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A lab-scale model system for cocoa bean fermentation

  • Applied microbial and cell physiology
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Abstract

Lab-scale systems modelling the spontaneous cocoa bean fermentation process are useful tools to research the influence of process parameters on the fermentation and the final bean quality. In this study in Honduras, a 1-kg lab-scale fermentation (LS-F) was compared to a 300-kg on-farm fermentation (OF-F) in a multiphasic approach, analysing microbial counts, microbial species diversity, physico-chemical parameters, and final dried bean quality. Yeast and total aerobic counts of up to 8 log CFU/g during the LS-F were comparable to the OF-F, while counts for lactic acid bacteria and acetic acid bacteria were up to 3 log CFU/g lower during the LS-F than during the OF-F. While species of the genera Hansenia, Saccharomyces, and Acetobacter dominated most of the fermentation processes, the genera dominating the drying phases were Pichia, Trichosporon, Pediococcus, and Acetobacter. Dried beans resulting from the LS-F, compared to the OF-F, were similar in contents of acetic acid, 6 times lower in lactic acid, up to 4 times higher in residual sugars, and 3–12 times higher in polyphenols. Dried beans processed at LS showed a similar flavour profile in terms of astringency, bitterness, acidity, and brown, fine, and cocoa flavours, but 2 units higher off-flavours than OF processed beans. With 81%, the share of well-fermented beans from the LS-F complied with industrial standards, whereas 7% over-fermented beans were above the threshold. Conclusively, the 5-day model fermentation and subsequent drying successfully mimicked the on-farm process, providing a high-throughput method to screen microbial strains to be used as starter cultures.

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Acknowledgments

The support of FHIA in field studies in Honduras and the infrastructural and technical support with sensorial analyses from the company Chocolats Halba are highly appreciated. We thank our students Katharina Bärtschi, Romina Berger, and Stefanie Streule for helpful contributions, Michael Pantic for setting up a temperature data logger, Alfonso Dié for support with HPLC-RI analyses, and Caroline Hyde-Simon for English proofreading.

Funding

This research was funded by the Commission for Technology and Innovation CTI (Grant Nr. 15813.1 PFLS-LS).

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Correspondence to Susanne Miescher Schwenninger.

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The authors declare that they have no conflict of interest.

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The article does not contain any studies with human participants or animals performed by any of the authors.

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Romanens, E., Näf, R., Lobmaier, T. et al. A lab-scale model system for cocoa bean fermentation. Appl Microbiol Biotechnol 102, 3349–3362 (2018). https://doi.org/10.1007/s00253-018-8835-6

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  • DOI: https://doi.org/10.1007/s00253-018-8835-6

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