Pichia kudrazevii and Candida nitrativorans are the most well-adapted and relevant yeast species fermenting cocoa in Agneby-Tiassa, a local Ivorian cocoa producing region

Abstract

Cocoa bean fermentation is a spontaneous and still poorly controlled process that very often leads to end-products of heterogeneous quality. This fermentation is driven by a succession of complex microbial communities where yeasts play key roles during the first stages of the process. In this study, we identified and analyzed the growth dynamics of yeasts involved in cocoa bean fermentation from the Ivorian region called Agneby-Tiassa. The results showed that Pichia kudriazevii and Candida nitrativorans were the dominant yeasts in fermented cocoa from Agneby-Tiassa. Five other species, namely Candida tropicalis, Candida intermedia, Candida nitrativorans, H. uvarum and H. guilliermondii, were also found but in smaller numbers. Additionally, intraspecies diversity was determined by examining the length polymorphism of the genetic marker ITS1-5.8S-ITS2 and its PCR-RFLP analysis. We showed that the dominant species, P. kudriazevii and C. nitrativorans, are well adapted to environmental conditions specific to cocoa bean fermentation as they are resistant to high temperatures (40°C) and high ethanol concentrations (20%). Moreover, P. kudriazevii and C. nitrativorans species exhibited pectin-hydrolysing enzymatic activities suggesting a key role in the degradation of cocoa bean pulp during fermentation. Furthermore, these pectinolytic activities occurred in acidic growth conditions (pH3–5), which correspond to the pH conditions of the early steps of cocoa fermentation. Taken together, these results show that P. kudriazevii and C. nitrativorans are key players in cocoa bean fermentation in the Agneby-Tiassa region and they are promising candidates for developing starter cocktails that could be used to improve the overall efficiency of cocoa fermentation in Ivory Coast.