Mapping the functional and strain diversity of the main microbiota involved in cocoa fermentation from Cote d'Ivoire

Evaluation of stress tolerance and design of alternative culture media for the production of fermentation starter cultures in cacao

Ecuador is one of the world's leading producers of cacao beans, and Nacional x Trinitario cacao represents one of the most distinctive varieties due to its flavor and aroma characteristics. This study aimed to evaluate the effect of the starter culture isolated from microbial diversity during the spontaneous fermentation of Nacional x Trinitario cacao. A total of 249 microbial isolates were obtained from spontaneous culture, with Lactiplantibacillus (45 %), Saccharomyces (17 %), and Acetobacter (2 %) being the most relevant genera for fermentation. Tolerance tests were conducted to select microorganisms for the starter culture. Lactiplantibacillus plantarum exhibited the highest tolerance at pH 5 and 6 % ethanol and tolerated concentrations up to 15 % for glucose and fructose. Acetobacter pasteurianus grew at pH 2 and 6 % ethanol, tolerating high sugar concentrations of up to 15 % for glucose and 30 % for fructose, with growth observed in concentrations up to 5 % for lactic and acetic acid. Subsequently, a laboratory-scale fermentation was conducted with the formulated starter culture (SC) comprising S. cerevisiae, L. plantarum, and A. pasteurianus, which exhibited high tolerance to various stress conditions. The fermentation increased alcoholic compounds, including citrusy, fruity aromas, and floral notes such as 2-heptanol and phenylethyl alcohol, respectively 1.6-fold and 5.6-fold compared to the control. Moreover, the abundance of ketones 2-heptanone and 2-nonanone increased significantly, providing sweet green herbs and fruity woody aromas. Cacao fermented with this SC significantly enhanced the favorable aroma-producing metabolites characteristic of Fine-aroma cacao. These findings underscore the potential of tailored fermentation strategies to improve cacao product quality and sensory attributes, emphasizing the importance of ongoing research in optimizing fermentation processes for the cacao industry.

Integrating shotgun metagenomics and metabolomics to elucidate the dynamics of microbial communities and metabolites in fine flavor cocoa fermentation in Hainan

The aim of this study was to investigate the dynamic profile of microorganisms and metabolites in Hainan Trinitario cocoa during a six-day spontaneous box fermentation process. Shotgun metagenomic and metabolomic approaches were employed for this investigation. The potential metabolic functions of microorganisms in cocoa fermentation were revealed through a joint analysis of microbes, functional genes, and metabolites. During the anaerobic fermentation phase, Hanseniaspora emerged as the most prevalent yeast genus, implicated in pectin decomposition and potentially involved in glycolysis and starch and sucrose metabolism. Tatumella, possessing potential for pyruvate kinase, and Fructobacillus with a preference for fructose, constituted the primary bacteria during the pre-turning fermentation stage. Upon the introduction of oxygen into the fermentation mass, acetic acid bacteria ascended to dominant within the microflora. The exponential proliferation of Acetobacter resulted in a decline in taxonomic richness and abundance. Moreover, the identification of novel species within the Komagataeibacter genus suggests that Hainan cocoa may serve as a valuable reservoir for the discovery of unique cocoa fermentation bacteria. The KEGG annotation of metabolites and enzymes also highlighted the significant involvement of phenylalanine metabolism in cocoa fermentation. This research will offer a new perspective for the selection of starter strains and the formulation of mixed starter cultures.

Yeasts as Producers of Flavor Precursors during Cocoa Bean Fermentation and Their Relevance as Starter Cultures: A Review

During the fermentation of cocoa beans, the yeasts produce volatile organic compounds (VOCs). Through reactions associated with amino acid metabolism, yeasts generate important aroma precursors as acetate esters and fatty acid ethyl esters are essential in developing fruity flavors and aromas in the final product (usually chocolate). In addition, some yeasts may have pectinolytic and antifungal activity, which is desirable in the post-harvest process of cocoa. The main yeast species in cocoa fermentation are Saccharomyces cerevisiae, Pichia kudriavzevii, and Hanseniaspora opuntiae. These produce higher alcohols and acetyl-CoA to make acetate–esters, compounds that produce floral and fruity notes. However, there are still controversies in scientific reports because some mention that there are no significant differences in the sensory characteristics of the final product. Others mention that the fermentation of cocoa by yeast has a significant influence on improving the sensory attributes of the final product. However, using yeasts as starter cultures for cocoa bean fermentation is recommended to homogenize sensory attributes such as notes and flavors in chocolate.

Acetobacter senegalensis Isolated from Mango Fruits: Its Polyphasic Characterization and Adaptation to Protect against Stressors in the Industrial Production of Vinegar: A Review

It has been more than a decade since Acetobacter senegalensis was isolated, identified, and described as a thermotolerant strain of acetic acid bacteria. It was isolated from mango fruits in Senegal and used for industrial vinegar production in developing countries, mainly in sub-Saharan Africa. The strain was tested during several spirit vinegar fermentation processes at relatively high temperatures in accordance with African acclimation. The upstream fermentation process had significant stress factors, which are highlighted in this review so that the fermentation process can be better controlled. Due to its high industrial potential, this strain was extensively investigated by diverse industrial microbiologists worldwide; they concentrated on its microbiological, physiological, and genomic features. A research group based in Belgium proposed an important project for the investigation of the whole-genome sequence of A. senegalensis. It would use a 454-pyrosequencing technique to determine and corroborate features that could give this strain significant diverse bioindustrial applications. For instance, its application in cocoa bean fermentation has made it a more suitable acetic acid bacterium for the making of chocolate than Acetobacter pasteurianus. Therefore, in this paper, we present a review that summarizes the current research on A. senegalensis at its microbial and genomic levels and also its specific bioindustrial applications, which can provide economic opportunities for African agribusiness.

Functional yeast starter cultures for cocoa fermentation

The quest to develop a performant starter culture mixture to be applied in cocoa fermentation processes started in the 20th century, aiming at achieving high‐quality, reproducible chocolates with improved organoleptic properties. Since then, different yeasts have been proposed as candidate starter cultures, as this microbial group plays a key role during fermentation of the cocoa pulp‐bean mass. Yeast starter culture‐initiated fermentation trials have been performed worldwide through the equatorial zone and the effects of yeast inoculation have been analysed as a function of the cocoa variety (Forastero, Trinitario and hybrids) and fermentation method (farm‐, small‐ and micro‐scale) through the application of physicochemical, microbiological and chemical techniques. A thorough screening of candidate yeast starter culture strains is sometimes done to obtain the best performing strains to steer the cocoa fermentation process and/or to enhance specific features, such as pectinolysis, ethanol production, citrate assimilation and flavour production. Besides their effects during cocoa fermentation, a significant influence of the starter culture mixture applied is often found on the cocoa liquors and/or chocolates produced thereof. Thus, starter culture‐initiated cocoa fermentation processes constitute a suitable strategy to elaborate improved flavourful chocolate products.