity or by sequential activity allows us to bring some order in the myriad of observations relating structure and function of complex networks.

HPLC-MS-based design of experiments approach on cocoa roasting

Modern statistical methods, such as the design of experiments and response surface methodology, are widely used to describe changes in multiparameter processes during the processing of food in both science and technology contexts. However, these approaches are described to a lesser degree in the case of cocoa roasting than other foods and processes. Our study aimed to use the design of experiments to establish a model of cocoa roasting for relevant flavor-related constituents. We have used HPLC-MS techniques to link standard process parameters with chemical compounds changing in concentration during cocoa roasting. Influence of time, temperature, the addition of water, acid, and base, on relative concentrations of procyanidin monomers, dimers, and trimers, an Amadori compound, and a peptide, was shown. High-quality models for each compound were established and validated, displaying good prediction accuracy. Such an approach could be used to optimize processing conditions for cocoa roasting in order to influence the concentration of certain chemical compounds, and in turn, improving the flavor of chocolate products.

Dissecting industrial fermentations of fine flavour cocoa through metagenomic analysis

The global demand for fine-flavour cocoa has increased worldwide during the last years. Fine-flavour cocoa offers exceptional quality and unique fruity and floral flavour attributes of high demand by the world's elite chocolatiers. Several studies have highlighted the relevance of cocoa fermentation to produce such attributes. Nevertheless, little is known regarding the microbial interactions and biochemistry that lead to the production of these attributes on farms of industrial relevance, where traditional fermentation methods have been pre-standardized and scaled up. In this study, we have used metagenomic approaches to dissect on-farm industrial fermentations of fine-flavour cocoa. Our results revealed the presence of a shared core of nine dominant microorganisms (i.e. Limosilactobacillus fermentum, Saccharomyces cerevisiae, Pestalotiopsis rhododendri, Acetobacter aceti group, Bacillus subtilis group, Weissella ghanensis group, Lactobacillus_uc, Malassezia restricta and Malassezia globosa) between two farms located at completely different agro-ecological zones. Moreover, a community metabolic model was reconstructed and proposed as a tool to further elucidate the interactions among microorganisms and flavour biochemistry. Our work is the first to reveal a core of microorganisms shared among industrial farms, which is an essential step to process engineering aimed to design starter cultures, reducing fermentation times, and controlling the expression of undesirable phenotypes.

Functional role of yeasts, lactic acid bacteria and acetic acid bacteria in cocoa fermentation processes

Cured cocoa beans are obtained through a post-harvest, batchwise process of fermentation and drying carried out on farms in the equatorial zone. Fermentation of cocoa pulp-bean mass is performed mainly in heaps or boxes. It is made possible by a succession of yeast, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) activities. Yeasts ferment the glucose of the cocoa pulp into ethanol, perform pectinolysis and produce flavour compounds, such as (higher) alcohols, aldehydes, organic acids and esters. LAB ferment the glucose, fructose and citric acid of the cocoa pulp into lactic acid, acetic acid, mannitol and pyruvate, generate a microbiologically stable fermentation environment, provide lactate as carbon source for the indispensable growth of AAB, and contribute to the cocoa and chocolate flavours by the production of sugar alcohols, organic acids, (higher) alcohols and aldehydes. AAB oxidize the ethanol into acetic acid, which penetrates into the bean cotyledons to prevent seed germination. Destruction of the subcellular seed structure in turn initiates enzymatic and non-enzymatic conversions inside the cocoa beans, which provides the necessary colour and flavour precursor molecules (hydrophilic peptides, hydrophobic amino acids and reducing sugars) for later roasting of the cured cocoa beans, the first step of the chocolate-making.

Microorganisms during cocoa fermentation: systematic review

Introduction. Cocoa (Theobroma cacao L.) originates from Ecuador. It is one of the oldest foods in the world. The fact that cocoa is the main component in chocolate industry makes it one of the most quoted raw materials today. The chemical, physical, microbiological, and sensory properties of cocoa determine its quality and, as a result, economic and nutritional value. The research objective was to conduct a detailed analysis of cocoa fermentation process and to study the transformations this raw material is subjected to during processing. Study objects and methods. The present article introduces a substantial bibliographic review based on three databases: Science Direct, Scopus, and Medline. The scientific publications were selected according to several factors. First, they had to be relevant in terms of cocoa fermentation. Second, they were written in English or Spanish. Third, the papers were indexed in high-impact journals. The initial selection included 350 articles, while the final list of relevant publications featured only 50 works that met all the requirements specified above. Results and discussion. The main characteristics of yeasts, lactic bacteria, and acetic bacteria were analyzed together with their main parameters to describe their activities during different stages of alcoholic, lactic, and acetic fermentation. A thorough analysis of the main enzyme-related processes that occur during fermentation makes it possible to optimize the use of substrates, temperature, time, pH, acidity, and nutrients. As a result, the finished product contains an optimal concentration of volatile compounds that are formed in the beans during fermentation. The study featured the main strains of fermentation-related microorganisms, their activities, main reactions, and products. Conclusion. This study makes it possible to improve the process of fermentation to obtain beans with a better chemical composition.

Monitoring the changes in low molecular weight carbohydrates in cocoa beans during spontaneous fermentation: A chemometric and kinetic approach

The low molecular weight carbohydrate (LMWC) profile has recently been investigated, showing considerable changes between fermented and unfermented cocoa beans. These differences are a consequence of the fermentation process, which is considered a crucial step in chocolate production. During fermentation, LMWC are involved in Maillard reaction, a crucial reaction for the development of aroma and taste precursors. However, there is a lack of information related to LMWC changes and of contextualization with changes in other physicochemical parameters (pH and dry matter) during spontaneous fermentation. The different approaches employed in this manuscript have allowed the identification of a sequential degradation of tetra-, tri- and disaccharides, as well as an increase in the monosaccharide content during fermentation. Moreover, a correlation was determined between some LMWC and physicochemical parameters. Besides that, the chemometric approach identified the fermentation period ranging between 48 and 96 h as determinant to produce noticeable changes in unfermented beans based on the indicators evaluated. Furthermore, different kinetic parameteres (reaction order, observed reaction rates (k_obs) and half-life values (t_1/2)) of different LMWC were determined, showing differences between them. The results showed in this manuscript provide unprecedented mechanistic details of spontaneous cocoa fermentation.

Formation of aromatic compounds precursors during fermentation of Criollo and Forastero cocoa

There are three main genetic varieties of cocoa (Theobroma cacao L) used in chocolate making: Forastero, Trinitario and Criollo, which are distinguished by their aroma, an attribute that determines their quality. Criollo cocoa is of the highest quality and is used in the manufacture of fine chocolates because of its fruity aroma. The aroma of Criollo cocoa is defined by volatile compounds such as pyrazines and aldehydes, which are formed during roasting of the bean, from aroma precursors (reducing sugars and free amino acids) that are generated inside the bean via enzymatic reactions during fermentation; for this reason, fermentation is the most important process in the value chain. This review discusses the production of aroma precursors of Criollo and Forastero cocoa by studying the kinetics of spontaneous fermentation and the role of starter cultures to produce aroma precursors. Fine aroma precursors produced in the pulp during the fermentation phase will migrate into the bean when it's permeability is improved and then retained during the drying phase. Diffusion of aroma precursors into the cocoa bean may be possible, this process is mathematically characterized by the coefficient of molecular diffusion D, which describe the process of mass transfer via Fick's Second Law. The current state of knowledge is analyzed based on existing research and reports some gaps in the literature, suggesting future research that will be necessary for a better understanding of cocoa fermentation.