Influence of two anti-fungal Lactobacillus fermentum-Saccharomyces cerevisiae co-cultures on cocoa bean fermentation and final bean quality

PLoS One. 2020 Oct 1;15(10):e0239365. doi: 10.1371/journal.pone.0239365. eCollection 2020.

Abstract

The growth of filamentous fungi during the spontaneous cocoa bean fermentation leads to inferior cocoa bean quality and poses a health risk for consumers due to the potential accumulation of mycotoxins. We recently developed anti-fungal cultures with the capacity to inhibit the growth of mycotoxigenic filamentous fungi on cocoa beans. However, it is not clear how these anti-fungal cultures affect the fermentation process and cocoa bean quality. For that, the anti-fungal co-cultures, Lactobacillus fermentum M017-Saccharomyces cerevisiae H290 (A) and Lb. fermentum 223-S. cerevisiae H290 (B), were applied to 180-kg box fermentations in Honduras in three time-independent replications each including a spontaneous control fermentation. The comparison of inoculated and spontaneous fermentation processes revealed that the co-cultures only marginally affected the fermentation process and cocoa bean quality. Microorganisms reached maximal levels of 6.2-7.6 log CFU/g of yeasts and acetic acid bacteria and 7.9-9.5 log CFU/g of lactic acid bacteria during all fermentations and led to maximal metabolite concentrations in bean cotyledons of 4-12 mg/g ethanol, 2-6 mg/g lactic acid and 6-14 mg/g acetic acid. The fermentation and drying processes resulted in 38-90 mg epicatechin equivalents/g in the cotyledons of dried beans. However, the co-cultures led to up to ten times higher mannitol levels in cotyledons of inoculated beans compared to beans during spontaneous fermentation, and caused a slower fermentation process, detectable as up to 8-12 °C lower temperatures in the centre of the fermenting pulp-bean mass and up to 22% lower proportions of well-fermented beans after drying. Co-culture B-with Lb. fermentum 223 -led to improved cocoa bean quality compared to co-culture A-with Lb. fermentum M017 -, i.e. cocoa beans with 0.5-1.9 mg/g less acetic acid, 4-17% higher shares of well-fermented beans and, on a scale from 0 to 10, to 0.2-0.6 units lower astringency, up to 1.1 units lower off-flavours, and 0.2-0.9 units higher cocoa notes. Therefore, the anti-fungal co-culture B is recommended for future applications and its capacity to limit fungal growth and mycotoxin production during industrial-scale cocoa bean fermentation should be investigated in further studies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaloids / analysis
  • Cacao / chemistry
  • Cacao / metabolism*
  • Cacao / microbiology*
  • Coculture Techniques*
  • Fermentation*
  • Food Quality*
  • Hydrogen-Ion Concentration
  • Limosilactobacillus fermentum / growth & development
  • Limosilactobacillus fermentum / physiology*
  • Polyphenols / analysis
  • Saccharomyces cerevisiae / growth & development
  • Saccharomyces cerevisiae / physiology*
  • Temperature
  • Time Factors

Substances

  • Alkaloids
  • Polyphenols

Grants and funding

This work was supported by the Commission for Technology and Innovation CTI (Grant Nr. 15813.1 PFLS-LS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.